Long-Term Water Budget of Two Rain Gardens in Madison
Project Number: BQY21
Project Chief: William R. Selbig
Cooperators: City of Madison
Period of Project: May 2003–September 2008
Standing water in two rain gardens after a storm event in Madison, Wis.
Guidelines on the construction of a rain garden are still in their infancy. Criteria for locating and constructing these infiltration devices keep the homeowner in mind and therefore do not require a lot of time or money. However, in order to increase the efficiency of a rain garden, soils are often engineered to maximize infiltration of runoff.
Additionally, rain gardens are often planted with native prairie species with deep root growth to promote infiltration. This can, in some cases, be cost-prohibitive for individual landowners. The benefits of native prairie species over more commonly used turf grass at infiltrating storm runoff are not well understood.
Furthermore, few studies have evaluated the performance of rain gardens located in varying soils (sand versus clay). Understanding how vegetation and soil type affect infiltration in a rain garden could help direct future management decisions.
The primary objective is to evaluate the effectiveness of two rain gardens with varying soils at infiltrating stormwater. Secondary objectives include, but are not limited to:
(1) Measuring the vertical flux of infiltrated water beyond the root zone as well as soil moisture available for evapotranspiration, and
(2) Measuring atmospheric parameters necessary to calculate potential evapotranspiration at each location.
This study will focus on two locations within the City of Madison where rooftop runoff can be equally divided and directed into adjacent rain gardens. One rain garden will be constructed using existing guidelines for the typical homeowner and include turf grass typically grown in area lawns. The other will utilize native plant species with deep root zones to optimize infiltrative capacities. Equipment will be installed at each location in an effort to calculate a volumetric mass balance per each rain garden based on the following equation:
Additionally, various atmospheric conditions will be monitored to determine potential evapotranspiration (PET) rates at each test site.
Vground = Vin + P – Vout – PET
Vground is the volume of water moving vertically through the soil column,
Vin is the volume of water entering the rain garden from the rooftop,
P is direct precipitation on the rain garden, and
Vout is the volume of water escaping the confines of the rain garden during larger storm events.
Publications and Reports
Selbig, W.R., and Balster, Nicholas, 2010, Evaluation of turf-grass and prairie-vegetated rain gardens in a clay and sand soil, Madison, Wisconsin, water years 2004–08: U.S. Geological Survey Scientific Investigations Report 2010–5077, 72 p.