Use of the hydro-salinity, crop production optimization model APSIDE to validate results from an updated regional flow model of the San Joaquin River Basin

Abstract

APSIDE is an optimization model capable of simulating irrigation hydrology and agricultural production under saline conditions. The model has been used in the past to predict future agricultural production under future climate change in the San Joaquin River Basin of California (Quinn et al. 2004). In this study the model was used to query the results from a highly-regarded, published regional surface-groundwater flow model of the Central Valley of California – CVHM (Faunt et al. 2009) which includes the San Joaquin Basin. The APSIDE model was updated using recent aquifer and climate data and provided common initial conditions to allow a 53 year comparative simulation of the models. Model outputs for individual water districts for parameters such as deep percolation and upflux in APSIDE were compared to identical drained subareas within the CVHM model. The comparison showed that the APSIDE model produced lower values of deep percolation and upflux than CVHM. CVHM’s deep percolation values were 18% higher in Panoche WD, 40% higher in Broadview WD, 68% higher in San Luis WD, and 46% higher in Pacheco WD. Unlike the CVHM model that assumes fixed levels of irrigation and drainage technology and static average water district irrigation efficiency APSIDE will substitute more cost effective irrigation and drainage technologies based on the calculated future benefit stream relative to the cost of production and impact of salinity on crop yields. An unpublished recent update to the current CVHM model (CVHM-2) which substitutes actual irrigation diversion records from delivery canals rather than usually-reliable Agency records - produced water district irrigation diversions that were approximately 50% of the previously provided diversion data. The new model produces water district aquifer recharge estimates that correlate closely with APSIDE model output. This study demonstrates the successful use of a complementary agricultural production optimization and hydro-salinity simulation model to help validate a radical and important update to a widely distributed and well-accepted regional flow groundwater model.