The Chehalis River is approximately 125 miles long, originating in the Willapa and Doty hills southeast of Aberdeen and flowing northeast and then northwest before emptying into Grays Harbor. In addition to the Willapa and Doty hills, the basin uplands include the western flank of the Cascade Mountains and the southern Olympic Mountains. The entire Chehalis drainage basin has an area of approximately 2,114 square miles, with 1,294 square miles draining above the Chehalis River at Porter gage and 895 square miles draining above the Chehalis River at Grand Mound gage.
From its headwaters in the extreme southwestern corner of the basin, the Chehalis River flows east for about 25 miles to its confluence with the Newaukum River at Chehalis. From Chehalis, the river flows north to its confluence with the Skookumchuck River at Centralia. The Chehalis then flows generally north and west for about 50 miles to its mouth at Grays Harbor on the Washington coast.
The Chehalis River valley is characterized by a broad, well-developed floodplain and low terraces surrounded by highly dissected uplands of low to moderate relief. The valley bottom lies at an elevation of approximately 150 feet, and upland elevations average 300 to 600 feet. The higher elevations in the basin range from about 1,000 feet in the lowland hills to 2,658 feet at Capital Peak in the southern Olympic Mountains, to 3,110 feet in the Boistfort Hills in the southern portion of the basin, and 3,800 feet in the foothills of the Cascade Mountains east of Chehalis and Centralia.
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The slope of the upper Chehalis River is steep from its source to Chehalis, falling an average of 16 feet per mile. The slope flattens to about 3 feet per mile in the valley surrounding Chehalis and Centralia, where the river occupies a meandering channel. Downstream from Chehalis, the average width of the floodplain is 1.5 to 2 miles. The floodplain in this region shows little relief, which has resulted in a sinuous river course with numerous oxbow lakes and abandoned channels.
The upper Chehalis River has three main tributaries: the Skookumchuck River, Newaukum River, and South Fork Chehalis River.
3.1.2.1 Skookumchuck River
The Skookumchuck River originates in the Gifford Pinchot National Forest northeast of Centralia. It drains an area of approximately 181 square miles and flows into the Chehalis River at RM 67. The Skookumchuck River basin ranges in elevation from 160 feet at the mouth to 3,800 feet at the headwaters, with approximately two-thirds of the basin located below elevation 1,000 feet.
The basin has three distinctly different hydrologic regions, all of which are of approximately equal size. The region above Bloody Run Creek has a drainage area of 66 square miles, and is a steep, forested, mountainous area with elevations generally above 1,000 feet. In this region, the river flows through a steep-sided, narrow floodplain and drains into the reservoir behind Skookumchuck Dam. The region from Bloody Run Creek to the mouth of the Skookumchuck (excluding the Hanaford Creek drainage) has a drainage area of 56 square miles and contains a relatively broad floodplain bordered by steep-sided ridges. The slope of the river to the town of Bucoda is steep, falling an average of 19 feet per mile; below Bucoda, the slope flattens to about 5 feet per mile. Hanaford Creek, the largest tributary, has a drainage area of 59 square miles and enters the Skookumchuck River at RM 3.8.
The Skookumchuck River is regulated by the Skookumchuck Dam, which is owned and operated by Scottish Power (PacifiCorp). The dam is located at RM 21.9, just upstream from Bloody Run Creek. The dam, which was completed in 1971, is an earth fill structure approximately 190 feet high with a crest elevation of 497 feet. The primary purpose of the dam currently is to supply water for the Centralia coal-fired power plant, which has authority to divert up to 54 cfs of water from the Skookumchuck River. A portion of the water supplies a Washington Department of Fish and Wildlife (WDFW) fish rearing facility located approximately 0.5 mile below the dam.
Outflow from the reservoir is either over the spillway crest at elevation 477 feet or through the outlet works with intake gates at elevations 449, 420, and 378 feet. The discharge capacity is approximately 220 cfs when the pool elevation is at the spillway invert. Because of the limited outlet capacity, the reservoir typically fills early in the flood season and subsequent flood flows are passed over the spillway, which has a capacity of 28,000 cfs. The normal active storage capacity of the reservoir is 38,700 ac-ft between elevations 400 feet (normal minimum operating pool) and 492 feet (maximum operating pool). Additional usable storage of 3,170 acre-feet is available between elevations 378 feet (invert of the lowest intake) and 400 feet. Dead storage is approximately 1,420 ac-ft between elevations 340 and 378 feet. At the normal minimum operating pool elevation, the reservoir extends approximately 3 miles up the valley and covers an area of approximately 640 acres.
3.1.2.2 Newaukum River
The Newaukum River drains 175 square miles of lowland and foothills southeast of Chehalis and enters the Chehalis River at RM 75. Elevations in the Newaukum River basin range from 180 feet at the confluence to a little over 3,000 feet in the upper basin.
The Newaukum River is composed of the North, Middle, and South forks. Upstream portions of the North and Middle forks have slopes of 83 feet per mile; the South Fork has a slope of 188 feet per mile above the town of Onalaska. The average channel slope for the entire Newaukum River basin is 35 feet per mile. The Newaukum River has no dams and is free flowing from its head to the confluence with the Chehalis River.
3.1.2.3 South Fork Chehalis River
The South Fork Chehalis drains 130 square miles and joins the mainstem Chehalis River at RM 86. The lower South Fork Chehalis Basin (up to RM 9) consists of a broad, flat valley with small streams draining the hills on either side. From RM 9 to RM 15, the valley narrows from 1.5 miles to 0.75 mile in width.
3.1.2.4 Other Tributaries
China Creek is a relatively small, short stream that flows through Centralia to the Chehalis River.
Its watershed encompasses approximately 6 square miles, draining an area that ranges in elevation from 180 feet to 570 feet. Much of the watershed is moderately steep. Most of the channel consists of pipes and culverts where the stream runs through Centralia.
Salzer Creek flows into the Chehalis River from the east, just south of the Centralia city limits.
Salzer Creek originates in the low-lying hills east of Centralia and Chehalis and drains an area of 24.5 square miles. The watershed has a maximum elevation of approximately 800 feet.
Dillenbaugh Creek also enters the Chehalis River from the east, at Centralia. It originates in the steep foothills southeast of Chehalis, and drains an area of approximately 15 square miles. The gradient of Dillenbaugh Creek in its upper reaches is steep, falling at about 70 feet per mile.
After the stream flows out onto the Newaukum River floodplain, the gradient drops as Dillenbaugh Creek parallels the Newaukum and Chehalis rivers for nearly 3 miles before entering the Chehalis River. The lower reaches of Dillenbaugh Creek collect much of the storm drainage from the City of Chehalis.
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The study area has a predominantly marine climate characterized by mild temperatures both summer and winter. Extreme temperatures are unusual for the area because prevailing westerly winds bring maritime air over the basin and provide a moderating influence throughout the year.
During the spring and summer, high-pressure centers predominate over the northeastern Pacific, sending a northwesterly flow of dry, warm air over the basin. The dry season extends from late spring to midsummer, with precipitation generally limited to a few light showers during this period. Average summer temperatures are in the 50s and 60s (øF), although hot, dry easterly winds that occasionally cross the Cascade Mountains can raise daytime temperatures into the 90s.
In fall and winter, strong winds and heavy precipitation occur throughout the basin. Storms are frequent and may continue for several days. Successive secondary fronts with variable rainfall may move onshore daily or more often. Heavy rainfall frequently is produced by these storms when warm, saturated air rises over the coastal range and west slopes of the Cascades.
The Centralia-Chehalis area receives moderate to heavy rainfall when storms move onshore and through the basin. Normal annual precipitation at Centralia is 41.6 inches, with 77 percent falling during the period October through March.
Snowfall in the region is generally low. The average annual snowfall is approximately 9 inches, with a recorded extreme maximum of 45 inches. Most of the snowfall occurs in January, with an average of about 4.5 inches.
Precipitation totals at Centralia for the ten largest one-day, two-day, and three-day storms of record are shown in Table 3.1-1:
Table 3.1-1: Precipitation Totals Ranked for 10 Largest Storms at Centralia.
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3.1.4.1 Stream Gage Stations
Table 3.1-2 summarizes information for stream gages maintained by the U.S. Geological Survey (USGS) in the upper Chehalis River basin. In addition to the USGS stream gage stations, the National Weather Service (NWS) maintains wire weight stage gages at the Mellen St. and Pearl St. bridges. These gages are used by NWS for flood forecasting and warning.
Table 3.1-2: USGS Stream Gages.
3.1.4.2 Runoff
Stream flow generated within the Chehalis River basin originates primarily from rainfall, although snowmelt occasionally augments runoff in the highest elevation reaches. Stream flows in the basin show seasonal variation characterized by sharp rises of short duration from October through March, corresponding to the period of heaviest rainfall. After March, flows tend to decline gradually to a relatively stable baseflow, which is maintained from July into October.
The average annual discharge of the Chehalis River at its mouth and at the USGS stream gage near Grand Mound is estimated to be 6.4 million ac-ft and 2.0 million ac-ft, respectively.
3.1.4.3 Historical Floods
Major flooding occurs during the wet season, usually from November through February. Storms that cover the entire basin can cause widespread flooding. Flooding may also be localized; for example, storms centered over the Willapa Hills can cause flooding in the upper Chehalis River, whereas those centered over the Black Hills and Cascade foothills may result in flooding in the Skookumchuck and Newaukum River Basins.
The largest flood discharge on the Chehalis River in the Centralia-Chehalis area recorded in the last 70 years occurred in February 1996. Table 3.1-3 summarizes the largest floods of record in the basin since 1971:
Table 3.1-3: Ten Largest Floods on the Chehalis, Skookumchuck, and Newaukum Rivers since 1971.
Brief descriptions of the three most recent, largest floods in the Centralia-Chehalis area (the January 1990, November 1990, and February 1996 floods) are provided below.
January 1990 Flood
The January 1990 flood was primarily the result of a series of back-to-back storms accompanied by heavy rainfall over the 8-day period January 3-10 (Hubbard 1991). The storm system was quite complex and included high winds and strong surges of precipitation. During the 8-day period, 8 inches of rain were recorded at the Centralia climatological station maintained by NWS. This represents 19 percent of the average total yearly precipitation recorded at that station. The most intense precipitation in the basin occurred near the headwaters of the Skookumchuck and Newaukum Rivers.
The surges in precipitation resulted in more than one flood peak in many of the basin's streams, and streams did not return to baseflow between storm surges. The early precipitation saturated soils in the basin and significantly increased the flooding potential when the heaviest rains arrived on January 9. Peaks of record, up to this event, were recorded at the Chehalis River gaging stations near Doty, near Grand Mound, and at Porter. These flood peaks were estimated at the time as the 100-year flood.
November 1990 Flood
Above average precipitation in October and early November resulted in saturated soils that contributed to the flooding potential when a major storm arrived during the period November 21- 25 (Hubbard 1994). Wet weather accompanied by cool temperatures in the first part of November lowered snow levels to approximately the 1,000-foot elevation. The Cascade foothills received 6 inches of snow at elevations of 1,000 to 2,000 feet, 12 inches at 2,000 to 3,000 feet, and 12 to 18 inches at 3,000 to 4,000 feet. As a warm front moved through western Washington on November 21, the snow changed to rain, and rising temperatures caused melting of snow up to elevations of 5,500 feet. Over the next three days, intense rain fell on drainages where streams were beginning to swell from snowmelt, and severe flooding followed. Floodwaters receded when a cold front moved that into the area on November 26 lowered freezing levels and diminished precipitation. These flood peaks were estimated at the time as the 75-100 year event.
February 1996 Flood
To date, the February 1996 flood is the flood of record on all the major drainages in the Chehalis River basin. By February 5, soils throughout the basin were at or near saturation from above average precipitation that had fallen in the preceding weeks (USACE 1996). A recent cold snap had caused snow to fall as low as the 500-foot elevation. Warm, moist subtropical air being transported from the Pacific Ocean caused freezing levels to rise above 8,000 feet and resulted in warm, moist rains on the snow pack in the foothills.
