A STUDY on
INFORMATION on
ENGINEERING DESIGN and
TECHNICAL CRITERIA for
THE CONTROL of SEDIMENT
FROM LOGGING HAUL
ROADS
BNVIROMBNTAL PROTECTION AGENCY
REGION X
JULY, 1974
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A STUDY OF INFORMATION
on
ENGINEERING DESIGN AND TECHNICAL CRITERIA
for
THE CONTROL OF SEDIMENT FROM LOGGING HAUL ROADS
Prepared by:
ARNOLD, ARNOLD & ASSOCIATES
1216 Pine Street
Seattle, Washington 98101
206-624-6280
for the
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION X
July, 1974
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ENGINEERING DESIGN AND TECHNICAL CRITERIA FOR
THE CONTROL OF SEDIMENT FROM LOGGING HAUL ROADS
TABLE OF CONTENTS
Page
CONTENTS j
LIST OF TABLES vi
LIST OF FIGURES viii
Chapter
I. INTRODUCTION I
A. Summary and Conclusions 6
B. Recommendations 9
ROUTE PLANNING & RECONNAISSANCE 10
A. Planning 12
I. Management-Engineering Dialogue 12
2. Engineer's Assessment of Management's \4
Dec is ion
2.01 "State of the Art" Techniques 14
2.02 Roads and Harvest Method Relationships 20
3. Conclusions 21
B. Route Reconnaissance 22
I. Factors Affecting Surface Erosion 24
I.01 Introduction 24
1.02 Soil Loss Equations 24
1.03 Universal Soil Loss Equation 25
1.04 Stream Sedimentation 34
1.05 Other Information Sources 35
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TABLE OF CONTENTS (Cont'd)
Page
2. Erosion and Mass Wasting Considerations 41
2.01 Introduction 41
2.02 Aids 42
2.03 Field Reconnaissance 47
3. Civil and Forest Engineering 60
3.01 Harvest Method 60
3.02 Existing Road Audit 61
3.03 Route Placement 62
3.04 Field Survey Information 66
C. Economic Evaluations 69
I. Cost Analysis 69
2. Economic Justification 73
Ml. DESIGN 75
A. Roadway 77
I. Horizontal and Vertical Alignment 77
I.01 Horizontal Alignment 78
1.02 Vertical Alignment 78
2. Road Prism 79
2.01 Excavation 79
2.02 Embankment 80
2.03 Balanced Construction 82
3. Road Surfacing 82
4. Buffer Strips 85
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TABLE OF CONTENTS (Cont'd)
Page
B. Slope Stabilization 88
I. Surface Erosion 88
I.01 Introduction 88
1.02 Seeding and Planting 89
1.03 Mulches and Chemical Soil Stabilizers 107
1.04 Mechanical Treatment 129
2. Mass Wasting 132
2.01 Introduction 132
2.02 Retaining Wai Is 133
C. Drainage Design 136
I. Ditches and Berms 136
I.01 Size and Placement 137
1.02 Ditch ProfiIes 143
1.03 Ditch Outlets 143
1.04 Sloped Roadway Alternate to 145
Roadside Ditches
1.05 Rock Sub-drain Alternate to 148
Roadside Ditches
2. Culverts 150
2.01 Sizing Culverts 155
2i02 Design Aspects of Culvert Installation 157
3. Water Course Crossings 161
3.01 General 162
3.02 Sediment Features of Stream Crossing Design 162
3.03 Stream Crossing Methods 165
i i i
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TABLE OF CONTENTS (Cont'd)
Page
4. Culvert Outlet Treatments 171
5. Hydrology 180
5.01 Logging and Roadbuilding 180
5.02 Subsurface Water Considerations 181
5.03 Forest Location 182
D. Construction Specifications 186
I. Standard Specifications 186
2. Special Provisions 187
3. Conclusions 190
IV. CONSTRUCTION TECHNIQUES 191
A. Clearing & Grubbing 192
B. Earthwork 193
C. Drainage 196
I. Drainage During Construction 196
2. Drainage Construction 197
D. Construction Equipment 199
V. MAINTENANCE ' 201
A. Drainage System 202
I.. Culverts and Ditches 203
2. Cut and Embankment Slopes 204
B. Road Surface 204
iv
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TABLE OF CONTENTS (Cont'd)
Page
C. SIide Dilemmas 207
I. Introduction 207
2. Recovering Slide Debris 207
3. Wasting SIide Debris 208
4. Relocation vs Correction 209
5. Failure Mechanism Investigation 209
VI. WATER QUALITY MONITORING 211
A. Sources of Water Quality Impairment 211
B. Parameters to be Monitored 212
I. Water Temperature 212
2. Turbidity 212
3. Dissolved Oxygen 213
4. Specific Conductance 214
5. Streamflow 214
C. Sampling Location 215
D. Sampling Frequency and Duration 215
I. Turbidity 216
2. Water Temperature 217
3. Dissolved Oxygen 217
4. Specific Conductance 217
5. Stream Discharge 218
REFERENCES 219
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LIST OF TABLES
Table Title Page
11 B-l Grain Size in mm. 28
II B-2 A guide for placing common soil and 58
geologic types into erosion classes
II B-3 Unified Soil Classification 59
II B-4 Siuslaw National Forest - Plant Indicators 68
II C-l Comparison of annual road costs per mile, 71
10,000 vehicles per annum (VPA)
II C-2 Comparison of annual road costs per mile 72
for 20,000 and 40,000 vehicles per annum
(VPA)
II C-3 Comparison of single lane versus double 72
lane costs for three different vehicle
per annum (VPA) categories
III A-l Protective-Strip Widths 87
III B-l Seed Mixtures for Washington and Oregon 93
III B-2 Seed Mixtures for Idaho 96
III B-3 Seed Mixtures for Southeast Alaska 97
III B-3a Grasses and Legumes for soil stabilization 106
III B-4 Average cumulative soil loss or gain on 12 110
backslop'e plots during the first year after
construct ion
111 B-5 Comparison of cumulative erosion from treated 112
plots on a steep, newly constructed road fill
III B-6 Erosion Losses for Longer Slopes 115
III B-7 Erosion Control Effectiveness of Covering 118
Material on Various Slopes - Effectiveness
Rat ing
III C-l Maximum permissible velocitjes in erodible 139
channeIs
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LIST OF TABLES (Cont'd)
Table Title Page
III C-2 Maximum permissible velocities in channels 140
lined with uniform stands of various grass
cover
III C-3 Cross Drain Spacing 147
III C-4 Settling Velocities for various particle 179
sizes 10.00 mm. to 0.00001 mm.
VI I
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LIST OF FIGURES
Figure
II A-l
II B-l
1 II B-2
II B-3
I 1 B-4
1 1 B-5
III A-l
III B-l
III C-l
III C-2
III C-3
III C-4
III C-5
III C-6
Title
"P" Factor Use
Relation of Annual Rainfall Erosion factor
to 2 year-6 hour Rainfall, West of the
Mississippi River
2 year-6 hour Rainfall (inches) for
Washington, Oregon and Idaho
Soil Erodibility Nomograph
Length and Slope Factors for Steep Terrain
Influence of Land Slope Shape on Sediment
Load
Water Bar
Soil Losses From 35 Foot Long Slope
Proper location for full flow water surface
in roadway ditch
Minimum ditch size
Berm
Ditch Placement
Ditch Outlet near Natural Stream
Rock Sub-Drain
Page
18
36
37
38
39
40
84
1 14
138
142
142
144
144
149
VI
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LIST OF FIGURES
Sect
III
III
III
III
III
III
II 1
III
1 11
III
III
III
IV
ion
C-7
C-8
C-9
C-IO
C-ll
C-12
C-13
C-14
C-15
C-16
C-17
C-18
B-l
Title
Ditch Inlet Structure
Ditch Inlet Structure with Catch Basin
Upstream Embankment Face Treatment
Gabion Ford
Culvert Out lets
Culvert Outlet Near Stream
Pipe Channe 1 Deta i 1
Rock Dike
Pipe Channel Detai 1
Gravel FN led Crib Wai 1
Energy Dissipating Silo
Culvert Outlet to Sediment Pond
Alternate Waste Site
Page
151
152
160
166
172
173
173
175
175
176
178
178
195
IX
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I. INTRODUCTION
Engineering criteria for the planning, design, construction and
maintenance of logging haul roads directed toward sediment minimization
is a part of the total engineering criteria needed for logging haul roads,
The appropriate spectrum of this criteria is related to the major role
logging roads play in forest land management.
Sediment control design criteria may be the same as, or parallel to,
other design criteria that will result in an efficient, economic logging
road system for sound forest land management. Examples of "overlap" or
parallei criteria are:
I. Relating road location and design to the total forest resource,
including short term harvest pattern, reforestation, fire pre-
vention, fish and wildlife propogation and water quality stan-
dards.
2. Relating road location and design to current timber harvesting
methods.
3. Preparing road plans and specifications to the level of detail
appropriate and necessary to convey to the road builder, be he
timber purchaser or independent contractor, the scope of the
project and enable him to prepare a comprehensive construction
plan of procedure, time schedule, and cost estimate.
4. Design investigations and- companion design decisions directed
toward minimizing the opportunity for "changed conditions"
during construction with their consequent costs in dollars and
time.
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5. Analysis of certain road elements relative to first cost versus
maintenance cost such as culverts and embankments versus bridges;
ditch lining versus ditches in natural soils; paved or lined
culverts versus unlined culverts; sediment trapping devices
(catch basins, sumps) versus culvert cleaning costs; retaining
walls versus placing and maintaining large embankments and em-.
bankment slopes; roadway ballast or surfacing versus maintenance
of dirt surfaces; and balanced earthwork quantities versus waste
and borrow.
Specific inclusion of design criteria to minimize sediment may be
appropriately evaluated as a broadening of the design criteria spectrum
under some conditions. In these circumstances additional first cost may
not result in companion maintenance cost reductions as suggested in the
previous paragraph. Examples of these circumstances are:
I. Spur roads built for one harvest in one season of a small area
and/or to one use landings.
2. Short term sedimentation control measures for use during road
construction and immediately thereafter until long term measures
are installed or. established.
3. Improvements outside of what has been regarded as the road right-
of-way or corridor such as specially constructed filter strips,
"downhill" culvert extensions, settling basins and provisions
for debris collect ion.
4. End haul of excess excavation to selected waste areas.
5. More restrictive limitations on the road construction season
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thereby, in some instances, requiring more seasons to complete
the road with companion delay in the timber harvest (time cost
of money).
6. 'Tipping the scales" in an evaluation of a fragile or sensitive
area toward the conclusion that existing road design and con-
struction technology will a I low JTO_ road construct ion.
7- Restriction or elimination of a timber harvest method due to the
road needs of the method (i.e. jammer logging) and conversion to
another harvest method that results in a higher long term harvest
cost.
Many regional writers believe that forest roads have often signifi-
cantly contributed to sediment reaching streams by surface erosion and
mass soil movement. George W. Brown states that: 'The compacted surfaces
of logging roads, skid trails, and fire lines often carry surface run-off
during storm events. Road surfaces are a significant source of sediment
in forests because of such run-off. (I) Fredriksen's studies in Western
Oregon watersheds report that "Landslides are the major source of stream
sedimentation" and that "their occurrence is more frequent where logging
roads intersect stream channels". (2) He also suggests that midslope road
mileage be minimized and further where these roads are necessary across
steep sideslopes, "all knowledge available to the engineer should be used
to stabiIize roads".
Swanston's investigations on mass soil movements in forests indicate
that road building is the most damaging activity and believes that soil
failures therefrom result primarily from slope loading with embankments,
sidecasting, inadequate provision for slope drainage and cut slopes. (3)
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Mass movements have occurred in the Alaska maritime coast, Idaho and on
the western slopes of the Cascades. These movements have often produced
companion sedimentation problems and significant water quality degradation,
Megahan and Kidd's studies of sediment production rates in the Idaho
Batholith showed increases of sediment production an average of 770 times
per unit of road prism for a six year study period. (4) Although surface
erosion following road construction decreased rapidly with time, major
impact occurred from a road fill failure after a single storm event.
This report deals with engineering techniques that have been used or
can be used to minimize the sedimentation originating from logging haul
roads. The techniques reported or discussed in this text do not have
universal application throughout all forested lands in Washington, Oregon,
Idaho and Alaska. To the contrary, the first and cardinal rule for the
solution of any engineering design problem is to deal with the actual cir-
cumstances at the individual site in question. As Robert W. Larse has
suggested, "the designer must have a knowledge and understanding of design
criteria and principles, but must be free and have sufficient experience
and ability to design for specific conditions, rather than to apply
generalized design rules'to all situations". (5)
In the Summary and Recommendations Section of their report on slope
failures in the Idaho Batholith, M. J. Gonsior and R. B. Gardner suggest
a need for a reorientation or philosophical change in engineering approach
as fo11ows:
"In addition, there appears to be a need for a subtle philosophical
change in the traditional engineering approach to problem solving
and design. Usually, the integrity of a road, dam, or any other
structure is viewed as the primary goal, and thus natural processes
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such as erosion, seepage, and settlement are considered as imposi-
tions on the structure which must be controlled or withstood. In-
stead, the road or structure might better be viewed as an imposition
upon the various natural processes, and location and design might
better be oriented toward assuring the continuity of, or at least
compensation for changes in, these natural processes. By so re-
orienting design philosophy not only should the integrity of roads
and structures be better guaranteed, but the chances for causing
undesirable changes in the functioning of natural systems should be
considerably reduced. Of course, by changing the question from
"What are the natural processes which will endanger the road's in-
tegrity"? to "How will the road influence natural processes"? the
designer is forced to consider a broader spectrum of environmental
factors. Thus, muItidisciplinary cooperation and teamwork become
not only desirable, but absolutely essential to the completion of
the planners' and designers' work". (6)
The chapters thert follow this introduction are in the order that a
logging road develops namely: (I) planning and reconnaissance, (2)
design, (3) construction and (4) maintenance. These divisions are not
meant to imply that an appropriate engineering organization for every
forest land owner will be similarly structured. Each owner's engineering
staff will be structured in accordance with his individual circumstances
in terms of size, terrain, policy, private or public, product and goals.
A good case can be made for the procedure that assigns to one individual
or team the responsibility to deliver a completed road. Such a procedure
provides continuity in the planning and reconnaissance, design and con-
struction phases. Also, an organization whose personnel policies result
in the maintenance of a stable engineering staff possessing many years
of experience on the land that it manages and/or harvests has a great
asset when approaching the problem of minimizing the creation and trans-
port of sediment.
Writings on the subject of sediment creation and transport in the
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forest are extensive. A large reservoir of knowledge is also possessed
by individual experienced forest engineers, knowledge that they have not
recorded. There are no doubt many successful techniques of sedimentation
control omitted from the chapters that follow.
A. SUMMARY AND CONCLUSIONS
There is an abundance of written material available on the subject
of minimizing the creation and transport of sediment accruing from logging
haul roads. Further sources of information are the experiences of indivi-
duals long associated with the design, construction and maintenance of
these roads.
The value of a thorough planning and reconnaissance program for a
proposed road is emphasized by many authorities. No amount of design or
construction expertise can recover from an approach based upon inadequate
reconnaissance information. Field reconnaissance evaluations must include
attention to the potential for mass movements as well as surface erosion.
In steep terrain, it is likely that the engineering investment to insure
a stable road will be much more exhaustive than on gentle terrain.
The general approach to design must be the classic engineering
approach of according individual treatment to the individual circumstances
of the site. Creative design is needed.
Many mass failures are drainage associated. Drainage design often
appears to have lacked attention to one or more of the following features.
I. Determination of the design flood.
2. Evaluation of the potential for debris blockage.
3. Choice of stream crossing method.
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4. Attention to installation requirements at both the design and
construction levels to insure structural integrity.
Minimization of surface erosion and sediment transport begins with the
appropriate treatment or design of slope protection and continues with
the necessary attention to ditch size, lining, culvert intakes, culvert
integrity and culvert outlets.
Under most conditions vegetative or other forms of permanent cover
are essential to prevent excessive surface erosion from cut and fill
slopes. Vegetation establishment should be initiated as soon after soils
disturbance as possible. Various grass and legume seed mixtures are
suitable for establishment of vegetation in Region X depending on climatic
and other environmental conditions. Seeding should be accompanied by
fertilization and re-fertilization as necessary and by watering to main-
tain vegetative vigor. Mulches, chemical soil stabilizer's, or mechanical
measures are necessary to prevent high initial rates of soil loss during
vegetation establishment and in some cases to aid in vegetation establish-
ment.
It is important to sequence the construction in a manner that affords
the least exposure to storm damage during construction. Contractural
relationships between owner a nd road builder should be such that a quick
response can be made by all parties to changed circumstances during con-
struction. Failure to respond promptly can greatly enhance the potential
for sediment creation and transport. New types of construction equipment
are needed for clearing and excavating for narrow roads in steep terrain.
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The key factor in a successful maintenance program is motivation
and knowledge of maintenance personnel. Individuals control sediment
transport attendant to maintenance operations.
Occasional slides can be expected along logging roads even with the
best of location and design practices. In some cases, abandonment of
the road may be preferable to removal of slide debris and correction of
the problem. Where it is necessary to remove slide debris, it should
be placed in selected spoil areas.
Water quality parameters including temperature, turbidity, dissolved
oxygen levels, and dissolved minerals concentrations should be monitored
before, during and for as much as a year following logging road construc-
tion. Sampling stations should generally be located directly upstream
and downstream of the subject area. Sampling should be timed to coincide
with significant construction activities and meteorological conditions.
Although inclusion of design criteria for sediment control may in-
crease initial capital outlay, it does not necessarily increase total
annual cost over road life. There may be offsetting savings in annual
maintenance costs. Stable cuts and fills and adequate culverts and
bridges are desired by forest owners and users for many reasons other
than sediment control. Features for sediment transport minimization con-
structed outside of the roadway corridor are the most obvious examples of
capital outlay for sediment purposes only.
When construction is accomplished in accordance with adequate plans
and specifications in a workmanlike manner under strict supervision, the
control of sediment tends to be coincident.
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B. RECOMMENDATIONS
The trend toward obtaining a thorough field reconnaissance for
logging roads should be continued and even accelerated.
The Universal Soil Loss Equation, with recent modifications, is an
acceptable methodology for prediction of soil loss by erosion for some
conditions. Considerable expansion, refinement, and potential modifica-
tion of the equation through research and field testing are needed before
reasonably reliable predictions can be made for a wide range of site and
design condit ions.
A system of high altitude rain and stream gaging stations, establish-
ed in advance of logging or road building operations, would be helpful to
the determination of mountain stream flows.
Organizations should assign responsibility and authority to experi-
enced engineers at the local level to plan and design the logging roads.
Personnel policies should support the retention of experienced engineers
in or near the forests they serve.
Highway engineering tools, criteria and techniques developed for
state, county or municipal roads should not be blindly applied to forest
roads.
Equipment manufacturers may have to be lured into developing the
kinds of equipment that will construct narrow roads in steep terrain with
relative economy and speed. Such incentives may come from denial of use
of current equipment by contract requirement and/or funding of appro-
priate applied research by the forest land owners.
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II. ROUTE PLANNING AND RECONNAISSANCE
Route Planning and Reconnaissance are regarded by many as the most
important phase of logging haul road development. It is at the planning
and reconnaissance level that first evaluations of soil erodibility, the
potential for mass movement, and the potential for sediment transport
must be made. These evaluations may confirm the proposed road corridor,
cause a change in forest harvest procedure, indicate the need to survey
an alternate corridor or contribute to a no road decision.
The importance of road reconnaissance has been expressed in numerous
ways. Crown Zellerbach Corporation's "Environmental Guide, Northwest
Timber Operations," states in Chapter V, Road Building: "Special
emphasis must be placed on proper road planning, design of cross sec-
tions, and field location to reduce soil erosion problems and consequent
stream siltation and stream blockages." (?) R. W. Larse, in a paper
entitled "Prevention and Control of Erosion and Stream Sedimentation from
Forest Roads," emphasized planning and reconnaissance when he stated:
"Road planning and route selection is perhaps the most important single
element of the road development job." (8) The U. S. Forest Service
Region 6's Recommendation 3-1 from "Timber Purchaser Road Construction
Audit" is: "Preconstraction geotechnical investigations, transportation
planning, and construction inspection on earthwork and drainage should
receive the highest priority for manpower." (9) The Siuslaw National
Forest's "Implementation Plan" to the Region 6 Audit agrees that "the
greatest potential for land impacts from road construction lies in
areas of steep topography and unstable soils." (10) The Boise National
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Forest's publication "Erosion Control on Logging Areas" states: "To a
great extent erosion can be prevented by controlling the location of
roads and skidways in relation to the natural drainage, slopes, and
soil conditions." (ll)
In the recommendations contained in "Flood Damage In The National
Forest of Region 6," Jack S. Rothacher and Thomas B. Glazebrook believe
that any procedures designed to minimize unusual weather impacts on soil
must be based on increased knowledge of geomorphic history, climate,
hydrology, vegetation, soils and landscape features of the land. (12)
"The importance of reconnaissance is indicated by the fact that failure
to consider all alternates may result in future excessive costs far
beyond any savings effected by not accomplishing a complete reconnais-
sance." (13) (Bureau of Land Management "Roads Handbook" 1965)
R. D. Forbes in "Forestry Handbook" quantified the total planning
and design effort required when he stated: "The importance of adequate
surveys, and careful planning for road construction justifies engineering
costs up to 5$ of total cost for low standard while 10$ to 15$ is reason-
able for engineering permanent heavy-duty hauling roads in rough country."
Neither the competent designer nor the competent road contractor can
economically overcome faults in a road concept that are related to inade-
quate planning and reconnaissance.
The discussion of route planning and reconnaissance that follows
begins at the point where the forest land manager has determined that a
road is required. The manager has made some preliminary decisions as to
the purpose of the road and companion decisions as to the general cor-
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ridor that is preferable from a management viewpoint. He conveys this
information to his engineering staff for implementation. Results of
the subsequent engineering planning-reconnaissance phase may alter the
initial management decision.
Section A of this chapter covers engineering planning aspects and
the engineer's communication with land management. Section B discusses
the field reconnaissance by geotechnical forest and civil engineering
personnel. Section C discusses economic evaluations. The chapter is
divided in this manner partly for the convenience of presentation. The
planning and reconnaissance activities are often very interrelated depend-
ing upon the type of organization and the nature of the road project under
study.
A. PLANNING
1.00 Management-Engineering Dialogue
The engineers' introduction to the Forest Land Manager's road re-
quirement may occur in a variety of ways (formal to informal). Often
this introduction develops into a dialogue between the two parties. The
communication may encompass road standards, intended use, harvest methods
and road life. The discussion may result in a program of road feasibility
studies or simply a direct road reconnaissance and design.
Initial communications become critical to the road development par-
ticularly when minimum environmental impact roads, including sediment
minimization, are required. In their communications, both the engineer
and the land manager must attempt to reach a complete and explicit under-
standing to avoid communication gaps. An illustrative case is the China
Glen Road on the Warren Ranger District, Payette National Forest, Idaho.
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The road was to serve a salvage timber sale in three fragile water
sheds. Special instructions from management were to minimize water-
shed damage. Road standards had, to some extent, been established by
the forest management. Engineering appeared to have accepted these
standards.
Prior to construction, management reviewed the design documents
and road construction was begun. However, gaps in their initial com-
munication became evident as is reported by W. S. Hartsog and M. J.
Gonsior.
"During field inspection, land managers expressed
concern that the road would have more impact than had
been anticipated. They felt th^at cuts and fills were
larger than desirable or necessary. Apparently, they
could not fully visualize the final product from the
design sheets, which indicates a need for better com-
munications." (15)
The China Glenn Road experience demonstrates the need for communi-
cation when roads in ecologically sensitive areas are envisioned. In
some cases, (particularly steep terrain) small soil and geologic dis-
turbances result in measurable ecological differences including stream
siltation and sediment. In these circumstances the responsible forest
engineer continues the dialogue and provides "feed back" to the forest
land manager by evaluating the terrain's situs condition. The engineer
will evaluate the terrain in such terms as elevation, aspect, soil
strength, ground slope, ground water, geologic formation and precipitation.
The need for the engineer to evaluate management's decision is
accentuated by the fact that a large part of the commercial forest lands
in Region X are located on land that requires a careful assessment of
the road's potential performance. This assessment should embrace a
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14
determination as to whether or not existing technology is equal to the
ambient circumstances within a particular road corridor.
2.00 Engineer's Assessment of Management's Decision
The technological tools available to the engineer to accomplish a
pre field reconnaissance evaluation of a proposed road corridor might
include his own knowledge of the area, performance of existing roads
in similar terrain, topographic maps, geology maps, soil resource maps
and hydrology data. His evaluation should permit him to advise manage-
ment that a preliminary assessment of the proposed road corridor has
led to one of the following answers:
1. There is no chance of a stable road being constructed.
2. The road envisioned by management cannot be constructed but
one of lesser design criteria in terms of width, grade and
horizontal curvature might be constructed pending confirma-
tion by field reconnaissance.
3. A road might be constructed into the general area with com-
panion modification of the harvest procedure.
h. Management's road might be constructed pending confirmation
by field reconnaissance.
5. Management's road can be constructed with relative ease pending
confirmation by a brief field reconnaissance.
2.01 State of the Art Techniques
Within the past few years, some forest land owners have developed
a keen awareness of the hazards of sediment production. From this aware-
ness, a number of land management devices which attempt to evaluate the
timber production land base have been developed. Several of these devices
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15
focus on the effect of unstable terrain on forest land management prac-
tices including road construction. These land evaluation tools are of
basically two orders, regional to sub-regional (i.e. Pacific Northwest
divided into homogenous land form unit like the Northwest Olympic
Peninsula), sub-regional to local (i.e. Northwest Olympic Peninsula land
form units of 10 acres or larger homogenous units). The following para-
graphs illustrate techniques which have been developed by Region X
researchers and practitioners to critique sensitive terrain.
1. The Forest Residue Type Areas Map produced by the U. S.
Forest Service for Region 6 is an example of the larger
scale. This information shows geomorphic provinces, timber
species associations and geomorphic sub-provences. The
smallest mapping unit is approximately 10 miles square. (l6)
2. The U.S. Forest Service's soil resource inventory for Forest
Service Region 6 and other regions represents the next level
of forest land identification. "Soils have been defined and
mapped at an intensity sufficient for broad management inter-
pretations which can be used to develop resource management
policies." (I?) (Gifford Pinchot National Forest Soil Resource
Report) In addition to these uses, forest soils are rated as
to their potential erosion class, very slight, slight, moderate,
1 severe and very severe. "The land manager can use this informa-
tion to determine which areas will need special erosion protective
measures. These will need to be developed on a site by site basis."
(l8) These maps serve transportation planning needs as well.
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"Conditions and problems can be met or avoided based on infor-
mation such as landscape stability, soil depth, soil drainage
and/or bedrock type and competency." (19)
3. The Bureau of Land Management, Oregon State Office, is accom-
plishing intensive inventories of its western Oregon lands.
The objective is to provide the manager with detailed, in
place information about timber production sites for which he
is responsible. (20) The intensive inventories deal with the
total land mass by separating the land base into various cate-
gories of potential forest production. One category, designated
as fragile, pertains to adverse soil and geologic conditions.
Fragile sites are defined by slope gradient, ground water, geo-
logic material (bedrock) and soil strength. Appendix 5 to
Bureau of Land Management Manual Supplement No. 5250 - "Intensive
Inventories", dated February 7, 197^, deals with procedures for
identifying fragile sites. "Guide to Reduce Road Failures in
Western Oregon" by Burroughs, Chalfant, and Townsend includes a
general outline of Western Oregon geology, and discusses basic
slope stability, and techniques for constructing stable roads on
specific geologic materials and soils. (21)
k. The Siuslaw National Forest has developed two schemes for eval-
uating terrain readability.
a. "Workload Analysis - Geo-technical Investigation
for Timber Sale Roads." (22)
b. "A Proposed Method of Slope Stability Analysis,"
Jennings and Harper.
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17
The work load analysis uses a factor "P" which expresses a per-
cent probability that a given section of road location will
require a given level of geo-technical investigation. Figure
11A-1 is taken from Appendix E of the Siuslaw Implementation
Plan and illustrates the use of the "P" factor.
The Proposed Method of Slope Stability Analysis attempts
to answer many forest land administrators and planners who have
expressed a need for a quantitative evaluation system to rate
slope stability. This report proposes a slope evaluation system
based on a soil mechanics safety factor formula and named "The
Stability Index (SI)". It is intended to describe the generalize
slope stability of a soil mapping unit, separating only the effect
of slope. It is not to be used to evaluate on-site stability for
specified projects "but with additional input it could be used as
a starting point for project site analysis." (23)
5. "Highway Cut and Fill Slope Design Guide Based on Engineering
Properties of Soils and Rock" by Larry G. Hendrickson and John W.
Lund is a valuable design guide for specifying cut and embankment
slopes. (2k) This design approach attempts to reduce the use of
intuitive techniques and substitutes a more rational approach.
This approach uses soil strength properties and recognizes the
need for flatter slopes as cut heights increase. This work is
incorporated into the U. S. Forest Service's Transportation
Engineering Handbook for Region 6 as Supplement No. 19, dated
February 1973- The supplement digest explains the Design Guide
as follows:
-------
HA-
AHALN5I6 -
I^VESTI 6AT\QHS
FOR TIMBER 6&L.E F?OAPS - 6ILJ6L&W NATIONAL
E. -
«O WL6S
MU REv/lEUU
r*3 FOPHUiL S6OT&lMt
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19
"Incorporates slope design guide. This is a guide
which provides general values or recommendations
for cut and fill slope ratios. Data needed to use
the guide are soil classifications, general field
conditions in respect to density and moisture, and
height of cut or fill.
"The recommendations given must be modified to fit
local conditions and experiences." (25)
6. Douglas N. Swanston and others of the U. S. Forest Service
developed a pilot program for determining landslide potential
in glaciated valleys of southeastern Alaska. This develop-
ment was in response to investigations which had shown erosion
to be a predominate problem in southeast Alaska.
Land stratification techniques were used to classify
potential landslide hazard. Data on land features were
characterized by "accurate location and distribution of all
active and potential land slides and snow slides and the esti-
mated or probable major variations in a slope stability
characteristics from one location to the next within the
investigated area." From this information a hazard rating
system was devised to stratify land zones. (26)
Their experience with the southeast Alaska's steep slopes
with shallow coarse grained soils lead them to use three clas-
sifications .
a. "A slope above 36° is highly unstable even under
the most favorable of natural conditions.
b. Slopes between 26°and 36° may or may not be stable
depending on local variations in basic soil charac-
teristics, soil moisture content and distribution,
vegetation cover, and slope.
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20
c. Slopes below 26° (U9/0) were considered stable
although local steep, hazardous areas not picked
up in the initial survey may exist, and opera-
tions on them should be governed by the rules
for more unstable areas."
Swanston emphasizes the many natural unstable slope condi-
tions in Southeastern Alaska and observes that man's activities
will aggravate them. He believes that the land manager must
decide whether "to accept the consequences of logging over
steepened slopes or to control the effects of these activities
in order to minimize mass movements." (2?) He suggests that
control can be accomplished by direct methods of slope stabili-
zation or by avoiding areas of known or expected instability.
2.02 Roads & Harvest Method Relationships
There is a general trend in forest land management toward a closer
coordination of road planning with harvest methods. One of the factors
supporting this trend is the realization that past practices have some-
times resulted in haphazard road patterns resulting in more total road
mileage than necessary. Minimizing the road mileage is a way to mini-
mize the need to deal with the sediment creation and transport problem.
Recognition of the problems attendant to over reading is not new.
In 1956, the Boise National Forest's guide lines for erosion control
reported a tendency for an excess of roads with the increased use of
heavy construction equipment and "especially if the construction chance
is easy." This publication further stated: "Too many roads within an
area completely destroy the protective soil mantle." (28)
Fredriksen studied erosion and sediment resulting from timber harvest
and road construction in watersheds within the H. J. Andrews Experimental
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21
Forest. (29) A -watershed harvested by clear cutting with Skyline
logging without roads yielded less sediment than a watershed harvest
by patch clear cutting, high lead logging and parallel logging roads.
Although harvest method - road relationships are not exclusively
the forest engineers domain, or are they exclusively pertinent to the
subject of sediment, serious attention to these relationships is believed
to be an important part of the engineer's initial discussions with the
land manager. The engineers pre-field reconnaissance response to the
land manager as to the engineering feasibility of a proposed road may
appropriately include a response to management's assumed logging method
as previously mentioned. Alternately, the engineer may be asked to
assist the land manager in determining the type of harvest method com-
patible to the type and location of road that can be constructed in the
proposed corridor.
Knowledge of the harvest method and its effect on road location,
width and alignment is of vital importance in defining the scope of the
field reconnaissance. Part B "Reconnaissance" of this chapter will dis-
cuss this aspect of the proposed harvest method in more detail.
3.00 Conclusions
After the engineer's report to the land manager, a mutually agreeable
definition for the road reconnaissance should be ideally established.
Since a "no road" decision is complicated in marginal terrain, a field
reconnaissance to affirm this decision may be desirable.
