WATER RESOURCES RESEARCH GRANT PROPOSAL
Project ID: 2004WI78B
Title: Design and Evaluation of Rain Gardens for Enhancement of Groundwater Recharge
Project Type: Research
Focus Categories: None
Keywords: groundwater, raingarden, infiltration, recharge
Start Date: 03/01/2004
End Date: 02/28/2005
Federal Funds: $36,242
Non-Federal Matching Funds: $35,037
Congressional District: 2nd
Kenneth W. Potter
University of Wisconsin
For about half of Wisconsin, groundwater is the primary water source for human activities. In highly urbanized areas, groundwater withdrawals significantly exceed recharge rates. In some locations, such as southeast Wisconsin, this has led to severe aquifer depletion and water quality degradation. In other locations, such as the Madison metropolitan area, pumping in excess of recharge has caused environmental damage through reduction of groundwater discharge to wetlands, lakes and streams. Urbanization also results in groundwater depletion through the reduction of groundwater recharge associated with the introduction of impervious surfaces.
In past and ongoing research, the PI has demonstrated that rain gardens (sunken gardens that receive surface runoff) have the potential to increase local groundwater recharge rates well above natural rates. His research has included both a modeling and experimental component. He has developed two continuous hydrologic models to simulate rain garden performance- a relatively complex model based on the Richards Equation, and a simpler, more efficient model based on the Green Ampt equation. Application of the Richards Equation model indicates that under favorable conditions local groundwater recharge can be increased 2-3 times by focusing recharge in a well-designed rain garden. The PI has also demonstrated how the model can be used to evaluate the frequency and duration of ponded conditions in a rain garden as a function of the design parameters.
To provide validation data and improve understanding of rain garden performance, the PI has constructed an experimental rain garden at the Lussier Family Heritage Center in Madison. Rainfall, surface water inflow, overflow, seepage and soil-moisture are all measured. Preliminary analysis of the results of three controlled experiments have indicated that the Richards Equation model is reasonable valid, although both modeling and experimental issues need to be resolved.
The proposed project has two components. The first is to develop guidelines to aid in the design of rain gardens. The second is to operate the experimental rain garden for the project duration to provide information on its long-term behavior and data for evaluating the ability of the models to simulate long-term performance.
Rain garden design primarily involves specification of area ratio, depression depth, and storage zone thickness, as well as selection of plant species. For any chosen design, given an estimate of the saturated hydraulic conductivity of the subsoil, one of the simulation models can be used to estimate long-term recharge as well as the frequency and duration of ponding events. In practice, however, rain garden designers (landscape architects, landscapers, builders, and engineers) may not have the ability or inclination to conduct the many model runs that would be required to design and evaluate a rain garden. The PI proposes to develop a set of performance charts that for anywhere in Wisconsin would provide information on expected annual recharge amounts and ponding frequency and duration for a realistic range of design parameters and values of subsoil saturated hydraulic conductivity. This information would greatly facilitate rain garden design.
The PI proposes to collect data from the experimental rain garden through at least 2005 to provide validation data for his models as well as information on the long-term performance of rain gardens.
The design charts and information developed in this project will greatly facilitate the design and use of rain gardens to enhance groundwater recharge in Wisconsin, and hence will contribute to the mitigation of aquifer depletion and groundwater degradation in highly urbanized and rapidly urbanizing portions of the state.