Abstract

Putah Creek (drainage area = 2,000 km2) drains the slopes of Cobb Mountain in Lake County, flowing 137 km southeastward into the Yolo Bypass near Davis, California. Lower Putah Creek, the 37km reach from the Solano Diversion Dam to the Yolo Bypass, is confined within a flood control channel.  Dry Creek (drainage area = 44km2) joins Putah Creek near Winters, California.  Putah Creek is regulated by water releases from Monticello Dam at Lake Berryessa.  Dry Creek flows only part of the year and has no dams. Southward channel migration of Putah Creek from the 1990’s was threatening Putah Creek Rd., a paved county road following the south bank of the evaluated stream-section.  The new location of the Putah Creek channel also reduced the amount of gravels entering Putah Creek from Dry Creek.  This was significant because dams reduced the amount of course sediment available from upstream, leaving Dry Creek as one of the only natural sources of the gravels important to the ecology of Putah Creek. In 2005, the Lower Putah Creek Coordinating Committee implemented a project to move the channel of Putah Creek northward to its approximate historical course.  The project included the removal of invasive giant reed (Arundo donax), in part because Arundo appeared to have contributed to the unwanted channel avulsion.  We evaluated the project performance towards the goals of 1. protecting Putah Creek Road, 2. keeping invasive plant species out of the area, 3. facilitating natural transport of Dry Creek gravels into Putah Creek, and 4. improving salmonid habitat.  Our evaluation found that 1. Putah Creek has stayed within the general path of the design channel and is not returning to the southern pre-1997 channel which threatened the road, 2. there is a mix of native plant species (e.g. willow, cottonwood) and invasives (e.g. Arundo, blackberry) in the floodplain, 3. There is no physical barrier separating Putah and Dry Creek, 4.  the channel and floodplain provide good habitat complexity for native fish, but fine sediments cover most of the potential spawning gravels.