A strong, polar jet stream extending into the central and western Pacific Ocean sustained and strengthened storms as they moved into the area off the eastern Pacific. An atmospheric blocking pattern caused stationary major troughs and ridges around the Northern Hemisphere.
The Pacific Northwest was situated between a trough to the west and a ridge to the east, creating a condition for weather systems to be at maximum strength when they reached the area. The atmosphere remained in this general pattern for at least 96 hours, during which large amounts of rain fell and quantities of water were released from the snow pack as stream flow. These flood peaks were estimated at the time as another 100-year flood.
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The Chehalis River Basin is unique in western Washington. It has the largest drainage area of all rivers on the west slopes of the Cascade Range. In addition, it does not adjoin the crest of the range, and contains very little high elevation terrain. Hence, snowmelt plays only a small role in its runoff patterns. Rather, the basin responds directly and relatively quickly to rainfall events, the largest of which occur typically in the fall and early winter months.
The core of the study area (RM 67 to 75) is also unique in that several streams (the Newaukum River, Dillenbaugh and Salzer Creeks, and the Skookumchuck River) converge within a 10-mile reach of the mainstem. Several smaller tributaries also join the mainstem in the core study reach.
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3.2.2.1 Floodplain Characteristics
The Chehalis River has a gradient of about 3 feet per mile in the valley surrounding Centralia and Chehalis, where the mainstem has a meandering channel that occupies a fairly uniform floodplain averaging over 1 mile wide. Most of the valley becomes inundated during large-sized flood events (PIE 1998).
From Chehalis to Montesano, the average width of the floodplain is about 1.5 to 2.0 miles.
Surficial sediments within the floodplain attain a maximum depth of 100 feet.
Glancy (1971) estimated the mean annual suspended sediment of the Chehalis River mainstem near Grand Mound at about 150 tons per square mile, and 98 tons per square mile for the mainstem near Porter. The Black River is the main tributary between Grand Mound and Porter, and joins the Chehalis River upstream from Oakville; however, Glancy affirms that the Black River contributes little runoff and sediment to the mainstem. The suspended sediment load passing Grand Mound appears to generally exceed that at Porter during periods of high runoff.
Glancy also observed a general decrease in average particle size from Doty to Porter, which may indicate that (1) the proportionate suspension of fine sediment increases in a downstream direction, (2) more of the coarser material moves as bedload past the stations near Grand Mound and at Porter, or (3) individual particle abrasion in a downstream direction effectively decreases average particle size.
Geologic evidence indicates that the Chehalis River has reworked its valley since the deposition of sand and gravel outwash derived from alpine glaciers. This sand and gravel forms the older river terraces that line the valley margins. This timeline would make the recent river deposits less than 7,000 to 10,000 years old. Conditions of the canyon wall imply a mature topographic landscape prior to river sedimentation. This type of landscape would contribute to the long-term, slow aggradation by the river system with deposition of fine sand and some fine gravel, but a predominance of silt, clay, and organic mud. Mapping of the Centralia-Chehalis area by the Natural Resources Conservation Service (formerly Soil Conservation Service) confirms that at least 50 percent of the deposits in the upper 5 feet of the valley sediments are organic mud, silt, and plastic clay.
The Secretary of War (1890) describes the navigability of the Chehalis River from Claquato (upstream from Centralia at RM 82) to its mouth. The mainstem is described as a river that becomes progressively shallower and increasingly blocked by snags and fallen trees in the upstream direction. From Elma to Claquato, "the river is practically blockaded during the summer and fall by snags, shoals, and a general lack of water; at this time the river is a succession of shoals and pools" (Secretary of War 1890, p. 2,984), many of which were recorded as shallow as 6 to 12 inches in depth. The GLO Survey Plat records provide additional accounts of numerous side channels, sloughs, and ponds hydrologically connected to the Chehalis mainstem, the Newaukum, and the Skookumchuck rivers (GLO 1833-1860).
3.2.2.2 Natural Influences
Most of the major physiographic features of the Chehalis River basin were likely in existence before Quaternary time (i.e., 1.6 million years before present) (Glancy 1971). The basin is underlain by a variety of lithologic units that reflect the area's complex geologic history. The principal units are igneous and sedimentary rocks of Tertiary age (the Tertiary period ranges from 66 million years to 1.6 million years before present) and unconsolidated deposits of Quaternary age; in most places bedrock is deeply weathered, with a soil mantle of varying thickness. The dense natural vegetation of the region generally protects the soil from sheet and rill erosion; however, mass-wasting processes supply large quantities of material to the stream channels for subsequent removal (Glancy 1971).
During Quaternary time, alpine and continental glaciation and eustatic changes in sea level exerted major influences on rivers located north of the basin, such as the upper reaches of the
Wynoochee River, Satsop River, and Cloquallum Creek basins (Glancy 1971). However, the basin was mostly unaffected by glaciation except for areas in the upper South Fork Newaukum River and in the Skookumchuck basin downstream from the Skookumchuck Dam (Huntting et al. 1961). The Puget Lobe of the Cordilleran Ice Sheet reached its maximum southerly extent at Centralia. Glacial outwash terraces can be observed in and around Centralia, and some are exposed along the banks of the Skookumchuck and Chehalis rivers, particularly downstream from RM 67 on the Chehalis.
Soils of the area are fine-grained and deep, primarily due to the extensive weathering when developed on bedrock, and due to deposit thickness when developed on alluvium (Evans and Fibich, 1987). Soils in the uplands are typically well drained, whereas those in the low-lying areas such as floodplains are poorly drained.
The climate in the basin is characterized by warm, wet winters and cool, dry summers. Partly due to topographic controls, a variable weather pattern within the basin results in precipitation that ranges from an average of less than 45 inches per year near Chehalis to an average of more that 120 inches per year in the upper reaches of the Chehalis River. The hydrology of the basin is described in detail in section 3.1.
3.2.2.3 Human Influences
The basin has experienced various forms of development since the mid-19th century. These include extensive logging, diking, road building, damming, grazing and other agriculture, and construction in general.
The Secretary of War's (1890) plan to improve the navigability of the Chehalis River included the removal of snags, overhanging trees, log jams, drift heaps, shoals, and other obstructions to navigability. In one year (1887), 293 large snags were removed from the main channel, beginning at Claquato and ending near Oakville (approximately 16 miles), and masses of log drifts and log jams were loosened or burned (Secretary of War 1887). The practice of removing woody obstructions continued for decades through this reach for purposes of floating logs generated by timber operations (Secretary of War 1892; Wendler and Deschamps 1955).
The earliest logging dams were built in the 1880's and construction of these dams continued through the 1920's. Splash dams were built on Elk Creek, Hope Creek, Chehalis River, South Fork Chehalis, Deep Creek, and the Skookumchuck River. The length of time that the dams remained in the streams ranged from less than one to more than 50 years, with an average of about 20 years. All splash dams were removed, washed out, or burned prior to 1944 except for one splash dam that remained intact on Elk Creek at least through 1955 (Wendler and Deschamps 1955). Splash dams were intentionally destroyed to carry logs downstream, a process termed "splashing." This process significantly affected channel dynamics. The floods of logs and water scoured or moved gravel bars, leaving only barren bedrock or heavy boulders (Wendler and Deschamps 1955). New channels were created in some areas and the geometry (width, depth, cross-section shape) of existing channels was modified. Splashing generally occurred on the average of once each week, but could occur as often as once a day.
If the sudden influx of logs into a stream below the splash dam caused a log jam, dynamite or black powder was used to clear the obstruction (Wendler and Deschamps 1955). Natural log jams were removed in the process as well. Extensive log jams on the mainstem were also removed in the mid-1800s to aid navigation. The lack of log jams and the scour from splash dams has resulted in a simplified stream system in which water and sediment are routed downstream much faster than before logging occurred.
Although much of the study area retains a rural character, the core of the study area has been extensively developed. The cities of Centralia and Chehalis occupy portions of the floodplain, and supporting infrastructure crosses the river and portions of the floodplain, as well as tributaries, and portions of their floodplains. Most of the floodplain is currently used for pasture and growing crops. There is a small amount of impervious surface in the low-lying portions of the floodplain.
3.2.2.4 Channel Pattern and Behavior
Between the confluences with the Newaukum and Skookumchuck Rivers, the Chehalis River is meandering, with a sinuous, single-thread channel and a wide floodplain. As measured from USGS 7.5' topographic maps, the sinuosity of the core reach is 1.95 (river length/valley length), whereas the reach immediately downstream from the Skookumchuck mouth has a sinuosity of 1.70. The lower 4 miles of the Newaukum have a sinuosity of 1.39, and the lower 4 miles of the Skookumchuck have a sinuosity of 1.51. Logjams provide an important mechanism in creating and maintaining multi-thread channels. In the absence of a large sediment load, the removal or loss of large woody debris (LWD) jams eliminate this mechanism for forming new side channels and can lead to the abandonment of existing side channels as the main channel incises and flattens over time.
Channel sinuosity is not so much a driver of channel processes as it is a result of those processes.
Sinuosity is most closely related to channel gradient and sediment characteristics. Flatter channels that transport predominantly sand or fine-grained material tend to be more sinuous than steeper channels that transport gravel-dominated sediment. Oxbows are remnants of multithread channels or portions of the main channel abandoned as the river avulses to new locations.
Primary mechanisms that can drive the formation of multi-thread channels and oxbows include high sediment loads that divert out of the channel through aggressive deposition and large accumulations of LWD that can divert flow onto the floodplain and form new channels.
Numerous oxbows are present in the core reach, although they are less common in the reaches above, below, and in tributaries. No recent meander cutoffs are present. In fact, a particularly narrow meander bend showed virtually no change during the last 50 or so years based on a comparison of aerial photographs taken over that time. The gradient of the core reach is 0.027 percent, meaning that it is gentler than reaches above, below, or in the tributaries (Table 3.2-1).
The floodplain is wide, flat, and very gently slopes down valley. In contrast, the floodplain upstream on the Chehalis is narrower and steeper. Downstream from the confluence with the Skookumchuck, the gradient is somewhat steeper, and the bed material is much coarser, including cobbles and gravel.
Table 3.2-1: Comparison of Key Geomorphic Indicators.
The spatial patterns of the channels in the study area may be a result of a change in substrate related to the Pleistocene glaciation of the area. The change in sinuosity and gradient coincides with the edge of glacial outwash deposits from the Puget Lobe. The transition from fine (sand and smaller) bed and bank material to coarse material (sand, gravel, and cobble) is abrupt. The river may not be able to transport the larger clasts, and this may be responsible for the inflection in the channel profile just downstream from the Skookumchuck confluence.
Based on aerial photograph analysis, the plan form pattern of the Chehalis River has been remarkably stable during the last 50 years, with maximum observed lateral migration of approximately 10 meters in one location, and smaller amounts of localized migration in a few other areas. Oxbows and other abandoned channel features visible in 1949 photos remain visible in 1999 photos, although these features have grown slightly smaller and more disconnected from the main channel, apparently through sediment deposition. The river formed no new abandoned channel features within the core area over the 50-year period of record. There are only four significant sediment bars within the core study area. Sediment bars were visible throughout the period of record in the same locations and showed no discernible change in size. These features were generally narrow and limited in extent. Sediment composition on these bars was predominantly sand and silt with small amounts of gravel (less than 1 inch diameter). The sediment characterization includes sediment samples from these bars that provide quantitative size distribution data (see Section 3.2.2.5).
Although the Chehalis River has changed little in 50 years, the Newaukum and Skookumchuck rivers have experienced changes that are more obvious. A portion of the Skookumchuck River was relocated at the time I-5 was constructed, and the location of the Skookumchuck River confluence has changed as a result. Channel migration on the Newaukum River has occurred within the first 5 miles above the confluence with the Chehalis River.
Channel cross-sections of the Chehalis appear to be relatively stable as well. However, throughout the study area, there are continuous sections of riverbank hundreds of meters in length with bare soils, or with slight vegetation cover, indicating active erosion. This is in apparent contradiction to the aerial photograph observations, and suggests recent erosional events. The recent series of peak flows during the 1990s (see Section 3.1) may be partly responsible for the raw banks. The channel has a low width to depth ratio (less than 10), and is incised into the floodplain. The removal of woody debris appears to be the cause of the incision.