A specific understanding of management objectives is a need that
was emphasized in Recommendation 6.1 of the U. S. Forest Service Region 6
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22
Road Audit. (30) The Siuslaw National Forest Implementation Plan urges
detailed management inputs including trade offs considered, allowable
impacts on road geometry that are acceptable to attain an objective and
the inclusion of "realistic confidence levels expected in the designer."
(3D
B. ROUTE RECONNAISSANCE
Route reconnaissance is the examination of the entire area surround-
ing the proposed project with the intent to segregate routes on their
relative merits of economics, service and ecological impacts. The talents
appropriately involved in a reconnaissance for a particular project will
vary with the scope of the proposed road, the relative sensitivity of the
terrain, the knowledge and experience of personnel and the amount of data
already available about the proposed corridor.
Larse points out that "all too frequently the location of a specific
road is a one-man effort with little consideration or recognition of al-
ternative opportunities, watershed values, land form or soil, character-
istics and stability, or other environmental conditions." (32) A recon-
naissance team might consist of a hydrologist, soil scientist or soils
engineer, geologist, landscape architect, forester, forest engineer, civil
engineer, watershed specialist, biologist and others. The disciplines
listed above might be those assembled for a major undertaking in highly
sensitive terrain about which little applicable data is available.
Members of a reconnaissance team whose duties would include observa-
tions for and the gathering of data to determine potential problems of
sediment creation and transport are the geologist and/or soils engineer,
the forest engineer and the civil engineer. The depth of investigation
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23
necessary for these disciplines cannot be generalized in the abstract
without specific knowledge of the actual site conditions for a proposed
road. As pointed out in Part A 2.01 of this Chapter, the Siuslaw
National Forest has a procedure for determining the depth of geo-
technical investigation required for a given road location.
As the introduction to this Chapter emphasized, an adequate field
reconnaissance is of great importance when the goal of sediment minimi-
zation is a part of logging road performance criteria. Historically,
road failures have been related to the following oversights or errors.
1. Inadequate geotechnical information.
2. Application of rigid rules regarding horizontal curvature and
vertical gradients.
3- Over reading or misplaced roads due to a lack of or a poor land
management and transportation plan.
k. Road locations to support an inappropriate harvest procedure.
The discussion that follows is divided into three parts: '(l) Factors
affecting surface erosion, (2) Erosion and mass wasting considerations, and
(3) Civil and Forest Engineering Reconnaissance.
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24
1.00 Factors Affecting Surface Erosion
1.01 Introduction
Planning for effective prevention and control of soil erosion
is dependent upon a basic understanding of erosion processes. Many
factors with often complex interrelationships are involved.
Considerable research effort has been expended on identifying these
factors and their relationships, but predictive methodologies
(mathematical formulas for calculating erosion as a function of measurable
field parameters) still fall short of accurate prediction of soil erosion
and resultant downgradient sediment production, particularly in a forested
environment. Additional information and data are needed and methods
need to be refined. However, the available research studies have
been invaluable in identifying the major factors influencing soil
erosion and providing a relative measure of their importance.
1.02 Soil Loss Equations
The relationships among the principal factors controlling soil
erosion, notably sheet erosion, have been embodied in several somewhat
similar predictive equations (33, 34 ). Most of the methods
available to date have been developed for cropland areas. Of these
methods, the "Universal Soil Loss Equation" for the prediction of
sheet erosion as presented by Wischmeier and Smith in USDA-ARS
Agriculture Handbook 282 (33 ) has gained the most widespread
acceptance. The equation was originally developed for cropland
areas east of the Rocky Mountains, but has since been adapted to
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25
other uses ( 36) as well as for forested areas including forests of
the Pacific Northwest (35 )• Although modified in consultation with
Wischmeier, it is important to point out that the Bureau of Land
Management's adaptations as proposed in Reference 35 have not been
field tested to any significant extent.
1.03 Universal Soil Loss Equation
The Universal Soil Loss Equation takes into account the influences
of rainfall characteristics, soil characteristics, topography, and
land cover conditions. The Universal Equation is as follows:
A = RKLSCP (Eq. II B- I )
where A is the potential soil loss in tons per acre per year, R is
a rainfall factor, K is a soil-erodibility factor, L and S are slope
length and steepness factors, C is a cover and management factor, and
P accounts for supporting conservation practices such as terracing,
strip cropping, and contouring. Use of some of these factors must
be modified slightly for use of the equation in a forested environment.
a. Rainfall Erosion Factor. The rainfall erosion factor, R,
accounts for the combination of rainfall kinetic energy available
for detachment of soil particles and associated runoff available to
transport them and to detach others. The factor is defined to be
the total kinetic energy of a storm times its maximum 30-minute
intensity as indicated by the following relationship:
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26
R -£EI QEq. II B-2 )
100
where E is the storm energy in foot-tons/acre-inch and I is the
maximum 30-minute rainfall intensity in inches/hour. For a season
or year, the total R is the sum of the individual storm values.
The kinetic energy of rainfall, E, is related to rainfall intensity
by the following formula (36):
E + 0.0916 + .0331 log1QI (Eq. II B-3 )
To compute E, the rainstorm is divided into increments of approxi-
mately uniform intensity and the energy for each increment is computed
using Equation II B-3 . The sum of these incremental values of E
for the entire storm represents the E value to be used in Equation
II B- 2 . The I value to be used is the maximum 30-minute intensity
during the storm.
R values have been computed for the U.S. east of the Rocky
Mountains and published as iso-erodent maps (33) . R values for
areas west of the Mississippi River have been correlated with the
2-year, 6-hour precipitation. The relationship is presented on
Figure II B-I . Wischmeier calculated R values for Portland, Oregon,
and they correlated reasonably well with values obtained using
Figure II B- I ( 35) . Actual R values for specific locations in
USEPA, Region 10 can best be calculated using local rainfall records
corrected for elevation of the subject area or as a less accurate
alternative, the R value can be obtained by converting the 2-year,
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27
6-hour precipitation values shown on Figure II B- 2 to R values by
means of Figure II B-I . Two-year, 6-hour precipitation values can
be obtained for the northwestern United States and Alaska from U.S.
Weather Bureau publications TP-40 ( 37 -) and TP-47 ( 38).
b. Soil Erodibility Factor. The erodibility of a particular soil
is dependent upon its resistance to detachment and once detached to
its susceptibility to transport. Water intake capacity and structural
stability are the overall controlling factors.
Extensive research on identification of individual soil character-
istics influencing erosion including studies leading to development
of simplified means for determination of the K-factor in the Universal
Equation indicates the interrelated involvement of numerous character-
istics including soil texture; type, amount, orientation, and chemical
properties of colloids (clay size particles), particularly the presence
of swelling clays; organic matter content; percentage of coarse
aggregates and other large, essentially non-erodible particle; and
chemical properties of the eroding fluid in the case of some clays.
Soil permeability and the presence of impervious layers at shallow
depth are also very important because of their effect on runoff.
Of the individual characteristics, particle size and degree of aggre-
gation have the most influence. Clays, for example, have very small
particle size which are easily transported by water, but are not
easily detached because of high aggregation. Sands,on the other hand,
are very easily detached, but are not easily transported because of
much larger particle size. Silts have relatively small particle size,
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28
although not as small as clays, and are generally relatively easily
detached and easily transported, thus making them most vulnerable
to erosion.
The soil erodibility factor, K, in the Universal Soil Loss
Equation defines the inherent erodibility of the soil. The K-value
for a particular soil is inherent in its makeup and is independent
of geographical or other factors. Data used to obtain the K-value
can be obtained by field and/or laboratory tests.
In development of the simplified means of determination of the
K-Factor, the standard USDA textural classification system commonly
used by the Agricultural research Service was found to correlate
poorly with soil erodibility. To obtain better correlation, it was
necessary to modify the size differentiation between silt and sand
as shown in Table II B-l because fine sand was found to behave like
silt. The Unified Soil Classification System,particle size classifi-
cations and U.S. Standard Sieve sizes for the classification divisions
in the Universal Equation are also shown for comparison.
TABLE II B- I
GRAIN SIZE IN MM
Clay
Silt
Sand
Universal
Size
<.002
.002-. 10
.10-2.0
Equation
U.S. Standard
Sieve Size
-
140
USDA
<.002
.002-. 05
.05-2.0
Unified
unspecified
- to .074
.074-4.76
10
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To facilitate use of the textural data, a parameter was developed
to describe the entire particle size distribution for a given soil.
This parameter takes into account the percentage of silt and the
clay-to-sand ratio. The parameter, in graphical form, comprises the
left section of the nomograph shown on Figure II B-3 . In general
terms, this parameter reveals that silt-size particles are most easily
eroded and that soils become less erodible as either the sand or
the clay fractions increase. For a given increment of silt, increases
in the clay-to-sand ratio decrease the erodibility.
Even though the new size distribution parameter alone accounted
for about 85 percent of the variance between actual and predicted
values of erosion from test plots, it was necessary to include three
more parameters to remove wide deviations between actual and predicted
values for a few plots. These new parameters, which comprise the
remainder of the nomograph shown on Figure II B-3 , include organic
matter content, soil structure, and permeability. Descriptive
definitions of soil structure and permeability are included on Figure
II B-3 . Unless extensive disturbance is expected, all values to
be used in the nomograph except permeability are for the top 6 to 7
inches of soil.
The test results used in developing the nomograph indicated that
organic matter content, is inversely related to sediment production.
This relationship was strongest for silts and silty and sandy loams
and declined significantly as clay content increased. Also, soils with
blocky or massive overall structures or with high permeability were
found less susceptible to erosion.
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30
The method developed for nomograph determination of the K-factor
does not take into account soils particles above 2 mm in diameter.
These coarse aggregates commonly comprise a significant percentage
of the upper soil profile in forested mountain areas of USEPA, Region
10. In introducing the nomograph, Wischmeier ( 39) states that the
percent of coarse fragments in the soil can have a significant
influence and that beyond some limiting density would be expected to
act much like a protective mulch. However, because of limited data
on erosion from soils with coarse aggregates, Wischmeier was not able
to state the minimum density required or provide any numerical
relationships quantifying their importance. From his extensive inde-
pendent study of factors influencing erosion on logging roads in the
northern Rocky Mountains, Packer ( 46) concluded that the presence
of water-stable aggregates larger than 2 mm in diameter on road surfaces
and cut slopes above roads had a very significant effect on preventing
erosive cutting. In modifying the Universal Equation for western
Oregon the Bureau of Land Management ( 35) suggested reduction of the
K-factor by the percentage of coarse fragments in the upper soil. This
approach appears reasonable until additional research data becomes
available.
c. Slope Length and Steepness Factors. The capability of runoff
to detach and transport soil material increases rapidly with increases
in runoff velocity. Theoretically, doubling velocity enables water to
move particles 64 times larger, carry 32 times more material in
suspension, and increases the erosive power 4 times (40). Runoff
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3i
velocity increases as the runoff rate increases, as the flow concen-
trates (often because of increased slope length), or as the slope
steepens. Increasing the steepness of a slope from 10 percent to
40 percent, for example, doubles the flow velocity.
The dimensionsless factors L and S in the Universal Soil Loss
Equation account for the effects of slope length (L) and steepness (S).
The slope factors have a value of unity for the basic test plot
dimensions of 9 percent gradient and 72.6 feet length as used in the
final stages of development of the simplified means of determination
of the soil credibility factor, K. Equations and a chart are presented
in Reference 33 for consideration of gradient and length effects on
slopes not exceeding 20 percent and of moderate length (approximately
400 feet or less). However, in mountainous forested areas of USEPA,
Region 10, slopes often exceed 20 percent by a large margin and may
have unimpeded lengths exceeding 400 feet.
In modifying the Universal Equation for use in western Oregon,
the Bureau of Land Management (35) presents new equations for computing
L and S factors for slopes with greater steepness and length. The
equations are presented below:
L - (slope length (Ft.)0'6 (Eq. II B-4 )
75
S • (% slope)1'4 (Eq. II B-5 )
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..32
The slope length (L) and gradient (S) have been combined as LS and
may be obtained directly from Figure II B-4 for slopes up to 50
percent with lengths up to 2,000 feet.
When a slope is irregular, the average steepness does not accurately
predict the slope effect. The soil loss rate at the toe of a convex
slope (steepening towards the toe) is greater than on a uniform slope
of equal elevation change while the opposite is true for a concave
slope. Significant differences in soil loss can occur in slopes of
equal elevation changes because of different shapes as illustrated on
Figure II B-5 . For more detailed information, the reader is advised
to consult references 41 and 42.
d. Cover-Management Factor. Raindrops striking bare soil act
like miniature bombs to break up soil aggregates and splatter soil
particles as much as 2 feet into the air. Raindrops also compact
the exposed soil surface causing increased rates of surface runoff.
Some conception of the striking force can be envisioned from the fact
that raindrops strike the ground at velocities of about 30 fps and
1 inch of water over an acre of area weighs more than 110 tons.
Erosion can be materially reduced by maintenance of a dense
ground cover as protection against raindrop impact. Vegetation is
the most effective means of providing this cover. Vegetation canopy
and resultant ground litter both act to absorb and disperse raindrop
Impact. Vegetation also stabilizes the soil surface with a dense
mat of roots.
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33
The cover-management factor, C, in the Universal Equation is
used to account for the efficiency of different cover and management
combinations in protecting against soil loss. C ranges in value from
near zero for excellent sod or a well-developed forest to 1.0 for
continuous fallow, construction areas, or other extensively disturbed
soils.
Although initially developed for cropland areas, the C-factor
can be applied to other environments. Along newly constructed logging
roads or other extensively disturbed construction areas, C reflects
the influences of various types and rates of mulch, application of
slash debris to slopes, methods of revegetation, degree of compaction
of fill slopes, as well as other such factors. The effects of some
of these factors have been investigated for specific environments and
the information published in numerous references. The effects of
different mulches and mulch rates on reducing erosion are discussed
in Section III B-1.03 of this report. This type of information can be used
to develop C-factors for logging roads in the forest environment.
e. Conservation Practices Factor. The conservation practices
factor, P, as developed.for cropland areas in the Universal Equation
reflects the runoff control and erosion-reducing effects of conservation
practices such as contour farming, terracing, or strip cropping. The
counterparts of these conservation practices serve equivalent purposes
i
in forested areas. Terraces, or benches, and diversions on steep
slopes above or below logging roads can be used to reduce effective
slope length and prevent concentration of flow in undesired areas.
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- 34-
Provision of buffer strips between areas disturbed by logging road
construction and stream courses, which is anaolgous to strip cropping
of farmland, is an important conservation practice in logging and
logging road construction.
Several researchers including Packer (46 ) and Trimble and
Sartz (47_.) have studied the effect of various types of buffer strips
and other factors on the movement of sediments downgradient of logging
roads. The reader is advised to consult these references for an
indication of the effectiveness of these various conservation factors
on reducing the movement of sediments.
1.04 Stream Sedimentation
It is important to note that the quantitative procedures embodied
in the Universal Equation are limited to on-site erosion. There is
no provision in the predictive methodology to compute the proportion
of eroded sediments reaching watercourses. To extend the predictive
ability, Dissmeyer ( 48, 49) has reportedly developed a method called
the First Approximation of Suspended Sediment (FASS) to evaluate
the impact of disturbances or control practices on suspended sediment
contribution to surface.waters. In addition to the contribution from
sheet erosion, FASS also takes into account gully and channel erosion.
When available, this method may have some application for the care of
logging road sediment contribution to streams. Several other predictive
equations developed to date can be used to evaluate downstream sedimenta-
tion for a given set of upstream conditions ( 40) , but only for watershed-
size areas and not for individual construction areas or for evaluation
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35
of specific conservation practices as would be required in the case
of logging road construction.
1.05 Other Information Sources
For more extensive and complete bibliographies on factors
affecting erosion and other closely related subjects, interested
readers are advised to consult references 36, 49 and 50.
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Relation of Annual El to 2-Year 6-Hour Rainfall
West of the Mississippi River
Figure II B-I
Source: Reference 35
w
I
-------
2-YEAR 6-HOUR RAINFALL (INCHES)
Fig IIB-2
Soured : Climatological Handbook
Columbia Basin States, Precipitation,
Vol. 2.
(also avail, for entire U.S. in
U.S. Weather Bureau TP40)
Meteorology Committee
Pacific N. W. River Basins
Commission, Sept. 1969
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38
Figure II B-3. Soll-Erodibility Nomograph
* SOIL STRUCTUftC
PROCEDURE: With appropriate data, enter scale at left and proceed to
points representing the soil's sand (0.10-2.0 mm), % organic matter, structure
and permeability, in that sequence. Interpolate between plotted curves. The
dotted line illustrates procedure for a soil having: si+vfs 65%, sand 5%, OM
2.8%, structure 2, permeability 4. Solution: K = 0.31.
Structure Index
1
2
3
4
Definition
Very fine granular
Fine granular
Medium or coarse granular
Blocky, platy, or massive
Permeability Class
1
2
3
4
5
6
Definition
Rapid
Moderate to rapid
Moderate
Slow to moderate
Slow
Very slow
Source: Reference 36
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Source: Reference 35
— Figure II B-4 ;';;.[.;.:
Extrapolated far beyond the range of the 7-
data. Use only as speculative estimates, ill
800 1000 1200
. . —SlopeJLeagth fPt )
1600
1800 t. 2001
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Fig. IIB-5
j Figure 3. Influence of land slope shape on
' Mdiment load.
(36)
(not original)
-. Influence of several mulch types and
rates on soil loss from 5:1 construction side-
slope (rain intensity = 2.5 inVriour; total
applied " 5 in.; slope length = 35 ft).
Fig. IIB-6
39. 6J
J25.6
In. 4
Ds.s
W NW.CH
2 T/A WOOCHIPS
15 T/A STONE
70 T/A MAYO.
2.3 T/A STRAM
60 T7A STONE
4 T/A WOOOCHIPS
7 T/A NOOOCmW
13S T/A STONE
240 I 375 T/A STONE
12 1 25 T/A WOODdftK
0 10 . 20 30 40
SOIL LOSS (tons/tcrc)
(43)
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44
2.00 EROSION AND MASS WASTING CONSIDERATIONS
2.01 . Introduction
Roads can have a serious impact on the hydrologic functioning of
watersheds. In many cases, 90 percent or more of the accelerated
erosion in forested watersheds has been attibuted to roads (53). Higher
runoff rates and increased surface erosion and mass wasting account for
these increases. Much of the soil movement could be avoided by proper
road location and design. Adequate field and office investigative work
is necessary to assure that the essential information needed for selec-
tion of the best route and proper road design is available (66).
During the planning process discussed earlier in Section IA, the
need for the road is established and road termini and intermediate
points are defined resulting in delineation of a general rosd corridor(s),
Other controlling design parameters such as type and volume of antici-
pated use, type of road, and any special features required are also
defined. However, prior to any actual design work reconnaissance
studies must be conducted to locate the best road alignment and gather
information needed for design of the road itself and associated drainage,
erosion, mass wasting, and other control measures. The source of the
reconnaissance information can range from office maps and reports
through detailed investigative programs involving field explorations
and laboratory analyses.
Information of various types from a broad-based team of technical
specialists is required to develop a road design that best suits its
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intended purposes while minimizing economic and environmental costs.
However, because of the scope of this study, only those factors affect-
ing road performance with regard to surface erosion and mass wasting as
they affect water quality are included herein. Some of the information
that may be required to guard against stream sedimentation resulting
from surface erosion and mass wasting includes soil texture and aggre-
gation; subsurface soil strength, depth, and other soil or rock
conditions; slope lengths, steepness and aspect; existing surface
erosion and mass movement behavior along the route; precipitation and
streamflow characteristics; groundwater conditions; surface drainage
network; soil fertility and other conditions affecting vegetation
establishment; and up-gradient and down-gradient slope vegetation
patterns.
The importance of the reconnaissance investigation cannot be over-
emphasized. It is during the reconnaissance work that the major
decisions are made. Once the road is located and constructed, mistakes
are often difficult or impossible to correct later on. Failure to do
an adequate job of reconnaissance can easily result in future construc-
tion, maintenance, transportation, and environmental costs far in excess
of savings realized from an incomplete or inadequate reconnaissance (62).
2.02 Aids
Use should be made of all available aids, including topographic
maps, geologic and soils maps and reports, aerial photographs, and other
sources in order to reduce the requirements for field investigations.
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•43"
However, these aids should only be used as supplements and not substi-
tutes for field investigations. As a minimum for simple cases where
information obtained from these aids is deemed sufficient for design
purposes, their accuracy should be field checked. Some of the available
aids and potential applications are described in the following sections.
a. Aerial Photographs. Aerial photographs are particularly
valuable in the planning stage for gaining an overall feel for a
general area and detecting differences between local areas that are
important to route corridor selection. However, they are also of
considerable value in final route selection and design during the
reconnaissance investigation. Aerial photographs of at least one usable
scale are available for most areas and in some areas more than one
scale is available. Many photos are available in stereoscopic pairs
permitting viewing in three dimensional perspective. Land forms,
vegetation, geologic, and hydrologic features are among the features
easily identifiable from such photographs.
Aerial photographs of small scale provide a broad scale perspective
of an area. Whole landscapes can be surveyed enabling study of drainage
networks, geologic features and land forms, and vegetation patterns.
Mass movements, particularly large failures, are easier to detect.
Rotational movements are often indicated by arc-shape bedrock exposures
accompanied by uneven lands downslope or variations or abrupt changes
in vegetative patterns. Avalanche activity can be similarly identified
by abrupt changes in vegetative patterns perpendicular to the ridge
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-44
system. Large features of this nature are often much easier to identify
from such photographs than through use of other aids or on-ground
observations.
Aerial photographs of large scale can be used to refine interpre-
tations made from the small-scale photos as well as enabling more
detailed inferences of drainage, geologic, topographic, vegetative,
and other factors. Geologic bedrock types can often be identified and
some degree of accuracy can be developed regarding the fracturing and
jointing pattern of a particular bedrock type. The extent of talus,
alluvial and other deposits can usually be identified. Slope gradients
can be determined with some degree of accuracy and stream channel and
other drainage characteristics can be studied. Vegetative patterns
and types can be identified. Other interpretations such as soil types
can often be made based upon interaction of geologic and land form
characteristics, vegetation, color, and other factors. Mass movement
of erosional activity of small scale can often be identified.
b. Topographic Maps. Topographic maps of various scales are
available for most areas. Such maps, particularly of the 7^- and 15-
minute series, are quite useful for road location and design purposes
(69). Information on slope gradients and other topographic features
can generally be obtained with a reasonable degree of accuracy,
particularly if over-story vegetation was not dense at the time of
photography for mapping. Geologic inferences, including landform,
slope steepness and irregularity, arrangement and incision of drainage
-------
45
networks, and other features can be made from topographic information.
Topographic maps provide considerable information on stream systems
such as gradients and channel sizes in easily obtainable form. Topo-
graphic maps are quite useful as base maps and provide an easily
available source of gradient information for trial road alignments.
c. Soil Surveys. Numerous types of soils are exposed during road
construction in US EPA, Region 10. They are formed from many different
parent materials including glacial till, alluvial deposits, and granite
to name a few. These soil materials commonly have various unfavorable
physical and chemical properties that affect road performance, stability
against erosion and mass wasting, and revegetation. Some of these soil
characteristics and related topographic conditions that may affect
subsequent road behavior include steep slopes, south and west exposures,
shallowness to rock or other restrictive layers, unfavorable pH, low
fertility, fine texture and low aggregation, low permeability, high
i
groundwater table, high shrink-swell potential, massive disturbance as
a result of previous slide activity, low strength characteristics, and
high compressibility.
Soil surveys furnish considerable information on the extent of
these interacting features. Such surveys are generally compiled as a
single unit for large areas such as counties or natural forest, thus
providing a wealth of information on a broad scale well suited to route
selecion as well as providing general guidance in road design. Soil
surveys are made and published by a variety of governmental agencies
-------
46
and private organizations but mostly by the federal government. The
Soil Conservation Service has published detailed soil surveys for many
counties within US EPA, Region 10, while the Forest Service has published
soil surveys for many of the national forests (69). New surveys are
continually being developed by these agencies and older surveys updated.
The Weyerhaeuser Company has recently completed and published an
extensive soil survey of their land holdings as well as contiguous
adjacent lands.
In addition to providing information on many of the individual soil
properties mentioned previously, most surveys also provide considerable
interpretative information on soil suitability for various uses, includ-
ing limitations on uses. Such ratings may include suitability for road
location and construction; surface erosion potential; susceptibility to
cut or fill bank, mass movement, sloughing, or raveling; limitations
on cut and fill slope seeding; suitability for various types of vegeta-
tion establishment; and numerous other behavioral characteristics under
various uses.
d. Geology Maps. Geology maps of various degrees of detail are
available for many areas. These maps range in scale from state or
areawide to maps of much smaller areas, such as portions of counties
or 7%- or 15-minute topographic quadrangles (69). Depending upon the
degree of detail, geology maps may include information on topography,
descriptions and extent of surface outcrop materials, geologic cross
sections, and strike and dip of formations. Such maps may also include
-------
'47
geologic hazards such as faults, degree of slope, flood-prone areas,
high groundwater table areas, landslide topography, and areas suscept-
ible to various types of surface erosion.
e. Other Aids. Several other less used but often equally
important aids are often of value. These include precipitation
intensity-duration maps, vegetation maps, hydrographic studies, or
other general or detailed reports available for the study area or
similar areas.
2.03 Field Reconnaissance
Field reconnaissance is an essential step in any road location or
design study. In all but the simplest cases where the designer has
access to proven aids and is thoroughly familiar with an area, a field
reconnaissance should be made before final route location or design.
The purpose of the field reconnaissance is to confirm inferences made
from the aids, verify the accuracy of the information obtained from
the aids, and to gather otherwise unavailable or more detailed informa-
tion needed for either .road location or design (68). In only rare cases
is published information generally of sufficient detail and accuracy to
be considered suitable for final design purposes.
During the field reconnaissance, the applicable published aids
such as maps and aerial photographs should be used. These are valuable
in determining the location of control points and are generally reliable
for use as base maps for field layout work.
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48
Generally, more than one field reconnaissance trip will be neces-
sary. Depending on the amount and quality of available data, these
field investigations may be a phase process in which a preliminary
field reconnaissance and soil survey of the corridor is accomplished
by a team of experienced specialists. The team of specialists should
include an experienced engineering geologist. The preliminary recon-
naissance and soils survey should establish the erosion and mass wasting
potential within the corridor and areas adjacent to the corridor. This
preliminary work should also include delineating areas of potential
hazard and, where possible, outlining alternate routes to enable avoid-
ing the hazards. The next phase of work should consist of detailed
investigations of the hazard areas and possible alternate routes. The
detailed investigation may include test pits, borings, undisturbed
sampling for strength testing, installation of piezometers to obtain
valid water table information; and in some cases installation of slope
indicators to determine the amount of existing or future movement.
Many factors must be considered and properly evaluated during
field reconnaissance surveys if surface erosion and mass movement are
to be minimized. The factors primarily include surface and subsurface
soil and geologic conditions; topography, including slope steepness,
length, and aspect; precipitation; groundwater conditions; and
vegetation. How each of these and other factors affects sediment
contribution to streams due to surface erosion and mass wasting will
be discussed in the following sections.
-------
49
a. Surface Erosion. Numerous factors affect the potential for
soil erosion from forest roads and contribution of such sediments to
streams. All except locational factors are incorporated in the
Universal Soil Loss Equation which is discussed in Section IIB-1.00.
These factors primarily include soil texture, aggregation, and other
intrinsic properties; topographic factors such as slope steepness,
length and aspect; nearness of the road to the stream system; precipi-
tation amounts and severity; and upgradient and downgradient vegetation.
Roadway design, including slope protection and drainage provisions, can
also have a large influence.
Intrinsic soil properties affecting erosion potential are discussed
in considerable detail in Section IIB-1.00. The nomograph provided to
determine the inherent erodibility of a particular soil is undoubtedly
the most accurate such aid developed to date.
By far the most important factor influencing soil erosion is soil
texture with silt-size particles being the most erodible and erosion
potential decreasing as the percentage of sand or larger and clay-size
particles increases. However, other soil characteristics, including
organic matter content, overall soil strength, and soil permeability
also have an influence.
Detailed evaluation of the soil texture and organic matter content,
which is necessary to make use of the nomograph, would be somewhat
difficult in the field because of need for use of scales, wet sieves,
hydrometers, heating and drying devices, and other such equipment.
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50
However, an equipment package containing these essentials could be
developed in semi-portable form for field use. Otherwise, laboratory
tests of bulk samples appears to be the most feasible method of making
these necessary determinations.
In many cases, experienced field personnel would be able to make a
reasonably accurate estimate of the textural and other necessary inform-
ation without resorting to field or laboratory analyses. Textural and
organic matter content, as well as overall strength and permeability
characteristics, can be determined approximately by visual inspection
and use of shake, pat, kneading, and other types of simple field tests.
One such field classification guide for use in estimating inherent
soil erosion potential was developed prior to the K-factor nomograph.
This guide is shown in Table IIB-2 (63). This guide is based on the
Unified Soil Classification System which is presented in Table IIB-3
(69) along with field identification procedures and several of the simple
tests that can be used to aid in classifying soils according to the
Unified System.
Although the Unified System does not define silt- and sand-size
particles within the same size categorization as required by the
Universal Soil Loss Equation, the system can be used as a field guide
for determining an erosion index. This may be desirable in situations
where the only information available for a subject area is Unified
Soil Classifications or where only rapid visual inspection of a subject
area is warranted. The Unified System is being used by the Forest
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51
Service (70) and others involved with logging toad construction, and its
use is increasing in popularity. Additional work will be required to
verify whether the Erosion Index as obtained from a Unified Soil Classi-
fication correlates reasonably with the K-factor nomograph.
There are numerous procedures which may be used during a field
reconnaissance to obtain soil samples for textural identification.
Among these are the hand-operated 1%-inch screw-type soil auger (ship's
auger). With the use of extensions, these augers are capable of obtain-
ing small samples of the soils from depths of 3 to 15 feet (65).
However, this auger is of limited use in soils containing large percent-
ages of gravel or in bedrock. Shallow samples for textural identifica-
tion could be obtained from hand-dug pits in the coarser-grained
materials. Also, information on shallow as well as deeper soil strata
can be obtained from exposures within or near the corridor and soil
conditions correlated with those along the proposed route.
Other soil factors besides those strictly influencing erosion and
mass wasting should also be investigated during the field reconnaissance.
Such factors include moisture regime and fertility. These factors are
of value in planning the revegetation program.
Topographical considerations are very important in road location.
Among these are slope steepness, slope length, slope aspect, and near-
ness to stream channels.
Roads should be located in stable areas well away from streams.
Routes through steep narrow canyons; slide areas; through steep,
naturally dissected terrain; through marshes or wet meadows; through
-------
52
ponds; or along natural drainage channels should be avoided. Where it
is impractical to avoid any of these conditions, corrective stabiliza-
tion measures should be incorporated into road design. Road locations
should be fitted to the topography so that minimum alterations of
natural conditions are necessary (54).
Valley bottoms have the advantages of low gradient, good alignment,
and little earth movement. Disadvantages are flood hazard, number of
bridge crossings, and proximity to stream channels. Wide valley
bottoms are good routes if stream crossings are few and roads are
located away from stream channels. Roads in or adjacent to stream
channels should be avoided. Roads should be located far enough away
to prevent transport of sediment into stream channels (65).
Roads in valley bottoms should be positioned on the transition
between the toe slope and terrace to protect the road slopes from flood
erosion, being careful to avoid undercutting an old slide or landflow.
Road drainage structures will also function better and discharge less
turbid water into live streams. Any stream crossings should be
selected with particular care to minimize channel disturbance, minimize
approach cuts and fills, and produce as little disturbance as possible
of natural stream flow. Valley bottoms should not be roaded where the
only choice is encroachment on the stream (64).
Hillside routes have the advantage of being away from streams which
eliminates flood and stream damage; and intervening undisturbed vegeta-
tion acts as a barrier. Disadvantages are higher grades, more
-------
•53-
excavation, longer slopes, poor alignment from following grade contours,
and cut banks that expose soil to erosion (65). When locating roads
along sidehill routes, benches and the flatter transitional slopes near
the ridge and valley bottoms should be used. Midslope locations on
steep, unstable dissected slopes, particularly in areas of deep plastic
soils or weathered or decomposed rock formations, should be avoided (64).
Ridge routes have the advantages of good alignment, good drainage,
light excavation, and fair grades (65). Other advantages include
practically non-existent upgradient slopes and large expanses of undis-
turbed vegetation or logging slash to act as buffer strips for stream
protection. Disadvantages are secondary roads that may have adverse
hauling grades and greater total road mileage (65). Ridgetop roads
should be located to avoid headwalls at the source of tributary drain-
ages. These are often extremely unstable slopes, and any erosion or
slope failure will flow directly into live streams (64).
Another locational characteristic, aspect, also has some influence
on soil stability. However, aspect influences the functional character-
istics of forest roads more than it does their geometric design and
stability. North-facing slopes retain snow and ice for longer periods
than south-facing slopes (63)- However, Renner's (60) study on the
Boise River watershed showed that erosion differed sharply according to
exposure. Soils on south exposures eroded most severely.
Packer and Christensen's (61) study showed that erosion rates are
higher on south-facing slopes. This was attributed to the loosening of
-------
the soil by frost heaving. Also, south and west slopes in many areas
are considerably less densely vegetated than north and east slopes.
