Controls on water quality during managed aquifer recharge

Over the coming decades, increased interannual variability in precipitation — wetter wet years and drier dry years — will place increased demand on our water infrastructure. Though we need additional water storage capacity to store water from rainy years for use during drought years, in many regions of the world water storage infrastructure is already maxed out. Flood managed aquifer recharge (flood-MAR) — an emerging technique in which working landscapes are flooded to replenish depleted aquifers — could meet this gap. However, identifying the most promising flood-MAR sites presents a challenge; many prospective sites are underlain by heterogeneous layers of sand and clay that can obstruct flow. In addition, the vadose zone beneath many flood-MAR sites can host a variety of contaminants, including fertilizers, salts and pesticide byproducts. A common conceptual model posits that initial flood-MAR operations will flush these contaminants to the saturated zone, degrading water quality, but in the long term, recharge operations will improve groundwater quality by diluting contaminant concentrations (Bachand et al., 2014).

We are combining high-resolution geophysical surveys with numerical modeling to understand the processes that control the flow of water and solutes during managed aquifer recharge. Future work will use machine learning surrogate models and airborne geophysical surveys to scale up our analyses from the site- to basin-scale. This work addresses a gap in our understanding of solute transport during extreme floods and provides actionable information to mitigate both flood damage and groundwater depletion.