BEST MANAGEMENT PRACTICES
FOR
AGRICULTURAL NONPOINT SOURCE CONTROL
.
.
III. SEDIMENT
North Carolina Agricultural Extension Service
Biological and Agricultural Engineering Department
North Carolina State University
Raleigh, North Carolina
In Cooperation With:
Agricultural Stabilization and Conservation Service, USDA
Economic Research Service, USDA
Extension Service, USDA
Soil Conservation Service, USDA
Environmental Protection Agency
North Carolina Agricultural Research Service
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STATE-OF-THE-ART REVIEW OF
BEST MANAGEMENT PRACTICES FOR AGRICULTURAL
NONPOINT SOURCE CONTROL
m. SEDIMENT
for the project
RURAL NONPOINT SOURCE CONTROL WATER QUALITY
EVALUATION AND TECHNICAL ASSISTANCE
USDA Cooperative Agreement - 12-05-300-472
EPA Interagency Agreement - AD-12-F-0-037-0
PROJECT PERSONNEL
DeAnne D. Johnson Project Assistant
Jonathan M. Kreglow Extension Specialist
Steven A. Dressing Extension Specialist
Richard P. Maas Extension Specialist
Fred A. Koehler Principal Investigator
Frank J. Humenik Project Director
Biological & Agricultural Engineering Dept.
North Carolina State University
Raleigh, North Carolina 27650
Lee Christensen USDA-ESS Participant
William Snyder USDA-SCS Participant
EPA PROJECT OFFICER USDA PROJECT OFFICER
James W. Meek Fred N. Swader
Implementation Branch Extension Service
Water Planning Division Natural Resources
Washington, D.C. Washington, D.C.
AUGUST 1982
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EXECUTIVE SUMMARY
Sediment from soil erosion is the greatest single pollutant in U.S.
surface waters; reducing stream and reservoir capacities, causing increased
flooding, disrupting biological systems, degrading drinking water supplies
and transporting nutrients, pesticides and bacteria to waterways (75). Farm-
land is recognized as the largest contributor of sediment to U.S. waters with
over 6.4 billion tons of topsoil eroded each year. The purpose of this paper
is to identify and discuss the state-of-the-art in Best Management Practices
(BMPs) for reducing sediment inputs from farmland.
Presently, several Rural Clean Water Program (RCWP), Model Implementa-
tion Program (MIP) and Agricultural Conservation Program-Special Water Quality
(ACP) projects across the United States are designed to demonstrate the
effectiveness of various control mechanisms for abatement of agricultural
nonpoint source water quality problems. In many cases, programs have been
hindered in efforts to achieve water quality goals by a lack of information on
the cause-effect relations between BMPs and water quality. Data from these
research efforts may expand current assessments of the applicability of indi-
vidual BMPs and BMP systems as water quality control mechanisms.
The literature establishes conservation tillage systems-systems which
leave protective amounts of the previous year's crop stubble by minimizing
the amount of tillage-to be the most efficient methods of dramatically re-
ducing sediment loss while maintaining productivity. Research conducted in
many areas of the country has consistently demonstrated the success of con-
servation tillage systems in reducing runoff volume as well as sediment and
nutrient losses. Yields are generally increased relative to conventional
tillage during dry growing seasons and decreased somewhat during excessively
wet years. No-tillage systems, which reduce field operations to a single
step of cutting a narrow slit and planting, consistently give sediment reduc-
tions of over 90% with comparable and often higher yields. The only potential
limitation of conservation tillage as a nation-wide BMP pertains to the effects
from increased use of pesticides which are not clearly understood.
Contour farming has also been proven to greatly reduce soil erosion on
both cropland and rangeland. Contouring is most effective when crop rows are
tilled up along the contour so that small ponds from along each row in heavy
storms. Terraces are highly effective in reducing runoff and sediment loss.
Several studies have shown terraces to be much more effective than countour
farming in the western Corn Belt. The two major limitations of the practice
are that terrace construction is relatively expensive and that nutrient leaching
to groundwater may be increased. Diversions and grassed waterways are practices
designed to facilitate the non-erosive dispersion of runoff. They reduce
erosion more than runoff volume and thus are best used in conjunction with other
runoff-reducing practices such as conservation tillage and contouring.
Rotating a sod crop with a row crop will result in large reductions in
soil loss. On steep highly erodible marginal cropland it may sometimes be the
only practical method of reducing erosion to a tolerable level.
i i
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Several studies have shown row crop yields to increase significantly following
the sod rotation. In the short-term, however, this is not generally sufficient
to offset total row crop production reductions over the rotation. Cover crops
can greatly reduce soil losses during the non-growing season. The practice is
limited only in northern areas where it may be difficult to establish a good
cover before winter freeze or where the cover crop may hinder spring soil warm-
ing and drying, thus delaying timely planting. Filter strips have been shown
to be effective in filtering and causing deposition of sediment from field runoff.
Filter strips are best employed in conjunction with erosion reducing practices
such as conservation tillage, contouring and sod-based rotations.
While there is evidence that various stream channel stabilization measures
can effectively reduce streambank cutting and channel scouring, the practice is
highly questionable as a BMP because this sediment source is generally a relatively
smaller contributor in intensively cropped watersheds. The contribution of
stream channels to sediment loads has not been adequately studied however, and
this source may be significant in some topographic regions or where upland sedi-
ment control measures have reduced other sources. Present knowledge would indi-
cate that efforts should generally be directed towards erosion and runoff con-
trol rather than channel stabilization.
Conclusions and recommendations regarding Best Management Practices for
controlling sediment inputs from agricultural land include:
1. Erosion reductions on cropland are generally proportional to
reductions in the amount of tillage performed. Conservation til-
lage systems can reduce soil losses from 60 to 99 percent compared
to conventional moldboard plow techniques and are an effective
alternative in areas where no-till is not well adopted. Surface
runoff from conservation tillage averages about 25% less than con-
ventional tilled fields.
2. No-till is extremely effective in reducing erosion losses with
reductions of 70 to 99% but is not adapted to all regions and
requires higher management than conventional tillage.
3. Reduced tillage systems also decrease absorbed pesticide and
nutrient losses but not to the same extent soil losses are
reduced. While overall nutrient losses are lower, dissolved
fractions may increase.
4. Contour farming is an effective practice for reducing erosion
and surface runoff by increasing rainfall infiltration. It is
best adapted to permeable soils and moderate slopes.
5. Terraces are very effective in reducing erosion losses with
reductions of 50 to 98% reported in the literature. Absorbed
pesticides and nutrient losses are dramatically reduced and
surface runoff decreased. However, terraces are relatively
expensive to install, and nutrient leaching to groundwater may
be increased when this practice is used.
iii
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6. The combination of diversions and grassed waterways is a widely
accepted system reducing erosion and sediment transport but
there are little quantitative data on loss reductions.
7. Cover crops can reduce erosion from 40 to 95%, increase soil
organic matter and may reduce nitrate leaching. Legume cover
crops provide available nitrogen for subsequent crops.
8. Rotations that include a sod crop can reduce erosion losses
from 40 to 90%, increase organic matter and infiltration,
and can improve yield of cash crops. The economic loss in
years when a cash crop is not grown reduces the acceptability
of this practice.
9. Sediment basins are effective in reducing sediment delivery
from severe storms and in trapping small (l-50u) soil particles,
but the cost-effectiveness of this practice relative to cropland
protection has not been determined.
10. Although few data are available it appears that streambank
stabilization is not a general BMP. One study estimated
that only 5% of all watershed losses were due to streambank
erosion, but a significant expenditure of funds was devoted to
this practice.
11. Although pesticide costs increase, the total costs of production
usually decline with use of conservation tillage systems,
primarily because of savings in labor and fuel costs.
12. The overall profitability of conservation tillage depends
primarily on the effects on yields on the conservation tillage
system. When yields are affected not at all or only slightly,
conservation tillage systems are generally more profitable
and contribute to water quality improvement.
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CONTENTS
Executive Summary ii
Figures vii
Tables viii
Preface x
1. Introduction ]_
2. The Erosion/Sedimentation Process 5
3. Relationship Between Erosion and Sedimentation 7
4. Proposed Best Management Practices g
Evaluating the Effectiveness of Proposed BMPs.. 10
Conservation Tillage Systems 12
Contour Farming 16
Cover Crops 18
Diversions and Grassed Waterways 18
Grasses and Legumes in Rotation 22
Sediment Basins 24
Stream Channel Stabilization 24
Terraces 26
Filter Strips 27
Irrigation 27
Summary 30
Hard Conclusions 30
Soft Conclusions 32
5. Economic Aspects of BMPs for Sediment Control 33
Costs of Installing and Maintaining BMPs 33
Effect on Net Farm Income 34
Cost-Effectiveness 36
References 36
6. Research Needs 38
7. Current Research 39
References 43
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FIGURES
Number Page
1 Land resource regions 11
2 Land resource regions with literature references and
projections indicating conservation tillage as a
BMP component 17
3 Land resource regions with literature references and
projections indicating contouring as a BMP component 20
4 Land resource regions with literature references and
projections indicating cover crops as a BMP component 21
5 Land resource regions with literature references and
projections indicating rotations which include grasses
or legumes as a BMP component 23
6 Land resource regions with literature references and
projections indicating terraces as a BMP component 29
VII
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TABLES
Number Pag<
1 Comparisons of Soil Loss and Crop Yields Between
Conservation and Conventional Tillage Systems 15
2 Comparisons of Soil Loss, Yields and Runoff Between
Contoured and Uncontoured Farming and Between
Contouring and Terracing 19
3 Comparisons of Soil Loss, Yields and Runoff Between
Terraced and Unterraced Cropping 28
4 Cost of Installing Conservation Practices 33
5 Typical Change in Variable Costs Associated with
Implementation of BMPs as compared to conventionally
Tilled Continuous Corn Grain 35
6 Fuel Requirements for Various Rotations and Tillage Systems 35
VI 1 1
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PREFACE
There are currently many programs and projects across the country for
reducing nonpoint source pollution from agricultural activities. Public
and private monies are being spent to implement agricultural Best Manage-
ment Practices (BMPs) for improving water quality. To assess these many
efforts on a nationwide basis a joint USDA-EPA project, "Rural Nonpoint
Source Control Water Quality and Technical Assistance," has been established.
This undertaking commonly known as the National Water Quality Evaluation
Project, will assess the water quality and socio-economic effects of BMP
use in the rural sector.
This document identifies and discusses the State-of-the-art in Best
Management Practices for controlling nonpoint source pollution from sedi-
ment. Any proposals for major changes in erosion and sediment control
practices must be assimilated with economic realities, production concerns
and institutional limitations. Conclusions and recommendations in this
document are not intended to reflect production or institutional
factors, and thus, inferences drawn from these statements should contain
appropriate caveats in regards to these factors.
The scope of the literature reviewed for this document was restricted
to published documents with supporting data. Two computer-based files, the
Southern Water Resources Scientific Information Cetnter (SWSIC) and AGRICultural
On Line Access system (AGRICOLA), were used for a large portion of the
literature retrieval. Much additional information was obtained through
citations follow-up, and interpretive insight was solicited from NCSU
professionals.
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SECTION 1
INTRODUCTION
Water pollution control efforts have historically emphasized abatement
of industrial and municipal point sources. As a result of criteria and stand-
ards development, refinement of on-site control technologies and increased
enforcement efforts mandated under PL 92-500, great reductions from these
point sources have occurred during the 1970's. However, the overall quality
of the nation's surface waters has not improved to an extent proportional with
these point source reductions, and it is becoming well recognized that control
of nonpoint sources may demand top priority in water pollution control efforts
during the next decade.
In sharp contrast to reductions in point sources, pollution inputs from
land activities, particularly agriculture, have increased greatly as land
previously thought too fragile or infertile has been brought into production
under the impetus of foreign grain sales (66). When such areas are brought
into crop production to meet demands for increased food supply, the erosion
problems are often much more serious than those on lands already being farmed
(38). Yield-increasing production technologies which rely on increased use
of chemical fertilizers and pesticides as well as more extensive soil
preparation have also contributed to the increase in agricultural related
water pollution. It has been estimated that agriculture related inputs are
the major water pollution inputs in two-thirds of the watersheds in the
United States.