Runoff and sediment trapping characteristics are greatly influenced by
this effect. This in turn influences the design of the road prism and
the drainage structures. Aspect also helps determine the degree of
success or failure in reestablishment of vegetative cover after disrup-
tion by road construction.
During the field reconnaissance, vegetation along the proposed
route should be surveyed. Vegetation along the route of the proposed
road is an indicator of other factors, such as soil fertility and
moisture regime, but most importantly is its effect on retarding runoff
both upslope and downslope of the road prism. Upslope vegetation and
ground litter can have a significant effect on the amount of water
reaching the road prism. Long, unimpeded upgradient slopes with poor
infiltration characteristics can contribute large quantities.of overland
flow causing erosion of the road prism.
Probably more important than upslope vegetation is the vegetative
and ground cover downslope of the road prism. Downslope vegetative
cover can retard overland runoff and discharges from cross drains and
other road drainage structures causing suspended sediments to be settled
out before reaching stream systems. Several investigators, including
Trimble and Sartz and Packer, have studied the buffering and filtering
performance of vegetation strips. Packer's investigative work was
particularly comprehensive as to the individual parameters affecting
-------
55'
buffer strip performance. Packer found that obstructions such as rocks,
stumps, and herbaceous vegetation and trees, as well as numerous loca-
tional and design factors such as soil aggregates, amount of disturbed
slope, cross drain spacing, and distance to the first obstruction, all
influenced buffer strip performance. More detailed information on
factors affecting buffer strip performance is contained in Section
III under road design. All of these factors should be considered
during field reconnaissance, especially during the road location work
to ensure that adequate buffering is provided between roads and stream
systems.
b. Mass Wasting. The most common and perhaps the most significant
erosion from forest roads is the result of mass movement caused by
undercutting unstable slopes, improper embankment construction, wasting
on steep slopes, and drainage system failures (64). Some of the factors
affecting mass wasting which should be determined during the reconnais-
sance are cross slope angles; soil texture, depth, and in-situ strength;
groundwater conditions; and identification of old, existing, and poten-
tial future unstable areas. Factors affecting mass wasting should be
investigated, not only within the corridor, but up and downslope of the
corridor.
There are several topographic and vegetation indicators that may
be used in identifying existing mass wasting. Among these are u-shaped
depressions, downslope depressions, stream bank overhang, mucky surfaces,
tension cracks, curved tree butts, and "jackstrawed or crazy" trees.
-------
56
Some of the indicators of potentially unstable areas are slopes greater
than 70 percent, horseshoe-shaped drainage headwalls, fracture patterns,
seeps and springs, and piping (71, 72). All of these factors can be
identified by an experienced engineering geologist.
Other important factors which should be determined to evaluate mass
wasting potential of an area are in-situ soil strengths, amount of
overburden to bedrock, and natural bedding planes within bedrock (71).
An approximation of in-situ soil strengths can be made by visual inspec-
tion of hand-dug pits and existing soil exposures, both within the
corridor and within areas outside the corridor, which are similar in
nature. The thickness of overburden is oftentimes difficult to determine;
however, an experienced engineering geologist familiar with the area
and its geologic past can often provide good approximations after a
field reconnaissance of the area. A geophysical survey may be required
along the alignment to evaluate overburden thickness (65,67). However,
this survey is ofttimes expensive and can only be used under certain
conditions. It must be remembered that a geophysical survey does not
evaluate the type or strength of the soils within the overburden.
In addition to these other factors, the location of the water table
(which in most cases will be perched) along the alignment should be
investigated during the reconnaissance phase of investigation. The
water table may be located by mapping springs and seeps in the corridor,
identifying certain types of vegetation which exist only where water is
readily available, and locating areas which exhibit some thickness of
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57
soft spongy highly organic materials. In addition, the water table may
be located through use of relatively shallow explorations such as hand-
dug pits, hand-auger holes, or by probing.
After completion, compilation, and interpretation of the data
obtained during the reconnaissance, areas which present potential hazards
should be further investigated by more sophisticated means. The major
problems involved in performing a detailed investigation of potential
problem areas is that these areas normally have only limited accessi-
bility and, in many cases, may require that equipment needed for such
an investigation be either packed in or flown in by helicopter.
Detailed investigation of these areas should be accomplished by a
specialist in soil mechanics or rock mechanics. Details of such an
investigation should be established on an individual basis and based
on the field conditions at each site.
In summary, it should be remembered that a logging road design
which limits potential for erosion and mass wasting is only as good as
the information which is available for the alignment; the best design
based on the wrong conditions is of little use. In addition, the
conditions encountered in the reconnaissance may vary somewhat from
the conditions encountered during construction due to the complicated
nature of deposition and formation of soils and bedrock. Provisions
should be made to alter the design during construction based on the
actual conditions encountered.
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Toble IIB—2k guide for placing common toil ond geologic typei Into erotlon clomi (63)
Erosion i , 1 ,,
Clou 1 ' 1 "
Erosion i .0
Index 1 10
^ SM'
c
o _
O °
i:ui
3
t; f-
x c
V (U M
-£§
~$2
"-o^
T3.5f
1^
^^
O
*/l
•-' ~ ~ ~"
VI
1*
vt
Q
U
_
O
0
O
w
VI
ML
Dccomp.
grono-
diorite
(C)
Highly
dccomp.
gran-
ites
(C)
20
SM
ML
Decomp.
sond-
sfone
(B,O
Mod'ly
drcomp.
gran-
ites
(B)
III
30
Silt (Un-
consoli-
datcd) (B)
OL
MH
Fine soils
derived
from rocks
high in
mica
(C)
IV
40
Silt (Con-
solidated)
(B)
OL
<•
MH
CL
Coorse
soils de-
rived from
rocks high
in mica
(C)
V
50
Silty
clay
loam (A)
Silly
clay (A)
VI
60
Clay
loom
(A)
Silty
loam
(A, B)
VII
70
Loo my
sand
(C)
Sondy
loam
(B)
Cloy, vorying with type,
cohcsiveness & compaction
Sandy
clay (B)
SC, GM,
OH, CH
(A)
Sondy
cloy
(B)
CH, GM
Sond
GC
VIII
80
Coarse
sand
(C)
SW
SP
Sand
(C)
t
Some volcanic ash or fine pumice
(C)
.
IX
90
Fine
gravel
(C)
SW
SP
X
100
Rock
(C)
Cobble
(C)
Grovel
(C)
GW. GP
Frac-
tured
loose
basalt
or
shale
(A)
NOTE: (A) indicates nonporous materials; (B) indicates moderately porous materials;
(C) indicates highly porous materials.
*SM, ML, etc. refer to the Cosogrande soils classification system.
Ui
O)
Source: Reference 63
-------
Tablo IIB3— Unlflod Soil Classification
.(Including Identification and Description) (68)
Major Division*
1
o
o
o
B
rt
.c
|3
?e
rt
C
ft
_c
1»
a
o
o
CM
6
c
ft
JC
-o -
£"*
f« C
n
"•o
**«
c
c
o
a
« &
'5 0
V "**
£ 2
-5 «
o
i
t
rt
1
"rt
£
1
S '
•= o
o
n d
- 2
V
2
X*A
C «
5 **
•— .— *- v J$
ju — *3 *
*• -G '« ^*"v
** 2 ? «
Oc-^ E s
•SSo »«
•• r O N >
o C£ '5 J;
ir d
rjf
V
JZ O
-a — P > £ -
C « M W "3
52 I
55*" °
**
x ^
*n
]m
In
Gravels with
Fines
(Appreciable
amount
of fines)
Ml
1 °?
a-2
Sands with
Fines
(Appreciable
amount
of fines)
0
-I*
r3 ^^ * *
?
"c ^
•i '5
5 5
CO
*\
a
3
u
2
Highly Organic Soili
Group
Synt Plots
3
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MK
CH
OH
Pt
Typical Namei
4
Well-graded gravels, gravel-land mix-
tures, little or no fines.
Poorly-graded gravels gravel-sand mix-
lures, lillle or no fines.
Silty gravels, gravel-iand-silt mixtures.
Clayey gravels, gravel-sand clay mix-
lures.
Well-graded sands, gravelly lands, little
or no fines.
Poorly -graded sands, gravelly lands,
lillle or no fines.
Silty sand*, sand-silt mixture!.
Clayey sands, !and-clay mixture!.
Inorganic silts and very fine sands, rock
flour, silty or clayey fine sands or
clayey silts with slight plasticity.
Inorganic clays of low to medium plas-
ticity, gravelly clays, sandy clays,
silty clftys, lean clays.
Organic silts and organic silty clays of
low plasticity.
Inorganic sills, micaceous or diatoma-
ceous fine sandy or silly soils, elastic
JlllV
Inorganic clays of high plasticity, fat
clays.
Organic clays of medium to high plas-
ticity, organic sills.
Peat and other highly organic soils.
Field Identification Procedures .
(Excluding particles larger than 3 inches
and basing fractions on estimated weight!)
5
Wide range in grain sizes and substantial
amounts of all intermediate particle sizes.
Predominantly one sire or a range of niies
wilh some intermediate sizes missing.
Nonplastic fines or fines with low plasticity.
(for identification procedures see Ml. below)
Plastic fines (for identification procedures see
CL below).
Wide range in grain sizes and substantial
amounts of all intermediate particle sizes.
Predominantly one size or a range of sizes
wilh some intermediate ai/c! missing.
Nonplastic fines or fines wilh low plasticity.
(for identification procedures &ee ML below)
Plastic fines (for identification procedures see
CL below).
Identification Procedures
on Fraction Smaller than No. 40 Sieve Size
Dry Strength
(Crushing
characteristics)
None to slight
Medium to high
SlixM >o
medium
Slight to
medium
High to very
high
Medium to high
Oilalancy
( Kejction
to shaking)
Quick to slow
None to very
slow
Slow
Slow to none
None
None to very
alow
Toughness
(Consistency
near I'D
None
Medium
Slight
Slight to
medium
High
Slight to
medium
Readily identified by color, odor, ipongy (eel
and frequently by fibrous texture.
1) Boundary classification!: Soil* possessing characteristics of two groups are designated by combinations of group symbol*.
FIELD IDENTIFICATION PROCEDURES FOR
KINE-GRA1NED SOILS OR FRACTIONS
These procedure! »re to be performed on the minui
No. 40 sieve site particles, approximately 1/64 m.
For field classification purposes. screening it not
intended, simply remove by hand the coarse particles
that interfere with the tests.
Dilataney (Reaction to shaking)
After removing particles larger than No. 40 neve
site, prepare a pat of moist soil with « volume
of about one half cubic inch, Add enough water
if necc-s-.ary to make the soil .loft but not iticky.
Place the pat in Ihe open pjlm of one hand and
• hake liurirmilally. sinking vigorously against
the other hand srvcrjl limes. A positive reaction
consist^ of the appliance of water on the sur-
face of the |>at whi'h changes to a livery con-
sistency ami bco.mrs g)u%! allowed to lose some moisture by
evaporation. Thrn the specimen is rolled otit by
hand on a smooth surface or between the palms .
into a thread aU.ut one eighth inch in diameter.
The thread is then folded and rerolled repeated-
ly. During (his manipulation the moislure con-
tent is gradually reduced ant) the specimen
' stiffens, finally Inses its plasticity, and crumbles
when the plastic limit is reached.
After the thread crumbles, the pieces should be
lumped together anil a slight kneading action
continued until the lump crumbles.
The toucher the thread near the plastic limit and
the slilfer the. lump wlien it finally crumbles, the
more potent is the colloidal clay fraction in the
soil. Weakness of the llircad »t the plastic limit
and quick loss of coherence of the lump below
the plastic limit indicate either inorganic clay of
low pl.isticily. or materials such as kaolin type
clwvs »nd organic clays wihch occur below the
A-line.
Highly organic clays have * very weak and tiK>nfjr
feel al the plastic limit.
Ul
Source: Reference 68
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60
3.00 Civil and Forest Engineering
The task of the civil and forest engineers on field reconnaissance
is to establish a road location that best satisfies the intended road
use within the constraints of the terrain. The engineers are assisted
and advised by geotechnical specialists (see the previous section) and
by field surveyors. Hopefully, experienced engineers enter the field
reconnaissance phase with some rational guidelines from their superiors
about road use and harvest method and with latitude to interpret these
guide lines in the light of actual field conditions.
3.01 Harvest Method
Planning aspects of the road-harvest method relationship are dis-
cussed in paragraph 2.02, Section A of this Chapter. Adoption of modern
cable logging methods appear to be increasing partially due to environ-
mental constraints that have the effect of reducing the miles of spur
and jammer roads. In addition to less roads, the advantage from the
sediment aspect is that landings for these operations are preferably
located near ridge tops or on high benches as uphill yarding distances
are much greater than downhill yarding distances. Roads that connect
these landings are therefore high on the hillside away from the live
stream. Yarding uphill permits at least one end of the "turn" to be
lifted clear of the land for a longer distance than does downhill yarding.
Downhill yarding concentrates ground cover disturbance at the road or
landing and may create the potential for sediment movement to roadside
ditches.
An exception to the above description of road location for modern
logging methods is the circumstance in much of Southeastern Alaska.
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61
Although Wyssen and high lead systems are used in Alaska, downhill
yarding is often employed. Many ridge or hill tops are above the
timber line or are above the zone of merchantable timber. Further,
it is often desirable to leave timber on the upper sections of a hillside
to inhibit avalanches. Roads tend to be appropriately located near
valley bottoms.
The high mobility of new equipment suggests that logging oper-
ations may be accomplished in more inclement weather than was previously
considered appropriate. Equipment size may place constraints on allow-
able horizontal road curvature. Equipment weight may require closer
scrutiny of the stability of proposed landings or the road itself if it
is proposed to utilize a road turnout as a landing.
3.02 Existing Road Audit
An audit of existing nearby roads in similar terrain and their main-
tenance and construction records may be of value to reconnaissance engi-
neers. This audit will be useful from an overall design standpoint as
well as for potential sediment control problems. Specific features
deserving attention are:
1. Surface condition of cut and fill slopes (Slope raveling).
2. Ditch adequacy in terms of size, shape, and effectiveness of
any lining.
3. Culvert entrances and exits.
h. Performance of sediment control devices such as trash racks,
settling basins, downslope debris barriers.
5- Culvert spacing.
6. Geology and soils as may be revealed by exposed cut banks.
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7. Road surface condition i.e. crown, ballast performance,
presence of surface rills.
8. Alignment relative to shape of terrain.
Maintenance records of the audited road, if available, or similar
roads may be valuable as a cross check of personal observations. The
records may provide a chronological order of events and data on the
amount and kind of work accomplished at each maintenance problem.
These records may indicate that certain culverts were undersized,
improperly constructed or should have had different entrance or exit
treatments. They might also indicate the extent and location of slough-
ing and roadside slumping and the frequency at which roads were reshaped.
These recordings will aid engineers in identifying potential problem
conditions during the field reconnaissance.
Construction inspection reports are not always available as a part
of maintenance records. These reports may record particular problems
during construction and indicate if they were due to the road design or
specific construction techniques.
3.03 Route Placement
In the process of establishing a route, the engineer may ask himself
the following questions as a device for ensuring a thorough study of the
circumstances:
1. What are the potential risks and attendant damages?
2. What precautions are necessary to mitigate the risks?
3. What deviations in the road standard are acceptable in order
to better accommodate corridor conditions?
h. What are the costs in time and money in the event of failure?
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5. What are the environmental results of failure?
6. What are the alternates in terms of road location, road
alignment and alternate solutions to specific features?
Natural features of the corridor that should receive particular atten-
tion with respect to the potential for a sediment problem include:
1. Proximity of live streams.
2. Capability of downslope areas to act as filters or buffers.
3- Terrain slope.
h. Shape of terrain in terms of degree of natural dissection.
5. Type of vegetative cover.
6. Evidence of natural soil erosion.
7. Presence of ground water-
8. Signs or indicators of natural slope stability or instability.
9- Circumstances at possible stream crossing points.
The civil and/or forest engineer will be assisted in the evaluation of
some of the above features by the geotechnical specialist. However, the
engineer, as the generalist, should make his own evaluation of the cir-
cumstances based on his knowledge of the area and his concept of the
potential effect of a road. Road effect includes not only the effect
after road completion but during construction bearing in mind the prac-
ticalities of construction season, construction practices and construction
equipment.
An important aspect in road location is the desirability of fitting
the road to the terrain. This aspect is stressed both in writing and
orally by experienced forest engineers. Although it may be appropriate
to enter a reconnaissance with idealized criteria about minimum horizontal
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64
curvature, maximum and minimum vertical gradients, and balancing of
earthwork quantities, these criteria must yield to the shape of the
terrain. For example, where short lengths of steep vertical gradients
will avoid or reduce midslope roads in the type of terrain described
by Frederiksen, (73) they should be utilized. Where a "field adjusted"
horizontal curve will avoid or reduce excavation into a potentially
unstable hillside, it should be considered over adherence to the math-
ematical niceties of a constant radius curve.
All other factors being equal, a minimum vertical gradient of 2 to
3$ is desirable to provide good drainage. Flatter grades are difficult
to drain, may contribute to ponding and consequent road surface deter-
ioration under heavy truck traffic. This in turn can cause sediment.
Rolled grades provide convenient places to collect and remove drainage.
Grades exceeding 10$ may require special attention to the potential for
ditch and roadway surface erosion.
Where roads are close to live streams, an evaluation of the ability
of the vegetation and the terrain between the road and stream to act as
a natural barrier to the transport of sediment should be made. Brown
believes the buffer strip has limited valve in the mountainous West be-
cause it assumes that sheet flow similar to eastern agricultural soils
is the major soil erosion mechanism. He points out that the highly dis-
sected, rough surfaced topography in most forest watersheds precludes
sheet flow. Water flows to rills or channels which converge to larger
channels. "Since channel flow predominates, eroded materials are carried
through a buffer strip." (7*0
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65
All other factors being equal, crossing a stream at right angles
to its axis affords the minimum construction in and around the channel.
The designer will rely heavily on the reconnaissance observations in
determining the appropriate stream crossing method. The importance of
stream crossings is discussed by many writers including Fredriksen's
studies in Western Oregon watersheds, (75) and Jack S. Rothacher and
Thomas B. Glazebrook's evaluation of Region 6 flood damage during the
19611-1965 floods. (?6)
Features of the proposed stream crossing requiring reconnaissance
evaluation include:
1. Non manufactured debris in the channel at and above the proposed
crossing.
2. Stability of natural banks.
3. Evidence of old abandoned channels or presence of natural over
flow channels.
k. Natural constrictions to high water.
5. "High water mark" signs.
6. Suitability of circumstances for ford, culvert or bridge.
7- Classification of visible soils strata.
8. Opportunity for flood water bypass channel over proposed
approach roadway.
9- If culvert, round, pipe arch or plate arch?
Advantages and disadvantages of type of topography are discussed in
paragraph B - 2.03 of this chapter.
Subsurface ground water can be converted to surface flow in moun-
tainous areas where a slope is cut to form a level roadbed. Shallow
coarse textured soils overlaying relatively impermeable bedrock is a
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circumstance where this phenomena can occur- Walter F. Megahan
observes that conditions are ideal for its occurrence in the Idaho
Batholith. (77) The potential for this circumstance to occur should
be evaluated during reconnaissance so that the designer may recognize
ground water effects in his design of drainage features and his evaluations
of the stability of cuts and fills.
3.0*1 Field Survey Information
In addition to the normal route traverse and cross sectioning done
by the land surveyors, there is field data to record relating specifi-
cally to the sediment control portion of the road design. The following
is a listing of such information:
1. Survey crews should be made aware of key vegetative slope sta-
bility and ground condition indicators (see Table II B-U for a
plant indicator key developed for use in the Siuslaw National
Forest). These indicators (plant colonies and tree dispositions)
should be plotted with the traverse.
2. Survey crews should be alerted to take additional cross sections
at suspect problem sites or abutting sensitive areas (i.e. loca-
tions adjacent to old slide areas and streams) as may be designa-
ted by the engineers and geotechnical specialists.
3. Additional information regarding cross sections at streams should
be emphasized by the engineer. This is particularly important
in order to design the appropriate culvert entrance and exit and
for determination of channel capacity. At a stream crossing
which will require a large culvert or bridge, the engineer must
visit the site with the land surveyor and prescribe the topography
required.
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h. The engineer, from his field reconnaissance, may direct the
land surveyor to take notes on natural residue and debris
which could prove to "be maintenance problems.
5- The surveyor should be directed to provide location data on
unique features that influence the road in the road corridor
and not just "on line" data. The following items are examples.
a. Rock outcroppings and condition thereof.
b. Hummocky surfaces.
c. Terracetts.
d. Over steepened slopes.
e. Ground cracks or fissures.
f. Islands of over or under vigorous trees.
g. Natural stream scouring (continuous or intermittent streams).
h. Natural drainage courses.
Survey notes are one of the designer's basic aids. Recorded observations
by survey crews and accompanying sketches, if appropriate, are of great
value. A portable dictating machine is of value for recording observa-
tions .
The USFS Region 6 audit points out that "inaccurate compaction factors
and unanticipated soil changes can lead to overwidth roads and earthwork
waste." (78) From the sediment aspect, it is desirable to handle the
minimum earth possible. "Overwidth" roads may not fit the terrain as
initially conceived thereby introducing extra load on steep terrain or a
stability problem for a sliver fill. Appropriate field survey data is
mandatory to the goals of obtaining accurate earthwork quantities,
minimum changes during construction, handling only the earth quantities
necessary and fitting the road to the terrain.
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TABLE II B-
SIUSLAW NATIONAL FOREST - PLANT INDICATORS
11-9-72
"\7
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69
C. ECONOMIC EVALUATIONS
The introduction to this report suggested that wherein sediment
control design criteria was the same or parallel to other road design
criteria, the capital cost of a road designed with sediment control
features specifically included may be no greater than had these features
not been considered. No forest land manager or logger relishes the
costs of a road failure to his operation in terms of repair cost and lost
time during a harvest season. R. B. Gardner observed that: "The invest-
ment that may be required to achieve satisfactory stability will generally
be repaid by the road's longer useful life, reduced maintenance cost,
serviceability and contribution to improved water quality and quantity."
(79)
1.00 Cost Analysis
The trend toward fitting the road to the terrain with companion
change or revision of road standards to support this goal often results
in less quantities of earthwork per station or mile than accrued with
wider roads and/or roads with higher traveling speed alignments. Off-
setting the potential cost reduction from less quantities of material
may be the earth handling method. The narrower road (less quantities)
constructed full bench with end haul of waste may cost more than did
the wider road (more quantities) with the waste sidecasted.
Wherein road elements are designed to satisfy the goal of road
stability such as stable cuts and fills and adequate stream crossings,
the cost of sediment minimization related to these elements is likely
to be included in the cost necessary to obtain a stable design. Other
road features lend themselves to analysis embracing construction cost
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versus maintenance cost such as ditch cleaning where tributary slopes
are bare versus ditch cleaning where tributary slopes are planted.
Elements specifically included for sediment control such as settling
basins and downstream check dams outside of the roadway corridor are
examples of capital costs that are likely to be unrelated to road
stability or maintenance savings.
The Western Wood Products Associations' Forest Roads Subcommittee
has studied the minimum land impact road concept. Appendix A to the
minutes of one of the committee's meetings listed the following as part
of criteria for minimum land impact roads.
1. "It should be understood that a minimum land impact road will
not necessarily be a low-cost road, especially in steep-sloped
terrain with highly erodible soils. However, provisions for
minimum roadway and clearing width in difficult terrain situations
will mean less cost for initial road construction and subsequent
maintenance, site restoration, and revegetation for soil erosion
control.
2. "The total cost of construction, operation, and maintenance of a
road should be carefully assessed at various design standards to
find the optimum output for the three principal cost centers.
The various levels of road design standards should be compared
to the degree of impact each design standard places on the re-
sources and immediate environment. A possible output mix of
costs and impacts could be developed for comparison between
alternatives." (8d)
Gardner offers some 'guidance on road standards, economics and environ-
ment in terms of amortized construction cost over road life, maintenance
and operating cost, the cost centers suggested by WWPA. Tables II C-l,
II C-2 and II C-3 are reproduced from his paper. Tables II C-l and II C-2
demonstrate the value of an investment in roadway ballast as the annual cost
of gravel roads is less than stabilized and primative roads. On the basis
that the minimum road has less environmental impact, Gardner suggests that
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the user cost for the environment is represented in Table II C-3 by
the difference in annual cost between two lane paved and one lane
gravel roads. (8l) The cost figures shown in the tables are not
applicable to all of Region X. Gardner does suggest a cost analysis
approach that includes environmental considerations.
TABLE II C-l
1.—Comparison of annual road costs per mile,
10,000 vehicles per annum (VPA)
Cost
distribution
Initial
construction
-^Depreciation
Maintenance
Vehicle use
Total annual
: Road standard
: 2-lane :
: paved :
50,000
^,360
200
2,200
6,760
2-lane :
chip-seal :
ho, ooo
3,^90
Uoo
2,300
6,190
2-lane
gravel
- - "DnT 1
30,000
dollars
2,610
600
2,700
5,910
: 1-lane :
: gravel :
ars per mi
20,000
per mile
i,7Uo
800
3,000
25,5Uo
1-lane
spot stabilization:
IP________
15,000
(20-year period) -
1,310
1,100
6,810
1-lane
primitive
10,000
870
500
8,500
9,870
20 years at &fo using capital recovery.
Lowest annual cost.
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TABLE II C-2
2.--Comparison of annual road costs per mile for
20,000 and Uo,000 vehicles per annum (VPA)
Cost :
distribution :
;
Initial
construction
Depreciation
Maintenance
Vehicle use
Total annual
Depreciation
Maintenance
Vehicle use
Total annual
Road standard
2-lane :
paved :
50,000
too
9,160
?8oo
8,800
2i3,96o
2-lane
chip- seal
to, ooo
3, ^90
800
28,890
3, too
1,600
9,200
1^,290
: 2-lane
: gravel
T)r\1 '
30,000
._-.(' PO
2,610
1,200
5, too
9,210
Ck
V*t
2,610
10,800
15 , 810
: 1-lane :
: gravel : spot
lars per mile -
20,000
OOO VPA ^ - - -
i,7to
1,600
6,000
9,3to
o noo VPA \
i,7to
3,200
12,000
i6,9to
1-lane :
stabilization:
15,000
1,310
2,200
8,800
12,310
1,310
17,600
23,310
1-lane
primitive
10,000
870
1,000
17,000
18,870
870
2,000
3*1,000
36,870
20 years' depreciation at 6$ using capital recovery.
Lowest annual cost.
. TABLE II C-3
3.--Comparison of single-lane versus double-lane costs for
three different vehicle-per-annum (VPA) categories
Source:
VPA
Total annual cost per mile
Difference
:
10,000
20,000
to, ooo
1-lane
gravel
5, 5 to
9,3to
l6,9to
: 2-lane
: paved
6,760
9,160
13,960
:
-1,220
+ 180
+2,880
the Environment," USDA Forest Service Research
Note INT-U5, August 1971, ^ pages
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73
For readers interested in vehicle operating costs on logging roads,
R. J. Tangeman has proposed a model for estimating these costs relative
to characteristics of forest roads. (82)
The Environmental Protection Agency's publication "Comparative
Costs of Erosion and Sediment Control, Construction Activities" includes
a procedure for determining the annual economic cost of conserving soil.
The procedure recognizes amortized cost of the capital investment and
annual maintenance costs. The report cautions that "each particular
location offers a unique soil loss potential, erosion control costs and
corresponding sediment removal penalties." (83)
2.00 Economic Justification
An economic justification for additional capital investment in road
elements to achieve greater road stability under adverse conditions is the
risk of potential cost of a road failure. To illustrate, culverts and
bridges should be designed to survive an anticipated storm event. This
will mean hydrology studies and site surveys at bridge and culvert cross-
ings . Hydrology studies and detailed site surveys cost money and the
results of these studies may produce large capital expenditures. However,
this type of investigation is essential if washed out bridges and culverts
are to be prevented.
The 196^-65 Winter season floods in Oregon have been classified as 50
year floods in higher elevations. "The transportation system suffered by
far the greatest monetary loss. Damage to roads, bridges and trails in
Oregon alone was estimated at $12,500,000 - U percent of the total invest-
ment of $355 million." (8U) This estimate does not include down time cost
or other inconveniences which accompanied these losses. The flood damage
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estimate to USFS Region 6 roads and bridges for the 1973-74 season is
in excess of the 196^-65 damage estimate.
Sediment control can also act as preventative maintenance. Slope
seeding for erosion control can prevent slope raveling. Slope raveling
can diminish the roadway prism and cause high ditch and culvert main-
tenance costs.
Economic justification should be related to the role the intended
road is to play in the overall land management goal. The broader the
goal, the more varied are the inputs to the economic analysis. Legal
requirements such as water quality criteria are "givens" to the engineer
as a part of the land management goal. Within these "givens", the engi-
neer must exercise his traditional role of preparing cost effective,
economic designs.
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III DESIGN
"Road design is the process of transplanting planning objectives,
field location survey data, materials investigations and other
information into specific plans, drawings and specifications to
guide construction." (85)
The designer's task is to translate this data into a design which recog-
nizes and provides for sediment control.
Upon initiating a design, a designer must grasp an understanding of
the field work, reconnaissance and planning that has proceeded him. He
must also understand management's objectives and policy. This informa-
tion may be provided to him in a number of ways depending upon the organ-
ization's structure. For example, in some cases the designer has been a
part of the reconnaissance, and will be the construction supervisor. In
other organizations, he may have only limited personal contact with recon-
naissance people. Regardless of the organizational size and procedures
or the designers disposition, there are several general features which
the designer should know in order to intelligently proceed. The follow-
ing list is not all inclusive.
I. The designer must be aware of the road's intended use, such as,
whether the road will toe used principally for a truck haul road
or will have other demands. Prior knowledge of this kind may
affect such choices as water bars or pavement, fords or
bridges, and grades and curvature.
2. A review of the reconnaissance and field information should in-
dicate to the designer the circumstances within the reconnaissance
corridor. If this review arouses doubt or lack of understanding,
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76
he must communicate with those who accomplished the field work.
Preferably, the designer should at least visit the site of
specific key features within the project such as stream cross-
ings and steep hillsides.
3. The designer should have authority to obtain additional field
information and to alter design standards in order that a stable
road will be attained.
4. The designer should know to what extent he will be able to follow
the job through, and what control he or others will exercise on
workmanship. Quality construction is imperative to the control
of sediment.
5. Will the road be used as a log landing or yarding platform.
The designer must familiarize himself with erosion control and road-
way stabilizing techniques. He must also develope a commitment to sedi-
ment control and exercise a degree of creative thinking. This chapter is
divided into four parts, Part A discusses matters of the roadway design
itself, Part B is devoted to matters of slope stabilization including a
discussion of seeding and planting, mulches and mechanical treatments.
Since many of the recorded mass failures on forest roads appear to be
drainage related, Part C is devoted entirely to drainage design including
ditches, culverts and stream crossings. Part D discusses features of
the construction specifications, prepared as part of the design task, that
support the goal of minimizing sediment.
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A. ROADWAY
Many features or concepts for the roadway design may have been
developed or established as a part of the reconnaissance. However, the
process of converting field reports, field survey notes and planning
goals to drawings with attendant horizontal and vertical control will
direct attention to the resolution of key details and controls that will
appropriately refine and execute the reconnaissance and planning infor-
mation. This part discusses sediment features of the roadway design
elements of alignment, roadway prism, roadway surfacing, and buffer and
fiIter strips.
1.00 Horizontal and Vertical Alignment
Horizontal and vertical alignment are design features that can be
used to develop a road sensitive to sediment control. In developing such
a road, these features must be manipulated by the designer to adjust the
road alignment as the constraints of the terrain demand. The discussion
on reconnaissance in Chapter II emphasized the importance of fitting the
road to the terrain.
The designer must also recognize the limits that may be placed on
him by the reconnaissance data and location as has been previously indi-
cated. With the aid of field surveys, geo-technicaI, civil and forest
engineering information, he can adjust the horizontal and vertical align-
ment to the terrain with companion attention to road use requirements.
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I.01 Horizontal Alignment
The potential for roadway sediment can be mitigated by utilizing a
horizontal alignment that reduces roadway cuts and fills, and avoids or
minimizes intrusion upon unstable ground. The designer must have flexi-
bility to adjust curve radii, if necessary, from that established by
arbitrary road standards. The designer's practical experience and judge-
ment are a part of his approach. The sediment control aspect has to be
weighed in company with other features.
1.02 Vertical AIignment
Vertical alignment, like horizontal alignment, can be used to aid in
controlling sediment. In unstable steep terrain, adjusting the vertical
alignment to reduce cuts and fills and to position the road on stable
benches is an intelligent approach. In level areas sediment control is
aided by providing appropriate drainage to the roadway and roadway ditch.
A minimum grade of 2% will prevent ponding and reduce subgrade saturation.
Roads from log landings provide another opportunity to practice
sediment control and preventive maintenance. A 5% adverse grade from
landing to road for approximately one hundred feet will reduce the poten-
tial for mud and debris movement to the haul road.
