Extent of California’s Perennial and Non-perennial Steams

The distribution of perennial and non-perennial streams in different regions of the State has direct bearing on several of the State Water Board’s current priority initiatives (e.g., biological objectives for perennial streams and rivers, and the Wetland and Riparian Area Protection Policy). However, currently best-available stream maps are replete with inaccuracies about the extent and classi cation of perennial and non-perennial streams. For example, a recent eld study in Southern California demonstrated that the ow status of greater than 50% of streams was misclassi ed.

The Surface Water Ambient Monitoring Program’s (SWAMP) Perennial Streams Assessment (PSA) gives us the ability to assess the magnitude of resource mis-classi cation in different regions of California. This Management Memo summarizes key findings on the extent of perennial and non-perennial streams and highlights the need for more refined base maps to define the extent of the water resources protected by State and Federal regulations.