Geospatial decision support system for ameliorating adverse impacts of irrigated agriculture on aquatic ecosystems

Abstract

Tributary stream systems provide an important source of water for sustaining adjacent irrigated agricultural enterprises. Unfortunately, irrigation withdrawals, depending on the timing and amounts, can have substantial negative impacts on critical aquatic ecosystems in the tributaries. Current regulatory trends in many regions point to increased restrictions on irrigation diversions for ecosystem protection, which could lead to increased risk of shortfalls in agricultural crop production. A geospatial decision support system (geo-DSS) integrating a spatially gridded hydro-meteorological flow estimation model (HL-RDHM) with a GIS-based river basin management model (GeoMODSIM) is presented for evaluating water management alternatives for maintaining the viability of irrigated agriculture while mollifying detrimental impacts on aquatic ecosystems and maintaining environmental flow requirements. As a case study, the geo-DSS is applied to the Feliz Creek basin tributary to the Russian River of northern coastal California which is home to a thriving viticulture industry while supporting spawning habitat for endangered and threatened fish species. The geo-DSS is applied on spatial (~1 km grid size) and temporal (daily) scales that are ecologically relevant for modeling agricultural operations and water rights priorities. The geo-DSS utilizes extensive sets of hydrologic forcing data varying from dry to wet conditions to assess baseline conditions and evaluate management alternatives. Baseline model results show that with minimum bypass flow restrictions in place for instream flow protection, the cumulative effects of upstream diversions can still be significant during low flow periods, while creating substantial risk of agricultural irrigation supply shortages. The case study application demonstrates that the geo-DSS is capable of locating, sizing, and managing off-stream farm ponds receiving optimally timed diversions from adjacent streams that are necessary for maintaining agricultural water supply while complying with environmental flow requirements for sustaining aquatic ecosystems.