Salmon Spawning Gravels as a Critical Indicator of Restoration Potential: San Joaquin River, California
The Bureau of Reclamation (Reclamation) has interests in a large number of river restoration projects. These projects are typically related to water delivery, water salvage, or avoiding impacts to endangered species. Reclamation is supporting restoration projects on the Truckee River, Trinity River, and Colorado River to name a few. A large amount of money has been directed towards these restorations and it is estimated that $1 billion dollars has been spent just in the Southwest since the 1980's.
The San Joaquin River Restoration Program covers a large extent of the San Joaquin River from Friant Dam to the mouth of the Merced River and involves fish passage improvements and flow rehabilitation. Recently, restoration flows to the San Joaquin River have been implemented as a first step towards developing a Chinook salmon (_Oncorhynchus tshawystcha_) fishery (Fisheries Management Work Group 2010). Spawning gravel and water quality assessments are considered important components in this restoration effort. Degradation of spawning grounds in streams and rivers has been implicated as one of the causes of salmon endangerment. During spawning activity, eggs are buried in the substrate, often at mean depths from ca. 30 cm to 45 cm. This relatively deep substrate region is often in the zone of surface water and ground water interaction, typically referred to as the hyporheic zone. Hyporheic conditions within the redd may differ markedly from those found at the surface and can differ in water quality, sediments, and invertebrate communities. All of these elements may impact the success of salmon egg survival and could be considered appropriate endpoints for measurement. This study is designed to collect information on these disparate elements and provide guidance into the potential quality of this environment for spawning below this Reclamation dam.
Need and Benefit
Reclamation has a need to understand how, and whether, restoration attempts that use water management associated with dam operations impact the environments and organisms that restoration efforts are directed towards. Reregulation of rivers below dams has been hypothesized as a way to sustain the natural attributes of rivers; however, actual tests of flow restoration and altering temperatures by selective withdrawal have not demonstrated any unambiguous successes.
Often impacts below dams are multivariate in nature, and changes in operations will not result in improvements to aquatic communities. Changes to a single attribute, like flow, may not positively alter temperature or, in many cases, sediment availability or transport.
Much of the present literature seems to suggest that there is an inability to control flows to the degree necessary for biological improvement.
The potential for limited success in progress towards biological goals below dams through management of flow changes indicates that the biological aspects of these operations should be thoroughly studied.
Fish and Game, California
Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Observations on the Hyporheic Environment along the San Joaquin River below Friant Dam (final, PDF,
By Mr. Gregory Reed
Report completed on October 18, 2011