Status of the Lower Sacramento Valley Flood-Control System within the Context of Its Natural Geomorphic Setting

Abstract

The Sacramento River’s flood-control system was conceived as a series of weirs and bypasses that routes floods out of the leveed main channel into natural floodways engineered to drain directly into the bay delta. The system, superimposed on a natural geomorphic setting consisting of geologic, sedimentary, and tectonic controls, still relies on weirs and bypasses to keep low-lying communities dry during floods. However, the Sacramento Valley bypass system exhibits widespread evidence of impairment by sedimentation, especially at prehistoric loci of alluvial splays. Episodic flooding in the basin delivers large volumes of sediment that accumulate throughout the flood bypasses, especially from legacy tailings fans that originated in the hydraulic mining era. In addition to decreasing flow capacity, these deposits promote colonization of vegetation, which, in turn, increases roughness and decreases flood conveyance. We document three bypass regions that are affected by natural geomorphic controls, where cons...