Sediment from soil erosion has been considered the greatest single
pollutant in U.S. surface waters (75). Soil is a water pollutant because
1) as sediment its mass volume often reduces stream and lake capacities; 2)
it can upset stream and lake ecosystems by settling out of the water column
destroying benthic habitats and can cause high turbidity which inhibits
photosynthesis; and 3) other pollutants such as nutrients, pesticides and
bacteria can be strongly adsorbed or attached and thus transported with
sediment particles (85, 37). By weight the sediment load in U.S. waterways is
500 to 700 times greater than the total sewage load discharged to streams
(33). Fortunately, however, by weight the pollution potential of sediment
is much less than that of most other pollution materials (28). About 50C;
of the sediment in the nation's waterways is thought to come from cropland
(78, 82), while it has been estimated that approximately 30°' of the total
probably represents the natural level of sedimentation (82). Other major
sources include streambanks, road ditches, construction sites, urban areas,
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rangelands, mining projects and forests (85).
In spite of the low pollution potential by weight of sediment, excessive
soil erosion and subsequent sediment deposition are being found to have severe
negative impacts on both agricultural production capacity and water quality.
It has been estimated (50) that in the Southern Piedmont grain yields could be
expected to decrease by about 5.7 bu/hectare for each centimeter of soil
eroded from Class II land. Soil is eroding at a record pace not only in rich
farm states like Iowa but also in the East, the South and the Pacific Northwest.
Much of the effect of cropland damage on yields has been masked by improved
mechanical, fertilizer and pesticide developments; however, a recent USDA
survey has warned that at present erosion rates, corn and soybean yields in the
Cornbelt states may drop by as much as 30% in the next 50 years as the fertility
of the soil declines (66). Erosion is the major crop production limitation on
nearly half of U.S. cropland (43).
Suspended sediment can greatly limit use of water sources for drinking
water supply. The maximum limit of one turbidity unit for finished drinking
water is based on health considerations relating to effective chlorine dis-
infection (84). Suspended sediment provides areas where microorganisms may
not come into contact with chlorine disinfectant (61). No standard has been
set for suspended sediment concentrations in drinking water sources because
the ability of usual water treatment process (i.e., coagulation, sedimentation,
and filtration)to remove suspended matter depends on the composition of the
suspended matter as well as its concentration (84). However, in general the
greater the turbidity of the water, the greater the water treatment costs since
additional coagulants and disinfectants are needed. These chemicals and filtra-
tion systems are one of the major expenses in the operation of many water
treatment systems.
Reduction in channel and reservoir storage capacities may be the most
serious and costly impact of excessive sedimentation. The median storage de-
pletion rate for all U.S. reservoirs is 1.5% per year (53). The sedimentation
rate is generally higher for small reservoirs than for large reservoirs (11).
Many are filling at3a rate of 5% of their capacity per year, while those with
less than 123,000 m are losing a mean of 2.7% or their capacity annually.
Replacement of sediment-filled reservoirs is often much more costly than
the original construction because less optimal secondary sites must be used
(85). It has been estimated (5) that $250,000,000 per year is spent on remov-
ing sediment from streams, harbors and reservoirs.
Sediment also increases flood damage by reducing stream capacities and
clogging channels. While little quantitative research has been done, it has
been estimated that flood water damages related to excessive sedimentation may
amount to one billion dollars annually (53).
Excessive sediment, suspended and deposited, has very deleterious ef-
fects on fish and other aquatic life. These effects can be divided into those
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occurring in the water column and those occurring following sedimentation on
the^bottom of the water body (84). A review by the European Inland Fisheries
Advisory Commission (24) identified four mechanisms by which sediment adversely
affects fish:
1) by acting directly on the fish swimming in water in which
sediment is suspended and either killing them or by reducing
growth rate or resistance to disease
2) by preventing the successful development of fish eggs and
larvae
3) by modifying natural movements and migration
4) by reducing the abundance of food supply
Fish kills generally occur as a result of silt clogging the gills of fish
or from oxygen-depletion caused by oxygen-demanding sediment (70, 59).
Deposited sediment which blankets the bottom of water bodies damage the in-
vertebrate populations, block gravel spawning beds, and if organic, remove
dissolved oxygen from overlying waters (21). It is thought that silt particles
attached to fish eggs prevent sufficient exchange of oxygen and carbon dioxide
between the egg and the overlying water resulting in low propogation success
(24).
Suspended sediment reduces light penetration into lakes and rivers,
reducing the depth of the photic zone, and thus reducing primary production
(84). In addition the near surface water layer is heated more than the bottom
resulting in a greater and more rapid stratification of the water body than
would occur at lower suspended sediment concentrations. This prevents vertical
mixing thus decreasing the dispersion of dissolved oxygen to the lower portion
of the water body.
Nutrients, pesticides and bacteria may be adsorbed on the surface of
sediment particles and then transported with sediment into waterways. Nutrients
and pesticides occur in highest concentrations on the smaller sediment par-
ticles because of their larger surface area to volume ratio. Unfortunately,
the smaller soil particles are those most easily eroded and transported to
waterways with the overall effect that these adsorbed pollutants are preferen-
tially removed from cropland. From a water quality standpoint, nutrients
available for algal growth and eutrophication rather than total nutrients
amounts are of interest. Phosphorus in particular has consistently been found
to be almost totally sediment-bound rather than dissolved in agricultural
runoff (64, 2, 48). It is unclear how much of this sediment-bound phosphorus
is available for algal growth, but some recent studies have indicated that
approximately 20% of the sediment-bound phosphorus is available depending on
sediment composition (20, 39). In the case of pesticides, field loss is
proportional to soil loss for strongly-bound types such as paraquat. More
weakly-bound pesticides such as methyl parathion and atrazine are lost
primarily in solution (74).
Sediment load estimates must be made for the specific watershed to be
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meaningful in terms of water quality. The largest annual sediment loads for
a given stream are often as much as 20 times greater than the minimum sediment
load. This can generally be correlated with those years of greatest runoff
(28). Johnson et al. (41) observed a ten-fold difference in sediment yield
between wet and dry years for an Idaho rangeland watershed. It was also
found that five to ten percent of the annual runoff transported fifty to
ninety percent of the annual sediment yield. A study in the Palouse region
showed that sediment transport during a wet year could exceed the combined
total of four or five other years indicating that sediment sampling programs
of one or two years duration may give very misleading results for water
quality trends (52). Large differences can occur in sediment yield from
adjacent streams discharging at the same rate depending on land use and
stream morphology. Even within the same stream, the concentrations of
suspended solids can vary by a factor of ten for a given rate of discharge
(78).
The lowest levels of sediment loss in the U.S. have been observed
in the Rocky Mountains where sediment loss from undisturbed forests is
generally less than 0.36 mt/ha (28). Mean sediment yields between 0.31
and 1.66 mt/ha were measured for a nine-year period from Idaho rangeland.
Very low levels of sediment are also seen in small forested New Hampshire
watersheds (78).
The areas with the highest erosion/sedimentation rates are generally
those which combine intensive agriculture, hilly topography and erodible
soil types. Of prominent concern among these are the Reelfoot Lake region
of western Tennessee where mean soil losses are estimated at 70 to 90 mt/ha
with losses up to 330 mt/ha and the Palouse basin of southeast Washington
with mean soil losses of 38 mt/ha ranging up to 450 .mt/ha. While soil
loss rates are somewhat less in Iowa, they are of even more concern since
this state produces fifteen and twenty percent of the nation's soybean
and corn crop, respectively, and over half of the original topsoil has been
lost (66).
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SECTION 2
THE EROSION/SEDIMENTATION PROCESS
The sediment producing process involves soil detachment, transport
and deposition. Erosion is generally defined as the detachment and trans-
port of soil by water, wind, ice or gravity (81). Soil detachment can occur
either from raindrop impact or from the shear forces of flowing water, but
raindrop impact is usually the principal mechanism at the field surface (26).
Primary clay particles are detached less easily than sand particles. Garriels
et al. (30) and Ghadiri and Payne (32) found that rainfall kinetic energy
was a major factor in the extent of soil detachment such that higher inten-
sity storms have much higher detachment potential than light storms even
if the total rainfall is equivalent. Calculations made by multiplying the
number of soil particles detached by a single raindrop by the several
million drops per square meter which occur during a rainstorm indicated
that raindrop impact can easily detach more soil than overland flow on
short slopes (27). Besides causing soil detachment, splashing raindrops
also break down the soil aggregates into smaller aggregates and particles
which are more readily transported. In addition the raindrop impact can
lift larger particles into overland flow than would otherwise be detached
and transported by the flow. These larger particles are then transported
a short distance downslope before settling back to the soil surface (26).
Soil particles detached by raindrop impact are generally transported
by shallow overland flow to rills. Once the sediment carrying capacity of
the rill flow is exceeded, deposition will begin to occur (85). Frequently
deposition, especially of large particles, will occur long before runoff
enters streams or lakes (55). It has been suggested (58) that eventually
nearly all sediment deposited in concentrated flow channels will be trans-
ported to waterways. The concept that deposition of sediment increases
flow energy thus causing more detachment and transport has been studied
by McDowell and Grissinger (53) who found that upland control measures that
decrease soil loss more than runoff can actually cause downstream channel
instability problems. Stream channels often become major sediment sinks
for eroded upland soil. If soil erosion is reduced without corresponding
reductions in runoff, this stored sediment will be remobilized during storm
events producing high sediment yields which may continue for several years
following upstream soil erosion abatement (80). It is presumed that the
process would continue until the stream has re-established its original
gradient and channel regime. For these reasons sediment control measures
which reduce runoff volume are generally more effective overall in improving
water quality. Also the time lag between source control implementation
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and observed water quality improvement must be considered in the evaluation
of the effectiveness of soil erosion control measures.
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SECTION 3
RELATIONSHIP BETWEEN EROSION AND SEDIMENTATION
A useful parameter for evaluating the relationship between erosion and
sedimentation is the sediment delivery ratio (SDR) which is defined as the
ratio of the amount of sediment delivered to a given stream station to the
amount of gross soil erosion from the upstream watershed. The percentage of
eroded soil in a watershed which becomes sediment in waterways will tend to
be less in situations where the major erosion sources are either located
distant from water courses or are separated from water courses by sediment
holding areas such as woodlands, other vegetated areas or sediment basins.
The SDR will also be minimized by larger drainage areas, course soil texture,
gentle topography and a predominance of sheet and rill erosion as opposed
to gulley erosion. Stewart et al. (75) have cited a range of 0.08 to 0.33
for SDRs. A major limitation in using the SDR to evaluate sediment related
pollutant loading is that this parameter is an estimate of only the total
sediment load. The percentage of finer soil particles, which carry the
majority of adsorbed nutrients and pesticides, may be much higher than the
overall SDR. From a water quality standpoint control of the smaller
fraction of materials may be more important than reducing total sediment
loads.
It is often assumed that if soil erosion is controlled, then sediment
will also be controlled. While this is undoubtedly true, since soil erosion
must occur to produce sediment, there are, as the previous discussion
suggests, usually several possible alternatives to be considered either
individually or in combination for controlling sediment in the most cost
effective manner. Sediment can be controlled at any point between source
and sink, while erosion can only be controlled at the field level. Sediment
control strategies may be divided into 1) those which reduce the amount
of field erosion and 2) those which reduce the sediment delivery ratio.
The selection of appropriate combinations of control measures will depend
on the relative importance of different objectives since erosion control
has beneficial impacts on both agricultural productivity and water quality,
while off-field sediment control practices will generally affect only
water quality .
For these reasons it is very important to be able to correctly
select the best control practices for specific production and water quality
goals as well as the most critical sediment producing areas in order to
implement the most effective sediment control. The following section is
intended to describe the proposed Best Management Practices (BMPs) for
sediment control and review research concerning their effectiveness in
reducing the severe negative impacts of erosion/sedimentation described
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in previous sections. The objective is to summarize what is known about the
effectiveness of the proposed BMPs (and other practices) and to highlight
areas where the effectiveness of these proposed control measures is still
not clearly known.
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SECTION 4
PROPOSED BEST MANAGEMENT PRACTICES
Many sediment control measures have been applied under the leadership
of the Soil Conservation Service over the past four decades. These have
bean directed at conservation of both soil and water resources and have
been implemented nationwide to widely varying extents. The most prominent
of these and a brief description of the manner in which they function
to reduce erosion/sedimentation is given below.
1. Conservation Tillage Systems - which include no-tillage,
sod planting, minimum tillage, chisel plowing and slot
planting involve leaving protective amounts of crop stubble
on the surface of the field. Such practices generally reduce
the volume of surface runoff and prevent erosion by reducing
both soil detachment and transport.
2. Contour farming - is farming gently (<8 percent) sloping
land so that plowing, planting, and cultivation are done
on the contour. Contouring is most effective when rows
are ridged and furrowed which allows ponding of surface
runoff resulting in greater infiltration and reduced
runoff volume.
