Innovative Drywell Designs and Applications for Enhanced Managed Aquifer Recharge

There is a critical need to optimize managed aquifer recharge (MAR) techniques to address groundwater depletion in many arid and semi-arid regions of the world. Numerical experiments were conducted to assess various drywell designs (e.g., drywell diameters, depths, and screening intervals) to enhance MAR. The cumulative infiltration (I) and recharge (R) decreased with the drywell diameter. However, only a 48% and 52% decrease in I and R were observed, respectively, after 1 year for a 5 cm in comparison to a 120 cm diameter drywell. Values of I and R also increased with the drywell depth and screening interval, especially when a heterogeneous soil profile allowed the drywell to bypass fine-textured layers and/or lenses. The lowest levelized costs associated with recharging a given water volume occurred for smaller and deeper drywells that recharged water over a shorter timeframe. Potential novel MAR applications of small diameter and deep drywells were discussed, including (i) repurposing of existing dried irrigation supply and domestic wells; and (ii) inclusion of drywells into existing irrigation canal systems. Widespread application of these MAR approaches is predicted to recharge tremendous volumes of floodwater rapidly (e.g., 8.30 × 108 to 1.66×109 m3 per year in Merced County, CA). However, technical challenges to implementing the proposed methods, such as clogging and potential impacts on groundwater quality, would need to be overcome by using low-cost pretreatments and/or optimizing the frequency of operation. Site-specific regulatory hurdles regarding water surface availability, land use, and groundwater quality would also need to be addressed. Pilot-scale studies are warranted to address these issues before large-scale implementation.