WORKING PAPER NO. 10
COLUMBIA RIVER BASIN PROJECT
For Water Supply and Water Quality Management
SEDIMENT PRODUCTION RATING
WILLAMETTE BASIN, OREGON
Date: January 1, 1962
Prepared by WEB
Reviewed by
Approved by
DISTRIBUTION
Project Staff
Cooperating Agencies
General
U.S. DEPARTMENT OF HEALTH, EDUCATION AND WELFARE
Public Health Service
Region IX
Division of Water Supply and Pollution Control
570 Pittock Block
Portland 5, Oregon
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This working paper contains preliminary data and information
primarily intended for internal use by the Columbia River
Basin Project staff and cooperating agencies. The material
presented in this paper has not been fully evaluated and
should not be considered as final.
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SEDIMENT PRODUCTION RATING
WILLAMETTE BASIN
OREGON
INTRODUCTION
Based on the experience gained in rating the Umpqua Basin streams, the
work was extended north into the adjacent Willamette Basin on areas of
similar geology, climate, cover, and land use. Here there is less avail-
able information from sediment sampling, and the rating estimates are
necessarily subjective. Some earlier estimates are available from studies
by the U. S. Forest Service Flood Control Surveys, the USDA Willamette
Basin Agricultural Program report, and the Corps of Engineers.
SUMMARY AND CONCLUSIONS
The high mountain portions of the basin occupying highly permeable lava
formations not subjected to extensive development and use have the lowest
sediment production rating. This is characteristic of the headwaters of
the McKenzie, Santiam, and Clackamas Rivers draining the Cascades on the
east side of the basin.
For entire watersheds, the Tualatin Valley at the extreme north end of
the basin, the Long Tom, Luckiamute and Mary's Rivers draining the Coast
Ranges, and the Calapooya River draining the Cascade foothills have the
lowest ratings.
The Mola1la River watershed has the highest rating, due'to recent extensive
road building and the channel disturbance caused by last year's flood.
Over-all rating for the entire Willamette Basin is 'Moderate".
A prime source of sediment is bankcaving in the deep alluvial soils along
the main watercourses in the valley. The several large multipurpose dams
built on all the major tributaries - and on several of the minor ones -
effectively stop large volume sediment movement from the upper parts of
the basin. They also regulate flow and thus tend to reduce the amount of
high flow season bankcutting in the lower watercourses, though the compe-
tence or sediment-carrying capacity of the regulated streams may be
increased.
DESCRIPTION OF THE BASIN
The Willamette River Basin is roughly rectangular in shape, about 80 miles
wide east to west, and ISO miles long north to south. Total area is
11,200 square miles. The basin lies between the Cascade Range on the
east, from which flow the major tributaries, and the Coast Range on the
west. The southern rim of the watershed abuts the Umpqua Basin. The Wil-
lamette River, formed by the confluence of the Coast Fork, the Middle
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Fork, and the McKenzie River in the vicinity of Eugene, flows north in a
broad low valley to its junction with the Columbia at Portland.
The rugged Cascade Mountains, composed primarily of igneous rocks, occupy
nearly half the basin.area. .Major streams from the Cascades feeding the
Willamette River are the Middle,Fork, the McKenzie, the Santiam and the
Clackamas. Lesser tributaries feeding in from the Cascade foothills include
the Mohawk, the Calapooya, and the Molalla. Elevations in the Cascades
range up to 10,000 feet at Mt. Jefferson and the Three Sisters. The
valley is filled with debris from ancient glaciers of the Cascades, and
covered with recent alluvium brought down by the Cascade tributaries.
The less rugged Coast Range on the west is composed largely of sedimentary
rocks, and occupies about one-eighth of the basin area. Elevations range
up to 4,000 feet on Mary's Peak in the center of the western rim. Tribu-
taries feeding from the Coast Range include the Long Tom, Mary's River, .
the Luckiamute, Rickreall Creek, the Yamhill, and the Tualatin River.
