Streamflow Analysis Tools in the Mokelumne Relicensing Collaborative

摘要

Pacific Gas and Electric Company and participating agencies and non-governmentalorganizations formed the Mokelumne Relicensing Collaborative (Collaborative) todevelop and recommend ecological and recreational streamflows for the MokelumneRiver Hydroelectric Project (FERC No. 137). The Project includes four powerhouses,20 miles of canal, 16.7 miles of tunnel, and seven storage reservoirs. The Collaborativeparticipants used an innovative approach that incorporated water year types and theresults of biological, geomorphic, and hydrologic analyses to recommend streamflows inProject-affected reaches that are anticipated to maintain or improve ecological function,sediment transport, and bedload movement while providing recreational opportunitiesand hydroelectric power production. An important objective was to mimic the shape andtiming of the unimpaired seasonal hydrograph. Several tools were used in the analysis,including unimpaired and regulated flow information that was developed for the periodof record. Another tool used in the analysis was the Indicators of Hydrologic Alterationsoftware that was developed by the Nature Conservancy in 1996. The softwareperforms statistical analyses to measure modifications of the hydrologic regime in agiven basin caused by hydroelectric and water resources projects. The participantsalso used study information to develop a matrix that displayed seasonal importance ofvarious ecosystem attributes. They also relied on a minimum flow derivation processthat was based on the unimpaired mean daily streamflows, incorporating effects ofdifferent water year types. Pulse flows were recommended based on geomorphic andflow recurrence information. The most useful tool, however, was the Collaborative itself,which used all these tools to develop the recommended streamflows. Therecommended streamflow schedules, when combined with monitoring and an adaptivemanagement program, are intended to address resource management objectives aswell as hydroelectric power objectives.