Analysis and Simulation of Conjunctive Water Use for Agricultural Settings with the Farm Process for Modflow
U.S. Geological Survey
MODFLOW with the Farm Process (MF-FMP) allows fully coupled simulation of the use and movement of water in the form of precipitation, streamflow and runoff, groundwater flow, and consumption by natural and agricultural vegetation that facilitates detailed analysis of conjunctive use. MF-FMP provides the ability to simulate natural and anthropogenic components of the hydrologic cycle and facilitates the supply-constrained and demand-driven simulation that accounts for all water throughout the simulated system. MF-FMP provides a dynamic allocation of surface-water deliveries, groundwater pumping, and return flows as runoff and groundwater recharge based on a requirement for crop irrigation necessary to satisfy the crop-water demand after using effective precipitation and root uptake from shallow groundwater. Simulation at different levels of spatial detail from individual farms (micro-agriculture) to aggregates of farms or irrigation districts (macro-agriculture) demonstrate the utility of MF-FMP to simulate and analyze conjunctive use at different scales. This includes the ability to simulate historical conditions as well as the ability to simulate the direct effect of future climate projections on estimated demand, surface-water deliveries, and groundwater pumpage. MF-FMP provides a tool to assess conjunctive use on local to regional scales within the context of a hydrologic cycle that includes natural and urban components. The ability of MF-FMP to dynamically analyze the supply and demand components of the water budget allows water managers to understand the potential effects of proposed conjunctive-use plans on the aquifer system and irrigated crops. This analysis could be difficult without embedding them in the simulation and these components of water use could be difficult to estimate independent of these dynamic relations a priori. Selected examples from across the western United States are used to demonstrate some of the unique features of MF-FMP.