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. To address the California Water Action Plan, the Department has conducted several studies in the Mark West Creek watershed. Watershed-wide flow criteria were determined using a combination of site-specific methods and analyses based on functional flows to support salmonid life stages, maintain natural flow patterns, and support the riverine ecosystem throughout the watershed. The site-specific study in upper Mark West Creek used a two-dimensional modeling approach to combine data on channel topography, river hydraulics, species- and life-stage-specific habitat preference, and physical habitat modeling to determine instream flow needs to support rearing steelhead and Coho Salmon. The Mark West Creek study components are complete. The technical reports, appendices (including model calibration procedures), and supporting materials are available below. Resources Watershed-Wide Instream Flow Criteria for Mark West Creek (PDF)(opens in new tab) Instream Flow Evaluation: Juvenile Rearing of Steelhead and Coho Salmon in Upper Mark West Creek, Sonoma County (PDF)(opens in new tab) Appendices to Instream Flow Evaluation: Juvenile Rearing of Steelhead and Coho Salmon in Upper Mark West Creek, Sonoma County (PDF)(opens in new tab) Mark West Creek Study Plan (PDF)(opens in new tab Click map to enlarge.