The Chehalis River Basin is the largest river basin in the state of Washington outside the Columbia River system (Figure 1). The total drainage area of the Chehalis Basin is 2,660 square miles of which approximately 85% is forest lands. Approximately 259 square miles (166,000 acres), or 9.7% of the basin is agricultural. Intensive agriculture and irrigation occur mostly in the low-lying valleys along the Chehalis River and its tributaries. Only 3% of the basin is urbanized (USDA, 1975).
Water quality in the Chehalis River Basin has been degraded by both point and nonpoint sources of pollution. In 1990, the Washington State Department of Ecology listed four Chehalis River segments, three segments of the Newaukum River, two segments of the Wynoochee River, three other tributaries - Salzer, Dillenbaugh, and Wildcat Creeks, and Inner and Outer Grays Harbor as water quality limited (WQL) (Ecology, 1990). Problems include low dissolved oxygen, high temperature, and bacterial contamination. Continued population growth and developmental pressure threaten to further impair beneficial uses of the Chehalis River, its tributary streams, and Grays Harbor.
The four major population centers of the basin, Chehalis, Centralia, Aberdeen, and Hoquiam, depend on surface waters for a portion of their municipal and industrial supplies. The Chehalis River system is largely rain-fed with precipitation levels which range from 45 inches per year in the valley near Chehalis/Centralia to over 220 inches in the Olympic Mountains. The Chehalis River system flows through three distinct ecoregions; the Cascade (including the Olympic Mountains), the Puget Lowland, and the Coast Range before emptying into Grays Harbor near Aberdeen (Omernik, 1987).
The basin is bounded on the west by the Pacific Ocean, on the east by the Deschutes River Basin, on the north by the Olympic Mountains, and on the south by the Willapa Hills and Cowlitz River Basin. Elevations vary from sea level at Grays Harbor, to 5,054 foot Capitol Peak in the Olympic National Forest.
The basin encompasses large portions of Grays Harbor, Lewis, and Thurston counties, and lesser parts of Mason, Pacific, Cowlitz, Wahkiakum and Jefferson counties (Figure 2). The mainstem and South Fork Chehalis drain uplands south and west of Adna. Two major tributaries in mid-basin, the Newaukum and Skookumchuck Rivers, have their headwaters in foothills of the Cascade Range. Another mid-basin tributary, the Black River, originates in wetlands near Black Lake. The largest tributaries, the Satsop and Wynoochee Rivers, arise in southern extensions of the Olympic Mountains and join the mainstem shortly before its terminus at Grays Harbor. The Humptulips River, as well as the Hoquiam and Wishkah Rivers, also have their headwaters in the southern Olympic Mountains and flow into Grays Harbor; the Humptulips into North Bay, the Hoquiam into the inner estuary of Grays Harbor, and the Wishkah into the Chehalis River near the mouth. The Johns and Elk Rivers flow into the South Bay of Grays Harbor.
Forests dominate the landscape of the Chehalis River Basin, especially at higher elevations. Seventy-six percent of the forested land is privately owned, most of it corporate owned. Public forest lands total about 350,000 acres (Figure 3). Agriculture is the principal land use in river valleys, particularly field crop production and animal pasturage (USDA, 1975).
The major population centers in the study area are Chehalis (6,000) and Centralia (12,000) in the upper basin, and Aberdeen (19,000) and Hoquiam (9,700) at the mouth of the Chehalis. However, southwest Thurston County is undergoing rapid development along the I-5 corridor and around Black Lake. The Chehalis Indian Reservation is located near the mouth of the Black River, and the Quinault Tribe has fishing rights from the mouth to the headwaters of the Chehalis River. The total population of the basin is approximately 130,000 people (Bureau of Census, 1990).
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Land Use
Land within the Chehalis River Basin is mostly forest cover with interspersed agricultural and residential areas. Forest lands, which constitute approximately 77% of the Upper Chehalis Basin (upstream of Porter) and 91% of the lower basin (downstream of Porter), are generally located on the upland areas with scattered amounts in the wet bottom lands (USDA, 1975). Most forested acres are corporate-owned with the remainder being privately or government owned (Capitol State Forest, Mt. Baker-Snoqualmie National Forest and Olympic National Forest).