However, if incision has occurred, the gradient has likely increased within the core reach. The gradient of the pre-settlement Chehalis River would have been even gentler than it is now.
The height of the riverbank above the water surface decreases progressively downstream between the Newaukum River confluence and the Skookumchuck River confluence. Field investigations conducted by the Corps 2001 showed that the bank height above water surface decreased from about 26 feet (typical) to 16 feet (typical) in this reach. Reported river stage at USGS gaging station 12027500 "Chehalis River at WWTP at Chehalis, WA," at the time of observation indicates that short-term changes in river stage do not account for this observation.
At approximately RM 72.3, floodwaters have recently flowed out of the channel and scoured vegetation and soil from the riverbank and floodplain.
3.2.2.5 Sediment Characteristics
The Corps 2001 conducted sediment sampling to collect information on the sediment load carried by the Chehalis. A grain size analysis indicates that within the core reach, sand and silt dominate the bed material. However, at the lower end of the study area (approximately RM 62- 67), the riverbed is dominated by gravel and cobbles. The average particle size of grab samples taken from sediment bars in this reach was 1.2 inches, which is two orders of magnitude greater than within the core reach.
Sediment samples collected along the Skookumchuck River at Rotary Riverside Park in Centralia contained mostly gravel and some small cobbles. The average particle size of all samples on the Skookumchuck was 1.3 inches, similar to the lower reach of the Chehalis.
Bank material within the core reach of the Chehalis is composed predominantly of fine sand and silt. One sample taken from an actively eroding bank was composed almost entirely of fines (97 percent), whereas another bank sample had an average particle size of 0.9 inch.
3.2.2.6 Large Woody Debris
Evidence from the Queets River provided by Abbe (2000) indicates that woody debris jams historically formed an integral element in large alluvial channels flowing through forested lands in western Washington. In particular, Abbe found that LWD jam formation is a principal mechanism that controls reach-level habitat diversity through the formation of scour pools, bars, in-channel islands, and riparian forest refugia. LWD jams may act as local hydraulic controls over several decades and possibly centuries.
The accounts provided by the Secretary of War and the GLO support the premise that LWD strongly influenced the geomorphic processes in the floodplain areas of the basin. The systematic removal of LWD and the removal of riparian vegetation have very likely changed the channel processes in these systems.
Although it almost certainly played an important role in channel form prior to settlement, there is a noticeable absence of LWD in the channel today. No debris jams or significant accumulations of LWD were observed in any of the study area reaches. This suggests that the supply of LWD is extremely limited. In the core reach, there are a few places with LWD that may be recruited into the channel. Additionally, the tributaries appear to lack the transport capacity to supply significant amounts of LWD to downstream reaches.
As described previously, analysis of aerial photographs indicates that channel migration has proceeded slowly over the past 50 years, and no new oxbows or other channel cut-off features have been formed during that period. Based on estimated sediment accumulation rates and the observed shrinking of the oxbows observed on the floodplain within the core reach, these cut-off features can be interpreted as young features that probably formed within the past few hundred years. These observations, combined with the documented removal and reduction of LWD within the study area, support the hypothesis that logjams drove the process of channel avulsion and oxbow formation, and this process has now been interrupted and discontinued due to the lack of LWD to support this process. The lack of LWD jams in recent years has reduced the length and area of side channels, decreased overall channel length, and allowed the channel to incise.
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Water quality in the upper Chehalis River basin is governed by the Water Quality Standards for Surface Waters of the State of Washington (WAC 173-201A) (WDOE, 1997). State water quality standards designate most of the upper basin as Class A (excellent). Class A waters must meet or exceed the requirements for all or substantially all uses as defined by the water quality standards. Characteristics of Class A uses include water supply (domestic, industrial, and agricultural); fish and fish rearing, spawning, and harvesting; wildlife habitat; recreation; and commerce and navigation. Water quality criteria for Class A waters are presented in Table 3.3-1.
The water quality standards also identify special conditions, which relax certain criteria for the mainstem Chehalis River near Centralia and Chehalis.
Table 3.3-1: Class A Freshwater Quality Criteria.
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The primary water quality problems in the upper Chehalis River basin are high temperature, fecal coliform, high pH, and low dissolved oxygen (DO). Water body segments that do not meet state surface water quality standards and are included in the final 1998 Section 303(d) Impaired Water Body List are presented in Table 3.3-2. The Washington Department of Ecology (Ecology) maintains ambient monitoring stations on the mainstem Chehalis (RM 101.7 to RM 59.9) and near the mouths of a number of tributaries, including the South Fork Chehalis, the Newaukum, and the Skookumchuck rivers. Recent water quality data are presented in Table 3.3- 3.
Upstream from Centralia, the Chehalis River is a relatively shallow and swift-moving stream.
However, in the Centralia reach (RM 65.8 to RM 75.2), the river channel deepens, and stream velocities decrease substantially. The Centralia reach is a natural sill in the river more similar to a reservoir or lake than to a river. Temperature stratification is established during summer months, which leads to higher surface temperatures and prohibits mixing between stratified layers (Pickett 1994). Additionally, oxygen depletion occurs with depth. This naturally slowmoving reach has merited separate criteria for DO and temperature for part of the year. The criteria for this reach include a special condition stipulating that DO shall exceed 5.0 mg/L from June 1 to September 15 and temperature shall be between 18 and 20.4 øC.
Table 3.3-2: Water Bodies on the Final 1998 303(d) List.
Table 3.3-3: Ambient Monitoring Water Quality Data (from Michaud et al . 2000).
A Total Maximum Daily Load (TMDL) study conducted by Ecology in 1991 and 1992 found that the upper Chehalis River had problems with low DO from RM 90.0 downstream, elevated temperature from RM 100.5 downstream, and high fecal coliform over the entire stretch with most of tributaries sharing these problems (Pickett 1994). The highest temperatures measured in the upper Chehalis River basin were in the slow-flowing Centralia reach (Pickett 1994).
Furthermore, the Class A criterion of 8.0 mg/L was met in less than half of the measurements made from the surface to 2 meters deep. During the summer months (when the special criterion of 5.0 mg/L was in effect) all measurements were above this criterion level; however, in waters 2 meters and deeper, the criterion was met only 70 percent of the time for regular conditions and 40 percent for special condition periods. Downstream from the Centralia reach, from the confluence with Scammon Creek (RM 65.8) to RM 59.9, water quality problems are mainly high temperatures and low DO.
Because of the low elevation, warm summer water temperatures may have been historically present in much of the Chehalis watershed; however, human activities have led to widespread riparian vegetation loss, reduced shading levels, and floodplain isolation contributing to increased water temperatures (Wampler et al. 1993). Floodplain isolation results in the loss of wetland and groundwater discharge, hindering the creation of localized areas of cool water habitat available to aquatic organisms. Additionally, the lack of LWD results in a homogeneous riverbed that reduces water penetration into the riverbed. This results in a reduction in intersubstrate flow that creates cooler, oxygenated water in deep pools. Livestock impacts (livestock access and poor livestock waste handling practices) are the primary suspected nonpoint source of fecal coliform bacteria and pollutants that cause low DO, although commercial and residential sources such as urban storm water and failing septic systems are also possible contributors (Pickett 1994).
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Pollutant loading sources to the Chehalis River system include both point and non-point sources.
Point sources are discharges regulated under the federal and state National Pollutant Discharge Elimination System (NPDES). The NPDES permit program is designed to protect the quality of receiving waters from various pollutant sources. The program includes permits for municipal wastewater discharge, industrial wastewater discharge, and stormwater discharge during construction and operation of development projects.
A number of facilities in the study area discharge as point sources under the NPDES program.
These facilities include municipal wastewater treatment plants (WWTP) at Pe Ell, Chehalis, and Centralia, and one industrial WWTP, WestFarm Foods, which discharge treated wastewater directly to the mainstem Chehalis River. National Frozen Foods and Midway Meats are facilities regulated under State Waste Discharge Permits for land application of wastewater. These operations apply wastewater on fields that border the Chehalis River and Salzer Creek (Pickett 1994).
The WestFarm Foods and Chehalis WWTP's have a significant influence on the water quality of the Chehalis River due to their location at the head of the Centralia reach (Pickett 1994). The National Frozen Foods spray irrigation system was the source of a major wastewater spill to Salzer Creek in 1979 that caused an extreme DO drop in the Chehalis River. A low-DO event in October 1991 was attributed to an upset at a permitted wastewater treatment facility at the head of the Centralia reach, and to non-point sources, most likely in the Stearns Creek basin or on the mainstem Chehalis River upstream from the Newaukum River and below Adna (Pickett 1994).
Additionally, the Chehalis WWTP raises the level of nitrogen in the river by two to six times the level upstream of the plant.
Currently, the Centralia WWTP discharges effluent into the Chehalis River at the Centralia reach, where natural conditions cause low, slow-moving flows, and high water temperatures in the summer (City of Centralia 1999). The Centralia WWTP has experienced a number of minor permit violations since August 1995 related to effluent concentrations of total suspended solids (TSS), biochemical oxygen demand (BOD), and fecal coliform (Pickett 1994). Centralia is proposing to construct a new regional WWTP with a discharge point downstream from the existing WWTP.
Recognized non-point sources of pollution in the upper basin include agricultural and forest practices; commercial, industrial, and residential development; urban stormwater runoff; land disposal of industrial waste, solid waste and residential sanitary waste; failing septic systems; and groundwater discharge (Pickett 1994). Land use within the upper basin is dominated by forestlands (82.7 percent) and logging activities in these areas can contribute suspended solids to the streams. Although agriculture represents only about 10 percent of the land use in the watershed, agricultural activities (primarily field crop production and animal pasturage) typically occur adjacent to the river corridor and contribute fecal coliform, dissolved oxygen demand (DOD) and nutrients, such as phosphorus and nitrogen, to the mainstem Chehalis River and many of the tributaries (Michaud et al. 2000).
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Federal law requires states to identify sources of pollution in waters that fail to meet state water quality standards, and to develop TMDLs for addressing those pollutants. The TMDL process is established by Section 303(d) of the Clean Water Act (CWA), and TMDLs are based on the total amounts of a pollutant a water body can receive from all sources and continue to meet water quality standards. Once the TMDLs for a specific water body are determined, the allowable pollutant quantities (calculated on a per-day or a per-liter basis) are divided among the existing dischargers.
As noted earlier, Ecology conducted a TMDL study to evaluate water quality in the upper Chehalis River (Pickett 1994). Over the 1991-1992 period, several surveys in the study area were conducted during the dry season (May to November). Past studies have documented areas of low DO during the summer in the Centralia reach. The Chehalis River and tributaries were evaluated for loading sources and other physical, chemical, and biological river conditions that contribute to the oxygen deficit.
The results of these surveys indicated that widespread thermal stratification occurs in the Centralia reach during the summer months. In deeper waters, hypoxia and anoxia were associated with the thermal stratification. DO was repeatedly below water quality criteria in the surface waters and the tributaries of the Chehalis River. Additionally, violations of both the temperature criterion of 18.0øC and the fecal coliform bacteria criterion were also found in the mainstem Chehalis River and its tributaries. The study found that almost two-thirds of the measurements in the Centralia reach exceeded the temperature criterion for Class A water quality standards during the dry season.
The TMDL for DO approved by Environmental Protection Agency on October 21, 1996 restricts the discharge of BOD material to the upper Chehalis River from May 1 to October 31 each year.
In the case of Chehalis and WestFarm Foods, the waste load allocation for the Centralia reach during the May 1 to October 31 period was reduced to zero pounds BOD and ammonia. This TMDL was revised in response to a settlement of legal action initiated by the City of Centralia, the City of Chehalis, and WestFarm Foods (Jennings and Pickett 2000). The revised TMDL modifies the seasonal restrictions on the pollutant discharge for each plant based on river flows, and requires that each plant discontinue direct discharge to the Centralia reach at low flows.
