WORKING PAPER NO. 11
COLUMBIA RIVER BASIN PROJECT
For Water Supply and Water Quality Management
SEDIMENT PRODUCTION RATING
YAKIMA BASIN
WASHINGTON
DATE: January 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
V
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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SSDIMGHX JRQJQHCI1QN _RAHJ8fi
YAKIMA BASIN
WASHINgTON'
INTRODUCTION
After finishing the field work on the Umpqua and Willamette Basins
west of the Cascades in Oregon, the survey was begun on the Yakima
Basin east of the mountains in Washington. Though climate and
geology and soils and land use are quite different in the Yakima,
the sediment production ratings based on field inspection of water-
shed lands and streams should correlate well with those of the basins
done earlier. No sediment sampling or reservoir sedimentation data
were available to guide the survey in this basin.
SUMMARY AND CONCLUSIONS
Overall, the Yakima Basin is rated "moderate" as a sediment producer.
The several reservoirs in the mountain areas trap much of the sedi-
ment coming from lands given a "high" sediment production rating at
the upper elevations. Sediment movement across flat valley lands
below "high" rated slopes and ridges in the lower watershed appears
quite limited.
Along the middle and lower reaches of the Yakima River, the bulk of
the sediment load most probably comes from bankcutting and rework-
ing of channel deposits at times of high flow, and from irrigation
return flows during the summer season.
Some special sediment sources such as the heavily grazed scab ridges
at middle elevations and the Swauk Creek dredge-mining spoil depos-
its are worth mention as particular problem areas; but generally
the sediment sources are widely distributed and attributable to a
number of different causes in each component watershed.
Only the Satiis Creek watershed was given a uniformly "high" rating;
a rating applied because of apparent extensive heavy grazing use on
areas of unstable geology and rough topography.
DESCRIPTION OP BASIN
The Yakima Basin is roughly triangular in shape, with the base of the
triangle against the Cascade mountains* The Yakima River drains east
from the southern Cascades in Washington to its confluence with the
Columbia near Pasco. Major tributaries include, from north to south,
Wilson Creek, Swauk Creek, Teanaway River, CleElum River, Taneum
Creek, Manastash Creek, Wenas Creek, Naches River, Ahtanum Creek,
Toppenish Creek, and Satus Creek. Total area of the basin is about
5,970 square miles. (1)
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Elevations range from about 8,000 feet on some of the peaks of the
Cascades along the western boundary of the basin down to 320 feet
at the confluence of the Yakima and the Columbia. The northern
boundary reaches elevations of 5,000 to 7,000 feet in the Wenatehee
Mountains, and the southern from 2,000 feet in the Horse Heaven Hills
to 3,500 feet in the Siracoe Mountains.
Several parallel ridges trending more or less east-west separate the
major tributary watersheds and divide the basin. Elevations on these
ridges range from 2,500 to 4,000 feet. The upper valley around
Ellensburg at an elevation of 1,500 feet is separated by a 20-mile
gorge from the middle valley around Yakima at an elevation of about
1,000 feet. Just below Yakima, the river spills through a short gap
to the lower valley extending from Wapato to Prosser.
Channel gradients are steep in the mountain sections and in the
gorges separating the valley parts. The relief is rugged, and char*
acterized by long steep slopes. Ridges generally are flat-topped.
Predominant geologic formations are the Oligocene and Miocene vol-
canic 3. Only a few small areas of older and nonvolcanic rocks occur
in the headwaters. Valleys are filled with recent alluvium, plus
eolian deposits around Ellensburg and Yakima, and glacial lake depos-
its in the lower valley. Soils include the light silty wind-deposited
soils, light sandy alluvial soils, and heavy residual soils developed
from the volcanic and older nonvolcanic formations. The lighter soils
are readily eroded by wind when denuded, and the heavier soils by
water*
Climate of the basin is of the winter wet and summer dry type,
strongly modified by the Pacific Ocean one hundred and fifty miles
to the west. In the extreme western mountain fringe of the basin,
the average annual precipitation reaches 100 inches. The average
falls off rapidly toward the center and lower end of the basin, where
it is less than eight inches at some stations. Average temperature
is at or below freezing a couple of months in the winter, even in the
lowest and warmest parts of the basin. Strong winds are common in
spring and fall.
