Topography and Geology
The Upper Chehalis subbasin above the Newaukum River drains about 450 square miles. The watershed is located in Lewis, Pacific and Cowlitz Counties. The main tributaries include the Main Fork, the South Fork, Elk Creek and Stillman Creek.
The Chehalis River originates in the Willapa Hills which are part of the Coast Range. Generally the elevation is below 2,400 feet with Baw Faw Peak being the highest point at 3,110 feet. The river valley on the main fork broadens out below Pe Ell and on the South Fork at the Lewis County/Cowlitz County line. The elevation at Centralia is 185 feet.
The Chehalis River is the principal river in this subbasin. Its headwaters are south of Pe Ell. The river flows northeast toward Chehalis-Centralia then turns northwest and eventually empties into Grays Harbor. The mean annual discharge of the upper Chehalis River at the U.S. Geological Survey gaging station near Doty is 575.4 cfs. A peak flow of 27,500 cfs was recorded here on January 9, 1990. A low mean flow recorded for the Chehalis River at this station was 18 cfs on one day in 1953 (USGS, 1992).
There are four major geological formations in the Upper Chehalis subbasin. They are: 1) alluvial deposits of the Quaternary Age, 2) alluvial terrace deposits of the late Tertiary to Quaternary Age, 3) volcanic flows and interbeds of the Tertiary Age, and 4) sedimentary rocks of the Tertiary Age.
The uplands of the basin are generally made up of rocks of the Tertiary Age, predominantly volcanic flow, and fine-grained sedimentary rock such as shale, siltstone and sandstone. Tertiary Age formations normally yield only small quantities of ground water and often this water is unsuitable for domestic use due to its high mineral content. Concentrations of dissolved solids greater than 500 mg/L, and hardness (as CaCO3) greater than 120 mg/L are not unusual in water supplies from these older formations.
Alluvial deposits of the Quaternary Age occur mainly in the valley of the Upper Chehalis River subbasin. They have a thickness which ranges from a few feet to more than 55 feet in the area of the Chehalis Indian Reservation. These unconsolidated materials consist of silt, sand and clay in the upper part, and sand and gravel in the basal portion. The porosity and permeability are not known. Most wells obtaining water from this geologic unit seldom pump in excess of 50 gallons per minute. However, yields of this size are obtained with no drawdown, indicating moderate to high porosity and permeability.
The soils have developed over a long period of time and therefore have deeply weathered parent materials and heavy textures. In spite of this, the majority have structures that can accommodate the penetration of water, air, and roots. Because they are leached and slightly acidic, their organic-matter content is moderately high, but supplies of available nitrogen and phosphorus are deficient.
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Climate
The Upper Chehalis subbasin has mild, rainy winters, and warm, dry summers. The upper basin is largely rain-fed with precipitation levels which range from 40 inches at Centralia to 120 inches in the Willapa Hills. About 85% of this annual precipitation occurs during the periods from October to April. Prolonged periods of drought occur occasionally in the summer with no rainfall for 30 to 60 days. Snowfall at the higher elevations occurs during the winter and can exceed 24 inches.
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Existing Population
Using 1990 U.S. Bureau of Census data and maps for the area, and relating census block numbers to the watershed boundary of the Upper Chehalis Basin, the subbasin population appears to be 5,200.
Based upon an average for the entire Chehalis River Basin of 2.29 people per household, there are close to 2,300 households in this subbasin.
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Beneficial Uses of Water
There are small diversions for irrigation and domestic use. A community water system serving Adna, Boistfort, and Curtis uses Stillman Creek as its source. Pe Ell obtains its municipal water from Lester, Grim, and Mahaffey Creeks; tributaries of the Chehalis River located on Weyerhaeuser timber holdings. Doty and Dryad receive their water from wells, but Elk Creek is being investigated as a source for a common municipal water system for these two communities.
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Existing Land Use Patterns
Land uses within the Upper Chehalis River subbasin are primarily forestry, agriculture, and residential. Forest lands are located primarily on the upland areas. Agricultural lands are concentrated in the river valleys. The residential areas are concentrated along Highway 6 and the small communities of Adna, Boistfort, Dryad, Doty and Pe Ell.
The forest products industry serves an important economic role in the Upper Chehalis subbasin. There is a logging operation located in the town of Pe Ell employing over 100 people. A transmission and distribution pole manufacturing facility located at Curtis employs over 30 people. There are many Christmas tree plantations located in the subbasin. Minor forest products such as ferns and fir boughs are also harvested throughout the subbasin.
Agriculture also serves an important role in the economy. The most intensive farming is done on the fertile alluvial floodlands. Field crops, poultry, beef cattle and dairy cattle are important elements of the agricultural economy. The farms in the subbasin are following the national trends of increasing in acreage while decreasing in number.
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Anticipated Population and Land Use
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) the 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 Upper Chehalis Basin:
1990 Pop. in 2000 Units in 2000 Pop. Units low hi avg low hi avg 5200 2300 5340 6552 5772 2362 2898 2553
By the year 2010, the growth rate could be 6.1% (low), 53% (high), or 23% (average):
1990 Pop. in 2010 Units in 2010 Pop. Units low hi avg low hi avg 5200 2300 5517 7956 6396 2440 3519 2829
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.
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Biological Resources
The Upper Chehalis subbasin is an important spawning area for anadromous fish: Chinook and coho (silver) salmon; and steelhead and sea-run cutthroat trout. The Upper Chehalis subbasin and its tributaries spawn many of the fish which are harvested by the sport and commercial fishing industries. Resident cutthroat and rainbow trout are other sport fish native to the basin. Sport angling for these species is a popular leisure activity in the Upper Chehalis subbasin.
Wildlife resources of the Upper Chehalis River include big game (blacktailed deer, black bear and elk), game birds (pheasant, grouse and pigeons), fur animals (beavers, minks, muskrats and river otters), and various waterfowl. Hunting is a popular activity in the Upper Chehalis River. Seasonally flooded lands provide habitat for some waterfowl. The Upper Chehalis subbasin also lies in the Pacific flyway for migratory birds including Canada geese.
The Upper Chehalis River Basin supports dense, natural vegetative cover as a result of the prevailing maritime climate. Forests occupy about 90% of the area. The species include Douglas fir, western hemlock, noble fir, silver fir, western red cedar, western red alder, sitka spruce, black cottonwood and big leaf maple. The understory includes evergreen blackberry, wild rose, skunk cabbage, salal, Oregon grape, vine maple and a variety of ferns. All of the natural mature and old-growth stands have been logged and only wild second-growth stands and managed plantations remain.
The dominant species is Douglas fir, accounting for 70% of the volume by species. Western red alder, sitka spruce, western red cedar and cottonwood are found in areas of poorly drained mineral soils. The river bottoms, under natural conditions, are generally occupied by a variety of herbaceous and wood vegetation including scattered stands of hardwoods and second growth coniferous timber.
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Water Quality Plans
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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Revised and corrected, April 2000 -