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Evaluating drywells for stormwater management and enhanced aquifer recharge
Citation:
Sasidharan, S., S. Bradford, J. Simunek, B. DeJong, AND S. Kraemer. Evaluating drywells for stormwater management and enhanced aquifer recharge. ADVANCES IN WATER RESOURCES. Elsevier Science Ltd, New York, NY, 116:167-177, (2018).
Impact/Purpose:
An investigation was conducted on the performance of dry wells (gravity supplied wells screened in unsaturated soils) for wet-weather capture of flows and aquifer recharge in the arid Southwest USA. A combination of computer modeling and field investigation was conducted at two dry well sites: National Training Center at Fort Irwin, and Torrance Regional Hospital, both in California. A new computer modeling tool was developed and tested. The results demonstrated that the Fort Irwin drywell was clogged with sediment due to lack of pre-treatment. The Torrance dry well design had a filter prior to introduction to the dry well, and was shown to be effective in recharging the aquifer with storm water. The findings will be of interest to municipal storm water managers and engineers.
Description:
Drywells are increasingly used for stormwater management and enhanced aquifer recharge, but only limited research has quantitatively determined drywells' performance. Numerical and field scale experiments were conducted to characterize the drywell behavior. 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 and Torrance Memorial Medical Center in Torrance, California to determine effective soil hydraulic properties (the saturated hydraulic conductivity, Ks, and the retention curve shape parameter, α) in situ by inverse parameter optimization. A good agreement between the observed and simulated water heights in wells was obtained for both sites. Fort Irwin and Torrance drywells had very distinctive soil hydraulic characteristics. The fitted value of K_s=1.21 × 10-3 m min-1 was large for the sandy soil at the Torrance drywell, which could easily infiltrate predicted surface runoff from a design rain event (~51.3 m3) within 5760 min. In contrast, the fitted value of K_s=2.47 × 10-6 m min-1 at Fort Irwin was very low, and more than an order of magnitude smaller than the previously reported value for the sandy clay loam soil at the 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.