Three sets of final limits were developed based on the flow rate of the river: "dry-weather" flows, "very low" flows and "wet-weather conditions." During periods when the river flow drops below the specific thresholds, the waste load allocations for Chehalis and WestFarm Foods remain the same as in the TMDL previously approved by the EPA. However, when river flows are above those low-flow thresholds, Chehalis and WestFarm Foods are allowed to discharge to the river within the Centralia reach at levels that protect water quality standards for DO.
As part of a 1997 agreement with Ecology, the City of Centralia proposes to move and expand the Centralia WWTP. The proposal involves moving the discharge point downstream from the Skookumchuck River confluence and upgrading treatment technology to improve the quality of the discharge (City of Centralia 1999).
A temperature TMDL for heat caused by solar radiation has been submitted to EPA for the upper Chehalis River basin (Butkus and Jennings 1999). Under Section 502(6) of the CWA, heat is considered a pollutant. The TMDL study indicates that heat generated by solar radiation from sunlight reaching streams provides enough energy to raise water temperatures. Very low- elevation streams are known to be the most dependent on shade to limit temperatures, and the Chehalis River basin has been affected by reduced tree canopy on over 90 percent of the mainstem. Anthropogenic activities, which have contributed to degraded riparian vegetation conditions, include agricultural and silvicultural activities, as well as residential and urban development. Instream flow and channel morphology are additional factors that influence heat distribution. Low flows may contribute to high temperatures by reducing the volume of water that can absorb incoming heat and channel morphology may influence heat distribution. With increased sediment loads, stream channels may become wider and shallower, allowing more thermal radiation to be absorbed by the water surface.
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3.3.5.1 Bunker and Stearns Creeks
Although neither Bunker nor Stearns Creek was included in the final 1998 Section 303(d) list for impaired water bodies, water quality problems have been observed in these streams.
Exceedances of temperature, DO, and fecal coliform criteria have been observed in Stearns Creek and observed DO levels have been consistently depressed below the 8.0 mg/L criterion during summer months in Bunker Creek (Pickett 1994).
Land use in the subbasin is primarily forestland (81 percent) with 17 percent agricultural and less than 1 percent residential and urban development. Sources of nutrient loading (primarily phosphorus, as Bunker and Stearns Creeks are nitrogen limited) are primarily agricultural (Michaud et al . 2000). A survey by the U.S. Fish and Wildlife Service (USFWS) found an estimated 26 percent of stream miles on these streams that were degraded by livestock access and impact and other pollutant inputs (Wampler et al . 1993).
3.3.5.2 Dillenbaugh Creek
Dillenbaugh Creek was included in the final 1998 Section 303(d) impaired waterbody list for fecal coliform and temperature. Two reaches were listed for fecal coliform and two reaches were listed for both fecal coliform and temperature. Previous surveys of the creek reveal a wide variety of point and non-point sources of pollution that contribute to water quality degradation (Crawford 1987; Pickett 1992 and 1994). High fecal coliform levels are most probably due to farming activities, such as livestock impacts and a dairy feedlot, although failing or inadequate septic systems adjacent to the creek may also contribute to the problem. Industries in the
Chehalis Industrial Park may contribute to temperature violations. Additionally, an urban storm sewer was found to be the source of several contaminated discharges (Pickett 1992).
This creek also has relatively high turbidity, (TSS), BOD, total organic carbon (TOC), total phosphorus (TP), and total nitrogen (TN) (Pickett 1994). Urban stormwater discharges to Dillenbaugh Creek have been identified as a potential contributor to the high pollutant levels.
Another possible source of pollution is the American Crossarm and Conduit (ACC) Superfund site adjacent to the creek. ACC was formerly a wood-treating facility that is now heavily contaminated with pentachlorophenol (PCP). The Remedial Investigation (RI) for the site (Weston 1991) found PCP levels in Dillenbaugh Creek as high as 19 ug/L during the spring of 1991. Additional site improvements have been made at ACC since 1991 as part of an emergency remediation, and levels of PCP have dropped to below established water quality criteria with acute toxicity not appearing to be present (Pickett 1994; Marti 2001).
3.3.5.3 Elk Creek
Previous studies indicate good water quality in Elk Creek with temperature, pH, and DO all within water quality criteria. The exception to this is fecal coliform bacteria (Pickett 1994). One reach of Elk Creek was included in the final 1998 Section 303(d) impaired waterbody list for fecal coliform concentrations. Livestock access and potentially inadequate septic systems may be sources of elevated fecal coliform, TP, and BOD concentrations (Pickett 1994; Wampler et al. 1993). The Elk Creek subbasin is dominated by forestland (98.4 percent) with some logging and agricultural activities (0.6 percent of land use) (Michaud et al. 2000).
3.3.5.4 Lincoln Creek
The 1991-1992 Ecology survey observed DO consistently below 6.0 mg/L, temperatures above 18.0øC, turbidity and TOC relatively high; the two fecal coliform analyses both well above water quality criteria (Pickett 1994). Lincoln Creek is included in the final 1998 Section 303(d) list for fecal coliform concentrations and temperature. A USFWS degradation survey identified livestock access, livestock waste inputs, and other pollutant sources at numerous locations (Wampler et al . 1993).
3.3.5.5 Newaukum River
Although previous surveys indicated mostly good water quality (Pickett 1994), water quality in the Newaukum River basin is degraded and the Newaukum is included in the final 1998 Section 303(d) list for temperature and fecal coliform concentrations. Elevated coliform bacteria levels were associated with the wet season and were not observed during the TMDL study, which was conducted during the dry season (Pickett 1994; Michaud et al. 2000).
Ambient water quality data for temperature, DO, pH, TP, inorganic nitrogen, TSS, and fecal coliform for the 1992-1993 water years are presented in Table 3-3.3. While the average TP concentrations were at the lower end of the range for tributaries, inorganic nitrogen concentrations averaged highest in the Newaukum at 0.61 mg/L, although still less than background concentrations of 0.8 mg/L (Michaud et al. 2000).
Agricultural activities (17 percent of land use) are likely sources of high inorganic nitrogen yields. Extensive stretches of reduced stream canopy observed between the confluence of the North and South Forks and the mouth of the Newaukum contributes to high temperatures (Michaud et al. 2000; Wampler et al. 1993).
3.3.5.6 Salzer Creek
Salzer Creek has been the focus of several water quality investigations. In 1979, low DO was observed in the Chehalis River. The source of the problem was identified as the failure of a food processing wastewater pipe leading to a spill in Salzer Creek. The wastewater was to have been land applied on fields adjacent to Salzer Creek by the National Fruit Canning Company (now owned by National Frozen Foods and currently holding a Washington State Discharge Permit to land apply food processing wastewater). In 1986, Ecology conducted a survey of the creek to identify point and nonpoint sources in the drainage and impacts on water quality (Crawford 1987). Low DO and high fecal coliform levels were observed as the main water quality problems. The causes cited were poor farm management practices and leachate infiltration from the Centralia Municipal landfill (currently undergoing corrective action as a federal Superfund site).
Subsequent surveys have found Salzer Creek to be heavily affected by several sources, including stormwater runoff from a drainage sump at the Southwest Washington Fairgrounds (suspected as a contributing source of high nutrients, fecal coliform and low DO), urban and residential sources, livestock activities, and possibly other unidentified sources (Pickett 1994). Salzer Creek was included in the final 1998 Section 303(d) impaired waterbody list for fecal coliform and temperature. Approximately 3 percent of the Salzer Creek basin has been developed for urban, commercial and industrial uses; agricultural uses comprise 12.9 percent; and forestlands dominate the subbasin at 83.9 percent.
3.3.5.7 Skookumchuck River
The Skookumchuck River is the only tributary in the study area for which flows are largely regulated by reservoir releases. Hanaford Creek, a major tributary of the Skookumchuck River, is the site of an open-pit coalmine and power plant. The Skookumchuck River is included in the final 1998 Section 303(d) list for fecal coliform concentrations, pH, and temperature. Land use in this subbasin is dominated by forestlands (86.5 percent), with agricultural activities representing 7.5 percent, commercial and industrial representing 2.4 percent, and urban development representing only 1.4 percent of land use.
During the 1991 survey, temperatures were above 18øC on several occasions and DO was always above the criterion of 8.0 mg/L. Hanaford Creek water temperatures were above 18øC on one of three sampling dates, and DO fell below 6.5 mg/L on one of three sampling dates. Conditions in the Skookumchuck River above Hanaford Creek were similar to conditions at the mouth of the river, with temperature elevated on one of three dates and DO consistently high; however, pH was much higher at the mouth and Pickett (1994) suggests a source in this stretch of the river.
Overall, the data indicated that water quality was generally quite good, with turbidity, BOD, TOC, nutrients and chloride all detected at relatively low levels. Hanaford Creek has slightly higher levels than the Skookumchuck for all parameters except inorganic nitrogen.
The Skookumchuck Dam and reservoir, located about 12 miles northeast of Centralia at Skookumchuck RM 21.9, were constructed in 1969-1970 to supply cooling water to the coalfired Centralia steam electric power plant. An instream flow agreement between PacifiCorp and Washington Department of Fish and Wildlife requires that instream water temperatures be maintained at 10ø to 13øC. The dam has a multi-level intake system located at elevations 449, 420 and 378 feet (between 28 and 100 feet below the water surface) that allows water temperature below the dam to be maintained at less than 16øC. When the reservoir drops below full pool and ceases spill, the water is then drawn from lower outlet gates, which lowers water temperatures in the stream below the dam. Currently, dam operations result in summer water temperatures at or below 13øC.
3.3.5.8 South Fork Chehalis River
The South Fork Chehalis River is included in the final 1998 Section 303(d) list for exceeding the state water quality criterion for temperature. This subbasin is predominantly forestland (89 percent) with some agricultural activities (9.5 percent).
Previous studies have identified widespread water quality impacts. The USFWS survey identified pollutant inputs in over 15 separate locations, and documented riparian canopy loss over approximately one-third of the river miles and cattle access in over 21percent of the river miles in this subbasin (Wampler et al. 1993). The Ecology TMDL study indicated temperature and fecal coliform as water quality problems (Pickett 1994). There are numerous dairies in the South Fork basin and agricultural practices may be a source of fecal coliform, high TP, inorganic nitrogen, and TSS yields (Pickett 1994).
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The Centralia area contains one large aquifer (the Fords Prairie aquifer), created by glacial outwash from the north along Waunch and Fords Prairies. The aquifer supplies all domestic water use for Centralia and is classified as a critical aquifer. Domestic water supply comes from several wells throughout the City service area. The total source capacity for the wells is 7,178 gallons per minute (gpm). If a shortage of water occurred due to an extensive drought, the City could draw up to 3,125 gpm from the Newaukum River.
In 1990, the Lewis County Environmental Health Department completed a groundwater study along Fords and Waunch Prairies and found that the underlying aquifer contained elevated levels of nitrates caused by an unknown number of failing septic tanks. In addition, a contaminant plume of tetrachloroethylene (PCE) approximately 1.5 miles long was discovered through routine, required testing for volatile organic compounds. A dry cleaning operation near the Trailer Village Mobile Home Park located near Harrison Avenue and Russell Road was closed approximately 12 years ago and since then, several wells within the trailer park and nearby homes were found to have elevated levels of PCE, ranging from 60 parts per billion (ppb) to 125 ppb. The Safe Drinking Water Act allows a level of 5 ppb. The PCE plume also contaminated a City well referred to as Eshom well located near Galvin Road and Eshom Road. The Eshom well is now closed and the trailer park is currently serviced with municipal water and sewer.
Dangerous levels of toxic chemicals contaminate two separate aquifers in the Chehalis area. Near the City of Chehalis, at the intersection of Hamilton and LaBree Roads, PCE is present in a shallow aquifer and affects two small public water systems and at least one private well. PCE concentrations are as high as 3,000 ppb in the drinking water supply and 36,000 ppb in the groundwater. This area of contamination is now a federal Superfund site.
Another shallow aquifer south of the Chehalis area is contaminated with several industrial chemicals. Contamination by halogenated organics and non-halogenated solvents has been confirmed in ground water under the Lewis County Central Shop at Forest, at the intersection of Jackson Highway and Forest-Napavine Road. Contamination of drinking water by petroleum is suspected at this location. Elevated levels of solvents have also been detected in off-site domestic wells.