3. Cover crop - is a crop of close-growing grasses, legumes
or small grains grown primarily for seasonal soil protection
and for conservation tillage residue (81). Purpose is to
reduce direct runoff as well as to reduce soil detachment
from raindrop impact during the nongrowing season.
4. Diversions - are channels with a supporting ridge on the
lower side constructed across the slope. Purpose is to
help reduce soil transport capacity of runoff by reducing
slope length and to prevent damage down-slope from the
diversion.
5. Grassed Waterways - are natural or constructed vegetated
depressions which carry surface runoff while preventing
the formation of rills or gullies.
6. Grasses and Legumes in Rotation - is establishing grasses
and legumes as part of a conservation cropping system. The
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closely grown sod crop significantly reduces detachment
from raindrop impact as well as the volume of surface
runoff.
7. Sediment Basins - are structures designed to impound
runoff and allow sediment to settle out. Their benefits
are primarily off-site since only downstream water quality
and not production capacity is affected. They can also
significantly reduce downstream flow rates important for
channel stability especially in small watersheds (26).
8. Streambank Protection and Stream Channel Stabilization -
are measures both structural and nonstructural which
reduce streambank erosion. They may also help to
maintain channels to reduce sediment deposition and
remobilization.
9. Terraces - are a combination ridge and channel
constructed across the slope (81). They reduce erosion
primarily by decreasing slope length. Secondarily they
function to reduce sediment delivery by allowing eroded
soil to be redeposited before reaching waterways
although this redeposition may eventually render the
terrace ineffective. Terraces also reduce runoff volume
due to increased infiltration but generally not to the same
extent that erosion is reduced.
10. Filter strips - are strips or areas of vegetation for
removing sediment from runoff. While having no effect
on soil erosion filter strips improve water quality by
reducing sediment delivery.
EVALUATING THE EFFECTIVENESS OF PROPOSED BMPs
Studies in various areas of the United States which have attempted
to determine the effect of the above practices on production and water
quality are summarized below. These studies provide the basis for a
national evaluation of the effectiveness of these proposed BMPs for
controlling sediment. They also indicate where more information is
needed before nationwide abatement strategies can be initiated with
convidence.
The effectiveness of most BMPs in a given situation depends on
variables such as topography, soil type, climate and type of crop.
For this reason research on individual sediment-control BMPs is
grouped by geographic regions for several practices. The geographic
breakdown chosen is the SCS Land Resource Regions shown in Figure 1.
A potential sediment control practice is shown as a BMP in a region
10
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LEGEND
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
R
S
T
U
Northwestern Forest, Forage and Specialty Crop Region
Northwestern Wheat and Range Region
California Subtropical Fruit, Truck and Specialty Crop Region
Western Range and Irrigated Region
Rocky Mountain Range and Forest Region
Northern Great Plains Spring Wheat Region
Western Great Plains Range and Irrigated Region
Central Great Plains Winter Wheat and Range Region
Southwest Plateaus and Plains Range and Cotton Region
Southwestern Prairies Cotton and Forage Region
Northern Lake States Forest and Forage Region
Lake States Fruit, Truck and Dairy Region
Central Feed Grains and Livestock Region
East and Central Farming and Forest Region
Mississippi Delta Cotton and Feed Grains Region
South Atlantic and Gulf Slope Cash Crops, Forest and Livestock Region
Northeastern Forage and Forest Region
Northern Atlantic Slope Diversified Farming Region
Atlantic and Gulf Coast Lowland Forest and Crop Region
Florida Subtropical Fruit, Truck Crop and Range Region
Figure 1. Land resource regions.
11
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if sufficient research has been done to confirm effectiveness. Practices
are projected to be BMPs in some regions where little or no study has
been done, based on topographic, soil, climatic and cropping similarities
with documented regions. Regions which either have 1) no data relative
to the effectiveness of a proposed BMP, 2) data which indicate the
practice is not a BMP, or 3) no applicability of the practice due to
lack of agricultural activities are also indicated in the figures.
CONSERVATION TILLAGE SYSTEMS
More research work has been done comparing various conservation
tillage systems with conventional tillage systems than on any of the other
BMPs in the past ten years. Conservation tillage seems to be one of the
most effective BMPs for reducing erosion, particularly in rolling or hilly
areas. While conservation tillage requires more herbicides to produce
a good crop, yields from conservation tillage are roughly equal to yields
from conventional tillage and are often better during dry years (81, 4, 56).
A recent review of work concerning conservation tillage systems
in the western Corn Belt states of Iowa, Minnesota, Missouri and the
eastern portions of Nebraska and South Dakota points out that the greater
soil infiltration capacity made possible by various conservation tillage
systems is extremely important in this region since evapotranspiration
normally exceeds stored moisture and precipitation during much of the
growing season. Burwell et al. (17) found that fall mulch-tilled fields
(one pass with a chisel plow) previously cropped in oats provided nearly
eight times greater infiltration capacity than conventional tilled fields
before runoff began to occur in Minnesota. In a Nebraska study (16), soil
losses from till-planted plots, were six times lower than from conventionally
tilled plots. Increased infiltration and reduced runoff volume have also
been noted by several other investigators (14, 22, 36).
One of the most comprehensive studies designed to evaluate the
effectiveness of conservation tillage in reducing agricultural water
pollution was done at the Watkinsville, Georgia, experimental site (49).
In this study various tillage methods were compared over four years.
In all cases the fields were tilled on the contour. The four tillage
systems studied were 1) spring moldboard plow (conventional), 2) fall
moldboard plow (conventional), 3) spring chisel plow, and 4) no-till.
It was found that runoff was reduced by 47 percent between conventional
tillage and double-cropped no-till. Soil loss, however, was reduced
86.9 mt/ha to 1.3 mt/ha or a 98 percent reduction. Moreover, actual
edge of field flume measured sediment was reduced 99 percent between
conventional and no-till systems.
Other studies have found considerable variability in the extent to
which minimum and no-till systems reduce runoff volume. Laflen et al. (47)
compared a wide range of plot watershed and simulated rainfall studies using
12
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various crop rotations and soils and noted that conservation tillage systems
reduced the volume of runoff by an average of about 25%, but that in a few
cases runoff volume was actually slightly greater from conservation than from
conventional tillage systems. In nearly all cases no-till produced less erosion
but somewhat greater runoff volume than minimum tillage chisel plowing. Simu-
lated rainfall studies in the eastern Corn Belt (Indiana, Illinois) showed
chisel, till-plant and no-till systems to reduce soil loss by 94, 69 and 85°;,
respectively, after an intense storm compared with conventional tillage (51).
Oschwald and Siemens (62) observed disk chisel and no-till to reduce soil
loss 89 and 91%, respectively, following corn and 71 and 85% after soybeans
from high intensity storms. The difference is presumably due to the larger
amount of residue left from corn crops. This difference is significant for
the region since many eastern Corn Belt farmers alternate corn and soybeans (34)
In a comparison of no-till and conventional till systems for soybeans
on small Mississippi plots of silty clay loam soil losses were seven times
greater with conventional till under continuous soybeans (54). Runoff volumes
and soil loss were lowest on plots of no-till soybeans double-cropped with
wheat. In Illinois on a silt loam soil conventional till plots lost three
and sixteen times as much soil as no-till plots on five percent and nine
percent slope respectively from a single winter storm (29). Crop yields for
the two tillage systems over nine years were approximately equal. A recent
study in north-central Oregon (31) shows that reduced-tillage methods can be
used successfully for wheat production. Erosion was reduced markedly when
1,120 kg/ha or more of wheat stubble was left on the fields, and yields were
not affected.
Baker et al. (7) have suggested that the soil loss reductions from
practices such as no-till and use of cover crops are a function of the percent-
age of soil covered by crop and crop residue. In a simulated rainfall study
they found that the percentage of ground cover could explain 78 to 89% of the
variation in soil loss between six different tillage systems. Similar results
were obtained by Laflen et al. (45).
The erosion control provided by conservation tillage nearly always
results in a reduction in total nutrient loss since the majority of nutrients
are transported by sediment rather than in solution (8, 6). However, dissolved
nutrient concentrations in the surface runoff are increased in most cases.
There appear to be several contributing factors involved. The incomplete
incorporation of fertilizers inherent in conservation tillage systems means
that nutrients are more easily transported with surface runoff. Also, while
sediment losses are substantially less under conservation tillage systems,
the sediment which is lost is comprised of the most easily eroded fraction
of the soil; i.e., the smaller particles with greater amounts of adsorbed
nutrients and pesticides. Other studies (9, 79) indicate that increased
nutrient concentrations may also be due to leaching of nutrients from plant
residues on the soil surface.
The effect of conservation tillage systems on crop yields appears to
vary greatly with weather conditions and geographic location. In an eleven-
year northwest Iowa study (4), minimum tilled corn gave superior yields
13
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during six years with water deficits during the growing season while for
years with adequate rainfall no yield differences were noted. Griffith
et al. (34) compared no-till, chisel and till-plant systems with conventional
tillage at four Indiana test sites. On well-drained sandy loam the conserva-
tion tillage systems equalled or exceeded conventional till corn yields; while
on poorly-drained soils no-till yield was substantially less than conventional,
and chisel and till-plant corn yields were slightly reduced. A West Virginia
study (12) showed significant increases in corn yield for no-till versus
conventional tillage following a sod cover crop. A comparison of studies on
no-till in Ohio indicated that no-till gave approximately ten percent greater
corn yields on well-drained soils, about equal yields on moderately well-
drained and somewhat poorly-drained soils, and decreases averaging about ten
percent on poorly-drained soils (25).
Climate has an important effect on the utility of conservation tillage
methods. Tillage-incorporated mulch aerates the soil which facilitates more
rapid spring warming. Lower soil temperatures delay germination, emergence
and early plant growth. Research indicates that no-till systems are less
successful in colder climates such as New York and New England for these
reasons (77, 63). One way these temperature effects can be partially offset
is by using a ridge-furrow system in which the crop is planted on the ridges.
Considerable soil temperature differences can exist between the ridge and
furrow depending on time of day and row direction (3). This system, used in
tin-planting, also reduces soil moisture and thus may provide an optimum
tradeoff between sediment control and yields in poorly-drained soils. Another
possiblity is the development and use of crop varieties compatible with cooler
soil temperatures (3).
Pest control is another key factor in determining crop yields under
conservation tillage systems. With little preplant tillage weed seeds accumu-
late near the soil surface, and many systems preclude the possibility of herbi-
cides being incorporated prior to planting. For these reasons increased use
of herbicides is almost always needed to ensure maximum production under
systems of conservation tillage at the present time. In many cases both con-
tact and systemic herbicides are necessary for optimal yields. Insects,
nematodes and plant diseases would also be expected to cause greater problems
under conservation tillage systems. Residues can serve as overwintering sites
for insects and plant diseases. Nematode densities would be expected to
increase in the unbroken root residue from no-till. The production, environ-
mental and water quality consequences of large-scale adoption of reduced
tillage systems in terms of increased pest risks and environmental contamina-
tion are at the present time not clearly understood.
In summary, sediment loss from cropland appears to be directly related
to the amount of tillage performed; and thus, reductions can be impressive
using minimum or no-till systems. Study results on soil loss and runoff re-
ductions are summarized in Table 1. No-till systems, while exhibiting the
greatest reductions in soil loss, appear to be best suited to wanner areas
14
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TABLE 1. COMPARISONS OF SOIL LOSS AND CROP YIELDS BETWEEN CONSERVATION AND CONVENTIONAL TILLAGE SYSTEMS
SCS Land Conservation
Investigator Resource Region Tillage Method
Bulter (16)
Lanadale et al. (49)
Lanqdale et al. (49)
McGregor et al. (54)
McGregor et al . (54)
McGregor et al. (54)
Mannering et al . (51 )
:-'armr-ring et al. (51 )
Mannering et al . (51 )
Oschwald and Siemens (62)
Oschwald and Siemans (62)
Oschwald and Siemans (62)
Oschwald and Siemans (62)
Gard (?9)
Hard (29)
fii'or.jf (31)
AiiifMiiiya (3)
An-pniya (3)
Torster (25)
K
P
P
P
P
f
M
M
M
M
t"
M
M
M
M
B
M
M
M
till-plant
chisel plow
no-till
no-till
no-till
no-till
chisel plow
till-plant
no-till
disk chisel
no-till
disk chisel
no-till
no-till
no-till
mulch-ti 1 lage
till-plant
till-plant
no-till
Conventional
Tillage Soil
Soil Loss Loss
Crop (m tons/ha) (m tons/ha)
corn
corn
sorghum
soybeans-wheat
soybeans
corn
corn
corn
corn
corn
corn
soybeans
soybeans
wheat
corn
wheat
corn
soybeans
corn
_
12.1 64
2.86 71.2
1.8 17.5
2.5 17.5
5.2 17.5
-
-
-
-
-
-
-
2.7 26.0
0.09 4.9
58.0 13.4
-
-
-
% Change % Change
Loss Reduction in Yield
83
81
98
90 -10
86 0
71 0
94
60
85
89
91
71
85
90 -14
98 +73
77
60-90 +3
0
-10 to +10
-------
with well-drained soils where, in general, higher yields can be obtained than
under conventional tillage. Other conservation tillage systems can provide
optimal tradeoffs between sedimentation and production under cooler climates
and more poorly-drained soils. Figure 2 shows the SCS land resource regions
where adequate research has been done to establish conservation tillage as
a Best Management Practice for reducing sedimentation. Shown also are areas
where research is lacking but climate, soil, cropping and erosion conditions
would indicate that some form of conservation tillage is a BMP- Northern
regions such as K and L are included in this category with the qualification
that no-till systems may result in prohibitive yield reductions but that other
reduced-tillage systems should provide a more optimal balance between produc-
tion and water quality goals in these regions.