Use of steep pitches to reach stable terrain must be accompanied by
appropriate treatment of the road surface, otherwise the road surface can
be subject to serious rill erosion. This matter is further discussed in
paragraph 3.00.
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2.00 Road Prism
The roadway prism is defined as the geometric shape generated by a
through fill, through cut, partial bench or full bench. Part C of this
Chapter discusses the roadway ditch portion of the prism, Part B discusses
slope stabilization and paragraph 3.00 of this part, roadway surfacing.
The following discussion is limited to excavation, embankment and balanced
construct ion.
2.01 Excavation
Back slopes can contribute up to 30% of the total road sedimentation
and up to 85% of the first year road sedimentation. (86, 87) Sediment
can be reduced by slope stabilization techniques as considered in Part B
and/or by designing the back slope for the given soil characteristics.
Part B of Chapter II discussed geo-technical and engineering reconnais-
sance techniques to develop field data for the design of stable back
slopes. There are two approaches to back slope design, experience, and
rationale or technical procedure.
Use of "rules of thumb" or "standard" backslope steepness guides
without knowledge of specific soils conditions is dangerous. If an able
forest engineer with long experience in a particular area has been suc-
cessful in establishing stable backslopes for road cuts, his approach,
advice and experience should be utilized.
Part A of Chapter II noted that the U. S. Forest Service has adopted
a method of specifying cut and embankment slopes developed by Hendrickson
and Lund. (88) This concise rational method does not require extensive
laboratory equipment to obtain soil type, grain size, and distribution
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80
for the unified soil classification. It, in addition, takes into con-
sideration blow count, ground water, site conditions and slope height.
This design method is presented in both graphical and tabular form for
convenient use along with illustrative examples. Also, and perhaps
equally important, are the application and limitation discussions which
accompany the design guide. (89)
Rodney W. Prellwitz has developed a slope design procedure for low
standard roads in USOA Forest Service Northern Region (Montana, Northern
Idaho and Eastern Washington). Prellwitz's procedures are most applica-
ble to Northern Region conditions of (I) steep natural slopes and cut
slopes, (2) seepage - often parallel to surface slope, (3) '"non-cohesive"
soils, (4) shallow and erratic soil depth, and (5) seasonal ground water
fluctuations. (90)
Vertical cuts in banks less tfoan six feet are being tried in various
parts of Region X including Idaho and Alaska. The rational behind the
vertical cut concept is that these cuts will reduce excavation quantities
and the area of exposed new backslope. However, it is difficult to pre-
dict the reliability of this practice from a sediment control standpoint
or how universally this practice can be applied as the practice is quite
new.
2.02 Embankment
Numerous researchers suggest that fill slopes are the great initial
producers of road sediment. They also point out thai fill slope erosion
can be drastically reduced by erosion control techniques. (See Part B)
Mass failure of the fill is the other source of sediment from fills.
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81
Mass failures can be the result of poor fill material, improper fill com-
paction, incorrectly designated fill slope, improper foundation prepara-
tion, weak foundation support, improper culvert design and installation
within the fill, or a combination of more than one of the above factors.
The design of a fill is a structural problem with the companion necessity
to recognize the site circumstances. The procedure developed by Hendrick-
son and Lund mentioned in the discussion on excavation has application to
the design of embankments.
Examination of the underlying strata where a fill is proposed must
be accomplished during the reconnaissance. If the strata is too weak
for the proposed load, the road must be relocated, the fill height re-
duced or an alternate structural solution such as a trestle considered.
A common fault has been failure to provide for proper preparation of
the ground by clearing and stripping of vegetation and organic material.
A further problem has been the presence of too much organic and vegetable
matter in fill material. Chapter IV discusses fill placement techniques.
Sidecasting, as a construction method, has limited value.
Benching of fills into sloping terrain has been utilized success-
fully. On narrow roads in steep terrain, the bench may be equal to the
road width suggesting that there is a point where terrain slope and road
width combine to require a full bench section rather than a fill from a
practical as well as a stability viewpoint.
A stable fill slope is dependent upon the quality of the fill
material and the amount of area of the supporting ground that must be
utilized to support the superimposed load.
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Provision for the passage of uphill overland water through a fill
can often be made by placing a granular blanket on the ground as the
-first fill layer. Otherwise, the fill may act as a dam to the water with
dangerous damage potential. This blanket is also advantageous when the
ground is soft to the operation of equipment.
The foregoing are a few observations on fill stability. The stability
question is broader in scope than the matter of sediment minimization only.
Waste sites are also fills and must be designed accordingly. Culvert de-
sign is discussed in Part C of this Chapter.
2.03 Balanced Construction
No simple statement can be made as to whether or not the concept of
balancing the quantities of excavation and fill materials has merit from
the viewpoint of sediment minimization. If the excavation can be confined
to the amount of earth needed for fill and other factors are aqua I, this
is advantageous.
On steep terrain, the necessity to excavate full bench to obtain
stability often results in the production of excess material. "Sliver"
fills on steep terrain have proven to be difficult stability problems.
In order to reduce excavation, an alternate to the"sIjver"fiI I might be
a driven sheet or soldier pile and logging wall. The economic tradeoffs
would be excess excavation costs plus haul of excess material and waste
site development versus the wall cost.
3.00 Road Surfacing
There is a broad range of surfaces and surface treatments used on
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83
logging roads. Selection of surfacing or surface treatment may depend
upon material availability, road use, road location and construction
practices. In Southeastern Alaska, nearly all roads are constructed with
"shot rock" ballast and overlaid with gravel or crushed rock. In some
areas of Oregon, Washington and Idaho, the absence of quality surfacing
rock may result in soil surface roads or bituminous surfacing.
There is no doubt that durable surface roads result in the potential
for less surface erosion. However, surfacing a road does not necessarily
eliminate sediment problems. The bulk of the stream sediment in the
Northwest occurs in the rainy season, late Fall to early Spring. In
many parts of the region the logging season carries into these transitional
weather periods and, in lower elevations, logging may contiue year around
with only occasional winter shut-downs. Log hauling operations during
this period place additional demands on roads. It is the designers task
to anticipate this use if appropriate and to design a base and surface for
the particular subgrade and wheel loads. (The design must be coupled with
good construction practice).
The road surfacing does more than provide smooth travel and a load
distributing media. It also provides a "roof" for the subgrade by being
a dense roadway surface, crowned sufficiently to rapidly disperse water.
Non-bituminous log haul roads should be crowned 4% minimum to insure the
movement of surface water, thereby reducing potential subgrade saturation.
In addition to designing a road base and surfacing to support truck
traffic and the selection of the road crown, the following are other
design considerations which may directly or indirectly effect the potential
for roadway erosion and sediment.
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84
I. Pit-run gravel surfacing must have an aggregate gradation which
will compact to a dense water dispersing surface.
2. Crushed rock surfaces rely on their angular faces and gradation
of the aggregate to knit the surface into a dense, near imper-
vious layer.
3. Asphaltic concrete or other pavements decrease the time for rain
water to concentrate in ditches and other drainage structures.
4. Granular surfaced roads can become sediment producers if a soft
crushed rock is used or if the gradation does not permit a
dense, locked, shear resistant surface.
5. Water bars are often used as cross drains on steep longitudinal
grades as shown in Figure III A-l.
JBolt w/ pipe spacer
WATER BAR
Fig. m A-l
However, they require continual maintenance if they are placed
in too flat a grade. A minimum longitudinal roadway grade of
5% is suggested for use of water bars.
6. If steep grades in excess of 10% are used, asphaltic concrete or
bimuninous surfacing may be required in lieu of water bars to
maintain a stable road surface.
7- Asphaltic concrete or bituminous surface can be used as approach
aprons to bridges. They reduce material tracking tracking which
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85
wears bridge decks, and sediment washing into streams.
8. Gravel surfaces may have an economic trade-off when the annual
traffic operating costs and maintenance costs offset those of
soil stabilized or primitive roads. (91)
9. Choice of gravel surfacing on outslope roads, versus stabilized
or soil surface is related to the potential for rill erosion.
See the discussion in paragraph 1.04 of Section C.
4.00 Buffer Strips
The concept of minimizing or retarding downsiope sediment movement
with vegetation and/or obstructions has been studied and used for a number
of years. The procedure is often coupled with the outslope road with sur-
face cross drains. Drainage features of the outslope road including
criteria for cross drain spacing are discussed in Part C-l of this Chapter.
Reservations regarding the ability of vegetation and terrain to act as a
barrier to sediment movement in the West as expressed by one writer are
mentioned in Chapter II, Part B.
Most of the data developed is on the basis of studies accomplished
in Idaho, Eastern Washington and Montana where the outslope road is quite
common. Harold F. Haupt studied sediment movement in the Boise National
Forest in 1959. He developed an equation relating sediment flow distance
to a slope obstruction index, cross ditch interval, embankment slope
length and cross ditch interval times road gradient. The Slope Obstruc-
tion Index was approximately equal to the average spacing in feet of
major obstructions along the direction of slope.
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86
"With proper substitution of the variables, this equation pre-
determines the distance or width of protective strip needed to
dissipate sediment movement that may occur from a road to be
built." (92)
Haupt pointed out that the method was a tool for the designers and was
not a substitute for experience and good judgement.
Packer believes that the interaction between the spacing of down-
slope obstructions and the kind of obstruction, and the spacing between
obstructions are the two most important factors in evaluating sediment
movement. Figure III A-l, "Obstruction Spacing," is reprinted from
Packer's 1967 Study. (93) Packer also discovered that, as the age of
the road increased, the distance sediment moved downslope increased.
This was because the remaining capacity of obstructions to stop sediment
decreased the longer they were installed.
Packer also developed criteria for protective strip widths based
on obstruction spacing, kinds of obstructions, age of road and cross
drain spacing. Table III A-l is reproduced from Packer's report. The
table is also contained in the booklet "Guides for Controlling Sediment
from Secondary Logging Roads" by Packer and George F- Christensen. (94)
This booklet is pocket field manual size and contains a complete treat-
ment of the subjects of cross drain spacing, and protective strip widths
and tells how to apply the information in a manner that will control
erosion and sediment. The booklet is for use in the USDA Forest Service
Northern Region.
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87
Table III A-I
Protective-sirip widths required below the shouIders(I)of 5-year old(2)
logging roads built on soil derived from basaIt,(3)having 30-foot cross-
drain spacing,(4) zero initial obstruction distance,(5) and 100 percent
fill slope cover density.(6)
Protective-strip widths
Obstruct i on
spacing
1
2
3
4
5
6
7
8
9
10
1 1
12
Depress ions
or mounds
35
37
39
40
41
Logs
37
40
43
46
48
50
52
53
54
Rocks
, FPP+- .
38
43
47
52
56
59
62
65
67
Trees and
stumps
40
46
52
58
63
68
73
77
81
85
88
Slash and
brush
41
49
57
64
71
77
84
89
95
100
104
Herbaceous
vegetat ion
43
52
61
70
78
86
94
101
108
1 15
121
127
(I) For protective-strip widths from centerlines of proposed roads, in-
carease above widths by one-half the proposed road width.
(2) If storage capacity of obstructions is to be renewed when roads are
3 years old, reduce protective-strip widths 24 feet.
(3) If soil is derived from andesite, increase protective-strip widths
I foot; if from glacial silt, increase 3 feet; if from hard sediments,
increase 8 feet, if from granite, increase 9 feet; and if from loess, in-
crease 24 feet.
(4) For each 10-foot increase in cross-drain spacing beyond 30 feet, in-
crease protective-strip widths I foot.
(5) For each 5-foot increase in initial obstruction distance beyond zero
(or the road shoulder), increase protective-strip widths 4 feet.
(6) For each 10-percent decrease in fill slope cover below a density of
100 percent, increase protective-strip widths I foot.
Source: Packer, Paul E.,
Roads to Control
"Criteria for Designing and Locating Logging
Sediment", Reprint from Forest Science,
Volume 13, Number I, March, 1967.
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B. SLOPE STABILIZATION
1.00 Surface Erosion
1.01 Introduction
The construction of forest roads is the major cause of stream
sedimentation in the forest harvest system. Large quantities of sedi-
ment can be contributed both as a result of surface erosion and mass
wasting.
Revegetation of areas disturbed by logging road construction is
the most effective means of reducing sediment production. Mulches,
chemical soil stabilizers, and mechanical treatment measures are often
required initially to aid in vegetation establishment and to reduce
erosion during the critical period while vegetation is becoming
established.
The reduction in erosion potential resulting from these slope
stabilization procedures is dependent upon the soil, weather, drainage,
and topographic conditions at each location. A great deal of research
is required before the qualitative effects of this reduction in erosion
potential can be assigned a value for use as the cover factor in the
Universal Soil Loss Equation presented in Section IIB 1.00. However,
each procedure does have a positive, effect on sedimentation potential
along the logging road. At this time the value for the Universal Soil
Loss Equation can only be based on the experience, even though limited,
of the design team.
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The various types of slope stabilization procedures and general
effect of reducing sedimentation are discussed in the following section.
1.02 Seeding and Planting
a. Introduction. Numerous studies indicate that forest cover is
one of the most effective vegetation types in maintaining and protecting
soil from erosion {104). This vegetation cover reduces the effects of
rainfall intensity, and raindrop impact through interception processes;
decreases runoff velocity and erosive power; increases granulation,
soil porosity, and biological processes associated with vegetative
growth; and dries soil by evapotranspiration.
Logging road construction removes natural vegetation and exposes
soils which commonly have properties unfavorable for plant growth -(101)
Revegetation by planting and seeding can be a successful method of
stabilizing backslopes and fills, of "putting roads to bed" that are
no longer being used, and of filtering sediment-laden water flowing
into water courses (.95)
The decisions as to which plant species and methods to use in
Region 10 for roadside stabilization are currently made by a variety
of agencies and individuals, usually the Soil Conservation Service,
individual county agents and landscape architects, and the Forest
Service. These decisions depend upon the management objectives as well
as the unique features of each site. Although there are published
Forest Service Standard Specifications for erosion control using
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revegetatlon techniques, the actual methods used vary from forest to
forest and even among the districts of a given forest (99).
b.. General. The "state of the art" is surprisingly variable from
one area in Region 10 to another. Each area has unique soil, climatic,
and financial problems with which to deal. Although revegetation
procedures are variable within Region 10, there are some recommendations
which apply to revegetation in general.
A 50 percent (2:1) slope is assumed to be the maximum slope upon
which vegetation can be satisfactorily established and maintained.
Optimum vegetative stability requires slopes of 25 percent (4:1) or
less. The maximum slope should only be applied to ideal soil conditions
where the soil is not highly erodible and has an adequate moisture
holding capacity. For droughty soils (those which exhibit a poor
moisture holding capacity due to excessively high permeability and a
low percentage of fines) and for highly erodible soils, the maximum
permissible slope should be considerably less than 50 percent (95).
Local soil conditions may require different rules of thumb. For
example, in northwestern Washington where soil is largely glacial till,
the maximum slope on which seeding is an effective erosion control
method is 2:1 on a fill slope and 1.5:1 on a cut slope (102).
Knowledge of the soil characteristics of the slope to be seeded
is essential to insure success of the project. For instance, the
volcanic tuffs and breccias of the Malheur, Umatilla, and Fremont
National Forests in eastern Oregon respond very well to grass seedings
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,(98). On the other hand, soils which hold water very poorly, such as
coarse shale and gravel, will probably require structural methods of
erosion control rather than revegetation.
Where it is impossible to avoid road building through areas where
roadside seeps and springs will be an inevitability, the most effective
methods to use around the seeps and springs will be structural ones
presented in other chapters.
c. Revegetation Objectives. The main objective of seeding road-
sides is to create conditions which favor re-colonization by native
shrubs and herbs {98) Native plants require the least expense and
maintenance as well as being visually harmonious with the forest land-
scape. In addition to physically enhancing the soil, seeded grasses
and legumes improve the organic-mineral balance of road cut soils.
They also act as "nurse plants" to young native plants by providing
shade which reduces the rate of water depletion from the soil.
Grass seeding is usually considered as an erosion prevention treat-
ment applied at a sacrifice to tree regeneration. However, in southeast
Alaska, grass seeding of. exposed mineral soils aids establishment of
spruce and hemlock seedlings by reducing the disruptive influence of
frost heave and by retarding alder invasion ,(106).
legume; any of a large group of plants of the pea family. Because of
their ability to store and fix nitrates, legumes are often plowed under
to fertilize the soil.
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92
Shrubs are sometimes planted on wet silty and clayey soils where
the slope is not steep. Native willows (Salix spp.) and alders (Alnus
spp.) are used in Region 10 because they absorb large amounts of water
from the soil and, in effect, dry out the soil. They are also more
deeply rooted than grasses or legumes.
d. Seed Mixtures. The seed mixtures in Tables III-B 1 through III-
B 3 are recommended for use in some part of Region 10 for erosion control
along forest roads, skid trails, landings, and firelines ^109)
Appendix III-B 1 provides a conversion table listing common names
and scientific names for all plant species mentioned in the tables.
Specific site requirements can be met by modifying the seeding mixtures
or the density of application. If, for example, a county agent recommends
a grass mixture designed mainly for use in rural non-forested areas,
increasing the percentage of fescue (Festuca spp.), a shade-tolerant grass,
and decreasing the percentage of bluegrass (Poa spp.), which typically
requires full sun, will contribute to a more shade-tolerant seed mixture
(I02)6ften on steeper slopes a more dense application of seed is required'(100)
Seeding mixtures often contain a legume - usually white Dutch
clover. The inclusion of a vigorous fast-spreading legume in the
seeding mixture in some cases results in a denser and longer-lasting
stand of herbaceous vegetation, presumably because of the nitrogen
incorporated into the soil (99). Seeding a legume requires that one also
apply an inoculant of the associated root bacteria. The inoculant is
usually "glued" to the legume seeds before the seed mixture is made (103).
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93
Table III-B 1
SEED MIXTURES FOR WASHINGTON AND OREGON
West of the Cascade Divide .(109)
Species Seeds Per Acre
Orchard grass 2 Ibs.
Timothy 2 Ibs.
Alta fescue 2 Ibs.
Perennial ryegrass 2 Ibs.
Total per acre 8 Ibs.
East of the Cascade Divide (109)
Seeds Per Acre
Inches of (effective) Precipitation
Species 0-9 9-12 12-15 15-18 18-25
Siberian wheatgrass 5 Ibs. 6 Ibs. 6 Ibs.
Nordan crested wheatgrass 5 Ibs. 6 Ibs. 6 Ibs.
Pubescent wheatgrass 8 Ibs.
Durar hard fescue 4 Ibs. 4 Ibs.
Topar pubescent wheatgrass 8 Ibs. 8 Ibs.
Intermediate wheatgrass 8 Ibs.
Greenar intermediate wheatgrass 8 Ibs.
Total per acre 10 Ibs. 12 Ibs. 20 Ibs. 20 Ibs. 20 Ibs.
Willamette National Forest, Oregon (J 12)
Species Seeds Per Acre
Perennial ryegrass 6 Ibs.
Meadow fescue 8 Ibs.
Colonial bentgrass 4 Ibs.
Total per acre 18 Ibs.
Fertilizer: 16-20-0 (16% nitrogen, 20% phosphorus, 0% potassium) at
400 Ibs./acre.
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94
Table III-B 1 (Continued)
Blue River District, Willamette National Forest, Oregon (6)
Species Seeds Per Acre
Colonial bentgrass 6^ Ibs.
Creeping red fescue 5 Ibs.
Perennial ryegrass 3 3/4 Ibs.
Alta fescue 8 3/4 Ibs.
White Dutch clover 1% Ibs.
Total per acre 25 Ibs.
Fertilizer: 16-20-0 at 400 Ibs./acre.
Oregon Highway Department j(JOO)
Species Seeds Per Acre
Creeping red fescue 18 Ibs.
Chewings fescue 12 Ibs.
Perennial ryegrass 4 Ibs.
White Dutch clover 6 Ibs.
Total per acre 40 Ibs.
Fertilizer: 16-20-0 at 400 Ibs./acre.
Forest Service Mixture No. 1, Oregon (100)
Species Seeds Per Acre
Alta fescue 20 Ibs.
Annual ryegrass 8 Ibs.
Creeping red fescue 3 Ibs.
New Zealand white clover 2 Ibs.
Big trefoil 2 Ibs.
Total per acre 35 Ibs.
Fertilizer: 16-20-0 at 400 Ibs./acre.
Forest Service Mixture No. 2, Oregon (100)
Species Seeds Per Acre
Orchard grass 20 lbs-
Annual ryegrass 8 lbs-
Creeping red fescue 8
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Table III-B 1 (Continued)
Forest Service Mixture No. 2, Oregon (100)
Species Seeds Per Acre
Colonial bentgrass 3 Ibs.
New Zealand white clover 2 Ibs.
Big trefoil 2 Ibs.
Total per acre 43 Ibs.
Fertilizer: 16-20-0 at 400 Ibs./acre.
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96
Table III-B 2
SEED MIXTURES FOR IDAHO
For Dry Areas, e.g. Low Elevation Ponderosa Pine Forests ,(96)
Species Seeds Per Acre
Annual ryegrass 20 Ibs.
Bulbous bluegrass 2 Ibs.
Crested wheatgrass 3 Ibs.
Intermediate wheatgrass 5 Ibs.
Smooth bromegrass "Manchar" 5 Ibs.
Total per acre 35 Ibs.
For More Moist Areas, e.g. Upper Elevation Ponderosa Pine Forests (96)
Species Seeds Per Acre
Annual ryegrass 20 Ibs.
Intermediate wheatgrass 5 Ibs.
Smooth bromegrass "Manchar" 5 Ibs.
Timothy 1 Ibs.
Orchard grass 3 Ibs.
Total per acre 34 Ibs.
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97
Table III-B 3
SEED MIXTURES FOR SOUTHEAST ALASKA
General, Southeast Alaska (Hi)
Species Seeds Per Acre
Alta fescue or orchard grass 4 Ibs.
Reed canary grass 4 Ibs.
Dutch white clover 2 Ibs.
Total per acre 10 Ibs.
Fertilizer: 10-20-20 at 200 Ibs./acre plus 100 Ibs./acre of ammonium
nitrate.
Southeast Alaska (J.05)
Group I - Suitable for:
Soil sites with few or no physical limitations.
Soil sites with moderate limitations due to low water-holding
capacity.
Soil sites with severe limitations due to low water-holding
capacity.
Revegetation of highly erosive or disturbed sites.
Variety Name
Species in Order in Order of
of Preference Preference Seeds Per Acre
Meadow foxtail Common 25 Ibs.
Timothy Engmo 10 Ibs.
Common
Kentucky bluegrass Nugget 20 Ibs.
Merion
Red fescue Arctard 20 Ibs.
Olds
Fertilizer: 60-60-60 at 400 Ibs./acre.
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98
Table III-B 3 (Continued)
Group II - Suitable for soil sites with moderate limitations due to
excess water.
Revegetation of highly erosive or disturbed sites.
Variety Name
Species in Order in Order of
of Preference Preference Seeds Per Acre
Meadow foxtail Common 25 Ibs.
Fertilizer: 60-60-60 at 400 Ibs./acre.
Soil sites with severe limitations due to excess moisture.
Must be drained. When drained refer to Group I.
Soils and sites consisting of wet peat materials.
No recommendations.
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99
One problem of including a legume in the seeding mixture is the
high palatability to deer, elk, and livestock of the readily available
species. Grazing animals will trample out mechanical structures, pack
the soil, and create a more erosive condition than existing prior to
seeding -{96).
The Forest Service Experiment Stations continue to search for
vigorous, unpalatable legumes for use in seeding mixtures ^97, 99, 107).
The following legumes are suited to use in the Northwest (99)
1. Big trefoil - well suited to Coast Ranges and Cascades of
Washington and Oregon; however, winter mortality is
higher in the Cascades.
2. White Dutch clover and New Zealand white clover - moder-
ately well suited to all of Region 10, but restricted to
the more gentle slopes (102).New Zealand white clover may
prove to be better adapted to west Cascades than white
Dutch.
3. Birdsfoot trefoil - moderately suited to west Cascades
and Coast Ranges.
4. Alfalfa - the most commonly used legume for conservation
seeding. It is adapted to a wider range of climate and
soil than other legumes. It is extremely palatable to
livestock and wildlife; and, therefore, not recommended
for use along logging roads.
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-JOO
Rarely are grasses seeded without legumes, and the choice of
legumes is an important decision (107).
e. Planting. The role of planting in logging road stabilization
is one of utility, not aesthetics. Where soils are plastic (e.g.,
silty and clayey), native willows or alders are planted to prevent
slumping because they deplete soil moisture rapidly, and their roots
bind soil to a deeper level than do those of grasses and legumes. Red
alder (Alnus rubra) is the species used in Washington and Oregon, and
Sitka alder (Alnus sitchensis) is used in southeast Alaska. There are
many species of willow common to Region 10, and nearly all root readily
from cuttings, as do the alders. Although plantings are rarely made
along logging roads in Idaho, nurseryman Bud Mason of Coeur d'Alene is
testing and cultivating native woody plants for use along roadsides in
the Pacific Northwest (Ml).
Plantings are much more expensive than seeding operations because
of the increased cost of plant materials and labor. Hand planting of
grasses and legumes in small, hard to reach sites which require
revegetation is done in some parts of Oregon and Washington (98). This
procedure is not yet used in Idaho or Alaska (97, I 10),primarily because
of the expense.
Commercial tree species are seldom planted on logging roadsides,
although when roads are "put to bed" the goal of revegetation is
sometimes forest regeneration.
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f. Techniques Used in Establishing Plants. Seeding, as mentioned
before, is much less expensive and, therefore, much more widely used
than other planting methods. Commonly used methods of seed application
are hydroseeding, hand-operated cyclone seeders, and truck-mounted
broadcast seeders. Hydroseeding is the application of a slurry of seed
and water to the soil (103).Up to one-half of the total amount of
fertilizer may be added to the slurry as well as legume seed bearing
the bacteria inoculant. Even the mulch may be mixed with the slurry.
A variety of mulches—wood cellulose fiber, ground hay, ground newspaper,
rice hulls—have been applied by this method. In a single operation,
two men can seed, mulch, and fertilize, often without leaving the road (103.
Hydroseeding is used in all parts of Region 10 by Highway Departments.
In Oregon and Washington, the Forest Service hydroseeds (98.). The Forest
Service in Alaska usually uses a cyclone seeder (97). In Idaho, seeding
is typically accomplished by using a cyclone seeder. If the seed bed is
packed, it may be necessary to drill the seed (96).
Hand planting of grass and legume plants in Washington and Oregon
is done in difficult-to-reach places (98). The soil surface, if not
freshly prepared, should be roughened along the contours in order to
reduce the chance of rilling and to provide safe sites for seed. In
Oregon, alder and willow cuttings are hand planted 3 to 4 feet apart (98).
g. When to Seed or Plant. From the standpoint of minimizing
sedimentation, roadside revegetation should be started as soon as roads
are constructed. The highest volume rate of soil movement off road cut
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-102
and fill slopes Is in the 1 to 2 months immediately following road
construction {100,1 12).Hopefully, this time will coincide with the
season which favors the species being planted.
In western Washington and Oregon, seeding before the fall rains
begin is recommended. One worker reported success with seeding in
September, another in April (100,1 12) .Evidently, if seeding is done
west of the Cascade crest anytime from April to September, it will be
effective. In Idaho, seeding should be done in late summer or early
fall in order to take advantage of the fall rains (96). In Alaska, seed
should be applied in April or early May, but summer application before
August 1 is acceptable where spring application is not possible (III).
For quick temporary cover in Alaska after the recommended planting
season, annual ryegrass can be seeded and then the area seeded the next
spring or summer to perennial grasses (105).
The advantage to seeding and planting prior to fall rains is that
the newly introduced plants are not subjected to undue moisture stress
as they would be in summer, at least in dry areas as eastern Washington
and Oregon and southern Idaho.
h. Fertilizers. In all cases, an application of fertilizer does
enhance revegetation efforts. Fertlizer is applied first with the seed
mixture and again the following spring. The recommended fertilizer
type and quantity is given in Tables I to III with each seed mixture.
In some cases, no specific recommendation was made, but experience
indicates that a fertilizer treatment always results in denser stands
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-103
in a shorter time period than seeding without fertilizer. Usually, a
nitrogen, phosphorus-potassium fertilizer is sufficient; although, if
the soil pH is less than 5, an application of lime may be required (105).
In general, ammonium phosphate-sulfate (16% nitrogen, 20% phosphorus, 0%
potassium) is excellent. Soil testing by extension agents of the Soil
Conservation Service will reveal any serious deficiencies, and these
people can recommend appropriate ameliorative measures.
Because native shrub and grass establishment is the primary goal
of roadside grass plantings in Washington and Oregon on Forest Service
roads, only one to two fertilizer treatments are applied. Continued
fertilizer treatments result in such a vigorous growth of the seeded
species that the natives are not able to establish on the seeded area {98).
i. Mulching. Mulching is essential if a proper seedbed cannot be
prepared, if seeding is made outside commonly accepted seasons, if soil
is highly credible, or if slopes are steep (108).
If seed cannot be applied immediately after construction, even an
application of a mulch, alone, will greatly reduce soil movement down
the slope. Common mulches used with grass-legume seed mixtures are
straw, hay, commercially prepared wood fiber mulches, and anchored types
such as jute-matting, cotton-paper and wood-fiber netting. On steep
slopes or easily erodible soils, and if seeding must be done during
periods of high runoff, a combination of mulches; e.g., a straw mulch
over seed anchored with a wood -fiber net, greatly decreases soil loss.
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- '104
There are a number of chemical products which can be used to anchor
seed or seed and mulch; for example, liquid asphalt, elastomers, and
polymers. These products are discussed elsewhere in this report in more
detail.
Mulches not only decrease soil loss by buffering rain effects and
slowing runoff, but they also retain soil moisture and provide shade for
better seed germination and seedling establishment.
In Washington, Oregon, Alaska, and Idaho, road banks are mulched
with whatever is available, usually grass, hay, wheat straw, woodchips,
or fiber mulch (98,110). If the slope is shallow and freshly prepared,
seedling establishment may be successful enough to significantly control
surface erosion without mulching.
In Idaho, mulches are seldom used by the Forest Service nor are
they used in Alaska, primarily because of the added expense (97,110).
Preparation of the seedbed by raking or otherwise roughing up the soil
surface creates small depressions which retain the seed. Dragging a
harrow or brush-drag over the seeded area helps to cover the seed (96).
j. Summary. In spite of the variety of methods used in Region 10
and the uniqueness of each roadside stabilization project, some general-
izations about the usefulness of plants for erosion control can be made.
The combination of vegetation and structural methods recommended depend
on the objectives of the action. A variety of seed mixtures used in
Region 10 are presented in Tables III-B 1 through III-B 3. Although
quite expensive, planting of willow and alder is an effective way of
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105
drying out wet, heavy soils. Hydroseeding and cyclone seeding are the
most common methods of seed mixture application used in Region 10. Hand
planting is expensive but necessary in hard-to-reach spots. Slope
stabilization projects should begin immediately after construction.
The best season in which to seed varies with climate. Applying
fertilizer and a mulch consistently improves seed germination and
minimizes erosion which can take place before the seedlings are
established.
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APPENDIX III-B 1
(Table Ill-B3a)
GRASSES AND LEGUMES FOR SOIL STABILIZATION
Common Name
Variety
Scientific Name
alfalfa
bentgrass
colonial
bluegrass
bulbous
Kentucky
bromegrass
smooth
Highland
Manchar
Medicago sativa
Agrostis tenuis
Poa bulbosa
Poa pratensis
Bromus inermis
canarygrass
reed
clover
white
fescue
chewings
creeping red
hard
meadow
red
tall
foxtail
meadow
orchard grass
ryegrass
annual
perennial
timothy
trefoil
big
birdsfoot
wheatgrass
crested
crested, standard
intermediate
pubescent
Siberian
Dutch, New Zealand
Durar
Arctard, Olds
Alta
Engmo, common
Fairway
Nordan
Greenar, common
Topar
Phalaris arundinacea
Trifolium repens
Festuca rubra commutata
Festuca rubra
Festuca ovina duriuscula
Festuca pratensis
Festuca rubra
Festuca-arundinacea
Alopecurus pratensis
Dactylis glomerata
Lolium multiflorum
Lolium perenne
Phleum pratense
Lotus uliginosus^
Lotus corniculatus
Agropyron cristatum
Agropyron desertorum
Agropyron intermedium
Agropyron trichophorum
Agropyron sibiricum
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•LOT
1.03 Mulches and Chemical Soil Stabilizers
a. Introduction. Measures intended for overall surface soil
stabilization of broad areas can generally be classified as either
mulches or chemical soil stabilizers, although some variations of each
exist. A mulch can be described as any organic or inorganic material
applied to the soil surface to protect the seed, maintain more uniform
soil temperatures, reduce evaporation, enrich the soil, or reduce
erosion by absorbing raindrop impact and intercepting surface runoff (1 13,
I 16). Chemical soil stabilizers can be described as any organic or
inorganic material applied in an aqueous solution that will penetrate
the soil surface and reduce erosion by physically binding the soil
particles together. Some chemical stabilizers also reduce evaporation,
enrich the soil, and protect the seed (113,116). in addition to their
functions in protecting against water erosion, these measures also
protect denuded soil, seeds, and young plants from wind erosion.