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The study area is located in the Puget Trough physiographic province described by Franklin and Dyrness (1973). This consists of lowland areas within a moderate climate. Pre-European settlement vegetation consisted of evergreen forests dominated by western hemlock (Tsuga heterophyla ), western red cedar (Thuja plicata ) and Douglas fir (Pseudotsuga menziesii).
Theriver valleys likely supported riparian gallery forests dominated by black cottonwood (Populus balsamifera ), big-leaf maple (Acer macrophyllum) , western red cedar, Oregon ash (Fraxinus latifolia ) and red alder (Alnus rubra ). Parts of the study area also support native prairies on the glacial outwash plains (i.e. Fords Prairie and Grand Mound). Typical native prairie vegetation consisted of Idaho fescue (Festuca idahoensis ) and white aster (Aster curtus ). Wetlands were also common, including peat systems around the northern boundaries of the study area. Typical wetland vegetation likely consisted of multiple species of rushes (Juncus spp. ), sedges (Carex spp. ) and willows (Salix spp. ). Other typical wetland plants would have likely included hardhack (Spiraea douglasii ), red-osier dogwood (Cornus stolonifera ), and salmonberry (Rubus spectabilis ). Typical vegetation communities found are described below:
3. 4.1.1 Forested Deciduous Community
This community is generally found near or adjacent to the major rivers and streams and is typical of riparian communities in the Puget Trough physiographic province. These can be either wetland or upland forests. The predominant canopy species are generally black cottonwood with patches of red alder, big leaf maple and Oregon ash or Oregon white oak (Quercus ga rryana ).
The understory can include snowberry (Symphoricarpos albus ), red-osier dogwood, and Indian plum (Oemleria cerasiformis ).
3.4.1.2 Coniferous Forested Community
Coniferous forests are found in the highland and/or well-drained portions of the study area.
Many of these have been in forest production and rotation and are either second- or third-growth forests. Typical community dominants include Douglas fir, western hemlock, and western red cedar. Common understory species include salmonberry, vine maple (A. circinatum ), and salal (Gaultheria shallon ) 3.4.1.3 Mixed Forested/Scrub-Shrub - Forest Dominant Community
This community is characterized by approximately 60 percent forest and can either be wetland or upland forests. The forest includes the deciduous and coniferous trees listed above. The understory species are highly variable and can include willows, Oregon ash, Pacific ninebark (Physocarpus capitatus ), red elderberry (Sambucus racemosa ), Indian plum, and Nootka rose (Rosa nutkana ). Invasions of blackberry (R. procera and R. lacinatus ) may also occur in the understory and in disturbed areas of the other community types as well.
3.4.1.4 Mixed Forested/Scrub-Shrub - Scrub Dominant Community
This community can either be wetland or upland scrub-shrub communities. Common shrubs of this community include red-osier dogwood, willows, snowberry, and bald-hip rose (Rosa gymnocarpa ). Black cottonwood usually predominates but other tree species found in this unit may include bitter cherry (Prunus emarginata ), black hawthorn (Crataegus douglasii ) and Scot's broom (Cytisus scoparius ).
3.4.1.5 Emergent Community
This community is most common in the study area and consists of wetland and upland pasture, upland prairie, and emergent wetlands. Emergent vegetation includes typical pasture grasses such as reed canarygrass (Phalaris arundinacea ), bluejoint (Calamagrostis canadensis ), red fescue (F. rubra ), tall fescue (F. arundinacea ), velvet grass (Holcus lanatus ) and bentgrass (Agrostis spp .). Cattail (Typha latifolia ), sedges, rushes are occasionally found in the emergent wetlands as well as the grass species listed above.
Priority plant communities within the study area are wetlands and riparian areas, as described below:
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Wetlands (along with other waters of the United States) are those areas specifically administered by the Corps and the (EPA) under the Clean Water Act. The following wetland definition was used for determining and mapping the wetlands within the study area:
" .those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas." [33 CFR 328.3(b) and 40 CFR 230.3(u)] The USFWS developed the following definition for a riparian classification system in the western United States. This definition was used for determining and mapping riparian areas within the study area:
"Riparian areas are plant communities contiguous to and affected by surface and subsurface hydrologic features of perennial or intermittent lotic and lentic water bodies (rivers, streams, lakes, or drainage ways). Riparian areas have one or both of the following characteristics: 1) distinctly different vegetation species than adjacent areas and 2) species similar to adjacent areas but exhibiting more vigorous or robust growth forms.
Riparian areas are usually transitional between wetlands and uplands." (USFWS 1998) The following discussion on wetlands and riparian areas is separated by those systems associated with the Chehalis (which includes the Newaukum River, Black River, Scatter Creek, Scammon Creek, Dillenbaugh Creek, Salzer Creek, Coal Creek, China Creek, Lincoln Creek, and numerous small drainages within the Chehalis River valley) and the Skookumchuck River (which includes Hanaford Creek and Coffee Creek). The reason for this distinction is the different hydrological and geomorphological characteristics of each river that have influenced the extent and characteristics of wetlands and riparian areas associated with them.
3.4.2.1 Chehalis River Wetlands and Riparian Areas
Chehalis River ecosystems are a remnant of a once extensive system of braided channels, wetlands, and riparian areas across a broad floodplain. The river was an extremely dynamic
system that carried a high load of organic materials (wood and other debris) with shifting channels. The wetland and riparian plant communities probably supported many of the same species found in the remnant systems today: shrub-shrub and emergent wetlands with evergreen and deciduous wetland and riparian areas along the higher flood terraces. These communities would be typical of a braided river system with frequently shifting stream channels. Functions associated with the historic wetlands would have included habitat for aquatic invertebrates, anadromous and resident fish habitat, wildlife habitat, export of organic matter, and biodiversity.
Because of the dynamic nature of the riverbed (rapid erosion and sedimentation), plants found in this environment were likely to be highly adaptable and highly productive as primary producers.
This would result in a rich food web supporting invertebrates and vertebrates. The Chehalis River system was likely a rich source of food for a vast variety of both fish and wildlife species.
The richness of cultural resource sites around the study area (see Section 3.14) indicates the river was also an important source of food and materials for Native Americans.
Euroamerican settlement brought dramatic changes to the system. Agricultural development resulted in the clearing and draining of all but the most difficult to access or drain wetland systems. Large areas of riparian forests were also cleared. As described in Section 3.2, LWD jams historically were the principal mechanism that controlled river habitat diversity through the formation of scour pools, bars, in-channel islands, and riparian forests in the Pacific Northwest (Abbe 2000).
The historic records support the premise that LWD strongly influenced the hydrologic characteristics of the Chehalis floodplain areas of the basin. The removal of wood and the clearing of riparian vegetation have very likely changed the channel dynamics in this system.
The mainstem appears to be undergoing a long-term trend of channel entrenchment since presettlement conditions, which likely began with the regular removal of woody debris. Woody debris removal resulted in concentrating river flow into one main channel. River transport of logs from logging operations also created conditions that further favored processes of entrenchment. Lastly, bank protection measures prevented (and continue to prevent) the mainstem from adjusting to flow events though channel changes.
Historic actions changed the Chehalis River wetland characteristics by reducing both the frequency and duration of low intensity flood events and by decreasing the ability of wetlands to store water. Draining wetlands and channelizing the river system decreased the ability of the entire system to store water (flood retention, ground water discharge), to augment low flows and reduce summer temperatures (discharge cooler groundwater during the summer drought months)
and to reduce the peak of flooding events. The Chehalis River system also lost biodiversity due to the loss and/or degradation of habitat and the loss and/or degradation of connectivity between habitats.
The impacts of the historic actions include loss of population and/or population isolation of many species (both plant and animal), loss of primary and secondary productivity, loss and/or degradation of fisheries habitat, loss of flood storage and low flow augmentation, and loss of biodiversity. Today, however, the Chehalis River ecosystem is still a relatively extensive complex of emergent, scrub-shrub and forested wetlands and riparian areas, as well as large area of agricultural wetlands that are actively cultivated during the spring and summer months. Much of the agricultural area of the floodplain has subsurface tiles and ditches to facilitate drainage.
Some of the ditches and drains were successful in converting wetland areas into uplands, whereas other systems have failed, resulting in maintenance of wetland hydrology. The extent of either situation is difficult to determine without supporting field observations, although the Soil Survey for Lewis County (USDA 1987) has mapped large units of hydric soils throughout the study area, including the areas currently under cultivation.
Interspersed with the wetland complexes are equally large areas of well-drained soils. This complex variety of soils is a result of the glacial-fluvial history of the area, which was historically part of a broad glacial outwash plain and is currently part of an active floodplain.
The Chehalis River wetlands are supported by a combination of high seasonal water tables, periodic flooding, and seasonal ponding. Those areas directly adjacent to the river probably experience both high seasonal water tables and periodic flooding. The areas away from the river likely are a result of high seasonal water tables and ponding.
The Chehalis River riparian areas are located in parts of the floodplain that are regularly inundated by floodwaters. Some of the riparian areas may also be wetlands, whereas others, located on the well-drained soils, are not inundated long enough to support wetland vegetation.
Functions likely provided by these wetlands include sediment and nutrient removal, peak flow reduction, baseflow support, shoreline stabilization, primary production and organic export, fish and wildlife habitat, and native plant richness. Functions associated with the riparian systems include habitat for passerine birds, small mammals, amphibians, LWD supply, and native plant richness.
Table 3.4-1 provides a summary of the acreage and type of wetlands and riparian areas found within the Chehalis River valley of the study area:
Table 3.4-1 Chehalis River Wetlands and Riparian Areas (in Acres) within the study
3.4.2.2 Skookumchuck River Wetlands and Riparian Areas
The historic impacts to the Skookumchuck River are less well documented than those to the Chehalis River. However, the position of the Skookumchuck River in the landscape and the Lewis County Soil Survey (including information on soil forming processes) indicate that historically the Skookumchuck River wetlands were not as extensive as those associated with the floodplain of the Chehalis River.
The confluence with Chehalis River, where the floodplain is the widest, likely supported the largest area of wetlands and riparian habitat along the historic Skookumchuck River. The existing river meanders suggest that this was an area of lower energy, which probably looked and functioned much like the historic Chehalis River in the same reach. Almost all of these wetlands and riparian areas were lost with the development of Centralia.
The Skookumchuck River probably also provided a source of LWD to the system, some of which was trapped with the construction of the Skookumchuck Dam. Although there are no specific records, it is also likely that historically this river system contained much more LWD and log jams than it currently does. These were probably removed to facilitate log transfer downstream, much like the work done on the Chehalis River.
Functions lost or degraded due to historic impacts of the Skookumchuck River include food chain support for invertebrates and vertebrates, sediment removal, shoreline stabilization, high biodiversity for both plants and animals, and high organic export.
The existing wetland systems associated with Skookumchuck River are not as large or diverse as those of the Chehalis River. The river floodplain is narrow and somewhat incised until it reaches the vicinity of Bucoda, where it broadens into its widest area at the confluence with Hanaford Creek and Centralia. Most of the area is in agricultural production, with the exception of the area within Centralia. Wetlands associated with this system are directly adjacent to the river or in the floodplain. This area does not contain extensive areas of hydric soils, which suggests that there may not have been extensive wetlands associated with the river above the confluence with Hanaford Creek. Hanaford Creek, in contrast, supports extensive emergent wetlands with extensive areas of mapped hydric soils (USDA 1987). Areas around the reservoir behind the dam are predominately rock vertical faced walls. There is a small area that could contain riparian habitat but would not be impacted if the water is stored during a flood event no longer than 5 continuous days.
The Skookumchuck River wetlands are supported by a combination of high seasonal water tables, periodic flooding, and seasonal ponding. Those areas directly adjacent to the river probably experience both high seasonal water tables and periodic flooding. The areas away from the river likely are a result of high seasonal water tables and ponding.
Like the Chehalis River systems, some of the riparian areas are also wetlands, whereas those found on well-drained soils are not. The riparian areas are found in parts of the floodplain that are regularly inundated.