Approximately 257 square miles (164,000 acres), or 9.7% of the Chehalis River Basin is agricultural (USDA, 1975). Commercial dairy, livestock and crop farming operations are predominantly located in the low-lying valleys adjacent to the Chehalis River and its major tributaries, including the South Fork Chehalis, Newaukum, Skookumchuck, Black, Satsop and Wynoochee rivers, and Scatter Creek. Principal crops include pasture, hay, and silage, with some vegetables and small grains. Berries are grown in the Chehalis-Centralia area. Several Christmas tree farms are located along the Skookumchuck River and in the Chehalis-Centralia area. Several private aquaculture facilities are located in the Grand Mound/Rochester area.
Industrial development is mostly limited to the Chehalis/Centralia and Aberdeen/Hoquiam areas and to the coal mine/power plant site south of Bucoda, with isolated industrial facilities located throughout the basin. The principal industrial use of water is in the manufacturing of wood, pulp and paper products. Aberdeen's industrial water system supplies most of this water from the Wynoochee River.
Only 3% of the Chehalis River Basin land-base is urbanized, but as population continues to grow, more and more land is being converted to residential use. The basin's location halfway between Puget Sound and the Columbia River, the proximity of major transportation routes, a rich natural resource base, and the aesthetic beauty of the area are factors which will continue to contribute to its rapidly expanding population base.
The existing anadromous fish resources of the basin are of regional and national significance to sport, tribal, and commercial fishing.
LandSat Satellite Imagery - Land Use in the Chehalis River Basin
In 1991, Weyerhaeuser Company purchased LandSat Thematic Mapper satellite data and, on a contract with the Lewis County Conservation District, analyzed it for land use in the Chehalis River Basin (Figure 4) (Weyerhaeuser, 1991). The overall accuracy of producing remote sensing land cover maps and associated statistics hinged upon the following factors:
A. - Existing data - LandSat Thematic Mapper dated September 10, 1989.
B. - Condition of data - less than 10% of the scene had cloud cover which had a limited impact on the quality of the land cover analysis. Note: The Thematic Mapper Scanner used for this data consisted of REFLECTED SPECTRAL VALUES ONLY (bands 2, 4, and 5). Reflected light records a value that is dependent on time of day, sun angle, season, atmospheric interference and terrain shadows. These variables are equalized for each database.
C. - Ground Truthing Data - All a priori knowledge of this watershed is based upon the Weyerhaeuser Geographic Information System (GIS), an in-house system referred to as the Forestry Inventory Regeneration System (FIRS).
FIRS data exclusively describes Weyerhaeuser timberlands - all lands outside of Weyerhaeuser ownership were classified from other commercial maps of intuitive landscape features, i.e. bodies of water, urban development, etc.
D. - Shadows - Terrain and cloud shadows obscured the actual spectral values of the land cover to some degree, especially in the south-east portion of the watershed. Since shadows do have a unique spectral signature, the land cover statistics will control for this interference as much as possible.
Under normal cloud-free circumstances the accuracy of a classified scene is generally 85%, however with the excessive atmospheric interference in this particular scene, the level of accuracy in land cover assessment is reduced.