Mulches and chemical stabilizers are generally temporary measures
which can be expected to lose their effectiveness within one to two
years or less. Their primary purpose is generally to provide suitable
short-term protection, including erosion reduction, during establishment
of permanent vegetative cover, usually over winter months or through hot
summer months until conditions are more favorable for vegetative
stabilization •(113.) Vegetation cover is generally the intended long-
term means of slope protection. However, some mulches can be used to
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-1.08
provide permanent slope protection in areas where adequate vegetative
cover cannot be established.
Some of the more commonly available mulches include hay or straw,
woodchips, and small stones or gravel. For the case of some mulch
applications, particularly hay or straw, it is necessary to provide
some means of holding the material in place. Methods of attachment
/
include mechanical means (e.g., notch-bladed disks, crawler tractor
with deep treads, sheepsfoot rollers, and others), asphalt or chemical
binders, or various commercially available netting products designed
for use as a cover over the mulch (I 13.). In order for mechanical means
of attachment to be effective, the surface of the slope must be free of
significant quantities of rock material.
Besides their applications for mulch stabilization, many of the
chemical stabilizers and netting products are designed for use alone
for slope protection under appropriate circumstances. Also, several
commercially available products incorporate netting and mulch in a
single cover. These products (e.g., Excelsior Blanket, Conwed Turf
Establishment Blanket, etc.) are more specifically applicable on steep
slopes, in small drainage swales, or in other areas where erosive
stresses are particularly high (113). Long wire staples are generally
used to fasten these and other netting-type products to the slope.
Numerous studies have been conducted to evaluate the need for
mulches and chemical stabilizers in the establishment of vegetation
and control of erosion during the interim period while vegetation is
-------
becoming established. Most of these studies have as their primary
purpose evaluated the relative effectiveness of different types of
mulches and chemical soil stabilizers in performing these functions.
The results of four such studies covering a broad spectrum of mulch
types and environmental conditions are summarized in Table III-B 4 to
III-B 7 and in Figure III-B 1.
Upon casual examination, the results of some of these and other
studies appear contradictory. The prime reason for any apparent
contradictions is the diverse circumstances under which such studies
fj
have been conducted. In the remainder of this section, the need for
slope protection to aid vegetation establishment and control erosion
during this critical period and the relative effectiveness of various
types of mulches, mulch rates, and chemical stabilizers in this regard
will be evaluated.
b. Need for Slope Protection During Vegetation Establishment.
Mulches serve two primary purposes during vegetation establishment: (1)
prevention of erosion while vegetation is becoming established, and (2)
provision of a suitable microclimate for vegetation establishment.
Erosion prevention and vegetation establishment are to some degree
interrelated. If erosion is severe, most of the seed is generally
washed off the slope, resulting in poor vegetation establishment even
if the microclimate is suitable. After vegetation establishment, the
need for mulch or other protection rapidly declines.
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I 10
Table III-B 4
II
AVERAGE CUMULATIVE SOIL LOSS OR GAIN ON 12 BACKSLOPE PLOTS DURING THE
FIRST YEAR AFTER CONSTRUCTION
Treatment
and
Block
Control (no mulch or seeding) :
1
2
Blue River District mixture
(no mulch) :
1
2
Mulch only:
1
2
Oregon Highway mixture and mulch :
1
2
Experimental mixture No. 1
and mulch:
1
2
Experimental mixture No. 2
and mulch:
1
2
April
-0.48
-0.45
-0.72
-0.42
-0.06
—
-0.12
-0.11
I/
+0.10 /
+0.01
+0.02
1968
June
In Inches
-0.55
-0.59
-0.72
-0.55
-0.08
-0.07
-0.13
-0.19
2J
+0.14
-0.07
+0.08
September
-0.83
-0.84
-0.77
-0.31
+0.05
-0.07
-0.20
-0.23
2J
+0.17
-0.07
+0.11
I/ Gain due to upslope ravelling.
2J Results invalidated by a small slump near the base of the plot.
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111
Table III-B 4 (Continued)
Researcher: Dyrness (
Location: Willamette National Forest - Oregon
Time of Application: Early fall, 1967.
Mulch: Wheat straw at rate of 2 tons /acre.
Fertilizer: All except control plots fertilized with 16-20-0 at the
rate of 400 Ibs./acre.
Soil Type: Clay loam at surface grading to silty clay subsoils.
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I 12
Table III-B 5
COMPARISON OF CUMULATIVE EROSION FROM TREATED PLOTS ON A STEEP, NEWLY
CONSTRUCTED ROAD FILL (IN 1,000 LBS. PER ACRE)
Cumulative : Cumulative : : : Group B
Elapsed : Precipita- : : Group A : (Seed,
Time : tion : Control: (Seed, : Fertilizer,
(days) : (inches) : Plot : Fertilizer): Mulch)
: Group C
: (Seed, Ferti-
: lizer, Mulch,
: Netting)
Plot Number
17
80
157
200
255
322
1.
4.
12.
15.
17.
20.
41
71
46
25
02
40
31.
70.
72.
79.
82.
84.
9
0
2
1
3
2
2
38.7
99.2
100.2
101.0
102.8
104.7
: 4
38.0
85.7
86.9
87.6
88.8
89.4
: 3
0.1
7.4
11.1
11.4
11.5
11.9
: 8
32.6
34.6
35.1
35.7
35.8
36.0
: 5 :
0
0.9
1.1
1.1
1.1
1.1
6
0
0
0
0
0
0
: 7
0
0.3
0.4
0.4
0.4
0.4
Researcher: Bethlahmy and Kidd (115).
Location: Boise National Forest - Idaho.
Time of Application: Fall, 1962.
Slope: 80 percent fill slope.
Soil Type: Loose, weathered granitic soils typical of the Idaho Batholith.
Plot Treatment:
Sequence of Treatment
Plot Number
1
2
3
4
5
6
7
Control - no treatment at all.
Contour furrows, seed, fertilizer, holes.
Contour furrows, straw mulch, seed, fertilizer,
hole. i
Polymer emulsion, seed, fertilizer.
Straw mulch, paper netting, seed, fertilizer.
Straw mulch, jute netting, seed, fertilizer.
Seed, fertilizer, straw mulch, chicken wire
netting.
Seed, fertilizer, straw mulch with asphalt
emulsion.
-------
I 13
Table III-B 5 (Continued)
Details of Treatment:
Seed - All except control plot seeded alike.
Mechanical treatment - Contour furrows placed 6 feet apart and
holes punched 2 inches deep at 6-inch intervals.
Mulch and chemical soil stabilizer rates - Straw mulch at 2 tons
per acre.
Polymer emulsion at concentration of 1 gallon Soil Set to 9
gallons of water.
Asphalt emulsion at rate of 300 gallons per acre.
All netting attached to ground with 12-inch pieces of No. 9 wire,
-------
I 14
FIGURE III-B 1
SOIL LOSSES FROM 35-FOOT LONG SLOPE
iiuiimmmmiumimuiui 39.6
iiummimimHumm 32.7
mmuiHsmmmm 27.1
25.6
14.7
lUilHHH 12.1
\\i\mi\\ 11.4
illlllll 8.5
mil 5.5
mi 3.5
II 2
No Mulch
Portland Cement
2 T/A woodchipsa
15 T/A stonea
70 T/A gravel
2.3 T/A straw
60 T/A stone
4 T/A woodchips
7 T/A woodchips3
135 T/A stonea
240 & 375 T/A stonea
(
12 & 25 T/A woodchips3
0 10 20 30 40
Soil Loss (T/A-tons per acre)
aBased on one replication only. Values for other treatments based on
average of two replications.
Source: Same as Table III B-6
-------
I 15
Table III-B 6
EROSION LOSSES FOR LONGER SLOPES2
Total Soil Loss from
100-Foot Slope Width
with Length of :
Treatment
No mulch
Straw
2/3 tons/a
Stone
15 tons/ab
60 tons/a
135 tons/ab
240 tons/ab
375 tons/ab
Gravel
70 tons /a
Woodchips
2 tons /a
4 tons /a
7 tons/ab
12 tons/ab
25 tons/ab
Portland cement
50 ft.
3.0C
1.0
2.8°
.7
.2
Trace
Trace
.8
2.3C
.9
.9
Trace
Trace
3.0C
100 ft. 150 ft.
13C 30°
3.9 9.8
13C 36C
2.7 8.4C
.6 1.0
Trace Trace
Trace Trace
4.4 17C
10C 25C
3.5CV 12C
8.2C 29C
.6 (d)
Trace Trace
13C 29C
Determined by adding inflow to upper ends of 35-foot plots while
continuing 2.5-inch per hour rainfall. These tests followed soil losses
caused by 5 inches of rain. Test results could be expected to be some-
what different if extensive damage had not occurred on some test plots
as a result of the earlier testing.
-------
M.6
TABLE III-B 6 (Continued)
"Unreplicated treatment.
cSevere rilling caused most flow to occur in rills rather than across
mulched area. Mulch rate had minor influence on erosion rate.
Severe movement of mulch occurred during high inflow rate, causing
abrupt breakdown in erosion control. Erosion rates following breakdown
were 10 times those just prior to it.
Researcher: Meyer, Johnson, and Foster (117).
Soil Type: 6-inches silt loam topsoil underlain by compacted calcareous
till (AASHO A-4) (Unified ML).
Slopes: Uniform 20 percent.
Mulches:
Wheat straw - chopper blown
Crushed limestone-ranging in size from 1/4-inch to 1-1/2 inches in
diameter with about one-half larger than 3/4 inch.
Washed road gravel - similar size distribution as crushed limestone.
Woodchips - mixed hardwood chopped in the green.
Portland cement - applied at the rate of 2 tons/acre.
Portion of soil surface covered by mulches at various application rates:
-------
H7
TABLE III-B 6 (Continued)
Mulch Type Mulch Rate (tons/acre) Average Cover (%)
No mulch
Straw
Stone
Gravel
Woodchips
Portland cement
a Natural gravel larger
cover .
2.3
15
60
135
240
375
70
2
4
7
12
25
than 3/8 inch
3a
95
16
62
90
100
100
62
32
68
88
99
100
3a
totaled about 5-tons-per-acre
Rainfall Rates:
Simulated rainfall at rate of 2-1/2 inches/hour. Slopes 35 feet
long - .1 hour the first day followed by two 30-minute applications
the second day.
Longer slopes - Tests conducted on same plots after completion of
35-foot long slope tests. Inflow uniformly added at upper ends
of plots during rainfall application to simulate longer slopes.
-------
118
TABLE III-B 7
EROSION CONTROL EFFECTIVENESS OF COVERING MATERIALS ON VARIOUS SLOPES
EFFECTIVENESS RATING I/
Jute Excelsior Straw Straw &
Asphalt
Sheet Erosion -
1:1 slope 9.0
Sheet Erosion -
2:1 slope 9.0
Sheet Erosion -
3:1+ slope 10.0
Rill Erosion -
1:1 slope 6.0
Rill Erosion -
2:1 slope 8.0
10.0 8.0 10.0
10.0 9.0 10.0
10.0 10.0 10.0
10.0 8.0 10.0
10.0 9.0 10.0
Asphalt
6.0
7.0
9.0
6.0
7.0
Wood Sod
Fiber
3.0 10.0
6.0 10.0
10.0 10.0
3.0 10.0
5.0
Rill Erosion -
3:1+ slope 10.0 10.0 10.0 10.0 9.0 10.0 10.0
Slump Erosion -
1:1 slope 10.0 8.0 6.0 7.0 3.0 3.0 8.0
Slump Erosion -
2:1 slope 10.0 9.0 7.0 8.0 5.0 -4.0 9.0
Slump Erosion -
3:1 slope Slumps usually do not occur.
I/ 10.0 = most effective. 1.0 = not effective.
Researchers: Goss, Blanchard, and Melton (Washington State Highway
Commission, Washington State University Agricultural Research
Center, and the U.S. Federal Highway Administration, Cooperating)
•
(119).
No. of Tests: Seven independent tests (1966-1969) including fertilizer
and mulch tests.
-------
TABLE III-B 7 (Cont'd)
Location: Highways in eastern and western Washington.
Slopes: 1.5:1 to 3:1 cut and fill slopes.
Soils: Silty, sandy and gravelly loams and glacial till consisting of
sand, gravel and compacted silts and clays. All are subsoil
materials without topsoil addition.
Slope Lengths: Apparently maximum of 165 feet.
Time of Application: Spring and fall.
Mulch Rates:
Cereal straw - 2 tons/acre
Straw plus asphalt - 2 tons/acre straw plus asphalt at rate of
200 gal/ton of straw (one test at rate of 100 gal/asphalt/ton
of straw)
Asphalt alone -.20 gal/sq. yd. (968 gal/ac)
Wood cellulose fiber - 1,200 Ibs/ac.
Sod - bentgrass strips 18 inches by 6 feet pegged down every third row.
-------
120
Numerous investigators have concluded that a good mulch or similar
cover is essential for protection against erosion for the first few
months following construction when the potential for erosion is most
critical. Dyrness (1I4)found that test plots seeded in early fall in
Oregon did not begin vegetation growth until the following April and
were not fully protected by vegetation until June. Of the various
means of slope protection studied by Dyrness (Table III-B 4), the only
plots to show consistently high losses by surface erosion during
vegetation establishment were the unmulched plots. All mulched plots
displayed considerably less soil loss. It was also noted that for the
control plot, dry season losses by ravelling were almost as great as
rain-caused soil loss. Dyrness concluded that mulching backslopes may
be essential for reducing soil loss to a minimum during the first few
critical months following construction. Dyrness also concluded that
contrary to appearances, a luxuriant growth of grass and legumes during
the first-growing season was not conclusive evidence that soil loss
was negligible during the preceding winter months.
Research conducted by Bethlahmy and Kidd(llS) in Idaho yielded
much the same results. Test plots without treatment or with mechanical
or chemical treatment in combination with seeding and fertilization
(Table III-B 5) had soil losses ranging from about 70,000 to 100,000
pounds per acre during the first 80 days following treatment, while
other plots that were protected with mulch and.mechanical treatment
or mulch and netting in addition to seeding and fertilization had soil
losses of less than 7,400 pounds per acre during this same period.
-------
121
In his study of the effectiveness of numerous mulches and mulch
rates, Meyer(l!7) found that soil losses as a result of simulated rain-
fall on specially-prepared test plots was over 20 times as great for an
untreated plot as for plots with effective mulch protection (Figure 1).
Several other investigators, including Plass 0 16) and Barnett,
et al(l20), have observed similar results from untreated test plots
when compared with test plots receiving adequate mulch or chemical soil
stabilizer treatment.
Research results differ considerably over the value of mulch
protection during establishment of vegetative cover. Apparently this
factor is particularly sensitive to the severity of individual environmental
conditions. In. Oregon, Dyrness (I I4)found that seeded but unmulched
plots produced good vegetative cover and that mulch in itself without
seeding also produced good vegetative cover. Only the control plots
without seeding or mulching produced poor vegetative cover. Plass (116)
tested the effects of numerous mulches and chemical soil stabilizers
on vegetative establishment and observed much the same results. Plass
concluded that some mulches and chemical soil stabilizers improve the
growth and vigor of grasses, and some appear to have the opposite
effect. Mulches were generally more effective than chemical stabilizers
in this regard, but excellent stands of grass on untreated control plots
indicated that neither treatment was necessary for vegetation establish-
ment in the eastern United States.
In their tests, Meyer et al (I 17)concluded that good mulch protection
was necessary for vegetation establishment. In September, after
-------
122
completion of erosion tests on their test plots, approximately 30 pounds
per acre of grass mixture and 400 pounds per acre of 15-15-15 fertilizer
were broadcast on the plots. Erosion damage was not repaired, and no
tillage was performed. Stands that had more than 75 percent of the seedlings
necessary for complete cover were established on the 240- and 135-tons
per acre stone, 12-tons per acre woodchip, 70-tons per acre gravel, and
straw-mulched slopes. The no-mulch and cement-stabilized slopes were
practically bare of vegetation. These treatments and the 15-tons per
acre stone mulcted plot had stands of less than 25 percent. Vegetation
on the remaining slopes was fair, but stands were generally uneven or
spotty.
Other researchers have reached similar conclusions as a result of
their work. Heath (123)reported that 50 to 90 percent of the seed planted
on a slope is saved from washing away when a mulch is used. Diseker and
Richardson(121) have stated that the use of mulch over seedings often
was the difference between success and failure and that mulch was
necessary on steep slopes. The question of need for mulch protection
for vegetation establishment is probably best summed up by Blaser (122)
who concluded that mulches aid in turf establishment, particularly
under environmental and moisture stress.
c. Performance of Various Mulches and Chemical Soil Stabilizers.
The effectiveness of mulches and other soil stabilization measures is
a function of surface cover and overall lateral stability of the
protection network including its ability to bind or penetrate into the
slope (117). Erosive and other environmental stresses determine the
effectiveness of a particular treatment measure under a particular set
-------
HZ3-
of circumstances. A mulch rate or combination of mulch and other stabil-
ization measures may perform satisfactorily under one set of circumstances
and be wholly ineffective under another set of circumstances. In choosing
stabilization measures for a given set of field circumstances, the
performance drawbacks and advantages of a particular treatment measure
must be considered in addition to its availability and economy.
Straw (or hay) is one of the oldest and probably by far the most
commonly-used forms of mulch materials. Until only recently has its
position been challenged by newer products and revived interest in
older products. Straw mulch has proven to be quite effective if used
within its moderate capabilities.
Dyrness (114) found straw mulch to be relatively effective in
reducing erosion in his studies (Table III-B 4). Bethlahmy and Kidd
(J I5)found straw mulch to be quite effective when supplemented by
mechanical treatment measures or netting (Table III-B 5). Goss et al
(1 I9)have noted that straw alone is moderately effective in a number of
erosion-prevention applications but that its effectiveness could be
improved somewhat when used in combination with an asphalt tack (Table
III-B 7). Straw plus asphalt emulsion was found to be one of the most
effective mulches. Bethlahmy and Kidd ('I 15) found straw mulch tacked
with asphalt to be effective but high soil losses were observed during
the first seven days after application (Table III-B 5). No explanation
was provided. Meyer et al (1.17) indicated that straw mulch is moderately
effective in erosion prevention but that its performance is considerably
exceeded by suitably heavy applications of other mulch products when
erosive stresses are high (Table III-B 6).
-------
124
In summary, it appears that straw or hay mulches are generally
effective if slope gradient, slope length, and rainfall intensity are
not too great. Straw mulches themselves are relatively stable and
protect the soil well against raindrop splash, but rill formation
underneath the mulch can be a problem. Several researchers, including
Meyer et al ('117), have observed breakdown of straw mulches through
rill formation. This conclusion is also supported by the test results
of Bethlahmy and Kidd (Table III-B 5) where straw mulch when used in
•combination with runoff reducing mechanical treatment measures (contour
furrows and holes) provided good slope protection. Similar deductions
can be made from the results of other studies. Besides supplementary
measures to protect against failure by rill formation, straw mulches
must also be provided protection against strong winds (113, 1)9).
Chemical stabilizers, mechanical measures such as contour furrowing,
and application of netting over the mulch can be used to improve
attachment of mulch to the slope, thus guarding against wind erosion
and rill formation. Properly secured netting has proven particularly
effective in this regard with good mechanical treatment following a
close second as far as water erosion is concerned (Table III-B 5).
Chemical soil stabilizers can also be quite effective (Table III-B 7
and Plass, (116).
Chemical stabilizers used as the sole means of slope protection
generally cannot be relied upon to be as effective as some other measures
(Tables III-B 5 and III-B 7). However, use of chemical stabilizers
in combination with mulches, or as a minimum with wood fibers added,
-------
125 •
generally increases their effectiveness significantly in controlling
erosion and encouraging vegetative establishment (116, 119).
Chemical soil stabilizers, by virtue of their chemical composition,
can have an effect upon vegetation establishment. Plass(1l6) reported
that some treatments improve growth and vigor of vegetation, while
others have an adverse effect. Adverse effects of some products on
vegetation establishment have also been noted by the Washington State
Highway Department (126).
A wide variety of chemical stabilizers probably totalling 40 or
more, with differing performance levels under different environmental
conditions, are available. Some of the current products may already
exceed the performance capability of commonly used mulches such as straw.
The chemical soil stabilization field is rapidly developing with new
products being introduced frequently. With continuing developments,
this field appears to offer good potential for the future.
Commercially-available combination mulch-netting products are
available. Some of these products have proven relatively effective,
even under severe conditions. Except for sod protection, Goss et al
(Table III-B 7) found one such product (Excelsior) to be the most
consistently effective product tested. Plass(N6) has also found some
of these products to be quite effective. However, the material and
installation costs may be too high to warrant their use for forest road
application except in the most severely-stressed areas. Similar
products such as jute netting have also been found to be effective
in erosion prevention. Use of jute netting is particularly attractive
-------
126
where high tensile strengths are needed to protect against slump erosion
(Table III-B 7). Good attachment of netting-type materials to the slope
is of prime importance to prevent rill erosion underneath. Jute, for
instance, has sufficient strength to bridge even large rills and allow
erosion to continue unchecked (119).
Meyer et al (Figure III-B 1 and Table III-B 6) have found gravel
and crushed stone mulches to be quite effective, even under relatively-
severe conditions. Various application rates of stone and gravel
mulches were found to be considerably more effective then 2 tons per
acre of straw mulch. Resistance to rill formation is one of their
prime advantages, as they slough into rills tending to impede their
formation rather than bridging them as do straw mulches or being swept
down the slope as do woodchip mulches when subjected to severe erosive
stresses. Meyer et al found a rate of application of 135 tons per
acre of stone mulch, which averages less than 1-inch depth, to be
effective under all conditions tested.
Stone mulches also appear to have other advantages. Meyer et al (JI7)
found grass stands on inert stone and gravel plots to be much more
vigorous than on the woodchip and particularly the straw plots where
grasses showed symptoms of a nitrogen deficiency. Also, unlike straw
and other mulches, stone mulches are not subject to rapid decomposition.
Their resistance to decay may render them uniquely valuable for permanent
applications where vegetative cover cannot be established.
Woodchip mulches appear to have promise for forest applications.
Along with stone mulches, Meyer et al (Figure III-B 1 and Table III-B 6)
-------
127
found woodchip mulches to be a good mulch material if applied at
adequate rates. Woodchip mulch at the rate of 4 tons per acre was
found to be more effective than 2 tons per acre straw mulch on 35-foot
long slopes. Woodchip application at a rate of 25 tons per acre (1^
inches depth) was found to offer good protection under relatively-severe
conditions of 20 percent slopes as much as 160 feet long ,( I 17,). Crabtree
(I24)found 5 tons per acre of woodchip mulch to be quite effective on
3 to 1 slopes in Iowa. Woodchip mulches are relatively long lasting
in comparison with other mulches such as straw or hay, require no tacking
to hold them in place due to their weight and shape, and are readily
available in forested areas. Use of wood mulches also appears to offer
potential for disposal of waste wood material necessitated by recent
restrictions on burning(I 13).
Adequate rate of application of woodchip mulches is particularly
important. Meyer et al(M7) noted that the consequences of breakdown
are more serious for woodchip mulches than for stone, gravel, and straw
mulches. When a woodchip mulch broke down, woodchips were grossly
displaced and large, deep rills developed. The stone, gravel, and
straw mulches were much more stable; and only the 15-tons-per-acre
stone treatment was severely rilled (Table III-B 6). Thus, choice of
an adequate mulch rate and uniform distribution of the mulch material
are more critical for woodchips than for stone, gravel or straw.
Anchoring the woodchips might improve their performance at some rates (125)
Wood fibers have also proven beneficial in preventing erosion when
used alone or in combination with chemical soil stabilizers. The
-------
Washington State Highway Department has found wood cellulose fiber,
particularly when used in combination with chemical binding agents,
to be economical and successful in western Washington where straw is
not readily available (J26^« A University of California study ( I27]bf
hydroseeding on clay-loam soils reported soil losses of 0, 1,000, and
9,000 pounds per acre, from plots with wood cellulose fibers applied at
rates of 3,000, 2,000, and 1,000 pounds per acre, respectively, compared
with 81,000 pounds per acre of soil loss from plots without any fiber
application. On the fiber-treated areas, there were 300, 262, and 86
grass seedlings per square foot compared with none on areas without
fiber treatment. Plass (II6)reported that plots treated with soil
stabilizers, but without wood fibers, generally did not have as tall
or dense vegetative cover as when stabilizers with wood fibers and
mulches were used. Plass noted that there is a growing trend toward
incorporation of wood fibers with soil stabilizers to increase their
effectiveness.
Others have reported less favorably on the use of wood fiber for
slope protection. Goss et al found that wood fiber does not have sufficient
damming ability nor tensile strength to prevent erosion on long slopes,
particularly if steeper then 3 to 1 (119}. Crabtree (124) found wood fiber
applied at rates of 1,000 to 1,400 pounds per acre to be only poorly to
moderately effective in checking erosion on 3 to 1 slopes in Iowa.
Protection of wood fibers against wind erosion has been found to
be important in eastern Washington. Chemical stabilizers have been found
effective for this purpose(126), However, when hydroseeded, wood fibers
-------
-129
have been found to resist wind and water erosion better than other
materials such as rice hulls, ground straw and ground newspaper.
1.04 Mechanical Treatment
a. Introduction. Mechanical measures may be utilized to inhibit
erosion on slopes. Several such measures are currently being successfully
used. These consist of diversions or terraces either atop or on slopes;
berms, serrations, or other variations in gradient; and roughening
or scarification of the slope. Although most of these measures can be
used individually for slope protection, their primary usefulness is to
supplement mulches and other forms of slope stabilization.
Mechanical slope stabilization measures generally function by
reducing the volume and velocity of surface runoff through reduction of
effective slope length and increases in filtration. These measures also
can be used to prevent concentration of flow in undesirable areas and
to provide an improved microclimate for vegetation establishment.
Although numerous references suggest the usage of or describe many
of these mechanical measures in a general way, very little specific
information is provided on their application, design, and effectiveness.
Specific design criteria must generally be developed on an individual
basis. Descriptions of the various mechanical measures in common usage
are provided in the remainder of this section.
b. Diversions or Terraces. Diversions or terraces are graded
channels with a supporting ridge on the lower side constructed across
or atop cut or fill slopes. Their purpose is to intercept surface or
shallow subsurface runoff and divert it to an outlet where it can be
-------
130
safely disposed of. They can be used to reduce slope length into
nonerosive segments or divert water away from critical areas. These
structures are generally temporary and may be graded or level in the
longitudinal direction. Level terraces have closed ends to retain the
runoff, while graded terraces should be designed to carry water at
nonerosive velocities to planned disposal areas.
Diversion outlets should be located so that water will empty into
natural drainage channels or into relatively low gradient upland areas
between drainage channels. Care must be exercised to avoid too great of
flow concentration as well as conveyance or discharge of water at
erosive velocities. Buffer strips of vegetation between points of
discharge and stream courses are extremely desirable to allow suspended
sediments to settle out.
c. Berms and Serrations. Berms are steps or benches in steep
slopes. Serrations are also steps or benches but are generally smaller
and more closely spaced. Also, serrations generally have vertical slope
segments between benches, whereas areas between berms are generally
sloped. If properly located and designed, these measures reduce slope
lengths and divide the volume of runoff into workable slugs that can
be more easily handled. Berms can be constructed level to retain
precipitation in place or graded with a longitudinal gradient and an
outside edge higher than the inside to function as diversions. The
benches on serrated slopes are generally graded level.
In addition to their function of retarding runoff down the slope,
benches provided by berms or serrations also provide an improved
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-131
microclimate for vegetation establishment on steep slopes. As a general
rule, a 50 percent (2:1) continuous slope is assumed to be the maximum
slope upon which vegetation can be satisfactorily established and
maintained (I 13).. Horizontal areas on steep slopes as provided by
benches or serrations better enable vegetation to gain a foothold.
Serrated slopes are a relatively new method of erosion control
and are only applicable under certain conditions, such as cut slopes
of soft rock or similar material that will stand vertically for a few
years in cut heights of approximately a couple of feet. The Washington
Department of Highways is currently using this method successfully in
selected areas (128).
Serrations generally consist of steps of 2 to 4 feet vertically
and horizontally cut along the normal intended slope gradient. After
construction, the slope is seeded, fertilized, and mulched the same as
for normal slopes. The horizontal areas provide an improved environment
for vegetation establishment free of sliding forces normally experienced
on steep slopes. The steps gradually slough and practically disappear
within a few years following construction after vegetation has become
well-established. If the' slope material is soft, it is recommended
that the slope be allowed to slough until about 1/3 of the steps are
filled before seeding; otherwise, grass may be destroyed by the excessive
rate of initial slough. This method is not applicable for any soil types
where the rate of slough is high enough such that vegetative cover
will be buried and destroyed. More information about the use of
serrated slopes can be obtained from (129).
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-132
d. Roughness and Scarification. Smoothly graded cut-and-fill
slopes are attractive to the eye, but they are not beneficial from the
standpoint of erosion control and establishment of vegetative cover.
Roughness and scarification serve to increase infiltration and impede
runoff (113). If the surface is to be seeded, the roughness or scarifi-
cation marks retain seed even after severe runoff. These measures also
serve to cause mulch to adhere better to the slope.
Slopes may be roughened by a wide variety of construction means.
Soils can be scarified by means of a bladed implement equipped with a
ripper attachment which loosens surface soils in place without turning
it over. Deep cleated dozers traveling up and down the slope can be
used to obtain a satisfactory texture on slopes too steep for normal
equipment operation. The Washington Highway Department(126) has found
that a sheepsfoot roller also works fine for roughening slopes.
The texture of the roughened slope should trend perpendicular to
the flow direction (113). Up and down angular cross slope scarification
or roughness texture do more harm then good by concentrating flow. Also,
care must be exercised to prevent excessive loosening of the upper soils
such that the propensity 'for rill and slump erosion are increased.
2.00 Mass Wasting
2.01 Introduction
From time to time during the course of road design, areas will be
encountered which cannot be avoided that will traverse either areas where
mass wasting has occurred or is occurring or where slope stability of
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133
the proposed road cuts are marginal; this includes areas where a safe
cut slope would involve removing a large amount of material upslope from
the road cut. In these areas slope stabilization must be achieved by
the design of some type of retention structure.
For development of soil pressures on the retention structure for
use in design, a good reference is Foundation Design by Wayne C. Teng,~
and for structural design of the retention structure a good reference
is reinforced concrete fundamentals with an emphasis on ultimate
strength by Phil M. Ferguson. The actual design of the soil structure
interaction depends upon the conditions encountered at each location and
therefore is not generalized in this text. The following is a discussion
of various types of retention structures and their possible application.
The design of each of these structures should be based on a detailed
investigation so that the site conditions at each location are known.
2.02 Retaining Wall
The first type of retaining structure is known as a gravity wall
which is usually made of plain masonry, rubble, stone or concrete.
This wall is usually the simplest and easiest to install but can be
only used for relatively low walls, that is less than 8 to 10 feet
with moderate soil pressures (130).
The second type of wall is a cantilever wall of which there are three
basic types. The first type is a plain cantilever wall that can be used
for heights up to approximately 25 feet. These walls usually consist
of a reinforced concrete stem founded on a reinforced concrete base slab.
The other two types of walls are modifications of a cantilever in which
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134
counterforts or buttresses are added to the wall. The counterforts or
buttresses add strength to the stem portion of the wall and a degree of
rigidity to the wall. The counterfort or buttresses may be used for walls
higher than 25 feet with most soil conditions ( 130.).
Another type of wall is a crib wall. This wall is essentially a
gravity-type structure made of timber, precast concrete or metal which
form an open structure of some dimension. This open structure is then
filled with soil forming a relatively-large massive structure. This
type of wall is usually suitable for small to moderate-height walls
which are less than 21 feet in height and subjected to only moderate
earth pressures (I30J.
In some cases where soil conditions permit, use of sheet pile
bulkheads may be advised. The sheet pile bulkheads may either
be cantilevered or restrained near the top with anchors. This method
of retention is oftentimes expensive. However, installation of the
cantilever-type wall is relatively simple and can be done without form
work. These walls are usually less than 20 feet in height if drainage
is provided behind the wall (I3lj.
In areas where soils are suitable, reinforced earth structures may
be constructed. This method consists of placing metal strips perpendicular
to the front of either a thin shell concrete or steel wall. Soil is
then compacted over the strips for a shallow depth, another set of
strips is then placed and the process repeated until the full height
of the wall is attained. This process is restricted to granular backfills
and walls usually less than 15 feet in height.
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•»35-
The selection of the proper type of wall to be used in any one
situation depends upon the purpose of the retention structure and the
foundation conditions at the site and the economics involved.
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136
C. DRAINAGE DESIGN
"A major contributor to both accelerated surface soil erosion and
mass soil failures was lack of adequate drainage provided at man-
made improvements. Drainage includes practices that prevent con-
centration of water and those that foster dispersal of water into
stabilized land areas or into stabilized stream channels. Failure
or impairment of road drainage facilities was involved in almost
all road-connected storm damage." (132)
To minimize sediment production and transportation from forest
roads, the planning, design and construction of drainage facilities must
be executed for the particular conditions encountered and not on a basis
of generalized criteria.
