Year 2 of Rewatering the San Joaquin River: Overview of Lessons Learned

The San Joaquin River fishery restoration goal is to re-establish self-sustaining, naturally reproducing populations of spring-run and fall-run Chinook salmon. A key element of the restoration program is designing an instream flow regime that is compatible with the life history and habitat requirements of the species within the framework of water supply uncertainties from one year to the next, land use considerations, and other constraints.  Hydrologic conditions within the San Joaquin River watershed are highly variable among years and predicting available water supplies for restoration flows during the late winter and early spring is inherently uncertain and results in a number of operational and management challenges.  In response to the variation in hydrologic conditions, instream flow hydrographs reflect a wide range of environmental conditions that are intended to meet biological objectives and provide suitable habitat conditions for adult holding, spawning and egg incubation, juvenile rearing, and juvenile and adult migration.  Baseflows as well as seasonal migration flows that provide suitable seasonal water temperatures, water depths, water velocities, and other habitat needs are the primary drivers of the annual hydrographs.  A variety of modeling tools have been developed to determine the effects of instream flow releases on reservoir coldwater pool management, river temperatures in response to hot San Joaquin Valley conditions during the spring, streamflows required to inundate floodplain rearing habitat and provide suitable depths within the river channel in addition to hydrologic predictions based on snow pack and runoff.  These tools form the framework for developing and refining annual instream flow management strategies.  Real-time monitoring of environmental target conditions provide feedback for adaptively adjusting reservoir releases.  Constraints on instream flows within and among years contained in the decision framework include, but are not limited to, changes in water supply forecast predictions, limitations of channel capacity, effects of instream flows on groundwater levels andresulting impacts to land use along the river corridor, response to variation in seasonal air and water temperatures, permit requirements, environmental documentation, and a variety of other factors. These constraints are evaluated on an interactive basis during each year as the instream flows are allocated and refined.  Opportunities exist to test the management strategies and implementation of the instream flows based on interim experimental flow tests that also provide a basis for evaluating the biological targets, models and decision tools, constraints, and basic accounting and planning tools used in developing and managing program implementation and performance.