Mark West Creek Study, Sonoma County released

Mark West Creek is one of five priority stream systems selected as part of the 2014 California Water Action Plan effort. The 59 square mile Mark West Creek HUC12 subwatershed, located within Sonoma County, is the second largest subwatershed in the Russian River basin. The creek supports several listed anadromous salmonid species including California Coastal Chinook Salmon, and Central California Coast Coho Salmon and steelhead trout. Salmonid populations within Mark West Creek and other Russian River tributaries have declined significantly. Coho Salmon, in particular, neared extirpation within the Russian River basin in the late 1990s, and their recovery is now supplemented by captive broodstock efforts that include juvenile releases into Mark West Creek. Prior assessments have indicated that the low summer and fall stream flows encountered by rearing Coho Salmon and steelhead juveniles is a contributing factor to the species’ decline within the Russian River basin and associated subwatersheds.

The goal of this study is to develop relationships between streamflow and salmonid habitat within upper Mark West Creek. To accomplish this, a combination of empirical and hydraulic habitat modeling approaches will serve as a basis to identify important streamflow thresholds that provide suitable habitat for juvenile Coho Salmon and steelhead. Study questions include:

What instream habitat is available during periods of low streamflow within upper Mark West Creek?
What streamflows are required to maintain suitable rearing habitat and hydrologic connectivity for juvenile Coho Salmon and steelhead?
What streamflows are required to support productive riffle habitat for benthic invertebrates (an important food source for salmonids)?

To help answer these questions, the Instream Flow Program anticipates evaluating existing data, surveying current instream habitat conditions, performing topographical surveys of the stream channel, constructing hydraulic habitat models, measuring streamflows, and conducting data analyses.