CONTOUR FARMING
Contouring works to reduce sediment losses by reducing the volume of
runoff by slowing water movement and allowing increased infiltration. It is
more effective in doing this on fields of moderate (<8%) slope which are free
of depressions and gullies. Water is also held on the field by contouring
when row crops are ridged and furrowed rather than "flat" planted (81). A
study conducted in west-central Iowa (67) measured a 55% reduction in runoff
volume from contoured plots. Since contouring reduces soil loss by increas-
ing infiltration, it would be expected to be more successful on permeable
soil rather than on soil of high clay content. Baver et al. (10) have shown
that this is generally the case. Various other studies (40) report reductions
in runoff volume in the range of 15 to 55% by contour farming depending on
type of crop and soil (40). Few data exist concerning the relationship be-
tween soil loss reduction and nutrient or pesticide reductions from contour
farming. Sediment reductions were found to be greater than nutrient reduc-
tions in one study using contoured continuous corn cropping in western Iowa
(2). This was a result of 1) higher nutrient concentrations in the runoff
relative to control fields between December and March presumably due to
leaching from stubble, and 2) the selective erosion of finer soil fractions
containing relatively more adsorbed nutrients from the contoured fields.
Wight et al. (86) used contour furrowing on semiarid Montana rangeland
and found significant increases in forage production with corresponding
decreases in rangeland erosion. A similar study (15) conducted in Colorado,
Wyoming and Montana concluded that contour furrowing is the most effective
treatment on medium and fine textured soils for conserving soil moisture
and reducing erosion. The practice helps to impede overland flow and reduce
flood peaks. Forage yields were increased by 118 and 136% in Montana and
Wyoming, respectively. The practice has not been widely adapted, however,
for economic reasons. The water storage capacity of the contoured furrows
decreases rapidly for the first five years after construction, stabilizing
after about nine years. In this time period, however, closer vegetative
cover can become established providing long-term erosion control benefits.
Crop yields from contour farming would be expected to increase relative
to non-contour farming under inadequate soil moisture conditions but be
16
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Figure 2. Land resource regions with literature references (///) and projections (:::) indicating
conservation tillage as a BMP component.
-------
reduced in areas with excess rainfall or poorly-drained soils. The USDA
reported (73) from 30 different studies a 17% average crop yield increase
from contouring. The practice is best used as part of a BMP system which
would generally include diversions or terraces to reduce length of slope.
Comparisons of soil loss, yields and surface runoff between contoured study
systems and noncontoured or terraced are summarized in Table 2. Figure 3
indicates regions where research has shown contour farming to be a BMP,
and areas where no conclusive data exist but where contouring would be ex-
pected to be a BMP. Region U is the only region where contouring would be
expected to have no value as a BMP based on typically wet soils and lack
of appreciable slopes.
COVER CROPS
The earlier discussion concerning the low sediment yields from forested
watersheds and the correlation between soil loss and amount of residue in
conservation tillage systems indicates that vegetative ground cover is an
important factor influencing erosion. Cover crops are being widely adopted
both as a sediment reducing and soil fertility building practice. In warmer
areas of the U.S. where legume crops can be established over winter, nitrogen
fertilizer requirements can be reduced significantly (57)- There is also
evidence that nonlegume cover crops may decrease nitrate leaching to ground
water as a result of plant uptake (76). Large-scale studies on Black Creek,
Indiana, watersheds (48) have clearly shown cover crops to reduce erosion.
A recent Missouri study (44) found rye cover crops to reduce soil loss by
over 95% versus conventional till continuous corn. Soil loss reductions
from the cover crop were equal to those using no-till practices.
The effect of winter cover crops on the yield of succeeding row crops
depends upon climate and soil moisture conditions (75). In warmer areas
under excessively wet. spring conditions, the cover crop can increase the
soil drying rate through transpiration allowing more timely planting and
hence increased yields. Counteracting the transpiration process, however,
is the fact that the cover crop will delay warming of the soil in spring
thus slowing soil drying by evaporation. This can be the overriding consider-
ation in northern regions of the U.S. where planting must be done as early as
possible to maximize yields. In addition the spring soil drying capability
of the cover crop depends on its growth stage. In northern regions little
fall cover crop growth will occur and thus the spring transpiration rate
will be less than in southern regions. For these reasons as shown in
Figure 4, cover crops are not recommended as a BMP in SCS regions F, K, L and
R. While cover crops will undoubtedly reduce soil losses in these areas,
production limitations suggest that other erosion-reducing practices such as
some forms of reduced tillage probably provide a more optimal balance between
production and water quality goals.
DIVERSIONS AND GRASSED WATERWAYS
Both of these structures are designed to facilitate the safe disposal
18
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TABLE 2. COMPARISONS OF SOIL LOSS, YIELDS AND RUNOFF BETWEEN CONTOURED AND UNCONTOURED FARMING AND BETWEEN CONTOURING AND
TERRACING
SCS Soil Loss
Land Resource Contouring
Investigator Region Practice (m tons/ha)
Hight et al. (86) G
Saxton and
Burwell et
Branson et
Alberts et
Spomer et
Spomer (67) M
al. (18) M
al. (15) D
al. (2) M
al. (71) M
Johnson and Moore (40) M
Stall ings
(73)
rangeland
contour furrowing
cropland
contouring
cropland 23.2
contouring
rangeland
contouring furrow
cropland 11.4
contouring
cropland 40.0
contouring
cropland
contouring
cropland
contouring
Soi 1 Loss % Reduction
Control % Reduction % Change in Runoff
(m tons/ha) in Soil Loss in Yield Volume
+ 165
55
1.1* -95*
+ 118
3.1* -73* - -42
3.4* -92* -67
15-55
+ 17
i'ontrol is level-terraced watersheds
-------
ro
CD
Figure 3. Land resource regions with literature references (///) and projections (:::) indicating
contouring as a BMP component.
-------
Figure 4. Land resource regions with literature references (///) and projections (:::) indicating
cover crops as a BMP component.
-------
of surface runoff. A search of the literature found no quantitative studies
conducted to determine the amount of sediment reduction accomplished by these
practices. Diversions generally serve to decrease slope length, and thus the
reduction in soil erosion can be estimated from the Universal Soil Loss Equation,
Grassed waterways are constructed in natural field depressions or at
field edges where runoff tends to concentrate. In this capacity they function
to prevent rill and gully formation. A secondary erosion-reducing effect of
grassed waterways is to filter sediment from runoff causing in-field deposition
of eroded soil. The sediment deposition capacity can be easily exceeded, how-
ever, as noted in the Black Creek, Indiana, study (48), in which case they are
quickly buried and rendered ineffective. The results of the Black Creek study
indicate that grassed waterways should be considered a measure to reduce
sedimentation in conjunction with other BMPs such as conservation tillage,
diversions and terraces.
Diversions and grassed waterways should have little effect on crop yields.
A small percentage of land is lost from production. Diversions, however, may
help remove excess water from fields allowing more timely planting with resul-
tant yield increases.
GRASSES AND LEGUMES IN ROTATION
Rotating row crops with sod crops inproves soil structure, organic mat-
ter content and infiltration relative to continuous row cropping. Adding a
sod crop in a three-year rotation has been shown to reduce soil loss by as
much as 80% relative to continuous corn (83). It is widely recognized that
closely sown sod crops result in significantly less runoff than row crops.
This effect is due primarily to an increase in soil porosity from the dense
root system of the sod crop. On very erosive marginal cropland, sod-row crop
rotations may be the only way to reduce erosion to tolerance limits. A
study by Adams (1) on a clay soil in Texas showed sorghum forage yields to
decrease 40% by the fourth year after clover (69). Cotton yields in the same
soils were significantly higher in rotations with a legume. Laflen and
Moldenhauer (46) determined soil losses and yields from various corn-soybean
rotations in plot studies. No differences were observed in soil losses between
corn-soybean, soybean-corn or corn-corn rotations; however, corn yields were
considerably higher for the soybean-corn sequence.
Kramer and Burwell (44) compared continuous corn rotations with a four-
year rotation of corn-wheat-pasture-pasture on a Missouri claypan soil. Corn
in both rotations was grown under conventional tillage. Results showed that
over 90% of the soil loss from the four-year rotation occurred during the
year the plots were in corn. In addition, the soil loss from the rotation
corn was only about 70% of that for the continuous corn even though both
were grown under conventional tillage. This would indicate that the rotations
of wheat and pasture have an erosion-reducing effect on soil structure.
Figure 5 shows regions where rotations which include grasses or legumes
are a confirmed or projected BMP. While such rotations give proven reductions
22
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Figure 5. Land resource regions with literature references (///) and projections (:::) indicating
rotations which include grasses or legumes as a BMP component.
-------
in soil loss, production of the row crop is lost during grass rotations so
that othererosion-reducing practices may provide a more optimal balance
between production capacity and water quality.
SEDIMENT BASINS
Sediment basins are designed to retain sediment which has already been
detached and transported from fields before it can enter streams or lakes.
Hence the benefits are strictly off-site and have no effects on crop yields
or farm operations. The most definitive work on the effectiveness of sediment
basins in an agricultural watershed was done in the Black Creek, Indiana
project (48). The most extensively monitored basin served a 209-ha drainage
area. Sediment depositions were measured by fathometer and with probes. The
basin was found to have a significant beneficial impact on water quality.
In the first two years of its operation, the basin collected over 1000 mt of
sediment or an average of 2.7 mt/ha/yr. for the entire watershed. Most of
this occurred from one greater than 50-year recurrence storm, the effects of
which overwhelmed many of the other BMP measures employed in the watershed.
Most importantly about 95% of the sediment trapped was composed of particles
less than 50 microns in diameter. This is a clear indication that sediment
ponds can effectively retain small particles which are the most difficult to
control by land treatment consistent with row crop agriculture (48).
Very little sediment was collected from low and moderate runoff events
showing that sediment basins have their greatest utility as a back-up measure
for severe storm events. If not used in conjunction with other BMPs, such
basins will receive an excessive amount of sediment even from lesser intensity
storm events. The larger the sediment load the sooner the basin will require
difficult dredging in order to remain effective.
STREAM CHANNEL STABILIZATION
In the Black Creek study (48) it was determined that streambank
erosion was responsible for less than five percent of the total sediment
entering the waterways. In other areas, perhaps as a result of upstream
erosion control practices, this percentage may often be larger; however, the
Black Creek results make stream channel stabilization measures very question-
able as a general BMP at the present time.
Erosion control measures which decrease soil loss to a greater extent
than runoff volume can increase downstream channel erosion and instability (53).
The reason for this is that the erosive capacity of water decreases as the
sediment concentration increases. Thus as stream sediment levels are reduced
by upland control measures, more erosion and undercutting of streambanks and
channel bottoms tends to occur. Since it is highly unlikely that upstream
sediment control measures will reduce sediment loads below the natural con-
ditions under which stream channel regimes were formed, upland control measures
will probably only remove channel-deposited sediment to the extent of returning
the channels to natural gradients and cross-sections.
Myers and Ulmer (60) have presented design criteria for streambank
24
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stabilization measures in Mississippi. These include slotted board fencing,
concrete jacks and loose stone riprap. The authors note that extensive deepen-
ing of channels and souring of streambanks are prevalent in this area from the
enlargement and straightening of channels which allow higher flows to enter
and move through channel systems at increased velocities.
