Tibbetts Creek Site X630

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King County Water Quality Monitoring

King County has been conducting monthly baseline water quality monitoring in Tibbetts Creek since 1976. The stream is sampled at one site (X630), located near the mouth, at the footbridge crossing over Tibbetts Creek in Sammamish State Park. (Click here for information about Special Studies of Tibbets Creek.)

Tibbetts Creek Watershed

Tibbetts Creek is placed in Ecology’s Noncore Salmon/Trout Aquatic Use Category which sets criterion for the protection of spawning, core rearing, and migration of salmon and trout, and other associated aquatic life.

Tibbetts Creek is a relatively short creek (4.3 miles long) that originates on Squak Mountain at an elevation of 1,080 feet. The stream flows through a steep headwater area, then in midcourse opens up to a broad flood plain that empties into Lake Sammamish. Though not a tributary to Issaquah Creek, it shares a common floodplain with the mainstem during large flood events.

Efforts to restore the damaged creek have been underway for more than ten years. In the summer of 2002 more than 10,000 cubic yards of mine tailings were excavated from where the debris had been dumped into a gully along Tibbetts Creek by mine operators. Prior to excavation, heavy rains would wash large quantities amounts of the tailings into the creek. The sediment clogged channels, impeding salmon and trout migration and contributing to downstream flooding. The mine closed in the 1950’s. (Seattle Times, November 22, 2002).

A site, roughly 5-acres in size, was replanted in 2002 on part of a 400-acre parcel between Cougar and Squak mountains deeded to Issaquah in May by the Talus developers. The transfer preserves valuable wildlife habitat, creating a mile-wide swath of public land that connects the Cougar Mountain and Squak Mountain parks. The restoration is a joint effort by Issaquah, local environmental groups and the developers of Talus and is meant to restore fish habitat, reduce flooding and eliminate a significant source of phosphorus

About 1,800 feet of new stream channel, complete with standing snags and strategically placed logs, has been built on Rowley Enterprises property south of Interstate 90. Rowley Enterprises has committed $1.2 million to the restoration project. The process also included the Muckleshoot Tribe; the city of Issaquah; the volunteer Friends of the Issaquah Fish Hatchery, and the state departments of Transportation, Parks, and Fish and Wildlife.

In the lower 2.2 miles of the creek, the state Department of Transportation will restore a portion of the creek, downstream of the Rowley property. The city will restore an upstream segment, and improvements will extend as far up as Tibbetts Creek Manor. The finished project also will include a trail linking to Lake Sammamish State Park, the Issaquah park system, a Park & Ride lot and other parks (Eastside Journal June 26, 2001).

Fisheries

According to King County’s 1989-1990 Status Report, Tibbetts Creek contains small populations of coho and cutthroat trout (Metro 1990). No salmonids were observed in the creek by volunteer salmon watchers in 2001 (King County June 2002)

Water Quality

In 1988 - 1989, water quality in Tibbetts Creek was characterized as fair (Metro 1990) due to relatively high sedimentation in the basin and subsequent high turbidities, high nitrate and ammonia concentrations, and low dissolved oxygen concentrations. The quarry/mining-related disturbances in the upper canyon area were considered the source of sediment build-up at the mouth of the stream. More recently, Tibbetts Creek was rated a stream of “high concern” using the Water Quality Index rating system developed by Washington State Department of Ecology. Findings from a more in-depth water quality analysis are summarized below. See Table 1 for a summary of water quality violations in the creek during the most recent water year.

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

 

Hydrology

King County maintains one streamflow gauge: Tibbetts Creek above Tributary 0170 (67a) and one precipitation gauge: Tibbetts Creek Rain Gauge (67u) on Tibbetts Creek.

Benthic Invertebrates

Stream health is monitored by collecting samples of benthic macroinvertebrates from selected streams. The stream is then ranked using a scorecard system. Benthic macroinvertebrate are being sampled in Tibbetts Creek as part of several programs.

King County monitors stream health by collecting samples of benthic macroinvertebrates from selected streams. King County will be monitoring sites along Tibbetts Creek as part of the “bug” monitoring program and as part of the SWAMP program.

Another source of benthic macroinvertebrate data is the Salmonweb.org Benthic Macroinvertebrate Program. Salmonweb is an organization whose purpose is to create, distribute, and coordinate a set of tools by creating a “virtual” community that support education, communication and ecological science focusing on salmon habitat. The ratings from a 1999 survey place upstream conditions as “poor” and downstream conditions as “fair”.