Topography and Geology
The Middle Chehalis basin consists of that portion of the basin draining into the Chehalis River between Grand Mound and Porter, excluding the Black River, which is treated elsewhere in this document. U. S. Geological Survey gaging stations are located on the Chehalis at both Grand Mound and Porter, providing information on water quality and quantity entering and exiting this section of the basin.
The middle Chehalis basin covers an area of approximately 259 square miles. Five major tributaries enter the river from the north: Scatter Creek, Harris Creek, Cedar Creek, Gibson Creek, and Porter Creek. Five major tributaries enter the river on the south side: Independence Creek, Garrard Creek, Davis Creek, Rock Creek, and Gaddis Creek.
The Chehalis River in the middle Chehalis basin cuts through the coastal hills, its valley forming a boundary between the Doty and Willapa Hills to the south and the Black Hills to the north. Elevations range from approximately 100 feet above mean sea level near Porter to 2,660 foot Larch Mountain, highest point in the Black Hills.
The Chehalis River flows through a broad, flat valley, ranging from one to three miles in width in the middle Chehalis basin. Slopes in excess of 50% are common in the upland areas.
Measurements of discharge are available for the Chehalis River at Grand Mound beginning in 1928 and from Porter beginning in 1952 (USGS, 1992). Average annual discharge at the two sites are about 2,800 cfs and 4,100 cfs at Grand Mound and Porter, respectively, representing a 46% increase in discharge as a result of flow contributions from the middle Chehalis basin and the Black River. The highest discharge recorded at the Grand Mound station was 68,700 cfs on January 10, 1990 and 60,400 cfs at Porter on January 11, 1990. A minimum discharge of 164 cfs was recorded at Porter in October of 1952, and a low mean flow of 82 cfs occurred at the Grand Mound station in August 1967 (USGS, 1992).
Discharge measurements are also available for some of the tributaries draining the Capitol State Forest. The Department of Natural Resources has maintained recording stations on several of these streams since the early 1980s. In addition, a station was established on the North Fork of Porter Creek in 1988, in conjunction with a fish habitat enhancement project.
The Chehalis River is still largely unconstrained through the middle Chehalis basin, with limited amounts of rip-rapping, channelization, or other flow-control measures. The only impoundment of consequence upstream from the middle Chehalis basin is located on the Skookumchuck River. During floods a large proportion of the valley in this stretch of the river is inundated, producing a channel often up to a mile wide.
Numerous oxbow lakes and sloughs are found along the Chehalis River through the middle Chehalis basin, although many wetland areas have been drained and converted to cropland or pasture.
Soils in this subbasin vary as a result of differing parent materials and the conditions under which they developed. Soils along the river are derived primarily from alluvial sediments and are deep and poorly drained. Soils on the uplands also are deep, but tend to be well drained. The upland soils of the middle Chehalis basin are generally stable and not excessively prone to landslides. However, there are some isolated locations where unstable soils on steeper slopes are found, particularly within the Capitol State Forest.
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The climate in this region is coastal, consisting of cool, wet winters and dry, warm summers. Mean monthly air temperatures at Oakville range from 39øF during January to 63øF during July and August (NOAA, 1991).
Annual precipitation in the middle Chehalis basin ranges from 45 inches to 60 inches, increasing with elevation and from east to west. The majority of the precipitation falls as rain, with short-lived snow packs common only at higher elevations. Precipitation intensity is low, with a 50 year recurrence interval, 24-hour, rainfall intensity ranging from 5.0 to 8.0 inches (Gladwell and Mueller, 1967).
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Using 1990 U.S. Bureau of Census data and maps for the area, and relating census block numbers to the watershed boundary of the Middle Chehalis basin, the subbasin population appears to be 13,000.
Based upon an average for the entire Chehalis River Basin of 2.29 people per household, there are close to 5,800 households in this subbasin.
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The primary land use in this region is commercial forestry in the uplands and agriculture along the Chehalis River and the lower reaches of the tributaries. Population densities are low.
Rochester is the largest unincorporated town in the middle Chehalis basin. Other areas of residential development include Oakville, Malone, Cedarville and Porter. Low density, rural residential development is scattered along the main river. Generally, all residential and commercial development is restricted to the main river valley and along the lower reaches of major tributaries. No residences are located on the land presently being managed for timber production.
Agriculture in this subbasin is concentrated along the Chehalis River. Dairy farming and crop production are both practiced in this area. Crops commonly grown include winter wheat, turf grass for sod, peas, and Christmas trees.
Forestry is the predominant land use in the middle Chehalis basin. The Washington Department of Natural Resources owns in excess of 100,000 acres of land in the middle Chehalis basin, approximately 40% of the total area, concentrated in the Capitol State Forest and the Lower Chehalis State Forest. This land in managed for timber production as well as recreational activities.
