Topography and Geology
The Satsop River originates on the southern slopes of the Olympic Mountains within Grays Harbor and Mason Counties. From this point, the river's four major tributaries (the Middle, East, and West Forks, and Decker Creek) flow for some 50 miles through heavily wooded hill country before joining the mainstem a few miles above the community of Satsop.
The Satsop below the forks flows south through a broad flat agricultural valley with scattered areas of deciduous vegetation. The upper areas largely consist of moderately sloping hills forested with second growth timber. The streambed is comprised of cobbles and gravel with a low gradient. The river averages 30 to 45 yards in width and provides a blend of long pools and short riffles. Rural and farm residences are scattered throughout the valley land. Minor tributary streams include one unnamed stream, and Mitchell and Sherwood Creeks.
The mainstem flows through a lightly agricultural river valley before discharging into the Chehalis River at RM 20.2. The total drainage of the Satsop River system amounts to approximately 186,282 acres, (291 square miles) with 111,285 acres originating in Mason County and 74,997 acres from Grays Harbor County. The mean annual flow is 2,016.3 cfs. Maximum recorded flow was 46,600 cfs in January of 1935, and minimum recorded flow was 166 cfs in September of 1938 (USGS, 1992). Approximately 30% of the flow of the Chehalis River at Cosmopolis in August is from the Satsop.
Several lakes are sources for some of the smaller creeks in the Satsop system. There are also three small reservoirs located about three miles north of the confluence of the East and West Forks.
The Middle Fork begins in the foothills of the Olympic Mountain range and flows southerly through steep valleys and canyons to its confluence with Baker Creek, then through a gradually widening valley to its confluence with the East Fork. Decker Creek flows south through broad prairie land and sloping valleys.
Most of the Middle Fork watershed is in second-growth timber production. Old growth timber is found in the foothills of the Olympics at the heads of several of the tributary streams. Small farms are found throughout the lowlands.
The East Fork flows southwesterly from the confluence of Phillips and Stillwater Creeks to Simpson State Salmon Hatchery at RM 17.5. The river flows through a broad flat valley of mixed coniferous and deciduous trees. One major tributary, Bingham Creek, and five smaller tributaries enter the East Fork.
The West Fork Satsop River begins in the steep foothills of the Olympic Mountains and flows southerly through a narrow valley to RM 33. Below here, the stream flows through a broad valley with low surrounding hills.
The majority of the West Fork's 154 square mile drainage is managed under the 100-year Shelton Cooperative Sustained Yield Unit agreement between USDA Forest Service and Simpson Timber Company. Other private lands managed for forestry practices or agriculture are a small percentage of the total drainage.
Today, 70% of the Satsop drainage timber stands are less than 35 years of age. Nearly 70% of the drainage has slopes greater than 65% with high erosion and mass wasting hazards. Road densities range from 4.3 to 5.8 miles of road per square mile of land. High road densities and subbasins not yet at a stage of hydrologic recovery create high sedimentation rates and instream impacts related to peak flows. Average rainfall ranges from 70 to 175 inches per year. Older roads constructed using sidecast waste designs, with poor drainage, and located on unstable mid-slopes create a high hazard for slope failure and erosion. Erosion and slope failures often reach a perennial watercourses.
Current forest practices on national forest lands incorporate site specific and cumulative effects analyses to reduce further impacts. An inventory of needed watershed improvements has identified hundreds of sites in need of erosion control or potential sedimentation sources through slope failures. Funding has been a limitation in addressing this watershed improvement need.
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Residential developments along the Middle Fork include the communities of Matlock and Deckerville. Recreational homesites are being developed at several locations in this watershed.
Using 1990 U.S. Bureau of Census data and maps for the area, and relating census block numbers to the watershed boundary of the Satsop basin, the subbasin population appears to be 5,000.
Based upon an average for the entire Chehalis River Basin of 2.29 people per household, there are close to 2,200 households in this subbasin.