There are wide variations in soil conditions, from the unstable soils
developed in the mountains on old volcanic mudflows, to the stable soils
developed on the valley floor alluvium. Major soil groups .include recent
alluvial or floodplain soils, old valley fill soils, residual hill and
mountain soils developed from sedimentary rocks, and residual hill and
mountain soils developed from igneous rocks.
Cultivated cropland, both irrigated and nonirrigated, occupies about
1,400,000 acres on the valley floors, benches, and lower foothills. (1)
Rangeland, with brush and weed and grass cover, occupies about 550,000
acres in a belt around the edges of the valleys. Forest, covering 70
per cent of the basin, occupies the foothills and mountains; 85 per cent
of the forest is Douglas-fir type, with subalpine mixt conifer type at
the higher elevations, and with hardwoods along the streams and on some of
the lower hills. The forest zone includes the important tributary water-
sheds that feed the Willamette River. Other land in the basin amounts to
about 280,000 acres; it includes urban areas, roads, and rocky barrens.
Water surface in streams and lakes totals about 35,000 acres within the
basin.
The climate is temperate, with dry warm summers and mild wet winters. In
the mountains the bulk of the precipitation is snow; average annual total
is about 80 inches. Valley areas receive average amounts from 35 to 45
inches; nearly all as rain. Rainfall rates as great as an inch in one hour
are rare.
Streamflow is variable from season to season and from tributary to tributary.
Streams draining the high Cascades show the greatest yield, while those
draining the inside of the Coast Range show the lowest yield. Total flow
of the Willamette River at its mouth is estimated to average 22,000,000
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acre-feet annually. Peak winter flow for the high month equals one-fifth
of the average annual, while late summer minimum flow is but one-eightieth
of the average annual. Tributary streams show similar ranges. Half the
time the month of high flow is December or January; for low flow, September.
Annual variation around the average ranges from a low of about 60 per cent
to a high of more than 150 per cent. The bulk of the streamflow is
derived from the forested mountain watersheds; the McKenzie and Santiam
Rivers contribute pore than a third of the total yield though they drain
less than a quarter of the basin. Major floods have been experienced about
once in eight years on the average; present flood hazard is far less
because of control afforded by dams on principal tributaries.
Ownership of basin lands is 38 per cent Federal (mainly National Forest),
2 per cent State, County and Municipal, and 60 per cent private. Nearly
all pf the public land and a bit more than half of the private is in forest.
It is used for lumber production and recreation and some grazing. Private
land includes three-fourths of the range and all of the cropland.
Land use has influenced sediment production. Development of access roads,
logging, heavy grazing use, and cultivation - particularly with clean-
tilled winter fallow - all have disturbed the soil and led to increased
erosion. Nevertheless, indications are that more than half the total sedi-
ment movement in the Willamette River has come from bankcutting (2) in the
lower courses of the streams. Dams in the middle and upper channels of
many of the tributaries act as effective traps for sediment.
RELATED STUDIES BY OTHER AGENCIES
Flaxman and High (3), reporting on studies by the Forest Service and the
Corps of Engineers, noted sedimentation rates ranging from 53 to 286 tons
per square mile in the major streams, up to 800 tons per square mile in
the minor tributaries. They cited also a Soil Conservation Service study
of the record erosion in February, 1949, showing maximum soil losses up
to 60,000 tons per square mile and assuming that 80 per cent of the soil
loss became stream sediment.
Lowest rates of average annual sediment production were found in the
Coyote Creek, Long Tom River and the Tualatin River watersheds. The McKen-
zie River watershed was almost as low. Highest rate was found in the
Luckiamute River I/watershed, more than twice as high as any others
reported, and six times as high as the lowest.
JL/ Three years suspended load sampling at a valley station; average 780
tons per square mile per year including the record year 1949. Bank-
caving and winter erosion of clean-tilled fields may be largely respon-
sible; the present survey of the watershed showed conditions to be good
and the soils well stabilized.
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Sixteen years of dredging in Portland Harbor at the mouth of the Willamette
removed 11,800,000 tons of sediment. This amounts to 66 tons per year per
square mile of contributing watershed.