Agriculture, logging, urban development, and the construction of Skookumchuck Dam have affected conditions in this reach of the Skookumchuck River. Agricultural development has changed the complexity and extent of wetlands as well as adjacent riparian forests. Urban development (mostly in Centralia) has resulted in the direct loss of wetlands and riparian areas and well as indirect impacts to the remaining habitats.
Functions likely provided by these wetlands include sediment and nutrient removal, peak flow reduction, baseflow support, shoreline stabilization, primary production and organic export, fish and wildlife habitat, and native plant richness. Functions likely provided by the riparian areas include habitat for passerine birds, small mammals, amphibians, LWD supply, and native plant richness.
Table 3.4-2 provides a summary of wetland and riparian acreage and type associated with the Skookumchuck River within the study area:
Table 3.4-2 Skookumchuck River Wetlands and Riparian Areas (in Acres) within the study
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Wildlife populations in the study area consist primarily of species associated with open forest canopies and young vegetation. The climax deciduous forests associated with the pre-settlement era were removed in the 19th century, converting the hardwood wetland floodplain and lowland habitat of the study area into agriculture and timber production. As development of the area has increased, forested habitat in the riparian zone along the mainstem Chehalis and tributaries has been reduced to narrow strips. Near Centralia and Chehalis, wildlife populations are characterized by species associated with urban development. Species that are not tolerant of human activity no longer use those areas. This section describes the species and habitats known to be present, as well as the existing conditions of riparian habitat along the mainstem Chehalis River within the study area. A more comprehensive catalog of faunal groups within the study area is presented in Appendix A.
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Field studies were conducted in 2000-2001 for Lewis County to identify wildlife habitats in the study area (PIE 2001). Detailed discussion of the results of these studies is presented in Appendix A.
Wildlife habitat associated with the Chehalis River riparian and riverine areas was evaluated by examining the width of the existing riparian zone, the riparian vegetation species and their value to wildlife habitat, and wetlands associated with the riparian corridor.
The majority of the Chehalis River within the study area lacks riparian cover, and the riparian zones that are present average only 45 feet in width. Consequently, there has been a loss of habitat connectivity and instream temperature protection due to reduced riparian function throughout the study area. The dominant tree species within the riparian zones along the Chehalis River are black cottonwood and big-leaf maple, with an understory shrub layer of vine maple and willow. The majority of wetlands in the study area are emergent wetlands dominated by reed canary grass and other pasture-type grasses. The following overview of the existing riparian habitat conditions along the Chehalis River is based on observations made during the 2000-2001 field surveys.
From the confluence of the Chehalis River and Lincoln Creek upstream to the mouth of the Skookumchuck River, the habitat is dominated by hardwood riparian woodland with a secondary or shrub layer beneath. This hardwood riparian area averages 51 feet wide throughout this segment, largely because of the wetland areas located along the right bank. The dominant canopy species are black cottonwood and big-leaf maple, with vine maple and willow dominating the understory. Some areas along the left bank have reed canary grass beneath a narrow margin of cottonwoods. Cottonwood snags are prevalent throughout this reach. Beyond the riparian buffers, the area is developed into either pasture lands or residential and commercial properties.
From the mouth of the Skookumchuck upstream to the mouth of the Newaukum River, 30 percent of the riparian habitat has no vegetative cover. Big-leaf maple is the dominant canopy species on the remaining riparian habitat. Where a shrub layer exists, red-osier dogwood is dominant. Ground cover is dominated by reed canary grass and Himalayan blackberry. The average width of the riparian buffer, where present, is 35 feet in this reach. The adjacent oxbows are bordered by western red cedar with an understory of big leaf maple, red-osier dogwood, and Pacific willow (S. lasiandra ), with reed canary grass beneath. LWD and snags are scarce; only one snag was observed in this entire section. Beaver, raccoon, and deer were observed throughout this section, and waterfowl utilize the oxbow ponds.
The section from the mouth of the Newaukum to approximately 5 miles upstream from the South Fork Chehalis River confluence contains dense stands of Himalayan blackberry and reed canary grass dominating the understory. Red alder and big-leaf maple are co-dominant in the overstory, and black cottonwood is sporadically present. The average riparian width is 42 feet in this section. There are emergent wetlands within the riparian buffer immediately adjacent to the river, with forested wetlands set back from the river. There are also areas devoted to agricultural use adjacent to the river. During the field surveys, waterfowl, otter, deer, songbirds, beaver and bald eagles were observed using these wetlands.
The remaining upstream portion of the Chehalis River within the study area has fewer riparian wetlands, yet the average width of the riparian buffer is 46 feet. Red alder and big-leaf maple with a red-osier dogwood and vine maple understory dominate the hardwood overstory. The valley bottom in this reach is narrower, with channel erosion evident along both banks and overhanging vegetation present. Snags and burrows were observed within this reach, with songbirds, deer, beaver, otter, coyote, and small mammals also evident. Significant portions of this valley are wetlands, but these areas are generally farmed and do not provide typical wetland functions.
Wildlife habitat has been reduced throughout much of the study area through depletion of riparian buffers and the loss of hardwood wetlands and off-channel areas as a result of agricultural, residential, and commercial development. This loss of quality riparian, wetland, and off-channel habitat and function limits the quantity and diversity of wildlife species present within the study area.
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Priority habitat is defined byWDFW as those habitat types or elements with unique or significant value to a diverse assemblage of species. Priority habitat that was identified within the study area is described below.
3.5.2.1 Freshwater Wetlands
This habitat supports (at least periodically) hydrophytic plants, has a substrate that is predominantly undrained hydric soils that are saturated or covered with shallow water at some time during the growing season. Freshwater wetlands are located throughout the study area, with higher concentrations along the Chehalis and Skookumchuck rivers (PIE 2001).
3.5.2.2 Fresh Deepwater
These are habitats where hydrophytes are the dominant plants; however, the water in these areas is too deep to support emergent vegetation. This environment also includes all underwater structures and features such as caverns, woody debris, and rock piles. Fresh deepwater habitat is found in the Skookumchuck reservoir, as well as in several large ponds along the Skookumchuck and Chehalis rivers.
3.2.2.3 Cliffs
Cliffs are considered priority habitat if they are greater than 25 feet high and occur below elevation 5,000 feet. They must also contain high densities of wildlife breeding and nesting area to be classified priority habitat. Cliffs were observed along the banks of the Skookumchuck reservoir during the 2000-2001 field surveys (PIE 2001).
3.5.2.3 Instream
This habitat comprises the physical, biological, and chemical processes and conditions that interact to provide life history requirements for fish, wildlife, and invertebrate resources in a lotic environment. Instream habitat is found throughout the study area, and includes all the major rivers and their tributaries.
3.5.2.4 Mature Forest
This habitat type includes tree stands with average diameters exceeding 21 inches diameter at breast height (dbh). The density of trees, number of snags and quantity of large downed logs is generally less than that of old-growth forest. Stands of mature forest are found throughout the upper Newaukum, Skookumchuck, and Chehalis River Basins (PIE 2001).
3.5.2.5 Riparian Habitat
This habitat includes the area adjacent to streams and other water bodies, beginning at the ordinary high water mark and extending to the terrestrial areas that are influenced by, or directly influence, the aquatic ecosystem. These areas include the entire floodplain and riparian areas of wetlands that are directly connected to stream courses. Riparian habitat has been reduced throughout the study area and is now present only in narrow strips along the lower portions of the Skookumchuck, Newaukum, and Chehalis Rivers (PIE 2001).
3.5.2.6 Rural Natural Open Space
This habitat includes open space that (1) functions as a corridor connecting other priority habitats (especially areas that would otherwise be isolated), (2) is an isolated remnant of natural habitat larger than 10 acres surrounded by agricultural or urban developments, or (3) provides habitat for a priority species. This habitat must also contain unique species assemblages in agricultural or urban areas to be classified as a priority habitat. Most areas of open space habitat within the
study area have been affected by agriculture or urban development and very few of these areas provide migratory corridors.
3.5.2.7 Talus Slopes
Talus slopes are a priority habitat if the rock rubble is homogenous, averages 0.5 to 6.5 feet in size, and is composed of basalt, andesite, and/or sedimentary rock. Mine tailings and riprap may also be included. One talus slope in the northeast corner of the Skookumchuck reservoir was identified during field surveys (PIE 2001).
3.5.2.8 Snags and Logs
Areas with abundant and well-distributed snags and logs are considered priority snag and log habitat. This habitat may consist of single snags or logs, or groups of snags or logs of exceptional value to wildlife due to their scarcity or location within the landscape. Snags must be greater than 20 inches dbh and 6.5 feet tall and logs must be greater than 12 inches in diameter at the largest end and at least 20 feet long in order to be classified as a priority habitat.
Snags and logs are present in many locations throughout the study area, but in limited quantity.
Reduced riparian buffers and the clearing of snags have depleted the sources of this habitat type within the study area.
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The following species appear on the List of Endangered and Threatened Wildlife and Plants, as authorized by the Endangered Species Act of 1973. These species have been identified as potentially occurring in the study area:
Candidate species:
Federal species of concern include California wolverine (Gulo gulo luteus ), Pacific fisher (Martes pennanti pacifica ), western pocket gopher (Thomomys mazama ), Pacific Townsend's big-eared bat (Corynorhinus townsendii townsendii ), long-eared myotis (Myotis evotis ), longlegged myotis (M. volans ), western gray squirrel (Sciurus griseus ), Northern goshawk (Accipiter gentilis ), peregrine falcon (Falco peregrinus ), olive-sided flycatcher (Contopus cooperi ), Pacific lamprey (Lampetra tridentata ), river lamprey (L. ayresi ), Columbia torrent salamander (Rhyacotriton kezeri ), Van Dyke's salamander (Plethodon vandykei ), Larch Mountain salamander (Plethodon larselli ), Cascades frog (Rana cascadae ), tailed frog (Ascaphus truei ), western toad (Bufo boreas ), valley silverspot (Speyeria zerene bremeri ), tall bugbane (Cimicifuga elata ), white-top aster (Aster curtus ), and pale larkspur (Delphinium le ucophaeum ).
Finally, several state-listed species of concern include the great blue heron (Ardea herodias ), bufflehead (Bucephala albeola ), wood duck (Aix sponsa ), osprey (Pandion haliaetus ), bandtailed pigeon (Columba fasciata ), and western pond turtle (Clemmys marmorata ). The Olympic mud minnow (Novumbra hubbsi ) is a state candidate species.
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Several of the species of concern are especially adapted for slack-water, muddy bottom conditions. These species include the Olympic mudminnow, Pacific and river lampreys, and western pond turtle. According to the WDFW Priority Habitats and Species (PHS) database, these species are found in ponds associated with low gradient streams (or along side channels or heavily vegetated banks of such streams), such as Hanaford Creek, Lincoln Creek, Bunker Creek, and Deep Creek. Western toad and Oregon spotted frog are found in shallow marshes, generally with stable water levels. The PHS database lists no western toads in the study area, and the Oregon spotted frog is known only from one location in the South Puget Sound region, in Thurston County, several miles from the study area. Western pond turtles are currently only known to occur in two locations in Washington, both near the Columbia River in Skamania and Klickitat counties. A small population has been introduced to a pond complex in Pierce County (WDFW 2002).
A few of the sensitive species listed for the study area are found almost exclusively in fastmoving, clear, cold-water streams. These species are the Columbia torrent salamander, Van Dyke's salamander, Cascades and tailed frog. These habitats do not occur along the mainstem Chehalis or lower reaches of the tributaries. Tailed frogs and Van Dyke's salamanders have been found in the Skookumchuck River and tributaries beginning about 5 miles upstream from the reservoir. Columbia torrent salamanders have been found about 10 miles southwest of the study area.
Amphibian and reptilian populations and distributions within the study area are poorly documented. The Washington State Gap Analysis Project (Dvornich et al. 1997) identified suitable habitat for amphibians and reptiles, then cross referenced these habitats with museum records and documented sightings. The results of the gap analysis, indicating habitat and recorded presence of amphibians and reptiles within the study area are included in Appendix A .