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In December 1966, the Washington Department of Fisheries completed construction of the experimental egg incubation channel on the East Fork. In May 1971, the Department improved a natural spawning channel just above Schafer State Park to improve potential chum spawning grounds, and cleaned the gravel at the inlet and outlet to the Satsop egg incubation channel. Simpson State Hatchery is located upstream from this section. Fish are released from these projects into the East Fork and Satsop River.
The Middle Fork supports very large runs of all three species of salmon found in the Chehalis basin. Chinook spawning occurs in the Middle Fork, Decker Creek, and Lower Dry Run Creek. Chum spawning occurs in these same reaches and also in several of the smaller tributaries. Coho are found throughout the accessible portion of the watershed. It is estimated that some 40 miles of mainstem in the Middle Fork and Decker Creek and some 34 linear miles of tributaries to these channels are presently utilized by salmon.
The majority of the Middle Fork watershed is in timber production. The steeper slopes near the headwaters are forested with mature, old growth timber, while the lower areas are in second growth timber with scattered, cleared farmland. There have been no residential developments in the Middle Fork watershed. Swinging Bridge Park is located at RM 7.3.
The West Fork Satsop River supports a run of chum, Chinook, and coho salmon. Chum and Chinook utilize the mainstem for spawning with major Chinook spawning below RM 20.0. The river is suited for chum and Chinook spawning to RM 33. The lower ten miles of Canyon River and the lower 0.8 miles of Little River are also suited for these species. Coho and a limited number of chum also spawn in all accessible tributary streams up to RM 35.5 on the West Fork Satsop River.
The lower section of the West Fork becomes warm during the hot summer months with temperatures known to approach, and likely exceed 70øF (Fisheries, 1975). Spawning gravels contain considerable sand silt which inhibit successful incubation. Low summer flows, lack of streambank vegetation, naturally high cut banks, and the logging of the steep slopes in headwaters all contribute to the problems which limit salmon production. A total of 562 acres have surface irrigation rights. Only one half of these are actually used (Ecology, 1980).
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Land ownership is broken down as follows: 33,022 acres-National Forest, 23,615 acres-Private, 117,010 acres-Corporate, 12,011 acres-State and 618-acres Municipal and County.
Present land use in the watershed includes: 176,772 acres-commercial forest, 2,283 acres-noncommercial, 5,084 acres-cropland, 280 acres-pasture, 668 acres-rural nonfarm, 449 acres-built up lands, and 100 acres-barren lands. A total of 562 acres have surface irrigation water rights (USDA, 1975) (Ecology, 1980).
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Wildlife found in the watershed include big game such as black-tailed deer, Roosevelt Elk, cougar, and black bear,: upland game, including grouse, pheasants, quail, and cottontail rabbit (mostly common to lower agricultural areas), and the furbearers; beaver, muskrat, raccoon, river otter, martin, weasel, and lynx.
Some of the waterfowl found in the area include ducks, and geese. There are also many other small species of animals such as various reptiles, amphibians, rodents, and song birds.
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Based upon projections from the Washington State Office of Financial Management, Forecasting Division (OFM, 1992), the entire Chehalis River Basin is experiencing growth. Using data from the three major counties (Thurston, Lewis, and Grays Harbor) this growth rate between now and the year 2000 could be 2.7% (low), 26% (high), or 11% (average).
Applying these figures to today's population and housing units results in the following estimates for the Satsop Basin:
By the year 2010, the growth rate could be 6.1% (low), 53% (high), or 23% (average):
While this subbasin has not experienced high or even average growth rates, high rates of growth in nearby population centers are encouraging residential development in rural areas. This spillover effect could cause growth to exceed traditional norms.
Residential developments in this subbasin include the communities of Matlock and Deckerville. Recreational homesites are being developed at several locations in this watershed.
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Water quality plans for this subbasin are reviewed in the basin-wide overview section of the Chehalis River Basin Characterization and the Water Quality Assessment.
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1990 Pop. in 2000 Units in 2000
Pop. Units low hi avg low hi avg
5000 2200 5135 6300 5550 2259 2772 2442
1990 Pop. in 2010 Units in 2010
Pop. Units low hi avg low hi avg
5000 2200 5305 7650 6150 2334 3366 2706