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Fisheries
The fish communities of the streams and ponds within the middle Chehalis basin are quite varied, representing a mix of native and introduced species. Of greatest commercial and recreational significance are the trout and salmon (collectively, salmonids). A recent review of the condition of salmonid stocks throughout the Pacific Northwest did not identify any Chehalis River stocks as extinct (Nehlsen et al., 1991). Wynoochee River spring Chinook salmon were the only Chehalis River race in imminent danger of extinction. No stocks using the middle Chehalis basin where identified to be at risk. However, the non-salmonid fish fauna of the Chehalis River contains at least one rare species.
The distribution of fish species found within the middle Chehalis basin is greatly influenced by size of the stream. The smallest headwater systems typically contain only a few species, usually cutthroat trout (Oncorhynchus clarkii ) and sculpin (Cottus sp. ), which are represented by several species in the middle Chehalis basin. In slightly larger systems, coho salmon (O. kisutch ), steelhead trout (O. mykiss ), and anadromous cutthroat trout are found, providing there is no blockage to migration. Non-salmonid fishes often found in these size streams include speckled and long-nosed dace (Rhinichthys osculus and R. cataractae ), redside shiner (Richardsonius balleatus ) and several species of sculpin. The lower reaches of the major tributaries and the mainstem are used seasonally by fall Chinook salmon (O. tshawytscha ) and chum salmon (O. keta ) for spawning and freshwater rearing, typically from September through June. Spring Chinook salmon adults and smolts migrate through the middle Chehalis basin from April through June. Non-salmonid fishes occupying these river habitats include a wide variety of native and introduced species.
Ponds, sloughs and other slow-water habitats in the middle Chehalis basin often support several introduced species in the family Centrachidae (bass and sunfish) as well as the Olympic mudminnow (Novumbra hubbsi ) (Beecher and Fernau, 1982) . The Olympic mudminnow, with a distribution restricted to coastal streams in Washington, is listed as a species of special concern by the state. A black color-variant of the three-spined stickleback (Gasterosteus aculeatus ) is unique to the lower Chehalis River basin. However, it is unclear whether this fish is found within the middle Chehalis basin.
Fish Habitat and Population Levels
A thorough survey of the salmonid fish populations and habitat conditions of several of the tributaries in the middle Chehalis basin was conducted during the early 1980s (Carman et al., 1984). All the streams surveyed were in the Capitol State Forest. The sites ranged in size, exhibiting mid-summer discharges ranging from 0.40 cfs to 4.98 cfs. Water temperature on the dates that fish populations samples were taken ranged from about 12øC to 17øC.
The low population levels of coho and cutthroat are likely due to a combination of factors, including fishing and water quality problems in the inner estuary of Grays Harbor. However, habitat conditions in these systems was radically altered during the 1920s, 30s and 40s as a result of railroad logging of the area. This type of logging, as well as splash damming, were common in the middle Chehalis basin. Both practices severely reduce amounts of large wood in the channels, a structural component of streams primarily responsible for the formations of pools (Bilby and Ward, 1989; 1991).
The proportion of the surface area of the study sites composed of pools ranged from 3% to 77%. Average for all the surveyed sites was approximately 43%. Coho and older-age classes of cutthroat trout favor pool habitat (Bisson et al., 1982). Thus, the relative scarcity of this type of habitat likely contributed to the low densities of these species and age classes in the Capitol State Forest streams.
Cover at the surveyed sites consisted of undercut banks, logs, and smaller woody debris. The relative amount of these cover items varied widely among the sites.
Wildlife Habitat and Vegetation
The majority of the land within the middle Chehalis basin is covered in second- and third-growth coniferous forest varying in age from recently cut to 60 years old. Little old-growth forest is found in this area, although remnant patches of uncut timber are found in a few locations. However, the Capitol State Forest is currently proposed for designation as a spotted owl habitat management area. If this area is so designated, substantial areas of older age classes of the timber will eventually be preserved.
The dominant tree species in the middle Chehalis basin are Douglas fir (Pseudotsuga menziesii ), western hemlock, (Tsuga heterophylla ), western redcedar (Thuja plicata ), and red alder (Alnus rubra ). Black cottonwood (Populus trichocarpa ) is common along the Chehalis River.
This subarea of the Chehalis basin supports a wide variety of wildlife species. Key species of recreational interest include blacktail deer, Roosevelt elk, black bear, waterfowl, ruffed grouse. Bald eagles and ospreys are common along the river, using the streamside trees for nesting and roosting. Spotted owls also are found within this drainage.
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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) 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 middle Chehalis basin:
By the year 2010, the growth rate could be 6.1% (low), 53% (high), or 23% (average):
While this subbasin
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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.
Back to top or back to Action Plan home page or back to Action Plan Vol II Index Revised and corrected, April 2000 -
1990 Pop. in 2000 Units in 2000
Pop. Units low hi avg low hi avg
13000 5800 13351 16380 14430 5956 7335 6462
1990 Pop. in 2010 Units in 2010
Pop. Units low hi avg low hi avg
13000 5800 13793 19890 15990 6154 8874 7161