MONITORING CHANNEL INITIATION IN SEDIMENT FORMERLY IMPOUNDED UPSTREAM OF A SMALL DAM REMOVED ON MURPHY CREEK, SAN JOAQUIN COUNTY, CA

Post-project geomorphic monitoring following the August 2003 removal of a small irrigation dam on Murphy Creek, an 8 km tributary to the Mokelumne River, CA, helps quantify re-establishment of physical processes intended to restore aquatic habitat for anadromous fish. The objective of this field study is to document changes in creek morphology as a new channel incises through sediment trapped in the former reservoir upstream of the dam and to document processes that account for these changes. Iterative longitudinal profile and cross section surveys conducted during the first year after dam removal show morphologic adjustment including: 1) headward migration of small knickpoints approximately 34 m upstream; 2) channel development through previously restrained sediment; and 3)dominant marshy zones where there is poor channel definition. These data contribute to a baseline set for long-term monitoring studies and may serve as the basis of models to predict the supply of fine sediment to downstream spawning habitat. This work is significant in characterizing the long-term geomorphic response to small dam removal for creek restoration.