Abstract
Throughout the western United States, water managers are facing pressure to account for limited water resources among competing uses. Groundwater is one example of a limited resource that is continually being depleted, especially for areas that use groundwater for irrigated agriculture. In certain hydrologic systems, irrigated agriculture can contribute substantially to aquifer recharge through surface water infiltration, and thus is a significant water balance term for regional groundwater models. This thesis developed a bucket model to estimate deep infiltration by modeling soil water content and root water extraction. The model was calibrated with in-situ soil data from an irrigated alfalfa field and tested for model performance over two subsequent years of field data. The model was applied to a regional scale using test scenarios that account for differences in climate, management, and environmental factors. We show that for sprinkler irrigation methods with improved application efficiency, applied irrigation can contribute between 10-40 percent of deep infiltration losses under dry climate scenarios. While losses may occur at the field scale, these model results describe gains in aquifer recharge at the regional scale. Thus, the model provides an applied tool for more explicit estimates of near-surface boundary conditions for use in regional water management.