Surface Water-Groundwater Interaction Report, Ventura River Habitat Conservation Plan, Ventura River, California

ENTRIX, Inc. was contracted by the Cooperating Agencies to perform an analysis of surface water and groundwater hydrology in the Ventura River basin as part of the Habitat Conservation Plan (HCP) for the Ventura River in Ventura County, California. The Cooperating Agencies consist of the County of Ventura, the Ventura County Flood Control District (VCFCD), the City of San Buenaventura, the Casitas Municipal Water District (Casitas), the Meiners Oaks County Water District (MOCWD), the Ojai Valley Sanitary District (OVSD), the Ojai Basin Groundwater Management Agency, the Southern California Water Company (SCWC), the Ventura County Water Agency, and the City of Ojai. These agencies all operate and maintain facilities that may affect sensitive biological resources along the Ventura River. To comply with the Endangered Species Act (ESA), the agencies are developing a HCP in consultation with the National Marine Fisheries Service (NMFS) and U.S. Fish and Wildlife Service (USFWS) to serve as the basis for an Incidental Take Permit.

The objectives of the surface water-groundwater interaction evaluation, outlined in The Ventura River Habitat Conservation Plan Technical Approach dated March 30, 2000, are to develop an improved understanding of the hydrologic system dynamics and determine the likelihood of groundwater pumping impacts on surface flows, based on available empirical data. The scope of work involved collecting and evaluating available surface flow and groundwater data and prior analyses of the surface and groundwater system. The focus of the evaluation was on the river reaches where the Cooperating Agencies can affect flow. The availability of concurrent surface flow and groundwater data determined the study period(s) and specific reaches analyzed. The study is focused on the Upper Ventura River and San Antonio Creek basins, and a brief discussion is also included for the Ojai Valley groundwater basin. The data reviewed as part of the evaluation included seasonal changes in groundwater levels and groundwater storage, groundwater flow relationships, and estimated contributions from groundwater to surface water.