Kokanee return to Tibbetts Creek

This is the first in a series of items to be published monthly in 2023 by FLSSP Board Members. Thank you to Trails Committee Chair Bill Way for this contribution.

Tibbetts Creek is one of four streams that enter Lake Sammamish State Park before draining into Lake Sammamish. The other creeks are Laughing Jacobs, Issaquah, and Pickering.

Nothing is known about historic fish use of Tibbetts. During the early 1990’s, electrofishing surveys showed a modest population of cutthroat trout. Various transplants of excess adult coho spawners from the Issaquah hatchery were done in the 2000’s and early 2010’s with little evidence of success. However, in the last couple of years spawning kokanee have been turning up in the creek.

During the coal mining era (1860’ to 1920’s) Tibbetts habitat was severely degraded by coal mining and the side-casting of its tailings. Tailings are rock material found associated with coal that are not useable. The largest coal mine tailings pile was on Tibbetts’ west bank, somewhat upstream of the present Talus entrance. The tailings pile was some 15’ high and some 350’ long. Any substantial flows in Tibbetts would undercut the tailings and transport them downstream. Since coal tailings are quite light, the channel would fill up with water and tailings, closing all intersecting roads multiple times a year. During the late 1980’s, roads closed during flooding were SR-900, 12th and Newport, 19th Avenue, and NW Poplar Way, isolating that portion of Issaquah. Sediment-ladened flood waters often got to within inches of breaching 1-90 and backwatered into Rowley’s storage units.

Because of the ongoing flooding issues, Rowley hired The Watershed Company in 1989 to develop a Tibbetts Creek Greenway Plan. Components of the Plan included 1) a temporary sediment trap at Tibbetts Manor, 2) removal of the coal mine tailings (by Talus as part of its development mitigation), 3) enlargement of road culverts including two I-90 bridges/bridge at Poplar/bridge at Northwest Sammamish Road, and 4) restoration of the stream channel itself. Some $17M has been spent on implementation of this Plan – making it one of the most intensive creek restoration projects in the country.

One component being wrapped up now is the de-commissioning of the sediment trap at Tibbetts Manor. While the excess supply of coal mine tailings was cut off decades ago, the City continued to mine the trap, with the unintended consequence of starving the downstream of gravel supply. This has meant that downstream sections are making up for loss of sediment supply by downcutting the bed and eroding the side of bank. Sediment transport is in relative equilibrium and the trap is no longer needed. And salmon and trout will have better gravel substrate to spawn in in the future.

The Kokanee Work Group, among others, is very encouraged by the recent spawning kokanee in Tibbetts. These spawners are apparently opportunistic strayers that hatched in other streams that drain into Lake Sammamish.