Chapter V of this report will discuss Maintenance but designers and
owners should recognize that the designs and suggestions contained under
this heading will not function adequately without inspection, maintenance
and possible change of individual drainage features. The first such in-
spections should be made, hopefully by the design engineer, during or
immediately after the first storm.
I.00 Ditches and Berms
There are two primary functions of ditches and berms; namely to
intercept runoff before -it reaches erodible areas; and to carry sediment,
during high flows, to properly designed settling basins when circumstances
warrant the use of these basins. Important places for the installation of
ditches or berms are at the top of cut and fill slopes and adjacent to the
roadway. Midslope berms with ditches may be especially helpful in con-
trolling sediment before erosion control cover is established.
The ditch size (area) can be determined by considering the slope of
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137
the ditch, area intercepted, intensity and volume of runoff, and the
amount of sediment that may be deposited in the ditch during low flow
conditions. The shape of the ditch may be trapezoidal or triangular,
whichever is appropriate to the particular location.
I.01 Size and Placement
For ditch design, a good reference is "Design Charts for Open
Channel Flow," Hydraulic Design Series No. 3, by the Bureau of Public
Roads, (Federal Highway Administration) 1961 or later revision. (133)
In addition to the ditch size required for full flow capacity, an allow-
ance should be made for anticipated sediment deposit. Minimum full
capacity flow velocities should be 2.5 to 3.0 feet per second to permit
sediment transport. Refer to Table III C-l for scour velocities in
ditches of various materials.
The full flow water surface for roadway ditches should be at least
one foot below the roadway subgrade. This position will prevent ditch
water from entering the ballast material, removing the fines and destroy-
ing the ballast's effectiveness in supporting the roadway surface. Figure
111 C-l shows the water surface level relative to the road subgrade. The
suggested minimum size of ditches along roadways or elsewhere is shown
in Figure I 11 C-2.
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138
i
^
^O
\
, v :
.c
(
_J
I I turfaang, if used,
\
\
FIG. EIIC-1
The depth of potential sediment deposit in ditches is directly
related to the credibility of the soils over which water flows to the
ditch and the ditch slope. The ditch depth allowance for sediment
deposit should recognize the soil credibility, the kind of erosion con-
trol cover planned for tributary slopes and the anticipated maintenance
program. Some ditches, due to their slope and/or soil type, may not
require a depth allowance for sediment build-up. The designer should
refer to the information obtained during the planning-reconnaissance
phase of the project for information relative to the erodibility of the
soils that will be encountered within the road corridor.
All ditches constructed in erodible soils are themselves subject
to erosion from runoff and may require stabilization by such means as
riprap, rock rubble lining, jute matting, seeding and/or other accept-
able erosion control device. Table III C-2 shows permissible velocities
for ditches lined with vegetation. Plastic sheeting can be used as a
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139
Table III C-l
Maximum permissible velocities in erodible channels, based on uniform
flow in continuously wet, aged channels*
Maximum permiss i bIe
velocities for—
Mater ia 1
Fine sand (noncolloidal
Sandy loan (noncolloida
Silt loam (noncolloidal
Stiff clay (very colloi
Graded, loam to cobbles
Graded, silt to cobbles
Alluvial silts (noncoll
Alluvial silts (colloid
Coarse gravel (noncollo
Cobbles and shingles .
Sha 1 es and hard pans »
)
1 )
)
da 1 )
(nonco 1 1 o i da 1 ) .
(co 1 1 o i da 1 ) . . .
a| )
j da 1 )
Clear
water
F.p.s.
1 .5
1 .7
2.0
2.5
2.5
2.5
3.7
3.7
4.0
2.0
3.7
4.0
5.0
6.0
Water
carry ing
fine
si Its
F.p.s.
2.5
2.5
3.0
3.5
3.5
5.0
5.0
5.0
5.5
3.5
5.0
6.0
5.5
6.0
Water
carry ing
sand and
grave 1
F.p.s.
1 .5
2.0
2.0
2.2
2.0
3.7
3.0
5.0
5.0
2.0
3.0
6.5
6.5
5.0
*As recommended by Special Committee on Irrigation Research, American
Society of Civil Engineers, 1926, for channels with straight alinemento
For sinuous channels multiply allowable velocity by 0.95 for slightly
sinuous, by 0.9 for moderately sinuous channels, and by 0.8 for highly
sinuous channels (45, p. 1257)
Source: Design of Roadside Drainage Channels, U. S. Department of
Commerce, Bureau of Public Roads Washington: 1965, page 54.
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140
Table III C-2
Maximum permissible velocities in channels lined with uniform stands of
various grass covers, well maintained* (2)
Cover
Slope range
Maximum permis-
sible ve loc i ty on-
Eros ion Eas ily
resistant eroded
soils so iIs
Percent f.p.s
0-5 ..... 8
Bermudagrass ............ 5-10 .... 7
Over 10 ... 6
Buffalograss ............
Kentucky bluegrass ......... 0-5 ..... 7
Smooth brome ............ 5-10 .... 6
Blue grama ............. Over 10 ... 5
0-5(3) ... 5
Grass mixture ..... . ..... 5-10(3) ... 4
Lespedeza sericea .........
Weeping lovegrass .........
Yellow bluestem ..........
Kudzu ............... 0-5(4) ... 3.5
Alfalfa ..............
Crabgrass .............
Common lespedeza (5) ........
Sudangrass (5) . . . . ; ...... 0-5(4) . . . 3.5
f.p.s
6
5
4
5
4
3
4
3
2.5
2.5
(I) From Handbook of Channel Design for Soil and Water Conservation.
(See footnote 5, table 2.)
(2) Use velocities over 5 f.p.s. only where good covers and proper main
tenance can be obtained.
(3) Do not use on slopes steeper than 10 percent.
(4) Use on slopes steeper than 5 percent is not recommended.
(5) Annuals, used on mild slopes or as temporary protection until perma
nent covers are established.
Source: Design of Roadside Drainage Channels, U. S. Department of
Commerce, Bureau of Public Roads Washington: 1965, page 54.
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141
temporary erosion control device during the construction period.
Riprap or rubble lined ditches will tend to act as a flow retardent
which will allow movement of water and retain the sediment at low flow
periods. The depth allowance for ditches lined with riprap or rock
rubble can be coincident with the depth allowance for sediment deposit.
Berms (Figure III C-3) can be constructed of native material pro-
vided the material contains enough fines to render the berm impervious
and the material can be shaped and compacted to about 90% of maximum
dens ity.*
Figure III C-4 portrays the general location for ditches and berms
in relation to a finished roadway section. Additional locations for
temporary ditches and other drainage facilities may be necessary during
the construction phase. Refer to Section IV, Construction.
Ditches at the top of slopes may be needed when:
I. The natural ground above slope "daylight" point continues up
sharply.
2. Ground cover above "daylight" point has low moisture absorbing
ability (i.e. rock or clearcut area).
3. Exposed soils on cut slope are highly erodible, the exposed
area is large, rain intensities are high and erosion control
measures need time for establishment.
4. Quantity of runoff will flood or tend to flood the roadway
ditch below the cut slope.
*Maximum density is a term used in earthwork specifications to mean the
oven-dry weight per cubic foot of soil at optimum moisture content. The
American Association of State Highway Officials (AASHO), the American
Society of Testing Materials (ASTM) and other organizations have estab-
lished field testing procedures to determine if compacted earthwork
meets a specified percentage of maximum density.
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142
RG. IBBC-2
F1G.IIIC-3
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143
1.02 Ditch ProfiIes
Roadway ditch profiles will generally follow the roadway grade.
The minimum grade should be \%. If flatter grades are necessary,
ditches may need to be larger or alternately, the ditch can be separately
profiled to obtain the necessary minimum gradient.
Other ditch profiles should be consistent with the ditch section
used and quantity of flow. As previously suggested, the full flow
velocity in all ditches should be at least 2.5 to 3.0 feet per second
to permit sediment transport. (See Section I.01)
1.03 Ditch Outlets
Ditches will outlet or discharge into natural streams, other drain-
age channels, culverts or settling basins. Ditches that outlet into
natural drainage channels or streams may require a catch basin with cul-
vert outlet or other sediment trapping device, 100-150 feet upstream
from the intersection with the drainage channel or stream as shown in
Figure III C-5. If the roadway cut slopes, fill slopes and ditches are
stabilized, there should be minimal risk of sediment entering the
stream or natural channel from the last 100-150 feet of the ditch shown
in Figure 11 I C-5.
Ditches will also outlet into culverts. If the soils are erodible
in and around the ditch, the circumstances may require a catch basin
structure prior to culvert entry. See Section 2.00 "Culverts" for
culvert and catch basin discussion.
-------
t goad vay
or
FIGJB1C-4
FSGJBSC-5
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145
1.04 Sloped Roadway Alternate to Roadside Ditches
Construct ion of out and in sloped roadways with surface cross
drains has been a popular way to build forest roads. Although this type
of construction has a place in forest road work, misuse of the concept
can result in a sediment problem.
From the "Proceedings of A Symposium Forest Land Uses and Stream
Environment" at Oregon State University, Larse recommends: "Design out-
slope or alternating inslope and outslope roadbed sections without a
drainage ditch when overland surface flows are slight and road gradients
can be 'rolled' sufficiently to self-drain without surface channeling."
(134)
In 1967 Paul E. Packer completed studies and published "Criteria
for Designing and Locating Logging Roads to Control Sediment." (135)
These studies were directed toward the control of rill or gully erosion
on outslope road surfaces in the Northern Rocky Mountains. Each study
site had to meet the following criteria:
I. "Drainage structures immediately above and immediately below
the road segment must have diverted all surface runoff and
eroded soil originating above them onto the fill slope below
the road without allowing any discharge to continue down the
road surface. .
2. The road segment must not have been affected by waterflow
from s ide drainages.
3. The road segment must not have had an inside ditch along the
toe of the road cut.
4. Sediment discharged from the lower or downgrade drainage
structure, or eroded from the fill below it, must have been
stopped on the slope before reaching a stream channel, a
downslope road, or a major topographic barrier, such as a
bench.
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146
5. The entire study site, including the slope above the road cut
and the slope below the fill, must have been located on soil
derived from similar parent materiaI.
6. The site must have been on an area where the timber sale was
not more than 5 years old."
The report included a table for cross drain spacing required to prevent
rill or gully erosion deeper than one inch on secondary logging roads in
certain types of soils on various road grades. The "Guides for Control-
ling Sedimentation from Secondary Logging Roads" by Packer and Christensen
also contains the table. The table is included herein as Table III C-3.
Care must be exercised in the use of the table to ascertain that it is
applied under circumstances that are closely comparable to the conditions
under which Packer's studies were made. Packer and Christensen recommend
that where combination of soil and topographic features require cross
drain spacings of less than thirty feet, "no logging roads should be
built unless they will be surfaced with gravel or crushed rock." (136)
In their China Glenn road report, Hartsog and Gonsior offer the
following conclusion as to the success of the outslope road section as
used at this particular location:
"The authors suspect that outsloping is more an idealistic concept
than a realistic solution to the water control problem. In theory,
water generally will be uniformly distributed in minimal concentra-
tion over the road shoulder. However, unless the road can be
graded to close tolerances and left undistorted, concentration is
virtually unavoidable. Depressions left by wheels allow water to
concentrate and run along the road. Even if the road has no grade,
water will tend to concentrate and spill over depressions. If
soils are loose and erodible, slight concentrations tend to erode
depressions and channels that lead to greater concentrations and
accelerated erosion. Although it can be argued that such problems
rarely occur, the major part of all stream sedimentation is caused
by relatively infrequent circumstances. Most of any stream's an-
nual sediment load is contributed and transmitted (under natural or
disturbed conditions) during a few hours or days. It is tentatively
recommended that outsloping be specified only where surfaces are
relatively nonerodible (e.g., at full-bench sections)." (137)
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147
Tab Ie III C-3
Cross-drain spacings required to prevent rill or gully erosion deeper than
I inch on secondary logging roads built in the upper topographic position
(I) of north-facing slopes (2) having a gradient of 80 percent. (3)
Road
grade
(percent)
Cross-drain spacing
Hard
sediment
Basalt
Granite
Glacial
si It
Andesite Loess
2
4
6
8
10
12
14
(1) On
midd 1
topographic
(2) On
(3) For
reduce
south
each
spaci
167
152
144
137
128
1 19
108
e topograph
154
139
131
124
1 15
106
95
ic position
position, reduce spaci
aspects, reduce spaci
10-percent
ngs 5 feet.
decrease i
137
122
1 14
107
98
89
78
135
120
1 12
105
96
87
76
, reduce spacings
ngs 36
ngs 15
n s 1 ope
feet.
feet.
steepness
105
90
82
75
66
57
46
18 feet;
below 80
95
80
72
65
57
48
37
on lower
percent,
Source: Criteria for designing locating Logging Roads to Control
Sediment, Paul E. Packer, Reprinted from Forest Science, Volume
le, Number I, March, 1967.
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148
The following conditions are favorable for the use of no ditch out-
slope roads with surface cross drains.
I. Short backs lopes
2. Terrain slope less than 20%
3. Seasonal road use
4. Spur (light traffic) roads
5. Favorable geographic area (i.e. Idaho)
6. Non continuous longitudinal grades steeper than 3%
7. Conditions permitting immediate planting and growing of
vegetation on cut and fill slopes.
The following conditions are unfavorable for the use of no ditch
outslope roads.
I. Long backs lopes
2. Continuous steep longitudinal grades
3. Terrain steeper than 20%.
1.05 Rock Sub-drain Alternate to Roadside Ditches
Another alternate is the use of the Rock Sub-drain. The Rock Sub-
drain is located between the toe of the cut slope and the edge of the
roadway as shown on Figure III C-6. An advantage for its use as compared
to an open ditch is that the total grading width of the road will be less,
Rock Sub-drains may be used when longitudinal grades are steeper than 2%.
Critical to the longevity of the sub-drain is the establishment and
maintenance of vegetation on the slopes above the drain. Any limitations
on construction procedures for installing the rock sub-drain in order to
maintain backslope stability and prevent contamination of the sub-drain
should be included on the plans or in the accompanying specifications.
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149
^
^
(
Vr'^ "•• ' Vv
\>7\>-:, .-(.
W^.
V-" }r",-—^
\~'^~\ .'-.
2^0
F8GJ8SC-6
Rock Sub-drains can outlet similarly to the open ditch, through
a "Ditch Inlet Structure" (See Section 2.00) and a cross culvert or to
a natural channel.
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150
2.00 Culverts
"A culvert is an enclosed channel serving as a continuation of and
a substitute for an open ditch or an open stream where that ditch or
stream meets an artificial barrier such as a roadway, embankment or
levee." (138) Forest road culverts are used primarily for draining the
roadway surface (outlettirig roadside ditches) and to allow streams or
natural channels to pass through a roadway embankment.
"Culvert failure, another common cause of road damage, was most
often related to plugging with debris. In most cases, the hydraulic
capacity of the culvert was sufficient to carry the volume of water as
long as it remained unplugged." (139)
The fact that culvert intakes do become blocked with debris, sedi-
ment, rocks, etc., requires that serious consideration be accorded the
use of a culvert intake protecting device. A "Ditch Grating Inlet Struc-
ture," with or without a Catch Basin (See Fig. Ill C-7 & Fig. Ill C-8),
is such a device. The degree or amount of culvert intake protection
needed will vary with individual site circumstances from a simple riprap
treatment of ditch bottom and sides at the intake point to the more
elaborate treatments that can include trash racks, catch basins and/or
the grating inlet structure. Intake protection should also be evaluated
in the light of the anticipated ditch and culvert maintenance program and
the companion treatment that may be accorded the culvert outlet. In a
series of several culverts outletting a ditch, varying degrees of treatment
to intakes might be considered so that at least one or more of the culverts
would function under very adverse circumstances.
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151
75-4
'I
/
Jj
Pitch
A
PLAN
SECTION A-A
DITCH INLET
FIG.ISSC-7
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152
DITCH INLET STRUCTURE
WITH CATCH BASIN
FIG. III C-8
-------
The roadway culvert should have a minimum depth of cover of approx-
imately four feet. This depth is required to prevent crushing the culvert
by passage of truck live loads. An inactive culvert (crushed) can cause
roadway wash-out, erosion and sediment.
"The frequency, location and installation method of ditch drainage
culverts is much more important than capacity or size. However, TninlTmim
sizes of 15 inch or 18 inch diameter is the accepted practice, depending
on the rainfall intensity (runoff and area intercepted) and the
influence of ditch debris" .(ll*o) A minimum diameter of 18 inches is sug-
gested.
Ditch outlet culverts should be designed so that the half full
velocities are 2.5 to 3-0 feet per second in order to transport sediment
through the culvert. Should the ditch become over silted and the catch
basin or other intake device fail to function, the sediment should pass
through the roadway culvert to outlet or other necessary downstream sedi-
ment collectors. Cleaning culverts is a difficult, expensive, neglected,
ignored and often an imperfect procedure. Provision for necessary sedi-
ment collection before or at the culvert intake and/or at or after the
culvert outlet is recommended. (See Section U.OO for discussion of
sediment collection devices at or beyond culvert outlet points.)
Common culvert materials are corrugated galvanized steel and cor-
rugated aluminum. When culverts are on steep slopes where design flow-
velocities are 10 feet per second and greater, paved inverts are
desirable to reduce barrel wear resulting from sediment scour. The type
of coupling band necessary for an installation and whether or not the use
of gaskets is appropriate should be related to the anticipated differential
-------
settlement that might occur along the length of the culvert. Culvert
separation under a roadway has great potential for causing roadway
failure and subsequent sediment transport.
The culverts used to pass streams under roadway embankments can be
round, structural pipe arch or structural plate arch. The latter two
are preferred. The structural pipe arch enables the wide flat bottom to
be buried in the stream bed. The structural plate arch has no bottom,
so the stream can remain virtually untouched if care is exercised during
its installation. (Refer to Section 3-00 for further discussion of
stream crossings.)
Outfall ends of culverts under roadways should ideally terminate
beyond the toe of the fill. When the fill is shallow this condition may
be satisfied by simply extending the pipe as a cantilever beyond the fill
slope a sufficient distance to clear the toe of fill. On deep embank-
ments, where the outlet point is a considerable distance above natural
ground, a culvert extension anchored to the fill slope may be required.
Half round culvert extensions are also employed for this circumstance.
Whether the half round will be satisfactory is dependent upon its
anchorage, the quantity and velocity of discharge, and the length and
steepness of the embankment.
Canvas or "elephant trunk" culvert extensions have also beem employed.
They have been subject to vandalism and to freezing shut in cold weather.
Placing riprap on the fill slope below the culvert outlet will aid in
preventing slope wash.
The problem of protecting the fill slope at the culvert outlet point
can be minimized by placing the culvert entirely on or within natural
-------
ground. Determination as to the adoption of this alternate is a matter
of evaluation of the circumstances at the culvert location in question.
2.01 Sizing Culverts
The complete hydraulic design procedure for a.n culverts requires:
1. Determination of the design flow - See discussion below and
paragraphs 3-00 and 5.00.
2. Selection of the culvert size.
3. Determination of the outlet velocity.
"The many hydraulic design procedures available for
determining the required size of a culvert vary from empirical
formulas to a comprehensive mathematical analysis. Most em-
pirical formulas, while easy to use, do not lend themselves
to proper evaluation of all the factors that affect the flow
of water through a culvert. The mathematical solution, while
giving precise results, is time consuming. A systematic and
simple design procedure for the proper selection of a culvert
size is provided by Hydraulic Engineering Circular No. 5,
Hydraulic Charts for the Selection of Highway Culverts and
No. 10, Capacity Charts for the Hydraulic Design of Highway
Culverts, developed by the Bureau of Public Roads." (l^l) (1^2)
(Federal Highway Administration.)
This method is based on the results of both laboratory experiment and
prototype tests. The method is believed to provide a more rational
approach for determining culvert capacity than older procedures.
"The procedure for selecting a culvert is to determine the head
water depth from the charts for both assumed inlet and outlet controls.
The solution which yields the higher head water depth indicates the
governing control." (1^3) However, the minimum velocity must be 2.5 to 3.0
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156
feet per second at half capacity for transporting sediment through the
culvert. The procedure stated above includes a determination of the
outlet velocity. Knowledge of this velocity is pertinent to the evalua-
tion of the potential for erosion at the outlet point of the culvert.
i
The sizing procedure, outlined above, may be augmented by the follow-
ing considerations:
1. Arbitrarily reduce roadway culvert spacing below the spacing
required by mathematical calculation, to recognize the potential
for debris and sediment blocking of culvert intakes and/or the
circumstances at the outlet end. Large volume high velocity
discharge may be difficult to control regardless of the sophis-
tication of the treatment.
2. Arbitrarily increase roadway culvert sizes and/or reduce culvert
spacing in recognition of the level of accuracy of data used in
determining the design flow.
3- In a run of three or four cross roadway culverts, make one a
size or two larger than calculations require as an "insurance"
mechanism for the circumstance of one or more culverts becoming
plugged.
If. Be realistic in forecasting or assuming the level of ditch and
culvert maintenance.
5. Size culverts at the low point of sag vertical curves for twice
the calculated flow or alternately size all culverts upstream
from the low point for 20 percent more than the calculated flow.
Provide an inlet structure for the culvert at the vertical curve
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157
low point. Make liberal use of trash rocks or inlet structures
for the culverts along the adjacent negative grades.
6. Since live stream culverts are preferably installed parallel to
stream gradient with invert buried in the stream bed, recognize
this circumstance in flow capacity evaluation.
7- Evaluate stream culvert calculated size relative to potential
stream bed constriction. Pipe arch or plate arch culverts have
advantages as described in Section 2.00.
8. Evaluate the potential for manufactured debris upstream from
stream culverts in terms of the land management program for the
drainage area. If the area is to be logged, provisions must be
made to keep manufactured debris out of the stream or the culvert
must be sized accordingly. The former is the better procedure,
the latter is guess work.
9- From the reconnaissance information, recognize the potential for
natural stream bed erosion during storms.
2.02 Design Aspects of Culvert Installation
Culvert design usually includes features of the installation that
are important to the performance of the culvert in accordance with design
expectations. These features, when appropriately specified by the
designer and accomplished by the installer, are germane to the sediment
creation potential occasioned by culvert failure.
a. Roadway Culverts It is usual to specify that the trench
width shall be limited (pipe diameter plus a distance) and
that the trench walls be vertical for a height at least
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:I58
equal to the pipe diameter and preferably more. These limitations are
used because wider trenches tend to increase load on the pipe and require
more excavation and backfill. Reasonable care in installation is assumed
for «.n design criteria or design tables developed for determing necessary
pipe gaB§» Handling the minimum amount of soil when installing a culvert
is also advantageous with respect to the potential for sediment creation.
Culverts may be crowned when installed to provide for the deflection anti-
cipated by embankment consolidation.
Culvert trenches are often over excavated and backfilled with select
material (pea gravel is popular) in order to obtain proper pipe bedding
in lieu of shaping the trench bottom for the pipe barrel, or because of
unsuitable foundation material. The select backfill is usually placed at
least to the spring line of the pipe. If a situation existed where water
was being forced along the outside of a culvert, the presence of pea
gravel backfill would tend to allow this passage as opposed to the circum-
stance of pressure build up and possible culvert blow out. Thus the use
of pea gravel backfill for reasons of the structural integrity of the
culvert could have the simultaneous advantage of minimi zing sediment
potential. The Ditch Grating Inlet Structure (Figures III C-7 & III C-8)
will act to reduce the opportunity for water to pass along the outside
of the culvert.
b. Stream Culverts
The advantages of using structural plate or pipe arch
culverts as a means of minimizing stream bed disturbance have been pre-
viously mentioned. As with roadway culverts, all of the installation
procedures important to the structural integrity of the installed culvert
(foundation, backfill quality and method) may have bearing on the potential
for sediment creation.
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Upstream fill slopes will usually require erosion protection by
the use of concrete headwalls, rock riprap or gabions. (See Figure III C-9)
A conservative estimate of the height and width of the fill slope adjacent
to the culvert requiring this protection is suggested.
In some circumstances, an additional safety factor can be in-
cluded by provision for an overflow channel across the roadway adjacent
to the culvert. The roadway profile might be adjusted to provide an
adjacent low spot or sag with companion fill slope armoring within the
planned overflow channel. Although some sediment creation and transport
may occur, the amount will be much less than that created by a culvert
"blow out".
Clearing of the approach channel of natural debris for some
distance upstream from the culvert is strongly recommended. The amount of
clearing necessary is dependent on the individual circumstances at the
site, 100
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160
FJG.III C-9
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161
feet upstream is offered as a guide line. Clearing of
the approach 'channel should be an annual accomplishment.
3.00 Water Course Crossings
One of 'the important forest road design problems is the live stream
crossing. Sudden earth slides and minor roadway surface disintegration
are capable of disabling a road but the potential for road loss and sedi-
ment creation and transport from a washout due to a plugged culvert or
extraordinary high water at a stream crossing is probably greater. It is
therefore extremely important to exercise the utmost care in the planning,
design and construction of water course crossings. Robert W. Larse
observed that: "Surveys of road damage and erosion resulting from high
stream flows indicates floatable debris to be a major contributing factor,
plugging small culverts and restricting flow at large culverts and bridges,
and causing severe road embankment, stream bank erosion or channel
changes". (iMO
•Design criteria for minimizing the sediment potential from stream
crossings is interrelated with other design factors whose application is
necessary to satisfy the functional requirements of the site. If these
criteria are not satisfied, the crossing will not provide satisfactory
service to the land manager. Therefore the following discussion of
criteria is necessarily broader than the topic of sediment minimization.
The discussion is not, however, a complete treatment of the design
spectrum for stream crossings.
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3.01 General
Each stream crossing must receive individual study to determine the
"best crossing method or medium. Sufficient site data must be available
to the responsible designer so that he can accomplish this individual
study. This data will be a part of the findings of the reconnaissance
phase supplemented by appropriate topographic, foundation and other infor-
mation that will define the ambient site circumstances in adequate detail
for design purposes. A site visit by the project designer is strongly
recommended.
The responsible design professional must know the use and purpose of
the road of which the stream crossing is a part. The intended road use
may relate to the designer's options in selecting a crossing medium, for
example, will a ford be satisfactory. His task is to meld the use require-
ments to the site requirements in a manner that will produce a satisfac-
tory result.
3-02 Sediment features of stream crossing design
The following aspects of stream crossing design have particular
relevance to the potential for sediment creation.
1. Hydraulic capacity of opening.
2. Allowances for debris.
3. Bank protection (stream or roadway slopes) adjacent to or within
the crossing area.
k. Effect of channel changes or relocation.
5. Amount of excavation or foundation work needed within wetted
perimeter of stream.
6. Timing of construction relative to high water.
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Based on the quality of information available to him, and his com-
petence, the designer can recognize and treat the first five items listed
above in his design solution. The sixth item involves those who program
the actual construction as well as the type of design. Appropriate com-
munication on this subject is mandatory.
Sufficient topographic field data for the designer to determine the
hydraulic characteristics of the stream channel is basic to analysis of
hydraulic capacity. This data is needed for several hundred feet up-
stream and downstream from the crossing point in order to determine the
water surface level relative to stream banks for various design flows.
Even with an adequate channel section at the crossing, an inadequate
section upstream could produce a circumstance wherein waters will over-
flow channel banks and result in erosion of approach embankments. Such
a circumstance may indicate a need to consider embankment protection rip-
rap, overflow culverts in approach embankments, overflow approach spans
for bridges, or provision for flood waters to overtop approach .embankments.
Determination of design flows for mountain streams and rivers is
more difficult due to the lack of stream gaging stations and rainfall
intensity records in high altitude areas. A nationwide series of water-
supply papers entitled "Magnitude and Frequency of Floods in the United
States" has been prepared by the United States Geological Survey.
Academic calculation of design flows by the USGS method or other approach
should be cross checked by the following:
1.. Known flood history of the area.
2. Performance of crossings of similar streams.
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3- All available gaging records of this and comparable streams.
U. Field data indicating high water marks, natural overflow
channels, old stream beds, etc.
Any proposed changes to natural channels or the inclusion of flood
way obstructions should be evaluated to determine the changes that might
occur in the hydraulic behavior of the stream. Channel relocations, when
constructed in the dry, are not necessarily detrimental to the stream.
Easing or elimination of sharp bends may remove a constriction to hydraulic
capacity. (Stream bed scour may also increase.) The rule is to make a
total evaluation of the proposed design. The U. S. Bureau of Public Roads
(Federal Highway Administration) "Hydraulics of Bridge Waterways" is a
good reference for the analysis of stream obstructions (i.e. bridge piers)
for streams or rivers. (1^5)
Tables III C-l and III C-2 in 1.01 give scour velocities for certain
kinds of ditch linings or ditch soils. Values shown in these tables pro-
vide an indication as to the maximum velocities that can be tolerated in
channels without using riprap treatments of rock or gabions. The U. S.
Bureau of Public Roads "Design Charts for Open-Channel Flow" includes
data for grassed channels. Design charts include a procedure for deter-
mining maximum permissible velocities without channel scour. (lk6)
Important to the satisfactory performance of riprap lined channels
is the sizing of the riprap and the companion channel side slope. The
Bureau of Public Roads "Design of Roadside Drainage Channels" 1965 in-
cludes procedures for evaluating the adequacy of channel linings relative
to channel slope and flow velocity. This publication recommends that
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"if the mean velocity at the design flow exceeds the permissible velocity
for the particular soil type, the channel should be protected from erosion".
(1^7) Design procedures for the use of various linings are discussed.
Riprap bank protections should extend to a minimum of two feet below
the stream bed. This is to prevent erosion of the bank material and sub-
sequent displacement of the riprap.
3.03 Stream crossing methods
There are three stream crossing methods employed on forest roads,
fords, culverts and bridges. Factors influencing the selection of the
appropriate crossing method include stream size, debris potential, ver-
tical position of road relative to stream, foundation conditions, con-
struction cost and maintenance cost, and contemplated road use and life.
a. Fords are an attractive alternate for secondary or spur road
crossings of small streams particularly if the road use is limited to the
dry season when little or no water is in the channel. Ford installation
requires minimal disturbance to the stream channel. Problems attendant to
bridge or culvert installation such as size of opening, provision for debris
passage and channel or embankment riprap are largely avoided.
Gabions for ford crossings have been successfully used in the
Modoc National Forest. Allen J. Leydecker in an article entitled "Use of
Gabions for Low Water Crossings on Primitive or Secondary Forest Roads"
(iW) describes the design used. A typical installation cost $3,000 in
1971 and was accomplished on a force account basis. The installation
consists of gabions placed at the roadway grade backfilled by stream
gravel to form the road surface. "In about a year's time, fines trans-
ported by the stream cement the gravel backfill and construction scars
heal, leaving a satisfactory stream crossing . . . . " Figure III C-10
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166
GABION FORD
FIG.Ill C-10
Source:
Leydecker, Allen D., "Use of Gabions for Low Water Crossings
on Primitive or Secondary Forest Roads"
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167
is a reproduction from Leydecker's paper portraying a section through the
ford. The ford was not damaged during the following winter when peak
flows were estimated by Leydecker to have been approximately ^00 cfs.
b. Culverts have been regarded by many designers as the economic
solution for small stream highway crossings during the past twenty-five
years. They have largely displaced the previously used short span bridge
for reasons of economy and the goal of maintaining an uninterrupted road-
way and shoulder width. The performance of culverts on forest roads
suggests that the determination of use should not be as quickly assumed
as has been the case for county roads, city streets and state highways.
The site circumstances that may be different from that of a typical public
highway installation are steepness of terrain, potential for debris,
ability of steep terrain to retain fills adjacent to the culvert and
difficulty in compacting fills with equipment usually used in forest road
construction. Reliability of the calculation for required culvert capacity
is another factor.
The foregoing discussion is particularly directed toward the round
culvert. No specific guidelines or "rules of thumb" are available to
assist the designer in making a choice between bridge or culvert. Attention
to the individual circumstances of the site by a competent professional
is the only known rule.
Other features of culvert design are discussed under Section 2.00.
c. Forest road bridges have been designed using a variety of
structural materials for substructure and superstructure. The selection of
a bridge type for a particular site is dependent upon the functional require-
ments of the site, economics of construction at that site, live load re-
quirements, foundation conditions, policies or opinions of the owner,
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maintenance evaluations and preferences of the project designer. The type
of design selected can have a "bearing on the potential for sediment creation.
The bridge design can go awry if insufficient attention is accorded
the site circumstances. A quick conclusion that the site permits the use of
an accomplished design from a "similar" site should be avoided.
Location of bridge foundations relative to the normal stream
channel and forecasted flood channel can be an important element. While it
is not suggested that all bridges must span flood channels, an evaluation
of the effect on the channel with an obstruction therein is necessary.
Channel obstructions can cause channel scour and contribute to debris
blockage.
Although there are different views on the minimum desirable hori-
zontal and vertical stream clearances in streams not subject to navigation,
some arbitrary rules based on judgment and experience in the area should be
established. Vertical clearances should not be less than 5 feet above the
50 year flood level plus .02 of the horizontal distance between piers.
Horizontal clearance, between piers or supports in forested lands or cros-
sings below forested lands, should not be less than 85$ of the anticipated
tree height in the forested lands or the lateral width of the 50 year flood.