Conditions which may occasionally require protective measures include:
1. Bare, nearly vertical, unprotected bank
2. Silt bar buildup on the inside or immediately downstream of
a curve
3. Channel bank sloughing on straight sections and curves
4. Rapid loss of streambank on the outside of the channel
curve (60)
Standard concrete jacks consist of three long concrete beams which are bolted
together at their midpoints. They are used to preserve or establish a desired
channel alignment. A row of jacks on each side of the channel can be used
to confine meander and reestablish bank stability. These devices increase
flow resistance and thus reduce flow velocities. Silt deposition then occurs
partially covering the jacks allowing vegetation to be established and further
protect the banks. Little information exists on the long-term effectiveness
of this practice in use.
Slotted board fencing is designed to ensure reduced stream velocity
against the banks. It is generally stronger than concrete jacks, and thus
can be constructed on sharper curves and larger streams. Rock riprap is the
oldest and most widely used streambank protection measure (60). The stream-
bank is sloped to a 2:1 slope or less for maximum effectiveness.
Before any of these measures are employed however, a thorough knowledge
of the original condition and regime of the stream channel must be available
to indicate what actual changes have resulted from upstream agricultural
activities.
Very little research has been done on the effects of streambank stabil-
zation on water quality. In the Black Creek study (48), various bank mulch
materials and slopes were compared for effectiveness in preventing streambank
erosion. Stone, straw and wood chip bank mulches were all effective in
controlling erosion and helping to establish vegetative cover. Of the three,
stone mulch was concluded to be superior because it was much less easily washed
away during high water flow. Vegetative cover establishment was most successful
where bank slopes were 2:1 or flatter. Estimates of the contribution of
streambank or channel erosion to the total stream sediment load should be made
before these measures are employed. As suggested in the above discussion,
present information indicates that stream bank and channel stabilization prac-
tices are not an appropriate starting point for controlling sediment in most
cases. However the problem may need to be increasingly addressed in the future
25
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on watersheds where sediment loading is significantly reduced by the implementa-
tion of upland sediment control practices.
TERRACES
Terraces are designed to reduce erosion rather than runoff volume. They
reduce erosion by decreasing slope length and steepness thereby reducing the
transport of detached soil particles. Terraces are of two general types:
graded terraces which divert water to a grassed waterway or similar drainage,
and level terraces which hold water on the field increasing infiltration. In
a study in the southern Mississippi Valley (19) soil loss reductions of fifty
percent from terracing of highly erodible loamy soils were observed. Richardson
(65) compared runoff volumes, soil loss and tillage efficiency between a
graded-furrow and terrace cropping system on Texas clay soil of uniform two to
three percent slope. Runoff was significantly less from the graded-furrow
watershed, although runoff volumes for both systems were less than nongraded-
furrow, nonterraced land. This was observed to be due to a more uniform
distribution of excess water. Soil losses from both systems was approximately
equal, but tillage efficiency was 21% better on the graded-furrow land though
this may have been partially due to the atypically uniform slope of the study
area.
Several studies in western Iowa, however, have found level terracing to
be more effective than contour farming in reducing runoff volumes and soil loss.
Two studies (2, 18) found soil losses to be over twenty times higher on con-
toured versus terraced corn cropland on these steeply sloping loess soils.
Similar though less dramatic differences were observed by Spomer et al. (72).
In all cases, however, contouring resulted in substantial reductions in erosion
relative to uncontoured cropland.
A comparison of the effectiveness of conservation tillage systems, contour
farming and terraces individually, and in various combinations for reducing
erosion and sediment yield was recently conducted on the steeply sloping, silt
loam wheat cropland of north-central Oregon (30). Terraces were found to be
less effective than the conservation tillage system (chisel plowing) and
contouring in reducing erosion, but were actually more effective in reducing
sediment delivery to streams since most eroded soil was redeposited within the
terraces. Sites which combined terraces with reduced tillage or contouring
exhibited no measurable erosion indicating the complementary nature of these
practices for reducing soil detachment and transport.
A 98% reduction of annual soil loss was observed by Saxton and Spomer
(67) when terracing was applied to highly erodible loess soils in Iowa. By
holding soil on the land, terraces should also reduce losses of strongly
adsorbed nutrients and pesticides such as phosphorus and paraquat (68).
Crop yields often decrease immediately following construction of terraces be-
cause the construction disturbs topsoil (69, 2). In dry areas, however, yields
are usually higher eventually since terraces help make more efficient use of
water. Also terraces are commonly used in drier areas with deep loess soils
which minimizes the effects of topsoil disturbance (71). Early studies
26
-------
in such areas showed substantial crop yield increases relative to nonterraced
land (73).
Research data on the effects of terracing on soil loss, crop yields and
runoff volume are summarized in Table 3. As the research described above
indicates, there is considerable variability in the relative effectiveness of
terraces in maximizing yields and sediment reductions between geographic areas.
Crop yields may be initially decreased in areas with less developed topsoils
due to soil disturbance during construction. In deep loess soils this effect
is less important. The research indicates that terraces are better adapted
to drier areas such as the western Corn Belt and central Oregon and Washington
where they facilitate more efficient water use by allowing increased percola-
tion. In the more humid areas of the Northeast, Middle Atlantic, and Pacific
Northwest they may, however, increase nutrient leaching to ground water,
particularly in the absence of good fertilizer management systems.
These geographic considerations are summarized in Figure 6. In several
of the regions where terracing is shown to be a proven or projected BMP, it
must be remembered that terrace construction costs are high and comparable
soil loss reductions can be achieved with alternative practices. In many
instances terracing may be a less cost-effective BMP than other practices such
as conservation tillage and contouring.
FILTER STRIPS
Filter strips are a relatively new practice for soil and water conser-
vation and little field research work has been specifically conducted concern-
ing their effectiveness. Karr and Schlosser (42) found that vegetative filters
could effectively filter sediment from both sheet and shallow channel runoff
flow. Variables which affect their utility include filter width, slope, type
of vegetation, sediment size distribution, degree of filter submergence, run-
off application rate and initial sediment concentration.
A study of logging impacts on stream biota in northern California (23)
compared invertebrate diversities for streams with and without buffer strips.
In logged areas with no streamside filter strips, significant changes and re-
duced diversity of invertebrate communities was observed; while for streams with
thirty meter buffer strips, invertebrate communities and physical stream
characteristics were unaffected.
Generally filter strips of four to five meters width are sufficient for
cropland of less than five percent slope. Widths should be increased for
steeper slopes (81). Filter strips are most effective in conjunction with
erosion-reducing BMPs since their sediment-retaining capacity is limited and
can be easily exceeded under high sediment inputs rendering them ineffective.
IRRIGATION
Sediment losses from irrigated farmland necessitate special types of
sediment control practices. In most cases annual rainfall is small and soil
27
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TABLE 3. COMPARISONS OF SOIL LOSS, YIELDS AND RUNOFF BETWEEN TERRACED AND UNTERRACED CROPPING
ro
oo
Investigator
George (31)
Carter et al. (19)
Saxton and Spomer (67)
Spomer et al. (71)
Spomer et al. (72)
Alberts et al. (2)
Burwell et al. (17)
SCS
Region
B
P
M
M
M
M
M
Crop
wheat
corn
corn
corn
corn
corn
corn
Terraced
Soi 1 Loss
(m tons/ha)
22.4
-
-
2.2
3.4
3.1
1.1
Unterraced
Soil Loss
(m tons/ha)
60.5
-
-
56
40.0
11.4
23.2
% Reduction % Change
in Soil Loss in Yield
63
50
98
95 -4
92
73
95
% Reduction
In Runoff
Volume
-
-
-
-
67
42
73
-------
Figure 6. Land resource regions with literature references (///) and projections (:::) indicating
terraces as a BMP component.
-------
loss occurs primarily as a result of applied water. Irrigation systems can
be divided into four general types: 1) sprinkler systems which include
stationary, side roll and center pivot systems, 2) flood systems which are
generally divided into open and border flooding types, 3) drop irrigation
systems which are used primarily on orchards but are becoming increasingly
popular for other crops because of their efficient use of water, and 4)
furrow systems which require at least a small amount of slope. Among the
variables affecting erosion on irrigated land are soil type, slope, crop,
suspended solids content of irrigation waters, type of irrigation system
and efficiency of water management in terms of irrigation rates and timing.
Studies on furrow-irrigated Idaho cropland (13) found that erosion
occurred primarily because tailwater ditches were deeper than the furrow
streams, thus causing small eroding waterfalls to move up the furrows from
the sownhill edge of the field. After several years the irrigated fields
assumed a convex shape. Soil loss also occurred when furrow streams were
larger than necessary. The results indicated that soil loss from irrigated
cropland could be reduced by 1) keeping the flow to the furrow only large
enough to sustain to the end of the field, 2) decreasing the depth difference
between furrows and tailwater ditches, and 3) planting vegetative filter strips
on the lower end of the fields to filter out transported sediment before
discharge to return flow. Present work at Rock Creek, Idaho, RCWP is
investigating irrigation management practices further and should provide
valuable information on the effectiveness of these practices on a larger scale.
An ongoing MIP project in the South Yakima watershed, Washington, has similar
goals.
SUMMARY
From the extensive research which has been done on the effectiveness
of various sediment control practices, many conclusions can be made. In this
section these are divided into "hard" and "soft" conclusions. "Hard"
conclusions are those which are based on extensive nonconflicting data in a
specific region. "Soft" conclusions carry less certainty and are based on
less data or where there is some conflict between studies and also for
regions where tentative conclusions can be projected based on research data
in similar regions.
Hard Conclusions
1. Conservation tillage systems reduce soil erosion (60-99 percent)
relative to conventional tillage regardless of geographic area,
soil type, slope, climate or type of crop.
2. All other factors being equal, the extent of erosion reduction
is a function of the amount of tillage performed. No-till
systems will reduce erosion and sediment production more than
reduced-tillage systems such as chisel plowing, which in turn
will give reductions relative to moldboard plowing.
3. Conservation tillage systems will generally give higher
30
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crop yields relative to conventional tillage systems on
well-drained soils or in dry years, while this trend will
be reversed for poorly-drained soils or in excessively
wet years.
4. No-till systems are better adapted to warmer climates
since in the cooler regions of the U.S. delayed soil
warming and drying as a result of previous crop stubble may
often interfere with timely planting causing yield reductions.
Other reduced tillage systems will generally provide a better
optimization of production and sediment reduction in these regions.
5. Contour farming will significantly (50-90 percent) reduce soil
loss relative to noncontouring on sloping cropland. Runoff
volume level is also decreased.
6. On deep loess soils in the western Corn Belt, level terraces
are more effective than contouring in reducing soil loss and
maximizing yields.
7. Cover crops can be considered a BMP for all topographies and
soil types in warmer climates but have limited applicability
in colder regions due to the difficulty of sufficient
establishment before winter freeze.
8. Sod-row crop rotations can reduce erosion 80 percent in sod
crop years and provide carryover effects when row crops are
planted.
9. Terraces are effective in reducing erosion (50-99 percent
reductions) but construction costs are high.
10. Initial crop yield reductions may occur with terraces due
to disruption and compaction of topsoil during construction.
11. Because sediment control measures can act either by reducing
on-field erosion or sediment delivery, combinations of the two
types may provide the best control strategy.
12. Although pesticide costs increase, the total costs of production
usually decline with use of conservation tillage systems,
primarily because of savings in labor and fuel costs.
13. The overall profitability of conservation tillage depends
primarily on the effects on yields on the conservation tillage
system. When yields are affected not at all or only slightly,
conservation tillage systems are generally more profitable
and contribute to water quality improvement.
31
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Soft Conclusions
1. Dissolved nutrient and pesticide concentrations from runoff
reducing practices will generally be higher than from
conventional tillage, but the total amount of nutrients and
pesticides lost will generally be less due to the decreases
in soil loss.
2. Sediment basins will retain sediment fines which are the
most difficult to control by erosion control measures.
3. Stone mulches or riprap are more effective than other
materials in preventing streambank erosion.
4. Some amount of trade-off between sedimentation and associated
nutrient transport, and leaching of nutrients to ground water
may be inherent in practices such as conservation tillage,
contouring and terraces which reduce erosion but increase
infiltration and percolation.
32
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SECTION 5
ECONOMIC ASPECTS OF BMP'S FOR SEDIMENT CONTROL
1
Economics of BMP's for sediment control can be viewed from three perspec-
tives: (1) costs of installing and maintaining the BMP's, (2) effects on net
farm income, and (3) cost-effectiveness. These three perspectives are briefly
discussed here and some readily available information presented.
