Modeling the Effects of Multi-Benefit Agricultural-Managed Aquifer Recharge in Colusa County, California

Intensive use of groundwater in the last century, as well as persistent and severe droughts, have diminished California’s groundwater resources to alarming levels over the last decade. Rising in prevalence as a way of both maintaining and improving groundwater levels is agricultural-managed aquifer recharge (ag-MAR), a technique that involves actively spreading water on the ground to encourage deep percolation to underlying aquifers. In the coming years, ag-MAR may be seen as a powerful tool in sustainable groundwater management. However, ag-MAR is not only a tool to replenish our groundwater resources, as the technique also provides multiple benefits to the environment, including nearby communities and wildlife. Flooded agricultural fields can provide temporary wetland habitats while recharging water to underlying aquifers. The goal for this study was to develop groundwater models using MODFLOW to quantitatively and qualitatively assess the benefits of ag-MAR for a groundwater basin in northern California in addition to being a wetland habitat for migratory birds. Through the development of a regional parent model and a more refined child model, we simulated the effects of ag-MAR and tested scenarios of increasing recharge rates and recharge duration. From the results of the model scenarios, we determined that increasing recharge rates, either by flooding more fields in a project area or prolonging the flooding periods, will yield a significant – and positive – hydrologic effect on groundwater levels and storage. With the analysis of the groundwater models’ results, it is possible to understand the hydrologic and environmental impacts of multi-benefit recharge projects, and how it can be scaled up spatially and temporally to increase the benefits to migratory birds and our groundwater resources for future projects across California