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3.6.2.1 Prairie Species
The Whulge's checkerspot, Mardon skipper, western pocket gopher, western gray squirrel, valley silverspot, white-top aster, and pale larkspur are all restricted to prairie habitats. Nearly all of the extant prairie habitats in the vicinity of the study area occur at Grand Mound Prairie.
The Boistfort Prairie also supports the checkerspot and skipper, Kincaid's lupine and pale larkspur. The golden paintbrush is known to occur in only 5 sites as of 1981 (WDNR 1981).
One of these sites was in Thurston County, presumably on Grand Mound Prairie. In the current Natural Heritage Database, the only extant population listed occurs in the Deception Pass area of Skagit County (WDNR 2002).
3.6.2.2 Species of Forested Habitats
Over 20 bald eagle territories are known to be in the study area (WDFW 2002), and individuals are often observed throughout the area during the winter. The primary prey base of these bald eagles is not known, but very likely includes anadromous fish returning to spawn, and waterfowl.
It is possible that bald eagles in the study area supplement their diet with resident fish, carrion, rabbits, and other small mammals, as these are known food items in places where anadromous fish spawn and waterfowl are scarce (especially during the eagle nesting season). No communal night roosts are known to occur in the study area (WDFW 2002).
Bald eagle nest sites have been identified along the mainstem Chehalis River. Nest sites also occur along the upper Skookumchuck River, and along the Newaukum River. Most of these nests are in large cottonwood trees, although some are in spruce trees. Bald eagle nesting was observed in the vicinity of the Skookumchuck reservoir during field surveys conducted in 2000- 2001 (PIE 2001).
The PHS database lists 4 observations of marbled murrelet flights within the study area. These do not necessarily reflect a nest location, but probably do indicate nesting activity somewhere nearby. All of these observations occurred west of the study area, and several miles south of the Chehalis River. There are no marbled murrelet observations within the Skookumchuck River Basin.
Suitable spotted owl habitat within the study area is limited due to extensive recent logging activities. The presence of mature forest is requisite to attract nesting pairs to the area. Only two spotted owl observations are known near the study area; both of these occurred several miles to the south and west.
The ranges of Canada lynx, gray wolf, and grizzly bear do not generally include the study area, although on occasion it may be possible for individuals to wander into the area. However, all three species are largely restricted to high elevations in the north Cascade Mountains in Washington, and are not expected to be found in the study area.
Other species restricted to forested landscapes include California wolverine, Pacific fisher, Pacific Townsend's big-eared bat, long-eared myotis, long-legged myotis, northern goshawk, olive-sided flycatcher, tall bugbane, and band-tailed pigeon. Only tall bugbane is cited in the PHS database as occurring within the study area. Three discrete populations are noted in the area. Although observations of other species are not noted in the database, it is likely that the two species of myotis, the northern goshawk, the olive-sided flycatcher, and band-tailed pigeon are all found in areas that still support mature or successional-stage forests. According to the PHS database, a California wolverine was sighted in the area several years ago. However, this occurrence is regarded as highly unusual, since the normal habitat for wolverine is high elevation forests.
3.6.2.3 Species of Riparian Habitats
Four state-listed candidate species, the great blue heron, bufflehead, wood duck, and osprey, are found in riparian habitats within the study area. The bufflehead and wood duck are cavity nesters. The heron builds nests in colonies in living trees and the osprey selects large, dead snags for nesting. All of these require mature riparian forests to develop trees and snags large enough to support large nests and cavities. A few areas of mature riparian forest occur along the mainstem Chehalis and Skookumchuck Rivers. During the 2000-2001 field surveys, great blue herons were frequently observed in and along the Chehalis, Skookumchuck, and Newaukum Rivers. No great blue heron nesting was observed within the study area (PIE 2001). During the field surveys, osprey were observed in the Chehalis and Newaukum River basins and one pair of wood ducks was sighted in the Newaukum basin (PIE 2001).
3.6.2.4 Species of Other Habitats
The peregrine falcon nests on cliffs, or tall man-made structures, including high bridges, and typically forages over open spaces. No peregrine falcon nests are known in the study area (WDFW 2002). The Larch Mountain salamander is found almost exclusively on steep talus slopes, where the rocks range in size from 0.5 to 2.5 inches in diameter (WDFW 1993). One talus slope in the northeast corner of the Skookumchuck reservoir was identified during field surveys (PIE 2001), but no records of the Larch Mountain salamander in the study area were found in the PHS database.
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The study area provides a variety of aquatic habitat types, each inhabited by a discrete community of cold and warm water fishes. Although the study area remains relatively rural, agricultural activities, industrial development, and urban growth have resulted in stream segments with high sediment oxygen demand (resulting in low DO), high summer water temperatures, and suspended sediment and contaminants from upland runoff. Existing side channels, wetlands, and riparian habitats have also been affected by development. Flood control measures, including construction of levees, have also affected streams in the study area by removal of riparian vegetation and, in some cases, triggering channel incision. The mouths of some tributaries have been altered as a result. Although some historic environmental concerns (e.g., point-source pollution, floodplain construction) affecting stream habitats have been reduced markedly, mainstem habitats are still in limited supply and runoff from some upland areas still contains high levels of fecal coliform bacteria and other common contaminants. High water temperatures in the mainstem and some tributaries remain a concern.
The following section provides a description of the community structure and habitat utilization of fishes within the study area habitats.
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The Chehalis River and its tributaries support many species of salmonids, including spring and fall chinook (Oncorhynchus tshawytscha ), coho (O. kisutch ), and chum (O. keta ) salmon.
Summer and winter steelhead (O. mykiss ), rainbow (O. mykiss ), and both sea-run and resident cutthroat trout (O. clarki clarki ) are also present (WDF 1975). Although sockeye salmon (O. nerka ) and pink salmon (O. gorbuscha ) have been observed in streams in the lower Chehalis basin, it is thought that these fish are strays from other river systems and are not indigenous to the Chehalis River Basin (WDF 1975; WSCC 2001). Brook trout (Salvelinus fontinalis ) have been introduced into some lakes and streams within the Chehalis watershed (Envirovision 2000).
Little is known about the distribution and status of brook trout, but populations appear to be small.
The Chehalis River watershed probably represents the southern end of the range of anadromous bull trout/Dolly Varden trout (Salvelinus confluentus/S. malmo ) on the west coast. In its final rule for determination of bull trout as a threatened species, USFWS noted that a subpopulation of native char was reported to occur in the Chehalis River/Grays Harbor basin (USFWS 1999).
However, data confirming the presence of such a subpopulation are limited; very few native char have been collected during monitoring studies over the past 30 years. A single fish was captured in the Chehalis River at RM 50 in 1997 and another was captured near Oakville in 1973 (USACE 2001). During the 11-year period that WDFW has operated a smolt trap in the Chehalis River, only one char has been observed (in 1997) (WDFW 1998b). The Corps conducted a literature review of bull trout in the lower Chehalis River, which revealed few instances of bull trout in the study area (USACE 2001). Char do appear to utilize the tidally-influenced lower reaches of the Chehalis River, as evidenced by the capture of 7 sub-adult char in Grays Harbor in the winter of 2001 by R2 Resources, Inc. The origin of these fish is unknown. There are no confirmed genetic data to determine whether the captured char are bull trout or Dolly Varden trout.
The Chehalis River system also supports white sturgeon (Acipenser transmontanus ), green sturgeon (A. medirostris ) and the non-native American shad (Alosa sapidissima ) (Hiss and Knudsen 1993). Several exotic warmwater species, including largemouth bass, perch, catfish, sunfish (Lepomis cyanellus ), and many other resident fishes are present.
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3.7.2.1 Chehalis River
The mainstem Chehalis River provides spawning and rearing habitat for salmonids as well as access to upriver habitat. In the Centralia reach, the mainstem generally lacks suitable riffles for spawning, while low flows coupled with high water temperatures during the summer and early fall limit the availability of rearing habitat. High sediment loads in this reach of the Chehalis River also decrease the area and quality of spawning and rearing habitat. No pools of sufficient depth or cover to provide holding or rearing habitat are present (PIE 2001). In the upper portion of the study area (upstream from the confluence with the South Fork Chehalis), the mainstem provides spawning and rearing habitat for spring and fall chinook, coho, and steelhead. Several quality pools are present in this area, along with LWD, which offers holding habitat for migrating salmonids (PIE 2001).
The timing of the Chehalis River spring chinook run is not known with precision. The Washington Department of Fisheries (1975) stated that fish enter the river in March through mid- August, but chinook catches in the Confederated Tribes of the Chehalis Tribe reservation fishery have been reported as early as February. Chinook spawn in the mainstem and in the tributaries in late August through September, with spawning in the upper basin occurring slightly later. Fry emerge late the following winter. Juvenile spring chinook generally remains in the river for over a year, with seaward migration taking place the second spring after emergence.
Adult fall chinook begin entering the Chehalis River in August, with the run peaking in September and tapering off through November (WDF 1975). Spawning generally occurs during October through mid-December. Within the study area, fall chinook salmon spawn in suitable riffles in the reach between the mouth of the Skookumchuck River and the mouth of the Black River, as well as in areas upstream from Centralia and Chehalis. Fall chinook fry emerge in late winter through early spring, and remain in freshwater for 3 to 5 months before beginning their seaward migration.
The Chehalis and nearby drainages produce more coho smolts than any other system along the Washington coast, and in 1999 was the third largest producer in Washington state (WSCC 2001).
Coho salmon begin entering the Chehalis in September and continue through November, with spawning occurring over the period from October through January (WDF 1975). "Late-run" coho, which enter the river in mid-November through February, are not found in significant numbers within the study area and upper portions of the basin. Coho tend to seek out smaller tributary streams, and the mainstem Chehalis River within the study area provides little suitable coho spawning habitat. Coho fry emerge from the gravel in late spring. They typically migrate seaward during April, May, and June of their second year, although some fry and fingerlings migrate downstream in their first year during periods of flooding and heavy runoff.
Chum salmon enter the Chehalis system in early October through mid-December and spawning peaks in mid-November. Within the study area, chum salmon spawn in suitable riffles in the reach between the mouth of the Skookumchuck River and the mouth of the Black River. Chum fry begin their seaward migration shortly after emergence in early spring.
Wild summer steelhead in the Chehalis River system is a distinct stock based on the geographical isolation of the spawning population. Specific spawning locations are unknown, but it is thought that wild summer steelhead may spawn in the upper reaches of the Chehalis River. Run timing is generally from May through October, and spawning is believed to occur from February through April. Wild winter steelhead are distinct from wild summer steelhead based on run timing. Run timing for winter steelhead in the mainstem Chehalis is December through May, with spawning occurring from mid-February through early June.
American shad have been observed in the Chehalis River as far upstream as Rainbow Falls (RM 97), but the largest concentration of shad spawning is thought to be near Rochester (Hiss and Knudsen 1993). Within the study area reach there is likely little shad spawning, as there are few areas of suitably sized gravels.
Sturgeon are known to be present in the Chehalis River as far upstream as the mouth of the Newaukum River. A few juveniles, apparently months old, were seined from the mainstem Chehalis during summer in the early 1970s (Hiss and Knudsen 1993). Within the study area, there are a few locations in the mainstem Chehalis River that contain larger cobble substrates that could be used for spawning. However, use of these areas by sturgeon is considered unlikely.
The Olympic mudminnow, which is listed by Washington State as a sensitive species, is not known to occur in the mainstem Chehalis River, although suitable habitat occurs in some offchannel ponds. This species is known to be present in China Creek, which enters the Chehalis near Mellen Street (City of Centralia 1999).
There are currently no dams or other man-made structures that block the upstream or downstream movement of anadromous fish in the mainstem Chehalis. As described in Section 3.3, water quality in the Centralia reach frequently fails to meet Class A water quality criteria for temperature and DO during the dry season. The combination of low flows, high water temperatures, and low DO levels in late summer and early fall may form a block to fish migration in the Centralia reach. Upstream from the South Fork confluence, there are numerous culverts on tributaries that are known to block passage of cutthroat trout, and several culverts that block passage for both cutthroat and steelhead (WSCC 2001). In addition, one culvert on a tributary to the East Fork Chehalis is known to block migrating coho. A natural barrier to salmon migration occurs at RM 97, where Rainbow Falls occasionally hinders passage of adult fish at low flows.