SURVEY METHODS
The field survey was made by observations while traveling through the
country, with particular attention to stream channel conditions. As many
watershed slopes and stream channels were checked as could be conveniently
reached by car. Areas were rated (as to sediment production) "very low",
"low", '^moderate", "high", or "very high", depending on signs of surface
erosion on the watershed, landslides and slumps, disturbance by road-
building, etc., and on the apparent stability of the channels and the
amount and kind of sediment in the channels. For example, a stable chan-
nel was assumed to be one that had a bottom shingled with rocks supporting
a wide variety of plant and animal life - evidence of little or no scour -
and banks protected by well-established brush and tree cover; this was
taken to indicate low sedimentation.
Field notes were made ou subwatershed maps. The notes cited specific
problem areas and causes, as well as classes of sediment production
rating. In the office these notes were checked against available informa-
tion from other agencies, and the ratings of the areas sampled were extra-
polated by checking aerial photographs to other areas of similar cover
and topography and appearance.
Weighting the sediment production rating classes by applicable areas as
determined from the field notes and the aerial photos gave a weighted
average rating class for each tributary watershed. These in turn were
combined into area-weighted averages to determine the average sediment
production rating for the whole Willamette Basin.
SURVEY FINDINGS
Timber access roads, dam construction, burned area erosion, landslips in
mudflow/7>Id volcanTc~l>indflow formations, and flood scour in channels are the
principal sources of sediment in the upper watersheds. Bankcaving and
erosion of clean-cultivated farmland are also important sediment sources
along the lower reaches of the streams. In a few places logging operations
were directly responsible for increased sedimentation, but any adverse
effects of logging generally were overshadowed by the effects of access
road construction. These were at their worst on Willamette National Forest
lands in the Blue River watershed tributary to the McKenzie River.
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Effects of the Hehe burn in the Fall Creek watershed and the Sardine Creek
burn in the North Santiara watershed are still noticeable. Quantities of
unstabilizc.d debris in the stream channels provide a continuing sedimenta-
tion hazard, although cover vegetation is coming back on the watershed
F, lopes.
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Dam construction and road relocation on the Hills Creek, Cougar, Green
Peter, and Carmen-Smith projects are causing massive soil disturbance and
a large immediate sedimentation hazard. This type of soil disturbance is
just beginning on the Foster and Wiley Creek dam projects on the South
Santiam River. This should be greatly reduced on completion of the projects.
Landslip effects are particularly noticeable in the Clackamas drainage
and in parts of the North Santiam drainage. In a few cases they are aggra-
vated by road construction, but in many instances the slumping is directly
into stream channels from undisturbed slopes. Sheep Creek and other small
adjacent drainages at the head of the South Santiam are underlain by
highly unstable mudflow and cinder deposits that are constantly in motion,
slumping into channels and providing a heavy sediment load.
Scouring of channels by the floods of the winter 1960-61 was particularly
severe in the Mola1la drainage and in one or two small tributaries to the
North Santiem River. The effects of the 1955 flood in Salt Creek are
still obvious, though clean-up work and slow natural stabilization pro-
cesses have resulted in considerable improvement.
On Thomas Creek and Crabtree Creek in Linn County tributary to the South
Santiam River, improvement work for flood control done this year will
temporarily increase sediment yields. River gravels wers dragged out of
the stream channel and used to build up the banks to avoid further bank-
cutting and to afford freer flow. Fine material disturbed by the operation
will be carried out by high flows this winter, but the channels should be
stabilized fairly well afterward. In one place the work was done on the
inside of a curve, but not on the outside; the vertical channel bank on
the outside is still subject to cutting and caving at times of high flow.
Some harm to fisheries resulted from the timing of the work, as eggs in the
gravel were dug up. Spawning beds, however, are still available to anadro-
tnous fish.
The Calapooya drainage was given a low rating because of the excellent
condition of the streambed gravels in the middle reaches and the lack of
any signs of serious soil disturbance in the upper watershed. Even the
excessive disturbance of the channel below Hoiley by machinery removing
rock and gravel for highway construction created only minimum turbidity.