E. - Chehalis River Basin Spectral Signature categories:
Per the request of the contractor (Lewis County Conservation District) and the capabilities of discriminating land cover/use values, the classification was grouped (recoded) into the following categories, along with the classified percentage of land use for each category:
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Climate and Hydrology
The climate of the Chehalis basin is characterized by mild temperatures both summer and winter, and by wet winters and dry summers. The greatest amount of precipitation falls between the months of October and May, with river discharge peaking between December and March. Approximate average annual discharge of the entire basin is 11,208 cubic feet/second (cfs). Annual precipitation varies from a minimum of 40 inches in the central portions of the basin to a high of 220 inches in the headwaters of the Wynoochee and Humptulips Rivers (Figure 5). Precipitation usually falls as rain with some snowfall in the higher elevations of the Olympics. Temperature variations prevent snow from accumulating over any prolonged period of time, except in mountainous portions. The frost free season varies from 163 to over 190 days except for mountainous localities. Average temperatures over much of the basin range from 38ø to 40ø F. during January and from 59ø to 64ø F. during July. Delayed runoff from snow melt is relatively minor, and likely restricted to the Wynoochee, Satsop, and Humptulips Rivers.
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Topography and Geology
In Wintergreen, Robert Michael Pyle's award-winning collection of essays about the Willapa Hills, and the "ring of rivers" around them, the Chehalis River is splendidly described.
"...The Chehalis empties into big, spade-shaped Gray's Harbor, where the twin cities of Aberdeen and Hoquiam share the north shore of its estuary. Chehalis water finds its way into the Pacific over the bar at Westport, a salmon-charter and whale-watching town on the tip of a spit. Seaside condominiums fall in line across the harbor's mouth at Ocean Shores.The bay to their backs is home to mills, industry, and shipping as well as to hundreds of thousands of shorebirds on the mud flats and salt marshes of Bowerman Basin. Dr. Steve Herman, Evergreen State College biologist, has been working with others to save Bowerman Basin from industrial expansion. Herman has called the Bowerman birds "a touchstone to a finer time, a richer time beyond our species' memory."
A heretofore neglected wetland stuck between a highway, an airport, and a sewage lagoon, the basin occupies just five hundred acres. As Janet Anthony, organizer of Friends of Bowerman Basin, has pointed out, this remnant constitutes only 2 percent of all inter-tidal habitat around Grays Harbor; yet half of the million shorebirds passing through the harbor depend on the basin in spring. Of international migratory importance, Bowerman's fate could redeem or confirm the ecological disasters of the rest of the region.
Following the Chehalis River upstream, east through a broad, rural valley, we pass at Satsop two doomed dinosaurs - twin nuclear cooling towers of the massive mistake known as WPPSS. When the Washington Public Power Supply System planned to build five new nuclear power stations to serve a market that didn't exist with electricity it could never afford to generate, it arranged to service two of the nukes with Chehalis water at Satsop. When WPPSS defaulted on the greatest private debt in fiscal history, the northwest edge of Willapa was spared (for the time being) entry into the nuclear age with all its anguish.
The Chehalis turns southeasterly around the flank of the Black Hills, a small range that separated the northern Willapa drainages from those of southern Puget Sound. Along the old Union Pacific-Northern Pacific railroad line, through the Chehalis Indian Reservation, runs the river that predates them both, and on into the town that bears it name, sister to neighboring Centralia. The stretch prior to Chehalis passes Grand Mound and Ford's Prairie, artifacts of glacial outwash grasslands. These prairies, a rare feature in western Washington, bear the famous and oddly symmetrical Mima Mounds - fascinating hillocks that we owe either to gophers or glaciers.
But what is this? Now the Chehalis, irresolute river, turns west again, its valley forming the route of the main (and only) state highway across the Willapas. It nearly reaches the crest when it gives up and strikes south once more, and that way continues to its headwaters high in the Gray's River Divide. Arising near the Chehalis, the Willapa River runs westward out to Willapa Bay, completing the midrange crossing that the Chehalis began. A third pair of twinned towns, South Bend and Raymond, perch on its outflow.
