Evaluating drywells for stormwater management and enhanced aquifer recharge

Authors: SASIDHARAN, SALINI - University Of California; Bradford, Scott; SIMUNEK, JIRI - University Of California; DEJONG, BILL - Torrent Resources; KRAEMER, STEPHEN - Us Environmental Protection Agency (EPA)

Submitted to: Advances in Water Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2018
Publication Date: 4/14/2018
Citation: Sasidharan, S., Bradford, S.A., Simunek, J., Dejong, B., Kraemer, S. 2018. Evaluating drywells for stormwater management and enhanced aquifer recharge. Advances in Water Resources. 1116:167-177. https://doi.org/10.1016/j.advwatres.2018.04.003.
DOI: https://doi.org/10.1016/j.advwatres.2018.04.003

Interpretive Summary: Runoff water is a potentially valuable freshwater resource in many areas of the world. Drywells are increasingly being used to capture runoff water, improve the water quality by soil treatment, and store it in aquifers for later use. Field experiments and computer modeling were conducted to characterize soil properties and assess the performance of two drywells. Results demonstrated that the field experiments and computer modeling could accurately determine the effective soil properties at these sites. One of the drywells was found to be functioning within design specifications, whereas water infiltration in the other drywell was very slow, likely due to clogging. This experimental approach and model will be of interest to scientists and engineers concerned with managing drywells for runoff water capture and aquifer storage.

Technical Abstract: Drywells are increasingly used for stormwater management and enhanced aquifer recharge, but only limited research has quantitatively determined the performance of drywells. Numerical and field scale experiments were, therefore, conducted to improve our understanding and ability to characterize the drywell behavior. In particular, HYDRUS (2D/3D) was modified to simulate transient head boundary conditions for the complex geometry of the Maxwell Type IV drywell; i.e., a sediment chamber, an overflow pipe, and the variable geometry and storage of the drywell system with depth. Falling-head infiltration experiments were conducted on drywells located at the National Training Center in Fort Irwin, California (CA) and a commercial complex in Torrance, CA to determine in situ soil hydraulic properties (the saturated hydraulic conductivity, K s , and the retention curve shape parameter, '') for an equivalent uniform soil profile by inverse parameter optimization. A good agreement between the observed and simulated water heights in wells was obtained for both sites as indicated by the coefficient of determination 0.95-0.99–%, unique parameter fits, and small standard errors. Fort Irwin and Torrance drywells had very distinctive soil hydraulic characteristics. The fitted value of Ks=1.01×10^(-3)m min^(-1) at the Torrance drywell was consistent with the sandy soil texture at this site and the default value for sand in the HYDRUS soil catalog. The drywell with this Ks=1.01×10^(-3)m min^(-1) could easily infiltrate predicted surface runofffrom a design rain event (~51.3 m ^[3]) within 5760 min (4 d). In contrast, the fitted value of Ks= 2.25×10^(-6)m min^(-1) at Fort Irwin was very low compared to the Torrance drywell and more than an order of magnitude smaller than the default value reported in the HYDRUS soil catalog for sandy clay loam at this site, likely due to clogging. These experiments and simulations provide useful information to characterize effective soil hydraulic properties in situ, and to improve the design of drywells for enhanced recharge.