The streambed still appears to be in good shape for spawning steelhead to
use.
The Tualatin River draining the hills west of Portland was also rated "low",
surprisingly enough, for its watershed occupies an intensively developed
area. The topography is not too rough, the climate is moderate, and the
soils quite stable. Soil movement is limited despite extensive suburban
development, intensive agriculture, and logging.
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Ratings applied to the various subwatersheds of the Willamette Basin are
as follows:
Watershed Sediment Production Rating
Tualatin River low
Yamhill River low to moderate
Luckiamute-Mary's River low
Long Tom River low
Coast Fork Willamette River low to moderate
Middle Fork Willamette River low !/
Mohawk-McKenzie River moderate to high —'
Calapooya River low
Santiam River moderate I/
Mola1la-Pudding River high
Clackanas River low to moderate
I/ Temporary disturbance from dam construction very high, but other dams
serve as sediment traps below.
Over-all sediment production rating for the whole Willamette Basin would
be "moderate", despite the "low" rating given the grcr.£ bulk of the area.
Since most of the larger tributary streams are damaiad at fvo-jo one to
several places, a large part of the rating is attributable to the rather
extensive bankcaving through the main valley.
Sediment production ratings may be interpreted as follows:
Average Sediment Load
Rating Class in ppm of
S Slight or very low under 50
L Low 50 to 150
M Moderate 150 to 500
H High 500 to 1500
VH Very high 1500 plus
DISCUSSION
Though there are specific problem areas in the Willamette Basin beyond the
few already cited, the types of problem seem more important. Of most
widespread occurrence and greatest significance, and probably the most
easily improved is the sediment contribution from timber access road con-
struction. If present practices continue as the timber harvest proceeds,
sediment production will increase markedly. However, application of present
knowledge to avoid and control movement of soil into channels could bring
about a reduction of sedimentation from the present road network and prevent
any large future increase as the road network expands. The same statement
applies to logging operations also. In neither case is there any need to
suffer the amount of sedimentation damage now occurring; it can be prevented
ot minimized.
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Flood effects, tremendous as they are when they occur, are felt sufficiently
infrequently to have any great over-all effect. The same is true for the
effects of fire. Both are occasionally locally severe, with effects that
taper off in a few years. Fire protection holds burned area down, and
channel cleanup reduces the sedimentation hazard in flood-ravaged channels.
Dams recently built or now under construction will modify flood flows in
the lower tributary stream courses and in the Willamette River and reduce
bankcutting from flood scour. At the same time they will trap much of the
sediment moving down into them.
Sedimentation from mudflow and similar unstable soil and rock formations
will continue to occur. However, its effects can be reduced by avoiding
unstable areas in road building. Soils mapping on forest areas is proceed-
ing, and before long the unstable areas will be marked out so that they
can be located and avoided much of the time.
Preservation of stable channel conditions and reduction of excessive tur-
bidity and sedimentation is desirable to maintain fish habitats as well as
to maintain water quality. According to Cordone and Kelly (4), "...even
small amounts of sediment may be harmful (and) may well result in gradual
destruction of the majority of our streams...the bulk of the damage is
unnecessary. It can be prevented with known land use methods, often with
little or no additional expense. Much of it is the result of carelessness."
RECOMMENDATIONS FOR IMPROVEMENT
On public lands, major improvement in reducing sediment production will
follow implementation by the land-managing agencies of their excellent
policy statements for protection of water resources. Failures to live up
to policy are due to one-sided pressures from a part of the public, to
lack of interest in and understanding of watershed and stream protection
requirements, and to inadequate job supervision. A continuing education
program both for the public - to equalize pressures - and for agency per-
sonnel - to develop needed skills and interest - is strongly indicated.
Much tighter supervision of on-the-ground jobs at the lowest levels, and
of contracting operators, to ensure compliance with policy requirements is
also necessary on a continuing basis.