Actually, the Chehalis is a two-headed stream. The main headwater branches, the South and East forks, bracket Baw Faw Peak between them. Baw Faw, the highest point in the Willapa Hills, rises to 3,110 feet but hardly warrants the title "peak." On its one side, the South Fork flows pastorally through a broad dairy valley with towns named Boistfort (the original of Baw Faw) and Wildwood, after sneaking down from its start in the hills. The East Fork arises on the other side of the mountain and is truly a mountain stream. At Fisk Falls, it cascades through deep green gorges of maidenhair and saxifrage, the haunts of dippers and Olympic salamanders. Constricted between stone walls, it runs six feet wide and ten deep in spring, but driftwood wrack high up on mossy bluffs betrays the astonishing depth achieved during winter flood. After the canyon, the green swirls spread into a broad, shallow, and sparkling sheet of stream that runs down to the tired logging town of Pe Ell. A final thrill before the gentle run to the sea, Rainbow Falls carries the East Fork to its confluence with the South.
Just a small eminence separates the Chehalis and Cowlitz rivers. In fact, their tributaries come within a mile of one another at two or three spots in the Cascades foothills. But for small quirks in the countryside, this river that couldn't make up its mind, the Chehalis, might have (a) run around the Black Hills into Puget Sound; (b) joined with the Willapa River not far below their near-common headwaters, for a much shorter trip to the Pacific than it eventually takes; or (c) popped down into the Cowlitz from the Chehalis, then southward to the Columbia. Instead, it twisted stubbornly and persistently around like a clock spring until it forged its own course west, to meet the sea on its own terms. Otherwise, there might have been no Gray's Harbor as we know it, and no cities of Aberdeen and Hoquiam...
...Of course, the river had no such choice in the matter. And the "small quirks in the countryside" that determine its course really consisted of such weighty matters as glacial dams melting and making the Black River as big as the Columbia where it joined the Chehalis; earth uplift on a gradual but decisive scale; and the Gray's River Divide, looks puny on a map or from a distance, but might as well be the Continental Divide to a river."
The rocks exposed in the basin vary from early Tertiary to Quaternary in age (Figure 6). They consist of marine and nonmarine sedimentary rocks with interbedded volcanic rocks. They are folded and faulted, and, in most cases, buried by glacial till and outwash deposits and by recent alluvium.
Minerals of economic importance found in this basin include coal, clay, sand, and gravel. A steam plant east of Centralia is fueled by coal from local sources. Clay found in the Chehalis vicinity is used for bricks and tile.
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Soils and Vegetation
Five major soil groups are found in the Chehalis River Basin (Figure 7). The most extensive (46.8% of the basin) is the Group E association which occupies the western two-thirds of the basin on the foothills and steep slopes between the Thurston County line and the coast (USDA, 1975). Vegetation is predominantly forest, and the two major forest types occur largely because of precipitation patterns. They are the Sitka spruce - western hemlock - western redcedar type along the coast with predominantly hemlock stands extending inland to the eastern portion of Grays Harbor County and the Douglas fir - western hemlock type in the eastern part of this soils group.
Soils Group A (5.8%), consisting of steep and very steep, well-drained soils is situated on the southern Olympic Slope in the northern tip of the basin. Stands of true fir and mountain hemlock dominate this area. The remaining eastern third of the basin consists of Group C lands (26.8%) found on steep glacial plains and gently rolling terrain surrounding the Chehalis-Centralia urban area. Scattered patches of Douglas fir and patches of Oregon white oak are interspersed with grassy, prairie-like areas. Scotch broom is increasing on these open lands.
Soils Group D lands (19.4%) consist of nearly level to gently sloping, alluvial soils in the Chehalis River flood plain and extending up the major tributaries. Western redcedar, red alder, black cottonwood and willows are found on the poorly-drained fringes surrounding flood plains, pastures and croplands. Douglas fir is found on better-drained soils. The immediate coast from Grayland north through Westport and on the north beach area to Copalis are in Soils Group B (1.2%). Soils are deep, sandy, poorly-drained deposits supporting shore pine. Adjacent to tidal estuaries, Sitka spruce, western redcedar and western hemlock exist.
