PNNL

Abstract

The Columbia River Basin (CRB) is heavily regulated by more than 250 dams on its river system while depends significantly on groundwater withdrawals in certain sub-basins. Neglecting the contribution groundwater to water supply in hydrologic models of the basin could result in inaccurate predictions of its water budget and fluxes and further mislead water management decisions. This study aims to understand how groundwater pumping could change the spatiotemporal patterns of regulated streamflow in the CRB using a modified version of the Variable Infiltration Capacity (VIC) model integrated with a water management component that accounts for ground water withdrawals, irrigation demands, and reservoir operation (VIC-GIRR). The VIC-GIRR simulations were performed in the daily time step at {1/16}\textdegree over the CRB basin. Three scenarios are analyzed based on the VIC-GIRR simulations: 1) A baseline scenario that only simulates the naturalized flow without considering any surface or ground water management activities; 2) A surface water only scenario in which the irrigation demands are met with the available surface water from local streamflow and upstream reservoirs; and 3) A surface water + groundwater scenario that combines surface water and groundwater withdrawals with reservoir operations to mimic reality. The VIC-GIRR simulations showed that considering additional groundwater withdrawals would alleviate the stress of irrigation water deficit in the Snake river basin with an average reduction of 10 km3/year. Such a reduction in water deficit resulted in higher streamflow along the Snake river, and therefore modulates the reservoir operation. For instance, the monthly storage in the American Falls dam increased with an average of 2.5\% of its capacity. Our results highlight the importance to explicitly connect groundwater withdrawals and reservoir operation to manage a multi-reservoir system and improve its effectiveness for agricultural productivity and power generation.