Much of the precipitation, particularly in the mountainous headwaters,
is received as snow. The streamflow regime is controlled primarily
by the spring snowmelt. Flow in the Yakima River averages about
3,920i'cfs for an annual yield of 2,837,000 acre-feet. Peak flows
_!/ U.S.G.S. records for Kiona gage and Corps of Engineers report.
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in excess of 65,000-' cf& have been recorded, and a minimum flow well
under 200-j'cfs. Average maximum is 6,260l' cfs, and average minimum
is l,06Oi'cfs, While high flows from rainstorms can occur in Novem-
ber and December, most high flows occur in April and May and June from
snowmelt. Spring and summer cloudbursts from limited area convectional
storms occur infrequently but have resulted in flood flows and excessive
sediment movement in some streams.
Headwater areas of the basin have a forest cover. At the upper eleva-
tions, this is a mixed conifer forest, quite dense* With decreasing
elevation, the forest changes to ponderosa pine, more open in charac-
ter. Below the forest is sagebrush and grassland. Valleys are culti-
vated, with fruit orchards, pastures, hayfieIda, and a variety of
truck and grain crops. Basin cropland totals about 1,750,000 acres,
of which about 450,000 acres are irrigated and the rest dry 'farmed or
pastured. Forest land equals about 1,620,000 acres, and rocky brush
and grass about 450,000 acres. Much of the so-called pasture might
be added to this latter category.
Forest occupies the areas of high precipitation that have water sur-
pluses to produce streamflow. Though average water yield equals only
nine inches for the basin as a whole, it equals 21 inches for the
forest area.
About 21 per cent of the basin land is owned by the Federal Govern-
ment, eight percent by State and local governments, 24 per cent is in
Indian Reservation, and 47 per cent is privately owned. National
forests occupy most of the Federal land.
RELATED STUDIES BY OTHER AGENCIES
No specific references to sedimentation have been found in reports
of other agencies. However, the Corps of Engineers (1) repeatedly
mention bank and channel erosion and deposition in connection with
flood occurrences and protective measures. Washington reports (2)
(3) note from sampling that turbidity ranges from 2 to 66 units,
and total dissolved solids from 26 to 358 p.p.m. This was summer
season work, with the streams at moderate to low levels. What part
of the observed turbidity and solids is due to sediment load is unknown.
SURVEY METHODS
As was done in the Umpqua and Willamette Basins, visual inspection
was made of the major stream channels and as much of the watershed
If U.S.G.S. records for Kiona gage and Corps of Engineers report.
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area as could be conveniently reached by road. Channel conditions with
respect to benkcutting, floatable debris, and sediment deposits were
noted. Four reservoirs, drawn down at the end of the irrigation season,
were visited to ascertain the amount of sediment accumulation in the
inflow channels. Logged areas, burned areas, and grazed areas were
inspected on different geology and topography to estimate relative
sediment contributions. Both dry-farmed and irrigated pasture and
cropland were also inspected. Effects of construction of an extensive
system of mountain roads for the timber harvest were noted.
Ratings of sediment production were made in five classes. These
classes can be broadly interpreted in terms of p.p.m. suspended sediment
in average annual total water yield as follows:
Average Suspended Load
Rating Class in p.p.m.
Slight Under 50
Low 50 to 150
Moderate 150 to 500
High 500 to 1500
Very High 1500 Plus
Estimated ratings are subjective, based on comparing physical conditions
of the Yakima with those of basins previously surveyed. No data were
available to support the estimates.
However, at the same time that the rating survey was going on, a series
of samples were taken along the Yakima River from Easton to Prosser.
