Management of Coarse Sediment in Regulated Rivers of California
There are significant problems in the management of coarse sediment (sand and gravels) in regulated rivers of California. Unfortunately, these have been generally treated (or ignored) on a case-by-case basis, however, the effects are pervasive and profound, with substantial costs and severe environmental impacts. Problems arise due to the human manipulation of coarse sediment through reservoir construction, which blocks the movement of coarse sediment down the river, and through instream gravel mining, which removes this material from the river system for use primarily in construction-related projects. Impacts identified include: bed material coarsening, channel incision, channel geometry changes, hydrologic regime alterations, and changes in transport of sediment. Many of these impacts result in damage to or destruction of anadromous fisheries habitat, and are partly responsible for the dramatic declines in anadromous fisheries resources in the last 50 years. other types of impacts include damage to instream structures, loss of riparian habitat, and increased risk of damaging channel changes.
We documented these types of impacts on a set of major river drainages on the western slope of the Sierra Nevada, along with several rivers in the Coast Ranges. We have reviewed the institutional and regulatory framework for both reservoir operation and instream mining, finding inconsistencies and lack of standard requirements for monitoring and mitigation of environmental impacts. various techniques that comprise the existing piecemeal approach to restoration and enhancement of coarse sediment resources were inventoried. We propose alternative strategies for management of coarse sediment that