The primary objective of this study is to evaluate the infiltration rates of four rain gardens at two locations. Each location has a different soil type (relatively undisturbed, silty soil and compacted, clayey soil with construction debris). The rain gardens at each site were planted with different vegetation (turf grass and native plants).
Secondary objectives include:
Measuring the vertical flux of infiltrated water beyond the root zone and soil moisture available for evapotranspiration
Measuring atmospheric parameters necessary to calculate potential evapotranspiration at each location and compare to actual evapotranspiration
- Determining if “mounding” of infiltrated stormwater below ground may lead to lateral spreading that may cause damage to building foundations
The study takes place at two locations within the City of Madison where rooftop runoff can be equally divided and directed into two adjacent rain gardens. Each rain garden was constructed using existing sizing guidelines for the typical homeowner. One garden at each site was planted with native species while the other was planted with typical turf grasses. As the two sites have dissimilar soils, we are monitoring the effectiveness of the types of plantings in the different existing soil types.
The City of Madison was responsible for the construction of each rain garden as well as the native vegetation plantings during the summer of 2003. Each rain garden was constructed from scratch and will continue to be monitored for a period of 5 years to allow each vegetation type to reach its maximum infiltration potential. The City is responsible for maintenance for the duration of the project.
Data analysis is performed by the USGS and will summarize the performance of each rain garden. All runoff, precipitation, soil moisture, and atmospheric data collected is stored in the USGS database as it becomes available.
Soil moisture data is used to determine the volumetric water content below the rain garden at multiple depths and whether water has a positive, neutral or negative flux. Soil moisture data is coupled with runoff data to calculate an estimated volumetric mass balance of water for each rain garden.
Data collected from each weather station will be used to predict potential evapotranspiration. Results will be compared to soil moisture data to determine if a relationship exists between potential evapotranspiration and soil moisture content.
You can now view the rain gardens' discharge and precipitation data on the USGS real time website: look under the Rock River Basin for the Owen and Old Sauk links. To view the temperature and humidity data select "Wisconsin Precipitation Table" under the Predefined Displays pull-down menu near the top of the page (Again, look under the Rock River Basin).
The USGS will produce a Water Resources Investigation Report to document the results of the study. The report should be completed around September 2008.