These samples showed a range from 20 to 451 p.p.m. total solids, and
from 1 to 173 p.p.m. suspended solids. This was a sampling of low flow
in September; the higher values are mainly those in irrigation return
flows. Average suspended load in 24 samples was 20 p.p.m. How much of
this is inorganic sediment was not determined.
SURVEY FINDINGS
In the mountainous parts of the basin, the higher ridges are bare and
subject to frequent avalanches. These areas are rated "high". Forested
slopes covered with the dense mixed conifer types are rated "low';; though
grazed areas in the open ponderosa pine type may occasionally be rated
as moderate sediment producers. Most of the headwater stream channels
carried heavy debris loads and were rated "high" or "very high". Wenas
Reservoir and Lake Cle Elum showed considerable sediment accumulation.
Major tributary and main river channels were rated "low" to "moderate";
Swauk Creek, however, was rated "high" because of the effects of the
dredge mining along several miles of its course. The hills of the central
and lower parts of the basin covered only with sparse sagebrush and grass,
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varied considerably in their ratings from "low" to "high". Heavily
grazed scab ridges at middle elevations were rated "high". Clean-
tilled hill croplands were rated "high", but most of the flat valley
croplands were rated "slight" or "low".
The overall rating for the basin is "moderate". One percent of the
basin area--scab ridges and areas of active channel cutting--was rated
'Very high1'; 25 percent was rated "high", 32 percent was rated ''moderate";
and 42 percent was rated "low". Except for Satus Creek, for the most
part rated "high", it would be difficult to establish ratings for individ-
ual tributaries. The rating pattern cuts across watershed boundaries
indiscriminately, being related more to cover type and elevation and
geology and land use.
DISCUSSION
While the appearance of many of the sparsely covered brush and grass-
lands in the lower hills indicated high erosion losses, with gullied
draws and recent delta deposits below, it is doubtful that much sediment
moves across the cultivated valley flats to reach stream channels. In the
mountain areas, reservoirs block passage of sediments from other areas
of high loss. During floods, there is considerable sediment movement,
bankcutting and reworking and redeposition of channel materials; this,
however, is of infrequent occurrence. In the dry northeastern side of
the basin, it is doubtful if the channels—actively cutting and sedi-
ment laden though they are--of the numerous minor tributaries carry
flows through to the main river very often. They are dry most of the
year.
More of the scab ridge areas which have long been subjected to heavy
grazing, compaction, and erosion, would be rated "very high" as sediment
contributors except that they have already lost most of their soil and
now have an "erosion pavement" or "stone mulch" on the surface. Though
the rate of soil loss has diminished, runoff rates are very high from
these areas.
Because of the extensive diversion of waters of the basin for irrigation
of the valleys and terraces, irrigation return flows carry more sedi-
ment than the main river much of the year. The amount, however, does
not appear excessive, though it significantly affects water quality and
stream habitat for fish.
RECOMMENDATIONS FOR IMPROVEMENT
More care to avoid excessive soil disturbance in building roads in the
mountains, stabilization of the Swauk Creek dredge mining spoil piles,
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rehabilitation of scab ridge grazing lands, less intensive grazing use
and better protection from fire on the lover brush and grasslands,
cultivation on contour for sloping lands, wider use of soil-binding
cover crops, and more efficient irrigation application all would help
reduce the sediment yield of the basin.
W. E. Builard
19 October 1961
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BIBLIOGRAPHY
(1) "Report on Yakima River and Tributaries, Washington", Corps of
Engineers, U. S. Army, September, 1956.
(2) "An Investigation of Pollution in the Yakima River Basin", Wash-
ington Pollution Control Commission Technical Bulletin No. 9,
1951.
(3) ''Research and Investigations on the Quality of Water of the
Columbia River and Effects on the Fisheries Resources",
R. 0. Sylvester, University of Washington, January, 1957.
(4) "Yakima Project, Washington, Supplemental Storage", U. S. Bureau
of Reclamation, Region I, May, 1956.
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