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Water Supplies
At the present time, there are few dams or diversion structures on the rivers of the basin. The Hoquiam and Wishkah Rivers have diversion structures to supply municipal and industrial water to the Hoquiam/Aberdeen area. These structures allow Hoquiam to remove 2.5 cfs from the Hoquiam River and Aberdeen to divert 10 cfs from the Wishkah River. Beneficial uses of the Wynoochee Dam on the Wynoochee River include fish and wildlife habitat, irrigation, recreation, flood control, and municipal and industrial water supply for the city of Aberdeen. The reservoir has a maximum retention capacity of 70,000 acre-feet. The Bloody Run Dam on the Skookumchuck River supplies up to 54 cfs for use in the Centralia Steam Electric plant. A dam on the North Fork of the Newaukum River contributes municipal and industrial water (up to seven cfs) to the cities of Chehalis and Centralia. Other small dams scattered throughout the basin contribute to rural water supplies (Figure 8) (USGS, 1992).
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Fish and Wildlife Resources
The lakes and streams within the Chehalis River Basin provide vital habitat for numerous species of fish. Streams range in character from cold, swift-flowing, high elevation tributaries to warmer, meandering, lowland valley rivers. There are 180 lakes, ponds, and reservoirs in the basin. Most of these are lowland waters which support varied fish and wildlife species.
There is a wide variety of wildlife within the basin. There are four main categories: big game, upland wildlife, fur bearers, and waterfowl. Forest harvesting activities open up browsing areas for big game animals. Shrubs and other ground cover invade the logged sites and provide ideal habitat for large grazing animals such as elk. Upland wildlife are the most widely distributed and numerous class of species in the basin. Furbearing animals generally dwell in protected, forested areas or near waterbodies. The Chehalis basin is an important migrating and wintering area for waterfowl in the Pacific Flyway.
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Land Use Impacts on Water Quality
Forestry Practices
Water quality problems related to forestry practices result from increased storm water runoff, contamination from pesticides and fertilizer, increased water temperatures, and siltation and sedimentation from erosion.
In 1975, there were approximately 2,800 acres of land in the basin with severe erosion problems due to loss of vegetative cover (USDA, 1975). Soil erosion is the major cause of water quality problems related to sedimentation and suspended solids. Erosion is the result of water flowing over steep, unstable soils. When vegetative cover is removed from unstable soils, the erosion process is greatly accelerated. Over 1,590,000 acres in the Chehalis River Basin have potential erosion problems, with nearly 76% having potentially severe erosion problems if vegetative cover is removed (USDA,1975).
The greatest potential erosion problem in this basin is associated with the harvest of commercial forests (USDA, 1975). Over 94% of the Chehalis River Basin land with severe erosion potential is commercial forestland. It is vulnerable to road building and other logging practices which can contribute to erosion problems. Almost 85% of the commercial forest land in the Chehalis Basin has moderate to severe erosion hazard potential (USDA, 1975). Using a conservative 2% annual harvest rate, 34% of the basin's timber lands have been harvested from 1975-1992.
Forest roads are recognized as a significant source of forestry related water pollution. The U.S. Forest Service has conducted an erosion inventory of the Satsop River headwaters in the Olympic National Forest (Lewis, 1992) which shows that 97% of the erosion sites are road related (68% sidecast failures or road drainage failure and 29% cutbank failure/erosion).
Agriculture
Most of the remaining 6% of the Chehalis Basin with a severe erosion hazard is in agricultural use, with the rest distributed among other land use categories. More than 62% of the land used for agricultural purposes, about 102,000 acres, has only a slight erosion hazard, while only 16,800 acres (10%) have a moderate erosion hazard, and 31,000 acres (19%) have a severe erosion hazard.
Agriculture will probably intensify within the basin as residential encroachment continues to reduce the agricultural acreage base and tax rates force higher returns from these lands. Of the 1.69 million acres in the basin, only 166,000 (9.7%) can presently be classified as agricultural. Seeded and hay pasture, brush pasture, and native pasture comprise about 94% of the agricultural lands. Intensification of agriculture may also induce the expansion of irrigated lands where land and water resources allow.