COSTS OF INSTALLING AND MAINTAINING BMP'S
Costs of installing and maintaining BMP's should be developed for each
project area since these costs can vary considerably depending upon different
local and site conditions. However, some BMP's in general are less costly
than others. Costs developed by the Soil Conservation Service in North
Carolina depict the differences among practices in installation costs, life
spans, annual operating and maintenance (O&M) costs and total annual cost
(Table 4). These data indicate such practices as crop residue, filter strips.
TABLE 4. COSTS OF CONSERVATION PRACTICES, NORTH CAROLINA, 1980
Practice
Conservation Tillage
Contour Farming
Cover Crop
Critical Area Pltg.
Crop Residue
Debris Basin
(Sediment Pond)
Diversion
Filter Strips
Grassed Waterway
Grasses & Legumes
in Rotation
Stripcropping
Terraces
Cost Per I/
Unit
$ 10/Ac
0/Ac
15/Ac
$ 900/Ac
5/Ac
5,000/Ea
.60/LF
.17/LF
1,200/Ac
5/Ac
.2C/LF
Unit Per
Acre
1
1
i
-
i
-
200 Ft.
175 Ft.
.06 Ac
-
1
400 LF
Cost Per
Acre
$10.00
0
15.00
-
5.00
-
120.00
30.00
72.00
175.00
5.00
80.00
Life
Span
1
1
1
25
1
25
10
10
10
3
10
10
Of
Annual
O&M Cost
_
3
3
5
r
5
-
I
5
Total
An n u a 1
Cost 2/
$11.00
0
16.00
111.00
5.50
618.00
24.00
6.00
14.00
6 8. CO
1.25
16.00
I/ Price Base 1980, Raleigh, N.C.
2J Based en 3" Interest Rate
Adopted from: Soil Conservation Service, USDA, "Benefits/Costs of Sol"! and /.-ate*
Conservation Practices for Erosion and Sediment Control," Da1eicn
June 1980.
N.C.,
section was prepared by Dr. L.A. Christensen and Patricia E. Norris, Economic
Research Service, U.S. Department of Agriculture (USDA), Athens, Georgia.
33
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strip cropping and conservation tillage are less costly than sediment ponds,
diversions, and terraces.
EFFECT ON NET FARM INCOME
The BMP could be a cost or benefit to the farmer depending upon the
effect on net farm income. This effect depends on (1) the impact of the prac-
tice on farm production and hence sales, (2) the changes in production inputs
and associated costs, and (3) the farmer's proportion of installation costs.
The impact on production would come mostly from changes in cropping pat-
tern and short term yields, but with lower soil loss, long term improvements
in soil productivity would also be expected. Also some practices such as
terraces and grassed waterways may also remove a small surface area from
production on the field.
Effects of a practice on short term yields depend heavily on soil and
moisture conditions and pest control. These things considered, yield effects
of some practices have been summarized as follows (5):
- Crop yields with conservation tillage are roughly equal to yields from
conventional tillage, and were often better during dry years.
- Crop yields with contour farming may be higher under dry conditions, and
lower under excess moisture or poorly drained soil conditions.
- Crop yields with grasses and legumes in rotation will likely be higher.
Production inputs and costs associated with various BMP's can differ
substantially from those under conventional tillage (Table 5). Terraces re-
quire additional construction and maintenance costs. Rotations and strip
cropping reduce the need for pesticides. Conservation tillage increases use
of pesticides (herbacides), but will reduce labor and equipment costs (unless
purchase of additional machinery is involved). Contour farming can increase
equipment and labor costs, particularly if smaller equipment must be purchased
and used.
Energy in the form of fuel is also an input which varies according to the
type of BMP used. Fuel requirements for various rotations and tillage systems
have been developed at Iowa State University (Table 6). These figures show a
decrease of about 50 percent in the use of fuel between fall-moldboarH and
no-till systems for both continuous corn and a corn-beans rotation on a loam
soil. The actual decreases are 3.8 gallons for the continuous corn and 2.75
gallons for the corn-beans rotation. Keep in mind that these figures will
vary with the soil types in the fields where practices are applied.
Cost comparisons made by Crosson between conservation tillage and
conventional tillage in 1979 for selected crops indicated total costs were
lower for conservation tillage (1). Labor, machinery, and fuel costs were
lower with conservation tillage, but pesticide costs were higher. For example,
total costs for conservation tillage compared to conventional tillage ranged
34
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TABLE 5. TYPICAL CHANGE IN VARIABLE COSTS ASSOCIATED WITH IMPLEMENTATION OF
BMP'S AS COMPARED TO CONVENTIONALLY TILLED CONTINUOUS CORN GRAIN
BMP
N Fertilizer
Pesticides
Equipment
Labor
Construction
Maintenance
Other
(Dollars/Acre)
Conservation
Tillage
Rotation I/
Contouring
Diversion 2/
Strip
Cropping
Terrace 3/
0
-10.40
0
-.80
-10.40
0
+9.60
-12.00
0
-1.20
-12.00
0
-4.00
-6.00
+2.40
+ 1.20
-4.40
+2.40
-3.60
40
+ 1.20
+ .80
+ .80
+ 1.20
0
.80
0
+6.00
.80
+40.40
_!/ Six year rotation with 3 years corn, one year oats, two years hay. Values are
average for the six years.
2/ One diversion ditch across center of 120 m slope, with contouring. Construction
costs amortized over 45 years.
3/ Terrace system had a terrace at 30 m, 60 m, and 90 m, respectively, above lower
edge of field with 120 m slope, with contouring. Construction costs are amortized
over 45 years.
Source: (SCS-USDA, Raleigh, N.C.)
TABLE 6. FUEL REQUIREMENTS FOR VARIOUS ROTATIONS AND TILLAGE SYSTEMS
Rotation
Continuous corn, moldboard, fall
Corn-beans, moldboard, fall
Continuous corn, chisel, fall
Corn-beans, chisel, fall
Continuous corn, chisel, spring
Corn-beans, disk, spring
Corn-beans, double chisel, fall
Corn-meadow, moldboard, fall
Corn-meadow, chisel, fall
Corn-meadow, chisel, spring
Continuous corn, no-till
Corn-beans, no-till
Light
6.28
4.57
5.96
5.89
5.96
4.46
4.61
2.70
2.99
2.99
3.00
2.44
Gallons per Acre
Medium I/
7.15
5.54
6.95
5.69
6.95
5.04
5.44
3.11
3.38
3.38
3.35
2.79
Heavy
8.40
5.95
7.10
5.98
7.10
4.88
6.06
3.65
3.79
3.79
3.61
3.05
\j These figures are for a Central Iowa loam soil. The "light" and "heavy" column
entries represent adjustments to these basic figures to reflect changes in
fuel consumption. For contour tillage, these figures are inflated by 5 percent.
Source: U.S. Dept. of Agriculture, Cooperative Extension Service, Iowa State
University, "Fuel Requirements for Field Operations," prepared by
George E. Ayres, November. 1976.
35
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from 86 percent for wheat to 95 percent for cotton. Labor was 50 percent
lower for all crops studied. Annual machinery costs were assumed to be $5
an acre less with conservation tillage, fuel consumption two gallons per
acre less, and pesticide costs were one-third more.
A Wisconsin study found a 3 percent increase in net returns when chisel
plowing (a form of conservation tillage) replaces conventional tillage, as-
suming equal yields with each practice (3). However, a 10 percent decrease in
yields was assumed when comparing no-till to conventional till, resulting in
a 13 percent decrease in net returns. With equal yields, there was a 14
percent increase in net returns. A Tennessee study found a 13-14 percent re-
duction in corn and soybean production costs with no-till (2). Thus, if
yields are assumed to be the same, higher net returns result for no-till farming.
A study in Missouri showed net returns from continuous corn were 13 per-
cent greater with minimum tillage and 2.4 percent greater with zero tillage^4).
For continuous soybeans, net returns were 22 percent greater with minimum til-
lage compared to conventional tillage.
COST-EFFECTIVENESS
Cost-effectiveness analysis of various practices requires matching up
cost data with measures Of the reduction in sediment delivery. What is included
on the cost side depends mostly on the availability of information. Ideally
for most analyses, the cost side would include both government (cost share,
technical assistance, education and information, and administrative costs)
and net private costs (net effects on farm income).
A system for estimating and displaying costs of soil conservation prac-
tices has been developed and applied to soils in Missouri (4). Some 50
practice combinations for corn production were ranked by the cost per ton of
reduced erosion. For example, minimum tillage alone would reduce erosion from
40.4 to 15.5 tons per acre at a savings of $3.50 per acre compared to conven-
tional practices.
A 1978 ACP Evaluation relating soil savings and costs for a variety of
conservation practices in the Southern Coastal Plains found that the cost per
ton of soil saved ranged from $0.10 with vegetative cover on critical areas to
$4.21 per ton for cropland protective cover (5).
REFERENCES
1. Crosson, Pierre, "Conservation Tillage and Conventional Tillage: A Com-
parative Assessment," Soil Conservation Society of America, 1981.
2. Hudson, Estel, "Economic Aspects of No-Till Farming," Southeast Erosion
Control and Water Quality Workshop, Nashville, Tennessee, November 1980.
3. Pollard, Richard VI., et al., "Farmers' Experience with Conservation Tillage:
A Wisconsin Survey," Journal of Soil and Water Conservation, September-
October 1979.
36
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4. Raitt, Daryll D., "A Computerized System for Estimating and Displaying
Shortrun Costs of Soil Conservation Practices," USDA-ERS Technical
Bulletin 1659, August 1981.
5. Soil Conservation Service, USDA, "Benefits/Costs of Soil and Water Conser-
vation Practices for Erosion and Sediment Control," Raleigh, N.C., June 1980.
37
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SECTION 6
RESEARCH NEEDS
From the previous discussion it is obvious that a great deal is^known
about the effectiveness of various proposed BMPs for controlling sediment.
There is no doubt that each of the individual BMPs discussed above can
reduce sediment either on the field or prior to entering waterways under
certain conditions. However, additional knowledge to most effectively address
the sedimentation issue on a national scale is needed in three major areas:
1. While much definitive information has been gathered on the
soil erosion effects of individual management practices,
considerably less is quantitatively known about the effective-
ness of combined systems of BMPs for controlling sediment.
2. Actual experimental information on sediment delivery ratios
is very limited even within fields and on small watersheds.
This means that we have limited knowledge of what level of
treatment will have a given sediment reduction in larger
watersheds and even more importantly, which areas should be
treated and to what extent for the most cost-effective
sediment control.
3. Most importantly, almost no information presently exists
on the actual water quality effects of the various proposed
BMPs. Studies have centered on determining erosion
reductions attributable to BMPs rather than on the resultant
downstream water quality changes. We have very little
information about how water quality in a large scale, real
world, agricultural watershed will change in response to
implementation of a given set of sediment control measures
or about the time-frame within which these expected
improvements may occur.
38
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SECTION 7
CURRENT RESEARCH
This section is intended to describe some of the more important on-going
research on sediment control practices and to describe how this research will
help to answer the above questions.
The most comprehensive study which has been completed to date is the
Black Creek, Indiana Section 108astudy (1972-1977). This pioneering effort
demonstrated that an overall improvement in sediment-related water quality could
be realized for a large scale system (5374 hectares) as a result of imple-
menting sediment-control BMPs. Considerable quantitative water quality
information relating to the use of specific practices such as conservation
tillage, grassed waterways, diversions and sediment basins was obtained.
Equally important was knowledge gained on how to best conduct such large-
scale studies in terms of successfully securing an adequate level of farmer
participation, selecting areas in most urgent need of treatment, and designing
the research to minimize confounding variables so that clear cause-effect
relationships between B.MPs and water quality could be distinguished. Several
lessons were learned that can be used to advantage in subsequent projects.
Most significant of these was that little attention was given to critical
area identification with the result that almost the entire watershed was
treated without regard to the accessibility of the sources to waterways. This
resulted in more extensive treatment at greater cost than needed for a given
level of water quality improvement. Also nearly thirty percent of the monetary
effort was directed to streambank stabilization measures while it was subse-
quently learned that this source contributed less than five percent of the
sediment entering the creek. The water quality monitoring effort is continuing
at Black Creek to determine the long-term effects of the BMP implementation and
to evaluate their performance under infrequent, high-intensity storm condi-
tions which have been shown to cause a major proportion of sediment production.
