Mapping of Non-Perennial and Ephemeral Streams

Nonperennial streams are defined as streams that lack surface flow for at least several days per year in typical years. Nonperennial streams comprise the majority of streams in southern California, but we have little information on which streams are nonperennial, nor how to characterize the diverse flow regimes nonperennial streams exhibit. Consequently, it is difficult for water quality programs to target waterbodies of interest, nor is it possible to be sure where policies that apply to perennial streams may be implemented. Updated hydrologic maps are needed because existing maps (such as those provided in the National Hydrography Dataset, NHD) do not adequately represent the location and extent of nonperennial streams. Because few nonperennial reference streams have been sampled throughout California, their hydrology and biology are not well described (particularly within the Santa Ana watershed). Preliminary research has shown that some nonperennial streams in San Diego are ecologically similar to perennial streams, suggesting that existing assessment tools used for perennial streams (such as the Southern California Index of Biotic lntegrity) may be adequate for some types of nonperennial streams. More data from a range of minimally disturbed nonperennial streams is needed to determine the extent to which existing assessment tools can be used for different types of nonperennial streams, particularly in regions outside San Diego. The goal of this project is to build upon previous work, refine and apply the stream periodicity model created for San Diego Regional Water Quality Control Board (RWQCB 9) to watersheds encompassed by the Santa Ana Regional Water Quality Control Board (RWQCB 8) in order to produce a map of likely non-perennial streams and associated stream flow metrics. The NHD and/or NHDPlus HydroDEM will be utilized as the base stream network for the model.