BENEFITS AND RISKS OF VARIOUS ON-FARM MANAGED AQUIFER RECHARGE APPROACHES (Invited Presentation)

Managed Aquifer Recharge (MAR) is an important tool to mitigate the adverse effects of drought, floods, and changing climatic conditions. Flooding of agricultural fields (Ag-MAR) and drywells have been proposed to sustainably manage groundwater supplies in the Central Valley of California. A drywell is a vadose zone infiltration system that has a small footprint at the land surface that is installed and releases water at varying depths into the vadose zone. This presentation highlights and gives examples of potential benefits and risks for on-farm MAR. Ag-MAR can capture and store large volumes of stormwater by utilizing existing infrastructures to deliver water from rivers to farms without changing the land use. However, potential challenges to successful Ag-MAR include disruption of farming operations if the water supply occurs at the wrong time, leaching of contaminants in the root zone and soil profile, and the presence of low permeability soil layers that can diminish infiltration and recharge, and produce ponding that damage crops and leads to water loss by evaporation. Drywells can be used to overcome many of these limitations because they circumvent the root zone, eliminate evaporation losses, concentrate leaching into a smaller portion of the deep vadose zone, bypass near surface low permeability soil layers, and do not impact farm operations and crop health. Contaminants in infiltrating water are treated by passage through the vadose zone in both approaches, but the residence time and travel distance to the water table is shorter for drywells. Clogging can also be more prevalent with drywells than Ag-MAR because the flow is concentrated into a smaller area, so pretreatments may be required.