Present large-scale research efforts are being conducted under several
programs including the Rural Clean Water Program (RCWP), the Model Implementa-
tion Program (MIP), and Agricultural Control Projects (ACP), as well as several
special projects. The MIP projects were initiated in 1977 to continue through
1981. Among those that are concentrating on sediment control as a major pri-
ority are the Indiana Heartland MIP; Maple Creek, Nebraska MIP; Lake Herman,
South Dakota MIP; and the Yakima Sulfur Creek, Washington MIP.
The Indiana Heartland MIP located near Indianapolis is a highly agri-
cultural watershed in which over 99^ of sediment loss is estimated to originate
from cropland. Sediment control practices being implemented in the 65,260 hectare
39
-------
study area include permanent vegetative cover, terraces, conservation tillage
systems, sediment basins, and grassed waterways.
In the Maple Creek, Nebraska watershed on the western edge of the Corn
Belt, soil erosion loss has been very high concomitant with the introduction
of intensive row cropping on steeply sloping land. Sediment control in this
MIP project is being' focused on terracing, contour farming and use of sediment
basins. Presently soil loss in the study area averages over 49 mt/ha.
The Lake Herman, South Dakota MIP is studying whether the eutrophication
process can be reversed and the time frame in which this can be accomplished
following BMP implementation. BMP systems for sediment reduction include
terraces, sediment basins and cover crops. Continued water quality monitoring
in these projects will provide data to evaluate BMP effectiveness.
The projects under the Rural Clean Water Program (RCWP), initiated
in 1979, are mostly in the operational phase and it is expected that BMP
implementation and water quality monitoring will continue through the entire
decade. These projects represent a major effort towards determining the most
cost-effective means of achieving given agricultural water pollution control
goals. These efforts should go far towards filling information gaps, particu-
larly concerning water quality effects of BMPs in large, agriculture-intensive
watersheds, and should point the direction for optimizing agricultural pro-
duction and water quality goals into the next century. Among the RCWP projects
with sediment control as a primary goal are: Lake Tholocco, Alabama; Prairie
Rose Lake, Iowa; Double Pipe Creek, Maryland; Reelfoot Lake, Tennessee; Oakwood-
Lake Poinsett, South Dakota; and Conestoga Headwaters, Pennsylvania.
The Lake Tholocco, Alabama RCWP is designed to control both sediment
and animal waste sources. BMP systems being implemented for sediment control
consist of combinations of terraces, grassed waterways, conservation tillage
systems, filter strips and sediment basins. The Prairie Rose Lake, Iowa
project is located in the hilly western Iowa Corn Belt and experiences an
average soil loss of 67 mt/ha. One goal of the project is to reduce sediment
loading to the lake by sixty percent emphasizing the use of terraces, water-
way systems, conservation tillage systems, and sediment retention basins. In
the Double Pipe Creek, Maryland project excessive suspended sediment concen-
trations following heavy storms have increasingly hindered drinking water
treatment. Sediment control systems being implemented in the 49,000 hectare
study area include strip cropping systems, diversions, grassed waterways,
conservation tillage systems, sediment basins and streambank protection
measures.
The Reelfoot Lake, Tennessee project represents an area with perhaps
the greatest soil erosion problems in the U.S. Reversing this process and
restoring the quality of Reelfoot Lake may be an impossible challenge, but the
project should establish the effectiveness of BMP systems under extreme
erosion conditions. Soil loss from cropland in the study area averages 114
mt/ha. Nearly all proposed sediment Best Management Practices are being tried
in the project, but those being implemented most widely include diversions,
filter strips, land-use conversion, pasture and hayland planting, contour
40
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farming and terraces. The goal is a significant reduction in sediment loading
to the lake. The project will also determine to what extent nutrient loadings
are reduced by controlling sediment.
The Oakwood-Lake Poinsett, South Dakota and Conestoga Headwaters,
Pennsylvania RCWPs are both primarily aimed at controlling nutrient inputs
to waterways by reducing sediment inputs. In the Conestoga Headwaters project
it is suspected that the use of some sediment-reducing practices such as ter-
races and conservation tillage may increase groundwater contamination. The
study should document the relationship between ground and surface water
agricultural pollution.
Several other large-scale projects with sediment control as a major
goal are underway nationwide. Among these are Saginaw Bay, Michigan ACP
project (108,000 hectares); Little River, Connecticut ACP; Allen and Defiance
County, Ohio EDA 108 project which is studying the effects of conservation
tillage on soil loss and water quality; the Chowan River Agricultural 208
Project in eastern North Carolina; and the Washington County, Wisconsin EPA
108 project.
The results of these projects should each contribute to an understanding
of how best to control sedimentation under varying conditions of climate,
soil type, topography and cropping pattern. Taken together they should greatly
enhance present knowledge about many aspects of sediment-related water pol-
lution including:
1. The overall effects of practices which reduce runoff and
increase infiltration to ground water systems, and how to
maintain the optimal balance between ground and surface
water quality in situations where both are a problem.
Projects focusing on ground water such as the Conestoga
Headwaters RCWP and Long Pine Creek, Nebraska, should
be helpful in answering these questions.
2. Determining the most critical areas in a watershed, i.e.,
those areas making the largest sediment contribution
to the waterways. The selection of these critical areas
depends both upon the magnitude of these sources and
their respective sediment delivery ratios. Increased
understanding of critical areas is essential, since
from the research already completed it is obvious that
treatment of all sediment-producing sources is not
economically or physically practical. Thus, allocating
resources towards agricultural pollution in the most
efficient and cost-effective manner will be contingent
on clear understanding of the relative sediment con-
tribution of various nonpoint sources.
3. The extent and time frame of actual water quality
41
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3. (continued)
improvements from erosion control and sediment reducing
practices.
4. The water quality effects of combinations or systems of
practices in large-scale, real world watersheds containing
agricultural as well as nonagricultural sources.
A final point to be emphasized in relation to the present work is
that while most of these studies (in particular the RCWP projects) may
take several years or even a decade to complete, the magnitude, urgency
and implementation lag time of the sediment related agricultural pollution
problem require that the information gained from these studies be translated
into agricultural management policy in an efficient and rapid manner. The
magnitude of the sediment problem with its degrading effects on both the
nation's land and productivity and water quality dictate that we cannot wait
a decade for conclusive and final study results before confronting the
problem with a comprehensive, national strategy based on our state-of-the-art
knowledge while acknowledging that adjustments in this strategy may be needed
based on increased information.
42
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REFERENCES
1. Adams, J.E., "Residual Effect of Crop Rotations on Water Intake, Soil
Loss, and Sorghum Yield," Agronomy Journal, 66:299-304, 1974.
2. Alberts, E.E., Schuman, G.E. and R. E. Burwell, "Seasonal Runoff Losses of
Nitrogen and Phosphorus from Missouri Valley Loess Watersheds,"
Journal of Environmental Quality, 7(2):203-207, 1978.
3. Amemiya, M., "Conservation Tillage in the Western Corn Belt," Journal of
Soil and Water Conservation, 32:29-36, 1977.
4. Amemiya, M., "Tillage-Soil Water Relations of Corn as Influenced by Weather,1
Agronomy Journal, 67:534-537, 1975.
5. American Society of Civil Engineering, "Quality Aspects of Agricultural
Runoff and Drainage," In: Proceedings by the Task Committee on
Agricultural Runoff and Drainage of the Water Quality of the
Irrigation and Drainage Division. Irrigation and Drainage Division,
American Society of Civil Engineers, Vol. 103, No. IR4, pp. 475-495,
1977.
6. Baker, J.L. and H.P. Johnson, "Evaluating the Effectiveness of BMP's via
Field Studies, National Conference on Agricultural Management and
Water Quality," In Press, 1981.
7. Baker, J.L., Laflen, J.M. and H.P. Johnson, "Effects of Tillage Systems on
Runoff Losses of Pesticides - A Rainfall Study," Transactions of the
ASAE, 21, pp. 886-892, 1978.
8. Barisas, S.G., Baker, J.L., Johnson, H.P. and J.M. Laflen, "Effect of
Tillage Systems on Runoff Losses of Nutrients," Paper No. 75-2304,
ASAE, St. Joseph, Mich., 1975.
9. Barisas, S.G., Baker, J.L., Johnson, H.P. and J.M. Laflen, "Effect of
Tillage Systems on Runoff Losses of Nutrients, A Rainfall Simulation
Study," Transactions of the ASAE, 21:893-897, 1978.
10. Baver, L.D., Garner, W.H. and W.R. Gardner, Soil Physics, 4th ed. John
Wiley and Sons, Inc., New York, 1972.
11. Beasley, R.B., "Erosion and Sediment Pollution Control," Iowa State
University Press, Ames, Iowa, 1972.
12. Bennett, O.L., Mathias, E.L. and C.B. Sperew, "Double Cropping for Hay and
No-Tillage Corn Production as Affected by Sod Species with Rates of
Atrazine and Nitrogen," Agronomy Journal, 68:250-254,1976.
13. Berg, R.D. and D.L. Carter, "Furrow Erosion and Sediment Losses on Irrigated
Cropland," Journal of Soil and Water Conservation, 35:267-270, 1980.
14. Blevins, R.L., Thomas, G.W. and P.L. Cornelius, "Influence of No-Tillage and
Nitrogen Fertilization of Certain Soil Properties After 5 Years of
Continuous Corn," Agronomy Journal, 69:383-386, 1977.
43
-------
15. Branson, F.A., Miller, R.F. and I.S. McQueen, "Contour Furrowing, Pitting,
and Ripping on Rangelands of the Western United States, Journal of
Range Management, 19(4): 182- f90, 1966.
16. Butler, R., "The Effect of Tillage Practices on Soil and Water Losses from
Croften Soil," M.S. Thesis, Univ. Nebr., Lincoln, 1968.
17. Bur-well, R.L., Sloneker, L.L. and W.W. Nelson, "Tillage Influences Water
Intake," Journal of Soil and Water Conservation, 23:185-188, 1968.
18. Burwell, R.E. , Schuman, G.E., Piest, R.F., Spomer, R.G. and T.M. McCalla,
"Quality of Water Discharged from Two Agricultural Watersheds in
Southwestern Iowa," Water Resources Research, 10(2):359-365, 1974.
19. Carter, C.E., Doty, C.W. and B.R. Carrel! , "Runoff and Erosion Character-
istics of the Brown Loam Soils," Agricultural Engineering, 49:296-301,
1968.
20. Dorich, R.A. and D.W. Nelson, "Algal Availability of Soluble and Sediment
Phosphorus in Drainage Water of the Black Creek Watershed," In:
Voluntary and Regulatory Approaches for Nonpoint Source PolTuTion
Control. R.G. Christensen and CJJ" Uilson. Eds.. EPA-305/9-76-001. pp.
179-180, 1978.
21. Edberg, N. and B.V. Hofsten, "Oxygen Uptake of Bottom Sediment Studied In-
Site and in the Laboratory," Water Research, 7:1285-1288, 1973.
22. Edwards, W.M., "Agricultural Chemical Pollution as Affected by Reduced
Tillage Systems," Proceedings No-Tillage Systems Symposium, Ohio
State University, Columbus, Ohio, pp. 30-40, 1972.
23. Erman, D.C., Newbold, J.D., and K.B. Roby, "Evaluation of Streamside
Bufferstrips for Protecting Aquatic Organisms," California Water
Resources Center, Univ. of California, Davis, Report No. 165, 1977.
24. European Inland Fisheries Advisory Commission, Water Quality Criteria for
European Freshwater Fish, Report on Finely Divided Solids and Inland
Fisheries, International Journal of Air and Water Pollution, 9:151-170,
1965. -
25. Forster, D.L., Rask, N., Bone, S.W. and B.W. Schurle, "Reduced Tillage
Systems for Conservation and Profitability," ESS 532, Dept. of
Agricultural Economics and Rural Sociology, Ohio State University
Columbus, Ohio, 1976.
26. Foster, G.R. and L.D. Meyer, "Soil Erosion and Sedimentation by Water - An
Overview," Proceedings of the National Symposium on Soil Erosion and
Sedimentation by Water. Chicago, in., pp. |.|3r -
27. Foster, G.R., Meyer, L.D. and C.A. Onstad, "A Runoff Erosivity Factor and
Variable Slope Length Exponents for Soil Loss Estimates," Transactions
of the ASAE. 20:76-80, 1977. -
28. Froehlich, H.A., "Inorganic Pollution from Forests and Rangelands," Publication
No. SEMIN-WR-021-76, Water Resources Research Institute, Oregon State
University, Corvallis, Oregon, 1976.
