Coal Creek Site 0442

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King County Water Quality Monitoring

King County monitors the ecological health of Coal Creek in a variety of ways including collecting and analyzing water, sediment, and benthic invertebrate samples. Station 0442 is at the USGS gauging station located near Coal Creek Parkway and 119th Avenue South. Water quality samples have been collected monthly at this station since 1972. Beginning in 1987, sediment quality samples have been collected from Coal Creek. In 2002 and 2003 benthic invertebrates were sampled from Coal Creek.

From time to time additional studies have been conducted on Coal Creek. Click here for more information about Special Studies involving Coal Creek.

Coal Creek Watershed

Coal Creek is located along the southern limit of the City of Bellevue. The headwaters of Coal Creek originate in the steep terrain of Cougar Mountain at an elevation of about 1,400 feet. The creek flows for about 7 miles through a series of steep, narrow ravines before entering Lake Washington along the eastern shoreline at Newport Shores. The drainage basin for the creek is roughly 4,550 acres and contains one large tributary – Newport Hills Tributary (Tetra Tech/KCM 2005). The watershed is within the shared jurisdiction of the City of Bellevue, King County and the City of Newcastle.

Extensive coal mining activities took place in the basin beginning in the late 1800s. The mining activities resulted in changed stream courses, channelized reaches, and mine tailing dumped along stream banks (McDonald 1987; Kerwin 2001). Headwater streams of the south fork of Coal Creek originate from a caved-in section of mine that seems to combine with an extensive mine drainage system (Skelly and Loy 1985).

Urban development within the basin in the last century has further altered the creek’s natural hydrologic characteristics, increasing the frequency, duration, and peak of flood events, stream bank erosion, and streambed sedimentation (Kerwin 2001). The channel was diverted southward in the late 1940s, then northward again in the late 1950s, because of the construction of an airstrip in the delta area of the stream. In the 1960s, as a feature of the residential development, two large canals were excavated just south of the stream mouth to allow moorage and waterfront amenities for inland properties. The stream has also been crossed several times by large municipal water and sewer mains.

A comprehensive basin plan for Coal Creek was produced by King County and the City of Bellevue in 1987 (King County 1987). As part of this planning effort a hydrologic model was developed. It was found that base flows in Coal Creek are augmented by approximately ten percent by flows from mine tunnels. Coal Creek was also found to have extensive sedimentation problems from stream bank erosion and the occasional catastrophic failure of tailing slopes that remain from the old coal mining activities in the creek’s headwaters and landslides of the steep slopes above the creek. Since 1997, the City of Bellevue has maintained two sediment retention ponds in the system, one immediately upstream of Interstate Highway 405 and another immediately upstream of Coal Creek Parkway. While the sediment ponds are helping to control excessive delta formation through the reduction of large particles, smaller particles and fine silts and clays remain suspended and wash downstream (Tetra Tech/KCM 2005). Thus the ponds provide no protection for spawning and rearing habitat (Kerwin 2001).

Currently, land use in the Coal Creek basin is predominantly single-family and multi-family residences and parks, including the Cougar Mountain County Park in the headwaters and Coal Creek Regional Park (Kerwin 2001). The basin has 15 percent impervious area within the 100-foot riparian area surrounding the creek.

Fisheries

The Coal Creek basin has few returning adult salmon of any species, although substantial supplementation of coho has occurred (King County 2001b, 2001c, April 2005; Kerwin 2001). The Washington Department of Fish and Wildlife reported planting between 9,000-13,800 zero age coho into Coal Creek from 1994-1997. Coho, chinook, sockeye, steelhead, and trout have been noted in the basin (Kerwin 2001).

Since 1997 volunteers with the Salmon Watcher Program have been recording salmon observations at various locations in Coal Creek. Volunteers have consistently seen coho salmon in the creek. Less commonly spotted are chinook and sockeye salmon.

Water Quality

Water quality samples are analyzed monthly for temperature, dissolved oxygen, pH, conductivity, turbidity, total suspended solids, ortho-phosphorus, total phosphorus, ammonia, nitrate-nitrogen, total nitrogen, and fecal coliform bacteria. Results are compared to State water quality standards. Water quality standards are designed to protect public health and aquatic life. Comparing monitoring results to water quality standards allows an understanding of how safe the creek is for recreational contact as well as for aquatic life. (See link at top of page to view current water data.)

State water quality standards were revised in 2003. Coal Creek was considered a “Class AA” water body under the 1997 rules. As the 2003 rules become effective Coal Creek is designated “Core Summer Salmonid Habitat” for aquatic life use and "Primary Contact" for recreational use. As part of the updated water quality standards, the lower portion of Coal creek has been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 13 ºC to be applied from September 15th to May 15th. Coal Creek is on the 2004 Washington Department of Ecology’s (Ecology) 303(d) list for violation of fecal coliform bacteria standards. See Table 1 for a summary of water quality violations in the creek during the most recent water year.

Coal Creek has historically had high dissolved oxygen concentrations and low temperatures (Metro 1990). However, sedimentation was a serious problem in the basin due to highly unstable soils. In 1987 King County and the City of Bellevue cooperatively produced a comprehensive basin plan for the creek (King County and City of Bellevue 1987).

Long-term Trends

A 25-year (1979 – 2004) trend analysis was conducted with baseflow data collected from Coal Creek. This analysis showed some improvements in the water quality since 1979. Conductivity, pH, total suspended solids and ortho-phosphorus have all shown a significant decrease over this 25-year time period. However, in stream temperatures and fecal coliform bacteria levels have increased significantly during this same time period.

Water Quality Index

A Water Quality Index (WQI) rating system was developed by the State Department of Ecology that evaluates several water quality parameters and gives and overall rating of “high,” “moderate,” or “low” concern. During the last six water years Coal Creek has rated “moderate concern”. To see how Coal Creek ratings compare with other stream sites, visit the Water Quality Index page.

For more information about long-term trends in other streams or to view charts of current water quality conditions in Coal Creek, please visit the links at the top of the page.

A review of the 2008 data shows the following violations of State water quality standards:

 

Hydrology

King County maintains one stream flow gauge on Coal Creek: Coal Creek Stream Gauge (06a).

Stream Sediment

Sediment data were collected from Coal Creek as part of the Stream Monitoring Program starting in 1987. Data were compiled and analyzed for the years 1987 through 2002. Data were analyzed for trends, correlations, and were compared to sediment quality guidelines. No significant trends were identified during data analysis for any of the parameters tested. Results indicate that Coal Creek sediments did not exceed any sediment quality guidelines. However, of the 27 streams monitored in King County, Coal Creek had the 5th highest metals concentration.

Benthic Invertebrates

In both 2002 and 2003, benthic invertebrate samples were collected, analyzed, and benthic invertebrate index scores (BIBI) were calculated for Coal Creek as part of King County's Benthic Invertebrate Program. Benthic invertebrates are an important link in the food chain for fish in the creek and are an excellent indicator of stream health. BIBI scores from both years indicate that conditions in Coal Creek were poor for benthic invertebrates. Around 50 percent of the species identified were tolerant of degraded conditions. Very few individuals of species that are long-lived or sensitive to degraded conditions were present. Longer-lived species tend to take longer to reproduce and along with sensitive species are among the first to disappear when a stream ecosystem is altered by human activity such as urbanization.

Special Studies

Water Resources Inventory Area (WRIA) 8

In WRIA 8, citizens, scientists, businesses, environmentalists and governments are cooperating on protection and restoration projects and have developed a science-based plan to conserve salmon for future generations. Visit the WRIA 8 Web page to see how Coal Creek is part of this WRIA 8 planning process.