The matrix below summarizes the timing of migration, spawning, emergence, and rearing of various species in the Chehalis system:
Table 3.7.2 Matrix of migration, spawning, emergence and rearing
3.7.2.2 South Fork Chehalis
The South Fork Chehalis River supports runs of spring and fall chinook and coho salmon, as well as steelhead trout. Coho are the most abundant salmonid in this stream (WSCC 2001). The coho stock in the South Fork Chehalis River basin is classified as part of the much larger population of coho found throughout the Chehalis River system upstream from the Satsop River confluence. Similarly, spring chinook and fall chinook salmon in the South Fork Chehalis are components of the Chehalis River chinook stocks. Winter steelhead in the South Fork Chehalis River are part of a larger population found throughout the Chehalis River basin upstream from the Satsop River (WSCC 2001). This stock does not include spawners in the Skookumchuck and Newaukum basins.
Although the South Fork Chehalis is used primarily for upstream access and rearing, there are some suitable, riffles that provide limited spawning for chinook. Coho and steelhead spawning is confined primarily to tributary streams containing suitable spawning gravels. Low flows, high water temperatures, high silt loads, and concentrations of predatory fish are factors that limit successful salmon spawning in the South Fork Chehalis.
There are limited opportunities for salmonid rearing and holding in the South Fork Chehalis River. One reach was identified as having side channel habitat that could be utilized by juvenile salmonids for rearing (PIE 2001). LWD functioning as holding habitat for fish was observed in two reaches; however, no pools of sufficient depth or cover that could provide rearing or holding habitat were identified. High silt loads from extensive bank cutting limit the availability of holding and rearing pools throughout the South Fork.
There are several culverts on South Fork tributaries that are known to be barriers to migrating salmon, steelhead, or both (WSCC 2001). The length of stream habitats blocked by these culverts has not been determined.
3.7.2.3 Skookumchuck River
The Skookumchuck River provides spawning and rearing habitat for spring and fall chinook and coho salmon, and supports winter steelhead and resident cutthroat trout. Chum salmon used this stream historically, but have not been found in the Skookumchuck for many years (WDF 1975).
The Olympic mudminnow is reported to occur in Hanaford Creek (WDFW 1999).
The spring chinook and fall chinook stocks in the Skookumchuck River are considered components of the larger Chehalis River chinook stocks. Chinook use the mainstem Skookumchuck River for spawning and rearing from the mouth up to the Skookumchuck Dam at RM 21.9.
The coho stock in the Skookumchuck River is classified as part of the much larger population of coho found throughout the Chehalis system upstream from the Satsop River confluence. Coho use the mainstem Skookumchuck up to the dam for spawning and rearing, and spawn in the accessible reaches of tributaries. Wild winter steelhead in the Skookumchuck River basin are considered to be part of a larger population that includes Newaukum River winter steelhead.
Prior to construction of the Skookumchuck Dam, coho and steelhead utilized the Skookumchuck River up to an impassible falls near RM 28.9. The dam, which was built in 1970, blocks natural passage to all anadromous fish. It is estimated that 3.6 miles of spring and fall chinook mainstem habitat and 7 miles of coho mainstem habitat were lost when the dam was constructed (WSCC 2001). WDFW traps returning steelhead at a collection facility at the base of the dam, and transports them to stream reaches upstream from the dam for spawning. Steelhead smolts are transported downstream by allowing water over the spillway from March 15 to June 1 (USFWS 1982). Following dam construction, cutthroat were planted above the reservoir by the Washington Department of Game, but this practice was discontinued in 1980.
Several reaches of the Skookumchuck River below the dam contain pools of sufficient depth and cover to provide quality rearing and holding habitat for salmonids, particularly in the upper and lower reaches (PIE 2001). Several side channels that provide rearing habitat for juvenile salmonids are present in the upper and middle reaches.
There are two culverts on Skookumchuck River tributaries in the upper basin that are known to be barriers to steelhead (WSCC 2001).
3.7.2.4 Newaukum River
The Newaukum River, including its North and South forks, supports runs of spring and fall chinook and coho salmon as well as steelhead. American shad use the lower Newaukum River for spawning (WDF 1975).
The spring and fall chinook stocks in the Newaukum are considered components of the Chehalis River chinook stocks; this drainage contributes an estimated 34 percent of the spawning population of Chehalis River spring chinook and an estimated 6 percent of the total spawning population of Chehalis River fall chinook (WSCC 2001). Spring and fall chinook spawn up to RM 12.5 on the North Fork and up to RM 31 on the South Fork Newaukum River.
The coho spawning in the Newaukum River are considered part of the Chehalis River population found upstream from the Satsop River. Coho salmon use the mainstem Newaukum River for rearing and transportation, and use tributary streams for spawning and rearing. Winter steelhead in the Newaukum River basin are considered to be part of a larger population that includes Skookumchuck River winter steelhead. Steelhead use the mainstem Newaukum River for rearing and transportation, and use tributary streams for spawning and rearing. Coho and steelhead have been documented as far upstream as RM 18.5 on the North Fork and up to RM 32.2 on the South Fork Newaukum River. Tributaries producing coho and steelhead include Allen and Taylor creeks (mainstem tributaries), Lucas, Bear, Mitchell, and Johns Fork creeks (North Fork tributaries), and Bearnier, Beaver, Frase, Gheer, Kearney, and Lost creeks (South Fork tributaries).
The South Fork Newaukum River contains a number of deep pools with cool water temperatures, which provide excellent rearing habitat for juvenile salmonids, as well as adult resting and maturation habitat. The area and quality of rearing and maturation habitat on the North Fork is limited by low flows, high water temperatures, high silt loads, and large concentrations of predatory fish (WDF 1975).
A diversion dam was built in 1918 at RM 12.5 on the North Fork Newaukum to provide water for the cities of Centralia and Chehalis. This dam blocked access for anadromous fish until 1970, when a fish ladder was constructed. On the South Fork, a series of falls upstream from RM 31 apparently block salmon from utilizing some potential upstream production areas (WDF 1975).
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Many Chehalis River basin wild salmon and steelhead populations have been extensively influenced by hatchery releases of non-native stocks (Hiss and Knudsen 1993; WSCC 2001).
Many hatcheries developed brood stocks from outside strains, and most Chehalis basin salmonid populations have had considerable non-native influence. Stocks occurring in the Study Area that
are considered to be of mixed origin include Chehalis River fall chinook, Chehalis River coho, and Skookumchuck/Newaukum River winter steelhead (Envirovision 2000).
Reports developed byWDFW and Western Washington Treaty Indian Tribes summarize the most recent information available on the status of salmonid stocks in the Chehalis basin and study area (WDFW and WWTIT 1994; WDFW 1998b and 2000).
Escapement estimates for years 1986-1996 for coho and fall and spring chinook within the study area are presented in Appendix A. Steelhead red count summaries for years 1989-1996 are also presented in Appendix A.
3.7.3.1 Spring Chinook
There is one stock of spring chinook found in the Chehalis River basin and the study area. The Chehalis River stock of spring chinook is considered a native stock and is maintained by wild production. The stock is considered healthy. From 1982 through 1991, escapement ranged from 610 to 3,488. With the exception of 1988 and 1989 (two strong return years), average escapement during the 1982-1991 period was approximately 1,400 (WDFW and WWTIT 1994).
Since 1991, the average escapement has increased to 2,379 (WSCC 2001). The population trend is considered stable or possibly positive (Envirovision 2000).
3.7.3.2 Fall Chinook
There are seven stocks of fall chinook in the Chehalis River basin, one of which (the Chehalis River stock) is found in the study area. The Chehalis River stock of fall chinook salmon is of mixed origin, and is maintained by wild production. The stock is considered healthy. From 1985 through 1990, escapement ranged from 2,971 to 7,837 (WDFW and WWTIT 1994). Estimates indicate that recent escapement levels have been stable (WSSC 2001). There is no recent population trend reported for Chehalis River fall chinook (Envirovision 2000).
3.7.3.3 Coho
Of the seven stocks of coho in the Chehalis basin, one (the Chehalis River stock) occurs in the study area. The Chehalis River coho stock is of mixed origin, with composite production of hatchery and wild fish. The stock is considered healthy. Between 1984 and 1991, escapement averaged 18,510, and then declined to an average of 14,625 between 1992 and 1998. However, a portion of the population has recently increased its level of returns, resulting in numbers similar to the 1984-1991 period (WSCC 2001). No recent population trend has been reported for this stock (Envirovision 2000).
3.7.3.4 Fall Chum
There are two stocks of fall chum in the Chehalis River basin, one of which (the Chehalis River stock) is found in the study area. The Chehalis River fall chum stock is considered native, and is maintained by wild production. The stock is considered healthy. Escapement levels and population trend for this stock are unknown (WDFW and WWTIT 1994).
3.7.3.5 Summer Steelhead
There are two stocks of summer steelhead in the Chehalis River basin. One, the Chehalis River stock, occurs in the study area. The origin of the stock is unknown; a native stock originally returned to the Wynoochee River and possibly other rivers, but there is uncertainty about the contribution by hatchery summer steelhead spawning in the wild (WDFW and WWTIT 1994).
The stock is maintained by wild production. The status of the stock and population trends are unknown. Escapement is not monitored for this stock, nor has an escapement goal been identified.
3.7.3.6 Winter Steelhead
Of the eight stocks of winter steelhead in the Chehalis River basin, two (the Chehalis River and the Skookumchuck/Newaukum River stocks) occur in the study area. The Chehalis River stock is native and is maintained by wild production. This stock is considered healthy. From 1984 through 1992, escapement ranged from 2,540 to 4,156. The Skookumchuck/Newaukum River winter steelhead stock is of mixed origin and is maintained by composite production. Production is partially sustained by hatchery production at the Skookumchuck Dam. The stock is considered depressed, with a negative population trend. From 1984 through 1992, escapement ranged from 644 to 1,202 (WDFW and WWTIT 1994). From 1996 to 1999, wild escapement ranged from only 193 to 473, below the wild escapement goal of 766 (WSCC 2001).
3. 7.3.7 Coastal Cutthroat
The Chehalis River stock complex of coastal cutthroat trout includes fish in the Skookumchuck and Newaukum Rivers, the smaller tributaries and headwaters of the Chehalis River, and tributaries downstream from the study area. The stock complex is considered native and is maintained by wild production. The status of the stock complex and population trend are unknown. Some researchers believe that that stock complex may be depressed (Envirovision 2000). However, WDFW (2000) indicates that cutthroat are relatively abundant and widely distributed in the basin, based on juvenile density sampling at over 80 sites in the upper basin and returns to a trap operated by the Quinault Indian Nation on the West Branch Hoquiam River.
3.7.3.8 Bull Trout/Dolly Varden Trout
A described in Section 3.6, the Coastal/Puget Sound population segment bull trout is listed as threatened under the Endangered Species Act. A native, wild-producing stock of bull trout/Dolly Varden trout has been identified in the Chehalis River/Grays Harbor system. However, most information on this stock consists of anecdotal accounts by sport fishers, and the stock status and population trend are unknown (WDFW 1998b).
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Political jurisdictions in the study area include Lewis and Thurston counties, the cities of Chehalis and Centralia, and the towns of Pe Ell and Bucoda. Unincorporated communities include Adna, Doty, Dryad, Fords Prairie, and Galvin.
The study area is generally devoted to rural residences, commercial agriculture, and timber production; small areas of commercial business and light industry are typically located near freeway interchanges. Large tracts of undeveloped land occur along the South Fork Chehalis River, to the east of Centralia along Hanaford Creek, and in the Skookumchuck River basin upstream from Bucoda. In the population centers of Centralia and Chehalis, land uses include a full range of residential, commercial, service, industrial, and public uses.
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The majority of the study area lies within the unincorporated portions of Lewis County. The overall character of the study area in Lewis County is rural re