Poorly adapted sites for livestock feeding and unregulated livestock waste disposal is causing pollution problems in many areas. Projected increased demands for dairy products and beef could accelerate waste disposal problems and require regulation of lands for this specialized use. The Washington Department of Ecology plans to institute a dairy waste permit program in 1993 for all commercial dairies in Washington.
Streambank Erosion
Streambank erosion is a serious problem in many areas. Approximately 544 miles of streambank have a moderate problem and 268 miles have a serious problem. Some of the worst problem streams include the Newaukum River with 27 miles of serious erosion, the Skookumchuck River with 12 miles, the Wynoochee River with 28 miles, the Humptulips River with 35 miles, the main Chehalis River with 41 miles, the Satsop River with 17 miles, the South Fork of the Chehalis River with 18 miles, the Wishkah River with 9 miles, and Lincoln Creek with 6 miles.
Flooding
Sediment is usually transported by floodwaters. Sediment is deposited on cropland and in urban areas, affecting both residences and business establishments. Sediment reduces water quality and destroys fish habitat in rivers and streams. While all areas that flood experience some sediment damage, the main problem is in Grays Harbor. Here, sediment fills in the navigation channel and smothers shellfish. The cost of dredging the harbor is over $500,000 annually (Corps of Engineers, 1982).
Development
Although most of the land in the basin is in forest or agriculture, pressures exist to convert some lands to other uses - primarily housing. Subdivision of land for urban or rural nonfarm residential development often has the effect of increasing taxes on adjacent land. These increased taxes often force owners to sell their land or to convert it to more intensive uses.
Land proposed for subdivision is often unsuitable for residential development because of septic tank limitations; usually sewage treatment facilities are unavailable. This can result in water quality degradation and health hazards from bacterially contaminated water. More than 81 % of the basin is classified as having severe to very severe limitations on septic tank operations (USDA, 1975).
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There are fourteen major subbasins, including Grays Harbor, comprising the Chehalis River Basin (Figure 9). The basin includes parts of eight counties and includes Water Resource Inventory Areas (WRIA) 22 and 23. Detailed descriptions of each subbasin follow this brief summary section:
A. - Upper Chehalis Drainage - above the Newaukum River
The Chehalis River originates in southwestern Lewis County and flows northeast to the Chehalis-Centralia area. The Upper Chehalis drains about 438 square miles with an average annual discharge of 1,600 cfs.
B. - Newaukum River Drainage
The Newaukum River originates in the eastern portion of the Chehalis Basin and flows westerly to join the Chehalis River near Chehalis at river mile (RM) 75.2. It drains a 158 square mile area, with an average discharge of 506 cfs.
C. - Middle Chehalis - below Newaukum River and above Grand Mound, excluding Skookumchuck River Drainage.
The Middle Chehalis Subbasin above Grand Mound consists of the minor streams between the mouth of the Newaukum and the gaging station at Grand Mound. The total watershed area is 118 square miles, and the two principal tributaries are Lincoln Creek and Salzer Creek. The average annual discharge of the tributaries is 271 cfs and the drainage area is 118.0 square miles.
D. - Skookumchuck River Drainage
The Skookumchuck rises in the westernmost region of the Mt. Baker-Snoqualmie National Forest and flows in a northwesterly direction to the town of Bucoda, and from there to a confluence with the Chehalis River at Centralia. With its tributaries, it drains 181 square miles. Much of the basin is in coniferous forest, but the river valley has agricultural use. The average annual discharge from the basin is estimated to be 540 cfs. A major tributary of the Skookumchuck is Hanaford Creek with a drainage area of 58 square miles and an average annual flow of 85 cfs.
E. - Middle Chehalis - below Grand Mound, between Grand Mound and Porter
The Middle Chehalis - below Grand Mound, is that portion of the Chehalis Basin between the USGS gage at Grand Mound and the gage at Porter, exclusive of the Black River Drainage. The watershed area is 263 square miles. The average annual discharge of the Chehalis River at Porter from January 1952 to September 1972 was 4,287 cfs.