44
-------
29. Gard, I.E., "No-Till Cropping Reduces Pollution," Illinois Research, 13:3-5,
1977.
30. Garriels, D., De Boodt,M. and D. Minijauw, "Dune and Stabilization with
Synthetic Soil Conditioners: A Laboratory Experiment of Splash Erosion,"
Journal of Soil Science, 118(5):332-338, 1974.
31. George, G., "Best Management Practices and Water Quality Demonstration and
Evaluation Project Five-County North Central Oregon Area October 1979
to April 1980," Special Report 606, Agricultural Experiment Station,
Oregon State University, Corvallis, OR, 1981.
32. Ghadiri, H. and D. Payne, "Raindrop Impact Stress and the Breakdown of Soil
Crumbs," Journal of Soil Science, 28:247-258, 1977.
33. Glymph, L.M. and C.W. Carlson, "Cleaning Up Our Rivers and Lakes," ASAE
Paper No. 66-711, ASAE, St. Joseph, Mich., 1966.
34. Griffith, D.R., Mannering, O.V. and C.B. Richey, "Energy Requirements and
Areas of Adaptation for Eight Tillage-Planting Systems for Corn,"
Proc. Conf. on Energy and Agriculture, Center for Biological and
Natural Systems, Washington University, St. Louis, MO, 1976.
35. Griffith, D.R., Mannering, J.V. and W. Moldenbauer, "Conservation Tillage
in the Eastern Corn Belt," Journal of Soil and Water Conservation,
32(l):20-28, 1977.
36. Harrold, L.L., Triplett, G.B., and W.W. Edwards, "No-Tillage Corn: Character-
istics of the System," Agricultural Engineering, 51:128-131, 1970.
37. Hartman, J.P., Wanielesta, M.P. and G.T. Baragona, "Prediction of Soil Loss
in Nonpoint-Source Pollution Studies," In: Soi 1 Erosion: Prediction and
Control, Soil Conservation Society of America, Ankeny, IA, pp. 298-302,
T97/T
38. Hildebaugh, A.R. and R.I. Dideriksen, "Potential for New Cropland and
Associated Erosion and Sediment Problems," In: Soi 1 Erosion: Prediction
and Control, Soil Conservation Society of America, Ankeny, IA, pp.
347-352, 1977.
39. Huettl, P.O., Wendt, R.C. and R.B. Corey, "Prediction of Algal-Available
Phosphorus in Runoff Suspensions," Journal of Environmental Quality,
8(1):130-132, 1979.
40. Johnson, G.S. and J.A. Moore, "The Effects of Conservation Practices on
Nutrient Loss," Dept. of Agricultural Engineering, Univ. of Minnesota,
1978.
41. Johnson, C.W., Stephenson, G.R., Hanson, C.L., Engleman, R.L. and C.D.
Englebert, "Sediment Yield from Southwest Idaho Rangeland Watersheds,"
ASAE Paper No. 74-2505, 17 p, 1974.
42. Karr, J.R. and I.S. Schlosser, "Impact of Nearstream Vegetation and Stream
Morphology on Water Quality and Stream Biota," EPA-600/3-77-097, 1977.
45
-------
43. Kimberlin, L.W., "Conservation Treatment of Erodible Cropland: Status and
Needs," In: Soil Erosion: Prediction and Control, Soil Conservation
Society of America, Ankeny, 1A, pp. 339-346, 19/7.
44. Kramer, L.A. and R.E. Burwell, "Land Use Treatment Effects on Claypan Soil
Runoff and Erosion," ASAE Paper No. 80-2016, American Society of
Agricultural Engineers, St. Joseph, Mich., 1980.
45. Laflen, J.M., Baker, J.L., Harting, R.O., Buckele, W.F. and H.P. Johnson,
"Soil and Water Loss from Conservation Tillage Systems," Transactions
of the ASAE. 21:881-886, 1978.
46. Laflen, J.M. and W.C. Moldenhauer, "Soil and Water Losses from Corn-Soybean
Rotations." Soil Science Society of America Journal, 43:1213-1215,
1979.
47. Laflen, J.M., Moldenhauer, W.C. and T.S. Colvin, "Conservation Tillage and
Soil Erosion on Continuously Row-Cropped Land," In: Crop Production
and Conservation in the 80's. ASAE Publication 7-81, pp. 121-123, 1981.
48. Lake, J. and J.B. Morrison, "Environmental Impact of Land Use on Water
Quality - Final Report on the Black Creek Project (Technical Report),"
EPA 905/9-77-007-B, 280 p, 1977.
49. Langdale, 6.W., Barnett, A.P., Leonard, R.A. and W.G. Fleming, "Reduction of
Soil Erosion by the No-Till System in the Southern Piedmont,"
Transactions of the ASAE. 22(l):82-86, 1979.
50. Langdale, G.W., Box, J.E., Leonard, R.A., Barnett, A.P. and W.G. Fleming,
"Corn Yield Reduction on Eroded Piedmont Soils," Journal of SoiJ
and Water Conservation, 34(5) :226-228, 1979.
51. Mannering, J.V., Griffith, D.R. and C.B. Richey, "Tillage for Moisture
Conservation," ASAE Paper No. 75-2523, ASAE, St. Josephs, Mich., 1975.
52. McCool, O.K. and R.I. Papendick, "Variation of Suspended Sediment Load in
the Palouse Region of the Northwest," ASAE Paper No. 75-2510, 17 p,
1975.
53. McDowell, L.L. and E.H. Grissinger, "Erosion and Water Quality," Proceedings
of the 23rd National Watershed Congress. Biloxi, Mississippi, pp"40-56,
54. McGregor, K.C., Greer, J.D. and G.E. Gurley, "Erosion Control with No-Till
Cropping Practices," Transactions of the ASAE. 18:918-920, 1975.
55. Meyer, L.D. and W.C. Harmon, "Rainfall Simulator for Evaluating Erosion Rates
and Sediment Sizes from Row Sideslopes," ASAE Paper No. 77-2025,
American Society of Agricultural Engineering, 1977.
56. Miller, E.L. and W.D. Shrader, "Moisture Conservation Potential with Conser-
vations Tillage Treatments in the Thick Loess Area of Western Iowa."
Agronomy Journal. 68:374-378, 1976.
46
-------
57. Mitchell, W.H. and M.R. Teel, "Winter-Annual Cover Crops for No-Tillage
Corn Production," Agronomy Journal, 69:569-573, 1977.
58. Moore, J.A., Onstad, C.A., Otterby. M.A., Person, H.L. and D.B. Thompson,
"Preliminary Identification of Literature Models and Water for
Evaluating Rural Nonpoint Nutrient Sediment and Pathogen Sources,"
Agricultural Engineering Dept., Univ. of Minnesota, USDA North
Carolina Soil Conservation Research Center, Morris, Minnesota, 1977.
59. Mulkey, L.A. and J.W. Falco, "Sedimentation and Erosion Control: Implication
for Water Quality Management," Proceedings of the National Symposium
on Soil Erosion and Sedimentation of Water. ASAE Paper No. 4-77,
American Society of Agricultural Engineers, St. Joseph, Mich., 1977.
60. Myers, C.T. and R.I. Ulmer, "Streambank Stabilization Measures in Mississippi,"
ASAE Paper No. 75-2517, ASAE, St. Joseph, Mich., 22 p. 1975.
61. National Academy of Sciences, National Academy of Engineering, "Water Quality
Criteria, 1972," U.S. Government Printing Office, Washington, D.C.,
1974.
62. Oschwald, W. and J. Siemans, "Conservation Tillage: A Perspective," SM-30,
Agronomy Facts, University of Illinois, Urbana, 1976.
63. Peters, R.A., "Status of No-Tillage Corn in New England," Northeastern No-
Tillage Conference, Albany, N.Y., 1970.
64. Reddy, G. Y., Mclean, E.O., Hoyt, G.D. and T.J. Logan, "Effects of Soil,
Cover Crop, and Nutrient Source on Amounts and Forms of Phosphorus
Movement Under Simulated Rainfall Conditions," Journal of Environmental
Quality, 7(l):50-54, 1978.
65. Richardson, C., "Runoff, Erosion and Tillage Efficiency on Graded-Furrow and
Terraced Watersheds," Journal of Soil and Water Conservation, 28:162-164,
1973.
66. Risser, J., "A Renewed Threat of Soil Erosion: It's Worse Than the Dust Bowl,"
Smithsonian, 11:121-130, 1981.
67. Saxton, K.E. and R.G. Spomer, "Effects of Conservation on the Hydrology of
Loessial Watershed," Transactions of the ASAE, 11:848-849, 1968.
68. Smith, C.N., Leonard, R.A., Landale, G.W. and G.W. Bailey. "Transport of
Agricultural Chemicals From Small Upland Piedmont Watersheds," EPA
Preliminary Copy, U.S. Environmental Protection Agency, Athens,
Georgia, 1978.
69. Smith, E.E., Lang, E.A., Casler, G.L. and R.W. Hexem, "Cost-Effectiveness
of Soil and Water Conservation Practices for Improvement of Water
Quality," In: Effectiveness of Soil and Water Conservation Practices
for Pollution Control. Haith. D.A. and R.C. Loehr, Eds., EPA-600/3-79-
106, 474 p. 1979.
70. Sparks, R.E., "Effects of Sediment on Aquatic Life," Illinois Natural History
Survey, Havana, 111., 1977.
47
-------
71. Sportier, R.6., Shrader, W.D., Rosenberry, P.E. and E.L. Miller, Level
Terraces with Stabilized Backslopes on Loessial Cropland in the
Missouri Valley: A Cost-Effectiveness Study," Journal of Soil and
Water Conservation, 28:127-131, 1973.
72. Spomer, R.G., Piest, R.F. and H.G. Heinemann, "Soil and Water Conservation
with Western Iowa Tillage Systems," Transactions of the ASAE. 19:
108-112, 1976.
73. Stal
1945.
lings, J.H., "Effect of Contour Cultivation on Crop Yield, Runoff and
Erosion Losses," Soil Conservation Service, USDA, Washington, D.C.,
74. Steenhuis, T.S., "Simulation of the Action of Soil and Water Conservation
Practices in Controlling Pesticides," In: Effectiveness of Soil and
Water Conservation Practices for Pollution Control, D.A. Halth and
R.C. Loehr, Eds., EPA-600/3-79-106, pp. 106-146, 1979.
75. Stewart, B.A., Woolhiser, D.A., Wischmeier, J.H., Caro, J.H. and M.H. Frere,
"Control of Water Pollution from Cropland, Vol. 1," EPA-600/Z-75-026b,
U.S. Environmental Protection Agency, Washington, D.C., 1975.
76. Stewart, B.A., Woolhiser, D.A., Wischmeier, J.H. Caro, J.H. and M.H. Frere,
"Control of Water Pollution from Cropland, Vol. II," EPA-600/2-75-026b,
U.S. Environmental Protection Agency, Washington, D.C., 1976.
77. Swader, F.N., "No-Plow Corn in New York," Northeastern No-Tillage Conference,
Albany, N.Y., 1970.
78. Sweeten, J.M. and D.L. Reddel, "Nonpoint Sources: State-of-the-Art Overview,"
Transactions of the ASAE, 21(3) :474-483, 1978.
79. Timmons, D.R., Holt, R.F. and J.J. Catterell, "Leaching of Crop Residue as a
Source of Nutrients in Surface Runoff," Water Resources Research,
6:1367-1375, 1970.
80. Trimble, S.W., "Denudation Studies: Can We Assume Stream Steady State?"
Science, 188:1207-1208, 1975.
81. USDA-SCS, "Benefits/Costs of Soil and Water Conservation Practices for Erosion
and Sediment Control," 1980.
82. USDA-SCS, "Environmental Assessment Report Rural Clean Water Program "
Washington, D.C., 1978.
83. U.S. Department of Agriculture, Soil Conservation Service, "The Universal
Soil Loss Equation with Factor Values for North Carolina," Raleiqh
N.C., 1976. y '
84. U.S. Environmental Protection Agency, Quality Criteria for Water. 256 p.,
I -7 / 0 •
85. Walter, M.F., Steenhuis, T.S. and H.P. DeLancey, "The Effects of Soil and
Water Conservation Practices on Sediment," In: Effectiveness of Soil
and Water Conservation Practices for PollutTon Control. b.A. Uaith and
R.C. Loehr, Eds., EPA-600/3-79-106, pp. 39-71, 1979.—
48
-------
86. Wight, J.R. and R.J. Soiseth, "Vegetation Response to Contour Furrowing "
Journal of Range Management. 31(2):97-101. 1978.
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