Physical measures applicable to any forest land for protection or rehabili-
tation of watersheds are well known and well documented, though unfortu-
nately not well enough applied. Professional society (5), inter-agency
group (6), State (7), and Federal agency (8), (9) publications, as well as
Federal agency operating manuals set forth clearly what situations are
harmful and what measures to apply. The publications listed are only a
few of many, but they are readily available here and now. Measures for
agricultural and range land are also well known but not everywhere applied.
Any County Agent can furnish information on agricultural practice to
prevent erosion and conserve soil and water.
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8
Highway planning and construction agencies, both State and Federal, need
to take an interest in the effects of their work on water resources, and
to pay attention to State law which should govern their operations. Pro-
tection for watersheds and water resources must be built into the highway
system, starting with planning and including adequate financing. The
common practices of diverting road drainage directly into streams, dumping
excess cut materials into channels or where it can erode into channels,
constricting and changing water courses, all without regard to downstream
effects on water or to effects on fisheries and recreation, are contrary
to State law and are economical only to the immediate highway construction
job.
Specifically, in all work on the land it is necessary to avoid undue soil
disturbance or denudation, to avoid dumping debris of any kind into streams,
to keep oil and pesticides and fertilizers from draining into streams, to
avoid working in stream channels or along channel banks with heavy equip-
ment, and to preserve the natural conditions of the riparian habitat as
far as possible. In roadbuilding this means laying out locations that
involve the least cut and fill, the least direct disturbance of channels,
and the least opportunity for rapid drainage into channels. In the timber
harvest this means high-lead cable logging uphill rather than tractor
logging downhill, leaving protective strips along streams, avoiding yard-
ing across streams, location of landings away from streams, clean-up of
slash that does get into channels, and application of soil stabilization
measures such as seeding temporary cover crops on disturbed soil or in-
stalling drainage diversions in skidtrails and temporary roads. In agri-
culture it means cultivation along the contour, sodding to stabilize drain-
age ways, cover crops for fields in winter fallow or underneath orchards,
and care in the application of chemicals for whatever purpose. In grazing
it means keeping livestock numbers at a level consistent with maintenance
of sufficiently dense vegetation cover to protect the soil and with main-
tenance of soil tilth and infiltration rates.
Dam construction necessarily involves extensive channel disturbance and
temporary increases in stream turbidity and sedimentation regardless of
the season in which the work is done. After construction, the dams effec-
tively trap and stop sedimentation, and the control of streamflow they
afford is beneficial in reducing bankcutting downstream. Other channel
work may cause much less disturbance if done during the low water season -
sometimes the only season in which it can be done - but may harm the
fisheries resource if spawning beds are disturbed during the August to
January period when eggs and fry are still in the stream bottom gravels.
Such work should be done as early as possible in June or July.
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BIBLIOGRAPHY
(1) "Report on Agricultural Program and Appendix to Survey Report,
Willamette Basin Sub Area, Oregon", by U. S. Dept. Agriculture,
May 1954
(2) "Suspended Sediment Discharge as Related to Streamflow, Topography,
Soil, and Land Use", by H. W. Anderson, Transactions AGU, Vol. 35,
No. 2, April, 1954
(3) "Sedimentation in Drainage Basins of the Pacific Coast States", by
E. M. Flaxman and R. D. High, USDA Soil Conservation Service, June
1955
(4) "The Influences of Inorganic Sediment on the Aquatic Life of Streams",
by A. J. Cordone and D. W. Kelley, California Fish and Game, Vol. 47,
No. 2, April 1961
(5) "Watershed Protection - A Manual for Forest Landowners", by the
Water Management Committee, Columbia River Section, Society of
American Foresters, 1961
(6) "Watershed Control for Water Quality Management", by the Pacific
Northwest Pollution Control Council, to be published 1961
(7) "Logging Regulations - Surface Water Areas", Washington State Depart-
ment of Fisheries
(8) "Effect of Logging and Forest Roads on Stream Sedimentation", by
E.G. Dunford, PNW Forest and Range Experiment Station, November
1960
(9) "Guide to Regulations Affecting Harvesting and Marketing Forest
Products" (1 - Oregon, 2 - Washington), by Division of State and
Private Forestry, U. S. Forest Service, Region Six, January 1960
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