F. - Black River Drainage
The Black River originates at Black Lake and flows in a southwesterly direction to join the Chehalis River near Oakville. It drains 136 square miles and has an estimated annual runoff of 330 cfs. Black Lake is included in this drainage, however, the natural channel from lake to river is choked by vegetative growth and beaver dams. The Black River may actually originate from springs in this area.
G. - Cloquallum Creek Drainage
The headwaters of Cloquallum Creek are about 6 miles north of McCleary, in Mason County. The stream flows southward about 20 miles to join the Chehalis at RM 25.2. The Cloquallum drainage area, with the inclusion of Wildcat Creek, covers an area of about 65 square miles. The average discharge of the Cloquallum is 375 cfs.
H. - Satsop River Drainage
The Satsop River originates in the southern part of the Olympic Mountains and flows southward to join the main stem Chehalis River at RM 20.2 near the town of Satsop. The Satsop has four major tributaries: the East, West, and Middle Forks, and Decker Creek. The subbasin covers 299 square miles. The average flow of the Satsop is 1,968 cfs.
I. - Wynoochee River Drainage
The Wynoochee River has its headwaters in the Olympic Mountains and flows southerly to join the main stem Chehalis River at RM 13.1 near the town of Montesano. The main tributaries to the Wynoochee are Schaefer Creek and Black Creek. The Wynoochee River drains a basin of 185 square miles. Rainfall averages range from 75 inches annually in the lowlands up to 220 inches annually in the Olympic Mountains. Retention time of basin runoff is characteristically short and river levels rise and fall rapidly. Since 1972, river flows have been regulated by the Wynoochee Dam about 46 miles upstream from the mouth. The average discharge is 1,316 cfs.
J. - Wishkah River Drainage
The Wishkah River Basin drains the southern slopes of the Olympic Mountains and covers an area of 100 square miles. Approximately 6 miles above Aberdeen, the East and West Forks of the Wishkah combine. They flow into the Chehalis Basin at RM 0.15. Average annual discharge figures are unavailable.
K. - Hoquiam River Drainage
The Hoquiam River originates on the southern slopes of the Olympic Mountain range and drains an area of 90 square miles. The East and West Forks and main branch all flow southerly and converge above the city of Hoquiam. The Little Hoquiam River flows eastward and joins the combined river about one-half mile upstream from the confluence with the East Fork. The river flows into Grays Harbor between the cities of Aberdeen and Hoquiam. No records for average flows are available.
L. - Humptulips River Drainage
The East and West Forks of the Humptulips River originate in the Olympic National Forest and merge 4.5 miles upstream of the town of Humptulips. The river flows southwesterly to Grays Harbor at North Bay. The Humptulips drains an area of 245 square miles. The average discharge is 1,344 cfs.
M. - Lower Chehalis Drainage - Below Porter
The Lower Chehalis drainage includes the remaining area below Porter not discussed in the Cloquallum, Satsop, Wynoochee, Wishkah, Hoquiam, and Humptulips drainages. The total area of the Lower Chehalis Drainage is 169 square miles. The two largest creeks that merge with the Chehalis River (below Porter, but above the mouth) are Mox Chehalis Creek, which drains 27 square miles, and Newman Creek, with a drainage area of 23 square miles. The two largest rivers in this subbasin that empty directly into Grays Harbor are Johns River and Elk River. These rivers drain forested areas. Average annual discharge figures are unavailable for this subbasin.
N. - Grays Harbor
Grays Harbor is the fourth largest coastal estuary in the western United States. The estuary is a shallow basin with an average depth of 20 feet at Mean Lower Low Water. Tidal flows dominate currents in this estuary. The Chehalis River is brackish and tidally influenced. The estuary is a partially mixed system and some salt water extends into the mouth of the Chehalis. Mean daily inflow into Grays Harbor is about 11,000 cfs, of which the Chehalis River contributes approximately 8,000 cfs. Summer low flows are about 1,000 cfs (Grays Harbor Estuary Management Plan, DEIS, 1981).
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Revised and corrected, April 2000 -