In considering a longer span bridge, there are economic tradeoffs,
higher superstructure cost versus possible reduction in foundation cost as
compared to a short span. Subacqueous foundations are expensive and involve
a degree of risk attendant to the operations of cofferdam construction,
seal placement and cofferdam dewatering. In addition to the water quality
degradation that can occur with a lost cofferdam, the time and money loss
will be significant. Subacqueous foundations often limit the season of
construction relative to water level and relative to fish spawning activities.
Thus, construction timing has to be rigidly controlled.
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Type of foundation support also deserves consideration from a sediment
perspective. If deep excavations are necessary to reach suitable strata
for direct bearing footings, pile supports may result in less disturbance
of the ground in and around the stream thereby reducing the amount of
excavation, shoring and backfilling. A careful review of the economic
tradeoffs is appropriate rather than an immediate conclusion that direct
bearing footings are correct because the support strata is present at some
depth.
The remoteness of many forest road bridge sites suggests the maximum
use of precast or prefabricated superstructure units for economic reasons.
The use may be limited by the capability to transport the units over narrow,
high curvature roads to the site, or the horizontal geometry of the bridge
itself. Precast or prefabricated superstructure units avoid a requirement
to falsework the stream as is required for a cast-in-place concrete bridge.
A cast-in-place structure may place limits on the construction season as the
falsework may block the stream and is very vulnerable to debris damage. Any
delays to construction (changed foundation conditions) that result in false-
work being placed later in the season than initially anticipated can be
hazardous. Some streams are subject to flash floods even in the "dry"
season.
The U. S. Forest Service is constructing nine steel girder bridges on
Forest Development Roads, South Tongass National Forest, Prince of Wales
Island, Alaska. Short construction season and the remote sites (no local
source of concrete aggregates) influenced the designer's decision to maximize
use of prefabricated steel elements for both superstructure and substructure
units.
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The abutments for three of the bridges are U-shaped made entirely of
steel sheet piling. The structures clear span the normal water level, end
supports interfere slightly with estimated high water. Although minimiza-
tion of the opportunity for the creation of sediment may not have been a
stated design goal, the abutment design is one that clearly accomplishes
this. Placing of the sheet pile abutments require minimum handling of
natural soils as compared to an abutment designed in reinforced concrete.
A conservative vertical clearance for debris at high water was also
provided. A lateral bracing system was provided in the plane of the top
flanges of the girders, a system was not provided in the plane of the lower
girder flanges because of vulnerability to drift and debris during high water.
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4.00 Culvert Outlet Treatments
The last opportunity to control or inhibit the movement of sediment
in the roadway drainage system is at or near the culvert outlet point.
The action of the water at the outlet point can also create sediment if
the flow velocity is of a magnitude that will scour the natural soils at
the out let.
Due to the many variables involved, all possible solutions to this
problem are not included in the following discussion. A few practical
solutions that can be adapted as the designer may determine are outlined.
If appropriate upstream measures have been taken for sediment control,
the degree of treatment at the culvert outlet may be minimal. Appropriate
upstream measures may include:
I. Adequately designed and constructed ditches with appropriate
linings as outlined in Section 1.00.
2. A "Ditch Inlet Structure with Catch Basin" that functions properly
to trap sediment, Section 2.00. Sediment that is not deposited
in the ditch and bypasses the catch basin is considered as flow-
ing through the roadway culvert to its outlet. Whether or not
storm waters are likely to contain significant sediment at the
culvert outlet depends upon the erodibility of soils over which
these waters have passed and the volume and velocity of flow.
Figures III C-lI and III C-12 show two roadway culvert outlet condi-
tions. The culverts shown in Figure III C-lI outlet at least 150 feet
from a live stream. For this condition a short length of lined culvert
apron at the outlet point to act as an energy dissipator and a scour
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L 1?6act way
SHALLOW FILL-SHALLOW CULVERT
HIGH FILL-SHALLOW CULVERT
CULVERT OUTLETS
FIG.IIIC-.11
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173
CULVERT OUTLET
NEAR STREAM
FIG.IIIC-12
FIG.HIC-13
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174
inhibitor has merit. The lining can be rock rubble, ten feet minimum in
length with a width equal to twice the culvert diameter as shown in Figure
II I C-13.
If the remaining distance to the live stream is relatively flat and
contains vegetation, channel flow velocity will tend to decrease. Remain-
ing sediment will tend to deposit in the vegetation. If the remaining
distance to the stream is steep and bare, additional energy dissipation may
be necessary in order to permit sediment deposit. The rock apron can be
continued further beyond the culvert outlet and a rock dike with height
equal to the culvert diameter and width equal to twice the culvert diameter
installed in the outlet channel as shown in Figure III C-14. In addition,
a further measure might be the placing of slash from the roadway clearing
to act as a sediment barrier.
Figure III C-12 shows a roadway culvert outlet in close proximity to
a live stream. In this case, placing the outlet end of the culvert in a
rock lined channel whose minimum depth is at least twice the culvert dia-
meter as shown in Figure III C-15 may be appropriate. If the culvert
exit velocity is 10 feet per second or greater, a rock dike as shown in
Figure III C-14 to act as an energy dissipator may be necessary in order
to insure sediment deposit before storm waters intersect the stream.
If suitable rock is not available for a channel lining, an alternate
might be the use of clearing slash to construct gravel filled crib wall
channel linings as shown in Figure III C-16. Gabions and sacked riprap
can also be used but they are costly. The use of slash has the secondary
advantage of providing a disposal method for some of the clearing debris.
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PLAN
ROCK DIKE
FIG. Ill C-14
FIG.III C-15
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176
o
(j (
0 0
IZJ7^
r^° r\
o
o D
O
0
PLAN
a
SECTION A A
GRAVEL FILLED CRIB WALL
FSG.IIIC-16
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177
An outlet treatment for a large culvert with high storm water flows
is shown in Figure III C-17, an Energy Dissipating Silo.
Even with the upstream sediment control features of catch basins
and rock lined ditches, there may be a period when excessive sediment
transport can exist. This period will be during construction and for a
time thereafter until new vegetation and soils stabilization measures be-
come effective. Figure III C-18 shows a roadway culvert (or combination
of culvert discharges e.g. collector ditch at toe of slope) discharging
into a sediment pond (basin).
The velocity of flow through the sediment pond should be approximately
one foot per second and preferably less in order for settling to take place,
Settling velocities of sand and silt in still water are shown in Table III
C-4.
The tabulation in this table suggests that the sediment pond should
be large enough to retain the maximum flow input for at least one hour if
the pond is designed for a two foot water depth in order to settle silt
sized sediment. The designer will have to determine the actual pond size,
dependent upon, topography, soils porosity etc. . . After a period of use,
the fines will tend to seal the pond. After the road project is completed
and upstream erosion control measures become effective, the performance
of the pond may be of less importance.
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fpipe
ENERGY DISSAPATING SILO
FIG.HI C- 17
CULVERT OUTLET_TO SEDIMENT POND
FIG.Ill C-18
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179
Table III C-4*
Diameter
of
Particle
mm.
10.0
1.0
0.8
0.6
0.5
0.4
0.3
0.2
0.15
0.10
0.08
0.06
0.05
0.04
0.03
0.02
0.015
0.010
0.008
0.006
0.005
0.004
0.003
0.002
0.0015
0.001
0.0001
0.00001
Order Sett 1 ing
of Velocity
Size
mm. /sec.
Gravel 1,000
100
83
63
Coarse Sand 53
42
32
21
15
8
6
3.8
Fine Sand 2.9
2.1
1.3
0.62
0.35
0.154
0.098
0.065
Silt 0.0385
0.0247
0.0138
0.0062
0.0035
Bacteria 0.00154
Clay Particles 0.0000154
Colloidal Particles 0.000000154
Time required
to settle
one foot
0.3 seconds
3.0 seconds
38.0 seconds
33.0 minutes
55.0 hours
230.0 days
63.0 years
From the tabulation it would appear that the sediment pond should be
large enough to hold the maximum flow input for at least one hour, if the
pond was built with a two foot depth, to settle out all sediment, down to
silt size. The designer will have to determine the actual pond size,
dependent upon, topography, soil porosity etc.
The Water Encyclopedia by David Keith Todd, 1970 (Page 86)
Water Information Center, Port Washington, N. Y.
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5.00 Hydrology
Preceding parts of this section on drainage design have pointed out
the importance of the determination of the design flow to the successful
performance of a drainage system. The designer is interested in deter-
mining whether the activities of logging and road building in the forest,
and the location of a forest, will have a significant effect on the flow
volumes he should provide for, with respect to road drainage and stream
cross ings.
5.01 Logging and RoadbuiI ding
Rothacher reports that an increase in annual stream flow in the
Pacific Northwest may be expected after clear cutting. He also points
to an increase in early Fall seasonal flows after clear cutting because
the soil moisture content is higher in a clear cut area as compared to
the soil moisture content under old-growth forest. Thus less of the Fall
precipitation is needed to recharge storage within the soil. Rothacher
does not believe that clear cutting significantly changes peak flood
flows in areas west of the Cascades. Flood flows normally occur after
the soil is saturaged, "wet mantle" condition, and are directly related
to the amount of precipitation. Rothacher points to some contrary evi-
dence on small drainages containing roads as well as having been clear
cut.
R, Dennis Harr and others believe that it is unlikely that there
will be culvert and bridge damage in Oregon Coast drainages as a result
of clear cutting, provided designs are made on a 25 year storm frequency
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basis. They believe that the effect on roads in small drainages can be
more serious as roads are permanent and will exist during large storms:
"Success or failure of a certain size culvert or bridge might
depend heavily on the amount of roads that eventually will be
built in the watershed whose outlet stream is to be contained
within a culvert or bridge." (150)
Rothacher and Glazebrook believe that the Pacific Northwest storms
of December 1964 and January 1965 were very unusual. They predict that
storms similar to these can be expected in the Cascade and Coast Ranges
at least once in 50 to 100 years. They also observe that localized
storms of these intensities can occur oftener: therefor "our plans and
actions must give them adequate consideration." (151) The authors state
that flood probabilities and forecasting have been evolved mainly for the
requirements of downstream communities and that "much of the information
currently in use has not been verified for mountainous areas."
These articles suggest that a conservative approach to the calcula-
tion of the design flow for a stream crossing be employed especially if
precipitation data for the immediate area is not available. Other con-
siderations involved in determining the appropriate opening size for
bridge or culvert are discussed in the previous sections on Culvferts
(2.00) and Stream Crossings (3.00).
5.02 Subsurface water considerations
Another consideration is the potential for roadway cuts to intercept
ground water flows thereby converting this flow to overland flow into
ditches of a roadway drainage system. Attention was invited to this
phenomena in Section B.3 of Chapter II with .respect to field reconnai-
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ssance. Megahan's studies in the Pine Creek drainage, a tributary of
the Middle Fork of the Payette River, Idaho showed that the quantity of
water whose source was intercepted ground water flow was many times
greater than the quantity whose source was overland flow.
"Interception of subsurface flow is one of the more insidious
effects of road construction because its occurrence often is not
readily apparent. Subsurface flows occur only during large rains
and/or snowmelt when large volumes of water are supplied to the
soil. Such flows begin, reach a peak, and recede within a short
period. Many times, the climatic event that generates subsurface
flows also limits access, making it impossible to see flows as they
occur. This is particularly true during snowmelt and rain-on-snow
events in the mountains. As soon as subsurface flow ceases, most
exposed roadcuts dry out completely and little evidence of flow re-
mains. Another factor leading to the lack of recognition of sub-
surface flow is the fact that flow emergence is not limited to
drainage bottoms, but may occur on straight or even convex side
slopes as welI." (152)
Megahan believes that total volume of watershed runoff increases
when subsurface flow is converted to surface flows. Whether peak flow
rates are increased is dependent on the simultaneous occurrence of the
normal peak flows from the watershed with the flow from intercepted sub-
surface water. Certainly the local effect on ditches and culverts at or
near subsurface discharge or outlet point could be significant.
Other effects are related to questions of stability of cut banks,
potential road surface erosion and stability of fills. Megahan believes
that much of the road erosion reported in the Idaho Batholith "is very
likely a direct result of subsurface flow interception."
5.03 Forest Location
There is little question that total precipitation amounts increase
with elevation, except in areas of pronounced rain shadow effects, but
considerable controversy appears to exist as to the effects of elevation
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183
upon rainfall intensity. Dorroh's (153) evaluation of rainfall data from
the southwestern United States indicated that, although both total pre-
cipitation and the frequency of thunderstorm occurrence tend to increase
with elevation, the heaviest individual rains occur in the valleys. Croft
and Marston (154), however, stated that higher rainfall intensities could
be expected on the windward slopes of the Wasatch Mountains in Utah than
in the adjacent valleys. In the very different climate of coastal
British Columbia, precipitation at higher elevations is apparently charac-
terized not so much by higher intensities as by longer duration at a given
rate. (155)
Schermerhorn (156) studied the effects of various parameters,
most notably elevation, upon annual rainfall amounts in western Oregon and
Washington, where extremes of 20 inches to 150 inches of average annual
precipitation occur. His work revealed very little relation between
station elevation and annual rainfall, but that most of the variation in
average annual precipitation for the 280 stations studied could be accounted
for by relatively simple indexes linked to broad scale topographic and
latitude factors. Three main index parameters were defined: index eleva-
tion, barrier elevation,'and index latitude. The index elevation was
based upon average highest elevations in the northeast quadrant within 10
miles of the station, while the barrier elevation was based on the average
highest elevations in the southwest quadrant between an arc 4 miles from
the station and the coast. The index latitude was defined as the actual
latitude of a point on the 124° meridian due southwest of the station.
Use of a graphical relationship involving these three main parameters to
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calculate annual precipitation for the 280 stations yielded an unadjusted
standard error of estimate of 7.2 inches for an average precipitation of
63 inches. Schermerhorn did not make any attempt to use his method to
develop elevation-rainfall intensity relationships.
Cooper (157) reported on an extensive study of elevation-precipita-
tion relationships within a 93 square mile area in southwestern Idaho
where continuous rainfall recorders had been installed at an average den-
sity of one per square mile and operated for four years. The area had an
elevation range of 3,500 feet and climatic variations resulting mostly
from elevation and topographic features rather than from regional air
mass differences. The rainfall data indicated average annual precipita-
tions increased about 4 inches for each 1,000 feet increase in elevation
ranging from 8 inches in the lower part of the valley to 28 inches at
the higher elevation. Numerous methods of data analyses to attempt to
establish other rainfall-elevation relationships indicated that there was
no relationship between elevation and peak rainfall intensity and elevation
and several other intensity-related parameters. The only relationship that
could be established was that the logarithm of the proportion of rainfall
exceeding a given intensity plotted as a straight line against intensity.
There was no difference in this relationship when the data were separated
by elevation classes. Cooper noted that this relationship is rather uni-
versal and holds true for many other parts of the world as well.
Cooper concluded that the apparent lack of relationship between
rainfall intensity and elevation suggests that data from accessible
valley stations can be used to estimate the relative occurrence of high
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intensity rains throughout an area of appreciable range in elevation.
At least under the conditions encountered in southwestern Idaho, about
the same proportion of the seasonal rainfall exceeds a given intensity at
high elevations as at low. Because there tends to be more total rain at
high elevations, there is likewise more intense rain at mountain stations
than in the valleys, but the relative proportions remain nearly constant.
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D. CONSTRUCTION SPECIFICATIONS
An essential part of the design for any road project are the com-
panion specifications. Preparation of these specifications must not be
separated or removed from the supervision of the forest or civil engineer
who is preparing the road design.
A serious mistake is made in those cases where separate personnel
are authorized to prepare the specifications for design plans prepared
by others. This inadequacy is frequently represented by notation on the
plans such as "see specifications for detailed requirements", "see speci-
fications for procedures", "see specifications for further requirements".
Such notations frequently mean the designer has not made up his mind as
to what the requirements or procedures should be. Definable accomplish-
ment cannot be attained without positive and non-contradictabIe plans and
specifications. The foregoing is a very brief analysis of the relation
between plans and specifications and is placed herein to emphasize the
need of the utmost correlation between the two companion documents.
1.00 Standard Specifications
Many design organizations have prepared volumes or multicopies of
specifications particularly oriented to their endeavor. The volumes have
such titles as Standard Specifications for Road and Bridge Construction
and set forth general, legal, and specific engineering requirements under
which the proposed construction is undertaken as a mutual agreement between
the owner and the contractor. These standards are revised from time to
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time and vary between regions because of different regional circumstances.
The U. S. Department of Agriculture has prepared such a volume entitled
"Forest Service Standard Specifications for Construction of Roads and
Bridges."
A further group of specifications published at regional, national
and international levels is devoted primarily to materials and methods of
testing materials. Prominent and valuable organizations in this group are
The American Society of Testing Materials, The American Standards Associa-
tion, The American Association of State Highway Officials. Frequently
specifications from one or more of this group are included by reference,
or quotation in the specifications published or adopted by the owner or
agency.
2.00 Special Provisions
To define and describe the individual items of work, local circum-
stances, special construction items (those not included in the Standard
Specifications), times of accomplishment, legal requirements, and payment
conditions, a further document is written for each project entitled
Special Provisions and is made a part of the contract documents. The
Standard Specifications and the Special Provisions combine to form the
Construction Specifications. Items specifically related to sediment con-
trol wi I I usually be a part of the Special Provis ions.
The Special Provisions should include a separate paragraph stipula-
ting that the successful bidder shall prepare and submit within 30 days
a detailed schedule of on site construction starts, material purchases
and phase accomplishments. The schedule can be of assistance in evalua-
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ting whether the contractor recognizes construction elements and se-
quences relating to sediment control as envisioned by the designers. It
can also point out potential problem circumstances during construction
due to the forecasted timing of certain operations relative to seasons.
A common practice in special provision writing has been to lump to-
gether certain "nuisance" items among them requirements for water quality
control within the work site. Elaborate descriptions are often written
about the Contractor's obligations, all of which are to be enforced at
the sole discretion of the Engineer and for which compensation is to be
considered as "incidental to the other items of work involved in the
project". Such procedures are of little practical help to a Resident
Engineer. While owner's representative and Contractor feud over whether
the particular issue is or is not one of the "incidental" items, the
problem may magnify and its potential for damage to completed work and
resources may increase.
The Special Provisions should provide that the Contractor'wiI I be
compensated for all labor, materials, tools and equipment he is to fur-
nish including items involved in temporary or permanent sediment control
features. They should advise the Contractor as to the manner in which he
will be asked to perform various tasks, whether the demand will be inter-
mittent, and whether "extra" or "standby" crews or materials are involved.
The importance of dealing with changed circumstances swiftly is discussed
elsewhere in this report. The Special Provisions should support this goal
by providing means for swift, equitable adjustments in contract compensation,
A possible technique is to establish compensation for certain
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emergency work on a force account basis with an estimated amount included
in the contract documents. This approach has merit provided the estimated
amount is a realistic assessment of the circumstances that may be encoun-
tered.
In the 'Timber Purchaser Road Construction" report by USFS, Region 6,
it was found that scheduling techniques are not being used by timber sale
road builders and the Forest Service.
"Historically timber sale road construction activities have been
triggered by the timber market demand. This factor is a basic
problem in the scheduling difficulty and affects the timing of
construction starts and construction progress. There is a general
lack of documented, or even oral disclosure of construction sched-
ules. Some inspectors wasted valuable time by constantly visiting
project sites just to find out when construction was start ing.(158)
Obviously, the potential for sediment creation during construction
is related to the season in which certain construction elements are being
accomplished. Contract scheduling should provide for construction activi-
ties to be accomplished in their appropriate season. If the project is to
extend over more than one season, the procedures and requirements for shut-
down at the close of each season should be specified. The basis for de-
termining when conditions warrant seasonal shutdown should also be included
in the special provisions.
Larse summarizes the construction activity thus:
"Although there are many commonly practiced techniques to minimize
erosion during the construction process, the most meaningful is
related more to how well the work is planned, scheduled and control-
led by the road builder and those responsible for determining that
the work satisfies design requirements and land management resource
objectives". (159)
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3.00 Cone I us ions
The foregoing discussion was written in terms of the owner-contractor
relationship. The comments are believed applicable in intent to the cir-
cumstances of road construction by a timber purchaser or road construction
by a land owner's own forces.
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IV. CONSTRUCTION TECHNIQUES
Section II of this report stated that Route Planning and Reconnai-
ssance are regarded by many as the most important phase of logging haul
road development. In Section III the planning and reconnaissance data
are translated by design into plans and specifications to meet all of
the road objectives and to guide the construction phase. Larse observed
as follows:
"Construction of the designed facility is a challenge to the road
builder to complete the work with a minimum of disturbance and
without damage to or contamination of the adjacent landscape, water
quality, and other resource values. Some of the most severe soil
erosion can be traced to poor construction practices and job manage-
ment, insufficient attention to drainage during construction and
operations during adverse weather conditions". (159)
The Engineer in charge (Resident Engineer) or the inspector is the
last link in the long chain of a total effort to produce a logging haul
road in a manner that will minimize sediment. Field changes are to be
expected. The Resident Engineer acting alone, or with the design engineer,
must decide the corrective measures to be taken. Other than field changes
the inspector must require adherence to the plans and specifications.
Man power may be a limiting factor to supply sufficient inspectors
for the work load in a given region. However as the work load peaks,
qualified individuals having other duties could be assigned to inspection
activit ies.
The Resident Engineer and the inspectors must be relentless in
their effort to implement fully the plans and specifications as envision-
ed and designed. The construction specifications should provide a means
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of payment for many of the processes that the contractor may need to
accomplish and which are of benefit in arresting sedimentation including
those attendant to changed conditions. These items arise from conditions
unforseen by the design engineer such as seasonal variations and founda-
tion and soils inconsistencies. The discussion that follows includes
construction features which require individual analysis and the applica-
tion of the appropriate construction technique in order that erosion or
sediment transport may be minimized.
A. CLEARING AND GRUBBING
The Forest Service Standard Specifications for Construction of Roads
and Bridges plus amendments clearly define clearing and grubbing activi-
ties and methods. Each Region supplements these specifications with
methods peculiar to its area.
Clearing and grubbing then is the first activity in constructing a
forest road that disturbs the forest floor and surrounding soils. Flash
storms under these conditions can produce instant erosion and sediment
problems. This work is a necessary part of the road work and a pre-
caution that should be taken to prevent a part of the potential sediment
flow is to not disturb more ground than is absolutely necessary until
a satisfactory drainage system is provided. The brush accruing from the
clearing and grubbing operation might well be placed at the tow of em-
bankments or below culverts to act as a filter and retardant to sediment
flow.
Attempt to begin excavation prior to the completion of clearing
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have resulted in slash and organic material being mixed with earth.
The mixed material acts as a contributor to the sedimentation problem
rather than as a filter. It also may have too high an organic content
to be used as fill material thus requiring wasting.
Merchantable timber from the clearing operation might be temporarily
stacked at the toe of a fill until the fill is stabilized. Small logs
may have use as walls for channel linings as was suggested in Part C-4 of
Chapter III and shown on Figure III C-15.
Clearing and Grubbing should be scheduled to proceed just in advance
of earthwork. Sections which are not going to be graded in the current
season should not be cleared and grubbed.
B. EARTHWORK
During excavation and embankment activities the total roadway prism
is vulnerable and is subject to erosion and sediment flow from rain
storms of relatively slight intensity. Larse states:
"When soil moisture conditions are excessive, earthwork operations
should be promptly suspended and measures taken to weatherproof the
partially completed work. . . clearing debris underlying, support-
ing or mixed with embankment material is a common cause of road
failure and mass soil movement. The necessary slope bonding, shear
resistance, and embankment density for maximum stability cannot be
achieved unless organic debris is disposed of before embankment
construction is started". (160)
Road builders on Washington's Olympic Peninsula have found that a
shovel can be worked in much wetter weather than can a bulldozer. The
shovel does not tend to disturb the subgrade in marginal weather to the
degree that a bulldozer does. Shovels on mats are a common soft ground
technique on the Olympic Peninsula and across Muskeg in Southeastern
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Alaska.
Embankment compaction should be accomplished by one or more of the
following types of equipment.
I. Tamping roIlers
2. Smooth wheel power rollers
3. Pneumatic-tired rollers
4. Grid roller
5. Vibratory rollers
6. Vibratory compactor
7- BuiIdozer.
In the past, the bulldozer has frequently been the sole compactor
used on forest roads. It has proven to be very ineffective when the
dozer blade is so wide as to prevent the tracks from covering the entire
roadbed width. The dozer may be used provided it can compact from out to
out of the total roadway. A more satisfactory compaction job will be
obtained by having the dozer do its primary job of moving earth and using
equipment specifically designed for compaction to accomplish the com-
paction.
Embankments should'be placed and compacted to the required density
to avoid instability, control drainage flow and deter massive movement.
Embankment placement in layers with attendant compaction is necessary.
The literature on forest road failures contains many references to
failures due to improperly constructed embankments.
Waste sites should be as carefully prepared as embankment portions
of the roadway. Waste material could be used as a portion of the road-
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way embankment (as shown in Figure IV B-l) instead of being end hauled
an excessive distance.
Borrow pits should be closed by dikes or dams to prevent sedimentary
flows into adjacent streams. The dikes or dams should be removed when
the borrow pit water ceases to carry sediment. Borrowing from running
streams should be prohibited.
ALTERNATE WASTE SITE
FJG,IV_B-1
The width and number of benches will be determined by the height of the
fill and the quantity and quality of waste material involved.
Ballast may be placed only on shaped and drained subgrades in a
manner that will not deform, rut or rupture the subgrade.
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C. DRAINAGE
No other item is as important to the permanence and usefulness of
the forest road and control of stream sedimentation as the drainage
system.
"In many places, careless and improper construction of a high
mountain logging road can nullify all the effort expended in well
considered design and location .... Poor construction and in-
adequate drainage have triggered land slumps in watershed after
watershed and have resulted in the most serious form of accelerated
erosion that occurs during timber harvesting .... Therefore dur-
ing all phases of road construction, protect water quality by using
every possible and applicable soil and water conservation measure."
(161)
1.00 Drainage during Construction
Section III C-1.01, "Drainage Design", indicated that temporary
ditches and other drainage facilities may be necessary during the con-
struction phase. To achieve the goals of permanence of slopes and road
beds and to minimize sedimentation, the following suggestions have been
of consequentiaI advantage.
"Protect all fill areas with surface drainage diversion systems.
Place culverts so as to cause the minimum possible channel disturb-
ance and keep fill materials away from culvert inlets and outlets
.... Allow road machines to work in stream beds only for laying
culverts or constructing bridge foundations. Divert stream flow
from the construction site whenever possible in order to prevent
or minimize turbidity. Clear drainage ways of all woody debris
generated during road construction. Windrow the clearing debris
.... outside the roadway prism (to use as a drainage filtering
system)." (162)
The previous paragraph mentioned several antidotes to control con-
struction drainage circumstances. Also the use of visqueen or plastic
sheets, temporary flumes, installation of a second culvert (preferably
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by jacking), culvert extensions and settling basins are other techniques.
Roadway surface dips should be installed as soon as possible so that they
can be utilized to control storm water while construction continues.
The most important technique, however, is that of observing, watching
and promptly correcting an installation that does not accomplish its
intended function.
During the initial construction period, the Resident Engineer must
have all design data, rainfall and stream flow records easily available
to him. If any drainage installation does not supply the desired results
as to capacity, turbidity, or indicates instability in the early stages
of construction, he must have the knowledge and authority to direct the
changes that will give the desired results of stability, capacity and
turbidity standards. Applying for a re-design study, awaiting authori-
zation from higher echelons and/or additional funds, will serve only to
magnify the adversity.
2.00 Drainage Construction
A prevalent concept of drainage construction must be abandoned and
a new one evolved. The -prevaIent concept that the contractor is permitted
to install various drainage features when he chooses based on available
equipment, subcontractors, accomplishment of like items at one time,
such as placing riprap or headwalls, must be pushed aside for the concept
of doing in order the things that are needed to stabilize slopes and re-
duce to a minimum the transportation of sediment. Without doubt applica-
tion of the new concept will cost more in initial expenditures for the
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drainage system than would accrue under the now prevalent procedure.
An economical comparison between the two would not be realistic unless
values can be assigned to the potential cost of reconstruction of water
damaged road features and the cost of excessive sediment transport.
The grading of a roadbed should not be extended beyond the construc-
tion of the companion and attendant drainage features. No slides should
occur on hillsides properly graded and drained, or on slopes guarded
against erosion. It is recognized that sudden rains can fall during the
construction season. If the ditches require rock linings, matting or
other protective measures, the actual ditch grading and shaping should
not be too far advanced ahead of the protective treatment. Always grade,
shape and finish ditches from the downstream end to the upstream end.
Culverts should be installed as the road work progresses. The cul-
vert and its related drainage features, as required, should be installed
in the following order:
I. Place debris and slash to be used as a filter system.
2. Construct sediment ponds.
3. Energy dissipating devices.
4. Rubble rock or matte lined channels.
5. The culvert laid from the downstream end to the upstream end.
6. Ditch inlet structure with or without catch basin.
It is important to note from the above tabulation that alI drainage
work should start at the downstream end and progress to the upstream end.
This installation procedure will enable surface and intercepted sub-
surface waters to flow in a finished channel downstream and away from the
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work area. The system must be kept operative at all times.
The reader is reminded of the discussion in Chapter III, Section
C-2.02 relative to culvert installation, that the designer assumes reason-
able care in culvert installation. Critical features are bedding, back-
filling and pipe joints. Hartsog and Gonsior's China Glenn analysis
indicates a lack of skill, supervision and appropriate equipment contri-
buting to difficulties with culvert installations. (163)
All drainage construction activities should be closely supervised to
insure that the various work items are meshing together at the scheduled
time. Correct those items lagging behind schedule immediately.
D. CONSTRUCTION EQUIPMENT
The U. S. Forest Service Region 6 Road Audit states:
'The use of improper and oversized equipment by timber purchasers was
identified as a problem area .... Special equipment is needed to
properly accomplish some construction tasks and to fully protect
forest values during the construction operation .... almost all
road construction was accomplished with a large crawler (D-8 or D-9)
with dozer. In many cases this was the only equipment .... Much
of the road construction equipment was developed for wide highway
and freeway construction. ... Evidence was found that timber sale
road inspectors adjusted their enforcement of specifications to meet
the capabilities of the contractors available equipment." (164)
Recommendations from this report include: (I) Constraints on the
maximum size of equipment that can be used for a particular road project.
(2) Direction and support of inspectors for enforcing specifications re-
lating to equipment size etc. . . (3) Revise cost estimating guides to
include costs of doing work with various sizes or kinds of equipment.
(4) Make equipment manufacturers who are continually developing new
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machinery aware of management objectives, such as minimum environ-
mental impact roads, minimizing soil erosion, sediment and aesthetic
impacts.
The use of the shovel to accomplish roadway excavation on the
Olympic Peninsula and in southeastern Alaska was discussed in Section B
of this chapter. The shovel is also commonly used in other areas with
steep terrain for the circumstance of excavating full bench sections
on narrow roads with waste end hauled. This method results in a much
higher unit earthwork cost than was previously experienced with a partial
bench and/or sidecast operation with bulldozer excavation. It also re-
sults in less road miles being constructed in the short season available
in many high altitude areas. Equipment specifically adapted or designed
for the circumstance of full bench excavation with end haul on narrow
roads is needed.
Hartsog and Gonsior believe that specialized equipment is needed for
clearing on steep slopes. On China Glenn, tractors often worked themselves
into places low on the slope where they had to be winched upslope by
another machine. They believe tractors with a low center of gravity and
equipped with a brush bl'ade are the best of the present equipment. The
purpose of specialized equipment would be to eliminate or reduce the
pioneer road required for present equipment because of the potential con-
tamination attendant to a procedure of excavating before clearing is com-
pleted. (165)
The necessity for appropriate equipment to install drainage facilities
has been previously mentioned.
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V. MAINTENANCE
Concerning maintenance, Robert W. Larse has stated:
"Planned regular maintenance is necessary to preserve the road in
its (as built) condition, but unfortunately is too often neglected
or improperly performed resulting in deterioration from the erosive
forces of the climatic elements as well as use ... It is neither
practical or economical to build and use a road that requires no
maintenance ... The additional expense of constructing a road,
with proper attention to its stability and proper drainage can gen-
erally be amortized within a few years by an offsetting lesser cost
of upkeep where soil erosion and sedimentation are of concern . .
. . ." (166)
To facilitate and expedite maintenance operations and procedures, a
complete set of "as built" plans with a record of all maintenance opera-
tions and observations should be maintained and be quickly available to
the maintenance engineer. This record system will help to equip and
supply new personnel with all the previous experience and observations of
their predecessors.
The "as built" records should contain the following information:
I. Complete job index.
2. Complete history of the project from start to finish of
construct ion.
3. Photographic records.
4. Exact location of culverts and other drainage features.
5. Unstable conditions in relation to cut and fill slopes and
roadway surface.
6. Wet areas that may have caused over excavation and replacement
with selected backfi11.
7. All major field changes that were made in the original plans.
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8. Catalogue and parts listing of all equipment, such as pumps,
valves, gauges, etc.
The greatest asset available for any maintenance program is the
experience history and knowledge gained by those who have in fact accom-
plished the maintenance operation. Usually this knowledge is not re-
corded, but every effort should be made by management to keep competent
experienced knowledgeable maintenance personnel at their tasks and/or
available for consultation and advice.
