Assessing drywell designs for managed aquifer recharge via canals and repurposed wells

Authors: SASIDHARAN, SALINI - Oregon State University; Bradford, Scott

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2024
Publication Date: 1/13/2025
Citation: Sasidharan, S., Bradford, S.A. 2025. Assessing drywell designs for managed aquifer recharge via canals and repurposed wells. Scientific Reports. 15. Article 1829. https://doi.org/10.1038/s41598-024-84865-4.
DOI: https://doi.org/10.1038/s41598-024-84865-4

Interpretive Summary: Drywells have been primarily used in urban environments to capture and store stormwater into soils. A computer model was employed to study the influence of drywell designs (diameters, depths, and screen intervals) on water infiltration and flow towards groundwater. Infiltration was found to increase with the drywell diameter, depth, and screening interval. However, economic analyses revealed that smaller diameter and deeper drywells were more cost effective at infiltrating a given volume of water. Repurposing of failed wells and use of drywells in irrigation canal networks were discussed as ways to infiltrate very large volumes in rural environments, but technical and regulatory challenges still would need to be overcome. This information will be of use to scientists, engineers, irrigation districts, groundwater sustainability agencies, and farmers concerned with groundwater sustainability for irrigated agriculture.

Technical Abstract: 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 relatively rapidly recharge tremendous volumes of floodwater (e.g., 8.30e+8 to 1.66e+9 m3 per year in Merced County, CA). However, technical challenges to the implementation of 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 with regard to water surface availability and land use, and groundwater quality would also need to be addressed. Pilot-scale studies are warranted to resolve these issues before large-scale implementation.