Geospatial DSS for Maintaining Agricultural Diversions under Environmental Flow Requirements

Abstract

Competing demands for scarce water supplies in irrigated alluvial valleys can lead to conflicts between disparate uses, resulting in an increased risk of restrictions on agricultural diversions. A tool for understanding the impacts of irrigation diversions on natural stream systems at the tributary scale is needed to evaluate solutions that protect environmental flow requirements for endangered and threatened aquatic species while maintaining irrigation water security. A geospatially referenced decision support system (geo-DSS) coupling a fine-scale [1/4 Hydrologic Rainfall Analysis Project (HRAP) or 1 km] gridded hydrometeorological model (HL-RDHM) with a GIS-based river basin management model (GeoMODSIM) is developed for irrigated stream-aquifer systems. In this proof-of-concept implementation, the geo-DSS is demonstrated on a representative tributary within the Russian River Basin in the Northern Coastal region of California with extensive wine grape vineyard acreage for an average water year using a daily time step. Results indicate that commonly used management practices that rely on direct stream diversions and on-stream ponds for irrigation can have severe negative impacts on instream flow rates by impeding the migration of endangered coho salmon and other species. Through the application of the geo-DSS, improved management practices such as the use of off-stream agricultural ponds are able to meet irrigation demands while satisfying minimum environmental bypass flow restrictions along with the determination of ideal sizes and locations for supplemental off-stream storage.