The maintenance discussion that follows is divided into three
parts: (|) drainage system, (2) road surface, and (3) slide dilemmas.
A. DRAINAGE SYSTEM
Drainage maintenance is not a spectacular task. The greatest and
best accomplishments occur in wet ditches, plugged culverts, or slides
that impair roadways. For forest roads, particularly in mountainous
areas, maintenance cannot be programmed on the yearly calendar but must
be accomplished when the individual site or circumstances dictate.
Little can be accomplished in snow or in frozen ground with the possible
exception of jacking in culverts or solid rock excavation. Snow melts
do not usually cause the maximum flows or carry fragmented rock, boul-
ders or fallen timber. The time to accomplish the major drainage main-
tenance is usually concurrent with the major forest operations of cut-
ting, hauling, planting or thinning.
In spite of this peaking of labor demand, the maintenance program
should never be postponed. Rules or procedures for drainage maintenance
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can be set up only as guide lines as there is a wide variance between
localities, construction accomplishments, workable seasons and climatic
factors. The following are offered as guide lines only, as each area
must modify or amend their procedures to suit their circumstances.
1.00 Culverts and Ditches
Ditches, culverts and catch basins must be kept free of debris and
obstructions. On new construction, catch basins may require frequent
cleaning, perhaps after each major storm. Grass in ditches should not
be removed during cleaning operations. Shoulder and bank undercutting
must be avoided. Damaged culverts should be repaired or replaced.
Culverts and inlet structures should be cleaned by flushing down-
stream only when adequate filtering to protect watercourses are avail-
able. Debris from cleaning operations should be hauled to a stable
waste site far removed from any watercourse.
"Regular inspections during or after storms will ensure good drain-
age because problems are detected before they become serious. In-
spections for detection of weaknesses in drainage systems are
especially important on new roads. As a general rule, roads should
be examined annually in the Spring after the first rains or at the
start of snow melt". (167)
Ditches and culverts are particularly vulnerable to debris blockage
when a logging operation is occurring on or adjacent to the road. Block-
age with limbs, needles and wood chunks can occur rapidly. Maintenance
personnel should be alert to the ongoing logging operations and aware of
their potential significance to the maintenance program.
Live streams with culverts should be completely free of transport-
able debris, for at least 100 feet upstream. If the initial construction
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did not call for debris deflectors or trash racks and subsequent exper-
ience shows they are required, install them as part of the maintenance
program. The downstream end should also remain free flowing. Debris
should be removed from streams or channels by grapples or tongs rather
than by equipment in the stream bed.
2.00 Cut and Embankment Slopes
Cut and embankment slopes are so individualistic that only the most
elementary precautions are set forth below. Each slope must receive a
separate study.
Erosion clefts in cuts may be filled with rock or coarse gravel to
create a trickling water movement through the rock fill material. Turf
should be replaced in bare earth areas.
Erosion clefts in embankments should be filled, turfed and the
water from the roadway directed to a culvert or flume. In the event of
indicated large movement, the slope may be dewatered by horizontal
drains, wells, or well points until the area becomes stable. Only per-
vious materials, preferably rock, should be placed as embankment on
water giving slopes.
Berms at the top of embankments intended to prohibit water from
flowing onto the slope should be monitored for breaks or ruptures and
repaired as required.
B. ROAD SURFACE
Road surfaces must be kept well crowned or sloped so they will
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drain. Surface blading should preferably be accomplished when the
moisture content of the material results in neither dust nor mud from
the blading operation. Particular attention should be accorded the road
crown or slope just in advance of the wet season.
Roads subject to traffic during the wet season will require con-
tinual monitoring for surface condition including ability to drain,
presence of rutting and loss of ballast. Provisions should be made for
ballast replacement where necessary as a condition to continuing opera-
tions on the road. Roads sufficiently ballasted for dry weather opera-
tions may not be satisfactory for all seasons.
Surface cross drains should be cleaned as required after the log-
ging season to restore their functional ability. If the cross drains do
not exist in a road intended for seasonal closure, they should be cut in
in advance of the rain and/or snow season.
The snow removal operation can damage the road surface by removing
ballast and/or destroying the roadway crown. Factors that contribute to
the potential for damage are improper snow removal equipment, improper
equipment operation and initiating snow removal at the improper time.
Road condition has to be monitored relative to the freeze thaw
cycle. The potential for surface disruption is greater when frozen sub-
grade or surfacing begins to thaw.
The foregoing express important provisions or guide lines for road
maintenance. The most important guide line consists of management
educating the maintenance personnel to the importance of minimizing
sediment transport to ditches. No one can control the amount or time
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of rainfall or the amount and rate of snowmelt. Therefore the only
control of sediment transport attendant to maintenance operations is by
individuals.
There will be circumstances both planned and unplanned wherein
sediment from roadway surfaces is transported to side ditches. When
such circumstances occur, maintenance forces must examine and properly
condition the next line of defense, be it catch basin, culvert, settling
pond or whatever to force separation of water and sediment with com-
panion disposition of the collected sediment. All procedures are point-
less unless this overall concept is kept in mind and the needed action
taken at the needed time. Here again, the local man, intimately familiar
with the circumstances, is the one who can make the decision as to what
and when to embark upon an undertaking.
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C. SLIDE DILEMMA
1.00 Introduction
One of the most difficult, time consuming and often reoccurring
maintenance problems along logging roads is the removal, recovery,
disposal and correction procedures for slides occurring both up and
down slope from the logging road. The slides may involve only minor
maintenance on a yearly basis along the road or may involve rebuilding
or relocation of the road. Through the proper engineering design of
the road the slides can be prevented or at least limited. However, there
are areas where active slide areas cannot be avoided and maintenance
must be expected. In addition there are areas which were stable
at the time of construction and shortly thereafter but due to some natural
occurrence have since become unstable. These type of areas require
extensive evaluation both as to remedial design if possible or relocation
if necessary after an evaluation of continual maintenance.
The slide dilemna raises many problems in conjunction with mainten-
ance and increased erosion potential along the road alignment. Several
of these problems are discussed in the following paragraphs.
2.00 Recovering Slide Debris
Slide debris which is deposited on roadways may cause significant
increased sediment loads in established roadway drainage systems and
may in some cases cause erosion channels to develop outside of established
drainages. The removal of this material on the road may be accomplished
by heavy construction equipment. However, sidecasting of the material
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should not be allowed. Slide debris which is located down slope from
the logging road poses a different and more difficult problem of removal.
The equipment necessary for removal of this material may be restricted
to working from existing roadway only. Another problem involved in
removing the material is the possibility of damaging surface vegetation
and other erosion control devices on the down slope side of the road
while trying to remove this debris. Therefore, an evaluation of the
potential for erosion from the slide debris versus the potential for
erosion caused by the removal of the slide debris should be made and
carefully examined before a plan of action is carried out. Specific rules
or guidelines for this removal should not be set and each case should
be evaluated on an individual basis dependent upon the conditions
encountered at each site.
3.00 Wasting Slide Debris
Once the slide debris is removed from its place of deposition the
problem arises as what to do with the material. Slide debris is often
composed of a mixture of soil, rock and organic debris, and is usually
very wet. Material in this condition normally cannot be placed and
compacted as fill within a roadway embankment. However, the material
may be placed in end-haul disposal areas. Proper placement and compaction
of this material must be achieved so that erosion may be limited. Again
it should be emphasized that slide debris material should not be sidecast
from the roadway or placed in a noncompacted fill which is susceptible
to erosion.
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4.00 Relocation Versus Correction
•
Proper evaluation of the erosion potential and economics of relocation
versus correction is essential and many factors should be considered
before a decision is made. Among these factors are, why did the slide
occur, how extensive is the slide, and will the slide occur again. These
questions will be discussed in more detail in the following section.
Other factors which should be considered before a decision is made
involve . determining the amount of erosion potential from construction
of the newly relocated alignment which may involve construction of a
considerable length of new road. This new road may have a higher total
erosion potential than the erosion from the slide debris. Correction
of the slide area may involve installation of retaining structures,
reshaping slopes and/or replacing fill in the roadway alignment. These
corrections are oftentimes more desirable than constructing new roads
which during their initial stages after construction have a higher erosion
potential than the existing roadway alignment. However, there will be
times when correction of the roadway alignment is impossible and the slide
will reoccur. It is at these locations that the detailed evaluation of
both the new alignment and the existing alignment with reoccurring slides
must be done.
5.00 Failure Mechanism Investigation
Before corrections can be made within a slide area the extent of
the slide, the reason for the slide and the potential for reoccurrence
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must be determined.
The first step in defining the failure mechanism should be a
detailed inspection by an experienced engineering geologist. From this
inspection an approximate failure plan can be developed and possible
causes evaluated. In many cases this inspection is all that is required
for a proper evaluation of the failure. In more extensive and complex
slide areas, this initial inspection should be supplemented with a
detailed subsurface investigation which would include drilling deep holes
from which undisturbed samples may be obtained for strength testing
and the installation of piezometers within and above the slide area.
In some cases the installation of inclinometers may be justified to
determine if movement is continuing and to what extent and range it may
be occurring. The amount and extent of this investigation is dependent
upon the conditions of that particular site. In any event this work
should be accomplished under the auspices of a specialist in either
soil or rock mechanics.
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VI WATER QUALITY MONITORING
Effective monitoring of water quality can provide a means to assess
the effectiveness of various erosion control measures and can also
provide a stimulus to designers and contractors for more conscientious
efforts to prevent water quality degradation.
Portions of the following discussion of water quality monitoring
are based on the publication "Design of Water Quality Monitoring Programs"
as prepared by the U.S. Forest Service—Pacific Northwest Region (168).
A. SOURCES OF WATER QUALITY IMPAIRMENT
Several water quality degrading effects originate from the construc-
tion and subsequent operation and maintenance of logging roads. Both
high short-term impacts during and immediately following construction
and generally decreasing long-term impacts during the life of the roads
occur. The major pollutants are eroded mineral sediments; organic
matter from the forest floor and in the soil originating from plant and
animal sources; tree debris (another source of organic matter) in the
form of leaves, twigs, and slash; pesticides if used in the maintenance
program; and nutrient elements (principally nitrogen and phosphorus)
either naturally occurring in soils and in plant and animal matter or
from fertilizers. Thermal pollution can also occur as a result of removal
of shade cover and consequent exposure of streamflow to solar heating. Of
these pollutants, sediment including both organic and inorganic consti-
tuents transported to surface waters by overland runoff or by landslides
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near streams is by far the most serious single cause of water quality
degradation (1.69). Additionally, sediment acts as a carrier of such
pollutants as pesticides and nutrients.
B. PARAMETERS TO BE MONITORED
Monitoring should normally be limited to those parameters most likely
to be significantly affected by road construction activities. These
parameters include water temperature, turbidity, dissolved oxygen, and
in some instances specific conductance and stream discharge. With the
proper equipment, all of these parameters can easily be monitored in
the field. Each of these key parameters is discussed below:
1.00 Water Temperature
The purpose of water temperature monitoring is to determine the
effect of shade removal or ponding effects on increasing water tempera-
ture. If shade is not removed as a result of stream crossings or other
construction in the immediate vicinity of streams or any ponding effects
introduced, the monitoring of water temperature loses its primary
importance but nevertheless should be recorded because of its relation-
ship to other tests as discussed subsequently.
2.00 Turbidity
Turbidity is a measure of an optical property of water normally
expressed in Jackson Turbidity or Candle Units (JTU or JCU). Turbidity
is related to the suspended sediment content of the water although the
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correlation can be quite variable from stream to stream and even for
the same stream at different locations and times of the year. The
purpose of measuring turbidity is to determine what effects soil distur-
bance, either leading to soil erosion by surface runoff, landslides, or
construction work in the streambed, have on the sediment content of stream-
flow.
3.00 Dissolved Oxygen
The primary purpose of monitoring dissolved oxygen (D.O.) is to
determine the effect of addition of woody debris to streamflow. Physi-
cally, the concentration of D.O. at any time is a function of water
temperature, which places a reducing upper limit on the saturation
concentration as temperatures increase, and channel characteristics
such as slope, roughness, and cross-sectional area which control the
rate of oxygen exchange between air and water. Biologically, the
concentrations of D.O. is affected by aquatic animal microorganisms
which utilize the organic material in the stream as an energy source
while extracting oxygen from the water in the process; and aquatic
plant microorganisms which supply oxygen to the water during daylight
hours as a product of photosynthesis. Reductions in D.O. can be
caused by increases in stream temperature due to canopy removal or
ponding; reductions in turbulence generally as a result of ponding above
road structures, landslides, or debris dams; and introduction of
organic matter to the water resulting in oxygen uptake during biochemical
degradation. Increases in water temperature have a twofold effect: the
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214
the D.O. saturation level is reduced and biochemical degradation activity
is stimulated. The most critical period for D.O. levels is generally
late summer when temperatures are highest and streamflow lowest.
4.00 Specific Conductance
Specific conductance is a measure of the water's capacity to
convey an electric current and is related to the total concentration
of ionized mineral substances in the water. These ionized substances
may enter the stream from leaching of newly exposed soils by overland
runoff. While the individual mineral ions are not identified by specific
conductance measurements, gross changes in the overall chemical make-up
can be detected. If significant changes are detected, the samples can
be subjected to analysis for individual parameters to determine what
parameters are causing the increase. Significant increases in specific
conductance as a result of logging road construction are not expected
in most situations.
5.00 Streamflow
Logging roads planned and constructed with reasonable caution
would not be expected to significantly affect streamflow. However,
in some instances, stream discharge measurements should be made for
the purpose of assisting in interpretation of the data collected for
other parameters. Precise measurements are often not required. Some-
times a reasonable estimate of discharge can be made from culverts
or other such structures. Major changes in discharge between the
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215
upstream and downstream ends of the monitored area may be an indicator
of extraneous influences possibly affecting the validity of the
monitoring results or may indicate environmental damage such as debris
dams or landslides resulting from the road construction activity.
C. SAMPLING LOCATION
Normally sampling stations should be located upstream and down-
stream from the area under study. This direct comparison generally
provides useful data within a short time frame and with a minimum of
effort. When using this method, selection of sampling stations where
there are intervening influences unrelated to the activity in question
(i.e., tributary streams, natural or man-induced sources of water quality
degradation, etc.) should be avoided if possible.
In some cases it may be necessary to gain background water quality
data before commencement of logging road construction. Under these
conditions, a relatively long prior monitoring period over a period
of at least one year may be required to attain adequate statistical
reliability of the sampling data.
D. SAMPLING FREQUENCY AND DURATION
Sampling frequency and duration are dependent upon many factors.
Among these are the needs of the particular situation, availability
of manpower, accessibility, and whether hand-operated or automatic
recording and sampling equipment is available. Advances in the develop-
ment of small, portable automatic equipment in recent years show particular
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216
promise for use in relatively remote areas where most new logging roads
are likely to be constructed. Although automatic equipment is considerably
more expensive than conventional manually-operated equipment, use of
such equipment would be particularly desirable for the sampling of some
parameters, particularly turbidity, in sensitive areas. Adverse effects
on water quality would be much more likely to be detected than if samples
are collected only periodically by hand. If hand samples are collected,
sampling frequency must be carefully established so as to be representative
of all ranges of water quality that might be experienced. This means
scheduling of sample collection with climatic and streamflow conditions
as well as the intensity of construction activities.
1.00 Turbidity
Automatic sampling or recording equipment would be particularly
useful in the monitoring of turbidity because major increases in turbidity
are most likely to occur during relatively high intensity, short
duration storms when accessibility and timing practically preclude
collection of hand samples. If turbidity is monitored by hand sampling,
samples should be collected no more than two weeks apart during construction
activities and at a decreasing rate after termination of construction
activities. It is particularly important that turbidity measurements
be made during work within or in close proximity to the streambed and
during or shortly following periods of moderate or greater intensity
rainfall when the brunt of soil erosion is expected to occur. The
timing of turbidity sampling is of utmost importance if serious
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217
Impairments of water quality are to be detected. Turbidity measurements
should generally be continued for a year or more following construction
unless very little potential exists for road-related sediments to reach
streams.
2.00 Water Temperature
Water temperature should be sampled primarily during the critical
summer months. Intervals between observations should generally not
exceed 2 weeks. Maximum-minimum thermometers, which are relatively
inexpensive, can be left in the stream during the intervals between
observations to record the upper temperature extremes.
3.00 Dissolved Oxygen
Dissolved Oxygen (D.O.) should be sampled primarily during the
summer months, generally at the same frequency and time water temperature
measurements are made. D.O. measurements are particularly important
when air temperatures are highest and streamflow lowest or following
suspected entry of organic matter into the stream. Finely-divided
organic debris, particularly needles and leaves which have simple
sugars, rapidly exert a high oxygen demand upon entry into the stream
system :(I70).
4.00 Specific Conductance
Specific conductance measurements should be made in connection
with turbidity sampling. Significant changes in specific conductance
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218
are most likely following entry of overland runoff into the stream
system. Normally increases in specific conductance as a result of
logging road construction are expected to be relatively minor.
5.00 Stream Discharge
Streamflow measurements can be made when other parameters are
monitored. The timing of streamflow measurements depends upon the parti-
cular need for the data.
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219
REFERENCES
Text
No.
1. .Brown, George W., "Forestry and Water Quality," School of Forestry,
Oregon State University, OSU Bookstore, 7^ pages, 1972.
2. Fredriksen, R. L., "Erosion and Sedimentation Following Road Con-
struction and Timber Harvest on Unstable Soils in Three Small
Western Oregon Watersheds," USDA Forest Service Research Paper
PNW-10U, 15 pages, 1970.
3- Swanston, D. N., "Principal Mass Movement Processes Influenced by
Logging, Road Building, and Fire," Proceedings of A Symposium on
Forest Land Uses and Stream Environment, Oregon State University,
August 1971.
U. Megahan, Walter F. and Walter J. Kidd, "Effects of Logging Roads
on Sediment Production Rates in the Idaho Batholith," USDA Forest
Service Research Paper INT-123, 1^ pages, May, 1972.
5- Larse, Robert W., "Prevention and Control of Erosion and Stream
Sedimentation from Forest Roads," Proceedings of A Symposium on
Forest Land Uses and Stream Environment, Oregon State University,
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6. Gonsior, M. J., and R. B. Gardner, "Investigation of Slope Failures
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Operations," 32 pages, July, 1971.
8. See Reference 5-
9. U.S. Forest Service Region 6, "Timber Purchaser Road Construction
Audit." A Study of Roads Designed and Constructed for the Harvest
of Timber, 31 pages, .January, 1973-
10. Siuslaw National Forest, Oregon, "Implementation Plan" to the Region 6
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11. Boise National Forest, Idaho, "Erosion Control on Logging Areas,"
36 pages, March, 1956.
12. Rothacher, Jack S. and Thomas B. Glazebrook, "Flood Damage in the
National Forest of Region 6," USDA Pacific Northwest Forest and Range
Experiment Station, Forest Service, Portland, Oregon, 20 pages, 1968.
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220
REFERENCES (Cont'd.)
Text
No.
13. U.S. Bureau of Land Management, "Roads Handbook." 9110-Road, Trails,
and Landing Fields, 200 pages approx.
ll* . Forbes, Reginald D. , "Forestry Handbook." Ronald Press Company,
New York, 1100 pages approx. , 1961.
15. Hartsog, W. S. and M. J. Gonsior, "Analysis of Construction and
Initial Performance of the China Glenn Road, Warren District, Payette
National Forest." USDA Forest Service INT-5, 22 pages, May, 1973-
16. U.S. Forest Service Region 6, "Forest Residue Type Areas."
Unpublished map of Region 6 showing geomorphic provences, timber
species associations and geomorphic sub -provences, 1973-
17. Snyder, Robert V. and LeRoy C. Meyer. "Gifford Pinchot National
Forest Soil Resource Inventory," Pacific Northwest Region, 135 pages,
July 1971-
18. Snyder, Robert V. and John M. Wade, "Soil Resource Inventory, Snoqualmie
National Forest." Pacific Northwest Region. 228 pages, Aug. 15, 1972.
19. See Reference 18.
20. United States Department of the Interior, Bureau of Land Management
Oregon State Office, "5250 - Intensive Inventories." 15 pages,
Feb. 7, 197^.
21. Burroughs, Edward R. Jr., George R. Chalfant and Martin A. Townsend,
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22. See Reference 10.
23. Jennings, John W. "A Proposed Method of Slope Stability Analysis for
Siuslaw National Forest," submitted to Forest Supervisor Siuslaw
National Forest, 37 pages, May 197^.
2k. Hendrickson, Larry G. and John W. Lund, "Highway Cut and Fill Slope
Design Guide Based on Engineering Properties of Soils and Rock,"
paper given at 12th Annual Symposium on Soils Engineering, Boise,
Idaho, 35 pages,
25. U.S. Forest Service Region 6, Supplement No. 19 to the Transportation
Engineering Handbook" 2.k pages, Feb. 1973-
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Text
No.
221
REFERENCES (Cont'd.)
26. Swanston, Douglas N. "Judging Landslide Potential in Glaciated
Valleys of Southeastern Alaska." An article appearing in The
Explorers Journal, Vol. LI, No. h. h pages, Dec. 1973-
27. Swanston, Douglas N. "Mass Wasting in Coastal Alaska," USDA
Forest Service Research Paper PNW-83. 15 pages, 1969.
28. See Reference 11.
29. See Reference 2.
30. See Reference ^.
31. See Reference 10.
32. See Reference 5.
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222
REFERENCES (Cont'd.)
Text
No.
33. Wischmeier, W.H., and D.D. Smith. Predicting Rainfall-Erosion
Losses From Cropland East of the Rocky Mountains. Agr. Handbook
282, U.S. Govt. Print. Office, Washington, B.C., 1965.
34. Musgrave, A.W., "The Quantitative Evaluation of Factors in Water
Erosion - A First Approximation," J. of Soil and Water Conser-
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35. Erosion Susceptibility for Western Oregon, Bureau of Land
Management, Oregon State Office, Portland, Oregon (unpublished).
36. Wischmeier, W.H., and L.D. Meyer, Soil Erodibility on Construction
Areas, published in Highway Research Board Special Report 135,
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37. Hershfield, D.M.: Rainfall frequency atlas of the United States,
for durations from 30 minutes to 24 hours and return periods
from 1 to 100 years, U.S. Weather Bur. Tech. Rept. 40, May, 1961.
38. Probable maximum precipitation and rainfall-frequency data for
Alaska for areas to 400 square miles, durations to 24 hours and
return periods from 1 to 100 years, U.S. Weather Bur. Tech.
Paper 47. 1963.
39. Wischmeier, W.H., C.B. Johnson, and B.V. Cross. A Soil
Erodibility Nomograph for Farmland and Construction Sites.
Jour. Soils and Water Cons., Vol. 26, 1971, pp. 189-193.
40. Chow, Ven Te, Handbook of Applied Hydrology, McGraw-Hill Book
Company, 1964.
41. Meyer, L.D., and L.A. Kramer, Relation between Land-Slope
Shape and Soil Erosion, Agr. Eng., Vol. 50, 1969, pp. 522-523.
42. Young, R.A., and C.K. Mutchler, Soil Movement on Irregular
Slopes. Water Resources Research, Vol. 5, 1969, pp. 1084-1089.
43* Meyer, L.D., C.B. Johnson, and G.R. Foster,, Stone and Woodchip
Mulches for Erosion Control on Construction Sites, Journal
Soils and Water Conservation, 1972.
44. Meyer, L.D., W.H. Wischmeier,, and W.H. Daniel,, Erosion, Runoff,
and Revegetation of Denuded Construction Sites, Trans. ASAE,
Vol. 14, 1971, pp. 138-141.
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223
Text REFERENCES (Cont'd.)
No.
45. Meyer, L.D., W.H., Wischmeier, and G.R. Foster. Mulch Rates
Required for Erosion Control on Steep Slopes, Soil Sci. Soc.
Amer., Proc. Vol. 34, 1970, pp. 928-931.
46. Packer, P.E., "Criteria for Designing and Locating Logging Roads
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a Logging Road be Located," Journal of Forestry, Vol. 55, pp.
339-341 (1957).
48. Dissmeyer, G.E., "Evaluating the Impact of Individual Forest
Management Practices on Suspended Sediment," Journal of Soil
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49. U.S. Environmental Protection Agency, Processes, Procedures, and
Methods to Control Pollution Resulting from Silvicultural
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50. California State Water Resources Control Board, A Method for
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Publication No. 50, 1973.
51. U.S. Forest Service, Pacific Northwest Region, Design of Water
Quality Monitoring Programs, 1972.
52. The Impact of Timber Harvest on Soil and Water Resources, Ext.
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53. Gardner, R.B., Major Environmental Factors that Affect the Location
Design, and Construction of Stabilized Forest Roads, Reprinted
from Vol. XXVIII, "Loggers Handbook," published by the Pacific
Logging Congress, Portland, Oregon.
54. Federal Water Pollution Control Administration, Northwest Regional
Office, Industrial Water Guide on Logging Practices. Febr. 1970.
55. Dorroh, J.H., Jr., Certain Hydrologic and Climatic Characteristics
of -the Southwest, Univ. New Mexico Publ. Eng., 1, 64 pp., 1946.
56. Croft, A.R., and Richard B. Marston, Summer Rainfall Characteristics
in Northern Utah, Trans, Am. Geophys. Union, 31, 83-93, 1950.
57. Sporns, U., On the Transposition of Short Duration Rainfall
Intensity Data in Mountainous Regions, Arch. Meteor. Geophys.
Biokl ., 13B, 438-442, 1964.
58. Schermerhorn, Vail P., Relations between Topography and Annual
Precipitation in Western Oregon and Washington, Water Resources
Research, Vol. 3, No. 3, Third Quarter, 1967.
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224
REFERENCES (Cont'd.)
Text
No.
59. Cooper, Charles F., Rainfall Intensity and Elevation in South-
western Idaho, Water Resources Research, Vol. 3, No. 1, First
Quarter, 1967.
60. Renner, F.G., Conditions Influencing Erosion on the Boise River
Watershed, U.S. Dept. Agr. Tech. Bull. 528, 1936.
61. Packer, Paul E., and George F. Christensen, Guides for Controlling
. :•£ Sediment from Secondary Logging Rpads, U.S. Forest Serv., Inter-
mountain Forest and Range Exp. Sta., 1964.
62. U.S. Bureau of Land Management, Roads Handbook, Aug. 1965.
63. Western Forestry and Conservation Association, An Introduction
to the Forest Soils of the Douglas-fir Region of the Pacific
Northwest, Portland, Oregon,' 1957.
64. Oregon State University, Proceedings of a Symposium on Forest Land
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65. Rothwell, R.L., Watershed Management Guidelines for Logging and
Road Construction, Forest Research Laboratory, Edmonton, Alberta,
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66. Hvorslev, M. Juul, Subsurface Exploration and Sampling of Soils
for Civil Engineering Purposes, edited and printed by Waterways
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67. American Association of State Highway Officials, Standard Method
of Surveying and Sampling Soils for Highway Purposes (A,A.S.H.O.
•.Designation-: T86-64).
68. The Asphalt Institute, Soils Manual for Design of Asphalt
Pavement Structures, Manual Series No. 10, Second Edition,
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69. .United States Geological Survey, Quadrangle Maps, 7.5 and 15
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70. See Reference 2.
71. See Reference 43.
72. See Reference 27.
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225
REFERENCES (Cont'd.)
Text
No.
73. See Reference 2.
7^. See Reference 1.
75. See Reference 18.
76. See Reference 12.
77. Megahan, Walter F., "Subsurface Flow Interception By a Logging Road
in Mountains of Central Idaho." National Symposium on Watersheds in
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78. See Reference 9.
79. Gardner, R. B., "Major Environmental Factors that Affect the Location,
Design and Construction of Stabilized Forest Roads", USDA Forest
Service reprint from Vol. XXVII of Loggers Handbook, 5 pages.
80. Western Wood Products Association, "Forest Road Subcommittee Minutes",
Feb. 2, 1972, 6 pages, unpublished.
8l. Gardner, R. B., "Forest Road Standards as Related to Economics and
the Environment," USDA Forest Service Research Note HTT-1U5, k pages,
August, 1971.
82. Tangeman, Ronald J., "A Proposed Model for Estimating Vehicle Operating
Costs and Characteristics on Forest Roads," USDA Forest Service,
Transportation System Planning Project, lUO pages, December, 1971-
83. U.S. Environmental Protection Agency, "Comparative Costs of Erosion
and Sediment Control, Construction Activities," Superintendent of
Documents, U.S. Government Printing Office, Washington D.C.,
205 pages, July, 1973-
Qk. See Reference 12.
85. See Reference 5-
86. Rothwell, R. L. "Watershed Management Guidelines for Logging and Road
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tion Report A-X-U2. Canadian Forestry Service, Department of Fisheries
and Forestry, 78 pages, April, 1971.
87. See Reference k.
88. See Reference 2k.
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226
REFERENCES (Cont'd.)
Text
No.
89. See Reference 25.
90. Prellwitz, Rodney W., "Simplified Slope Design for Low Standard Roads
in Mountainous Areas," USDA Forest Service, Missoula, Montana,
19 pages, Unpublished, not dated.
91. See Reference 8l.
92. Haupt, Harold F., "A Method for Controlling Sediment from Logging
Haul Roads," USDA Forest Service Misc. Pub. No. 22, Intel-mountain
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93- Packer, Paul E., "Criteria for Designing and Locating Logging Roads
to Control Sediment," reprinted from Forest Science, Volume 13,
Number 1, March. 196?, 18 pages.
9^. Packer, Paul E. and George F. Christensen, "Guides for Controlling
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mountain Forest & Range Equipment Station, kl pages.
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REFERENCES (Cont'd. )
Text
No.
95, Becker, Benton C., and Mills, Thomas R., and The Maryland Dept. of
Resources, Annapolis, Md.; Guidelines for Erosion and Sediment Control
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96. Boise National Forest, Boise, Idaho, Erosion Control on Logging Areas.
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97- Collins, Tom, Soils Scientist, U.S.D.A. Forest Service, Juneau, Alaska,
personal communication, May 28, 1974.
98. Corliss, John, Regional Forester, U.S.D.A. Forest Service, Pacific North-
west Region, Portland, Oregon, personal communication, May 28, 1974
99» Dyrness, C. T., Grass - Legume Mixtures for Roadside Soil Stabilization,
U.S.D.A. Forest Service, Pacific Northwest Forest and Range Experiment
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100, Dyrness, C. T., Stabilization of Newly Constructed Road Backslopes by
Mulch and Grass-Legune Treatments, U.S .D. A. Forest Service, Pacific North-
west Forest and Range Experiment Station Research Note PNW-123, July 1970.
101., Franklin, Jerry F. and C. T. Dyrness, Natural Vegetation of Oregon and
Washington, U.S.D.A. Forest Service, Pacific Northwest Forest and Range .
Experiment Station, General Technical Report PNW-8, Portland, Oregon, 1973.
102.. Gustine, Tim, Landscape Architect, King County, Washington, personal
communication, May 20, 1974.
103- KaYf Burgess L., "Hydroseeding", Agrichemical Age, pp. 6-8, June 1973.
Rothwell, R. L., Watershed Management Guidelines for Logging and Road
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105- Soil Conservation Service, Alaska Agricultural Experiment Station,
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106, Stephens, Freeman R. , Grass Seeding as a Site Preparation Measure for
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107. Swanson, Stanley L. , Legumes and Other Plants for Cover, Oregon State
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108. Turelle, Joseph W., "Factors Involved in the Use of Herbaceous Plants
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Text REFERENCES (Cont'd.)
No.
1Q9. U. S. Department of the Interior, Federal Water Pollution Control Adminis-
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Logging Practices, February 1970.
110, Warrington, Gordon, Soils Scientist, U.S.D.A. Forest Service, Sand
Point, Idaho, personal communication, May 29, 1974.
111. Wilson, Carl N., Grass Seeding for Erosion Control in Southeast Alaska,
U.S.D.A. Forest Service, Alaska Region, December 1965.
112% Wollum II, A.G., Grass Seeding as a Control for Roadbank Erosion, U.S.
D.A. Forest Service, Pacific Northwest Forest and Range Experiment
Station, Research Note 218, June 1962.
113- U.S. Environmental Protection Agency, Guidelines for Erosion and
Sediment Control Planning and Implementation, EPA-R2-72-015, August
1972.
llU. Dyrness, C.T., Stabilization of Newly Constructed Road Backslopes
by Mulch and Grass-Legume Treatments, U.S. Forest Service Research
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115- Bethlahmy, N., and W.J. Kidd, Jr., Controlling Soil Movement from
Steep Road Fill, U.S. Forest Service Research Note INT-45, 1966.
116. Plass, W.T., Chemical Soil Stabilizers for Surface Mine Reclamation,
Highway Research Board Special Report 135, 1973.
117•. Meyer, L.D., C.B. Johnson, and G.R. Foster, Stone and Woodchip
Mulches for Erosion Control on Construction Sites, Journal of Soil
and Water Conservation, Nov.-Dec. 1972.
US., Gardner, R.B., Major Environmental Factors that Affect the Location,
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119.. Goss,R.L., R.M. Blanchard, and W.R. Melton, the Establishment of
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