Evaluation of Hydrologic Effects on Stormwater Runoff from a Rain Garden in Lodi, Wisconsin
Project Number: 9KH32
Project Chief: Charles P. Dunning
Project Topics: Rain garden, urban runoff, storm water, bioretention
Cooperators: Wisconsin DNR, Lodi Parks Commission, Friends of Scenic Lodi Valley, UW Madison, Wisconsin DOT
Period of Project: 2005-2008
Lodi Rain Garden at Veteran’s Memorial Park in Lodi, WI. Three years after planting.
Unplanted 3 Celled Rain Garden at Veteran’s Memorial Park in Lodi, WI. Each cell is constructed of 2 feet of engineered soil on top of 2 feet of coarse aggregate stone. Stormwater enters the upper cell, infiltrates through the soil, fills the spaces in the aggregate layer, and then discharges to the creek through a drain tile that is located at the interface between the soil and aggregate layers. As more water enters the rain garden it flows into the subsequent cells, receiving the same infiltration process before discharging to the creek.
Developed watersheds contain large areas of impervious surfaces. These surfaces prevent stormwater from infiltrating into the soil and alternately direct stormwater into storm sewers that may empty directly into surface waters. The water exiting these sewers tends to be high in sediment, nutrient, and metal content. It also may be of a higher temperature than naturally recharging water which can upset the balance required by many fish for survival. Discharge from storm sewer systems also enters surface waters at a faster rate than pervious areas causing rapid increases in stream discharge which result in increased erosion and flooding situations. Many practices have been developed to control and improve the quality of this runoff. One such practice is the use of rain gardens. A rain garden is a planted depression that collects stormwater runoff from impervious areas. The collected rainwater has the opportunity to infiltrate through the soil before exiting the rain garden. During the infiltration process some of the water quality improvements that can occur are: a decrease in water quantity through absorption, transpiration, evaporation and infiltration; a decrease in pollutant concentration through sediment settling, absorption and plant nutrient uptake; and temperature decrease through water transport through the cooler soil.
The objective of this study was to evaluate the hydrologic impacts of the three celled natively planted rain garden installed in Lodi, WI and provide additional information to the growing body of data regarding the effectiveness of rain gardens. The use of rain gardens for abating stormwater runoff intensity and for decreasing stormwater runoff temperatures were explored. The data were collected from August 2005 until October 2008.
In September of 2003, the city of Lodi constructed a three celled rain garden to collect the runoff from a 7 acre residential watershed. Equipment was installed by the USGS throughout the system to monitor various hydrologic aspects of storm events. The aspects monitored were:
- discharge into the system
- discharge that bypassed the rain garden
- discharge that entered the rain garden
- discharge that exited the first cell of the rain garden
- temperature at the inlet of the rain garden
- temperature at the outlet of the first cell of the rain garden
- shallow, intermediate and deep well data (including temperature) within the first cell of the rain garden
- rainfall amounts
- rainfall and discharge durations
These data were used to determine the effectiveness of the rain garden in decreasing the intensity of storm events and decreasing the temperature of discharging stormwater. The data will also be used in the calibration of the urban stormwater runoff model SLAMM.
What we have learned about the Community Rain Garden on Spring Creek –three years later. Presented at the Lodi Parks Commission Meeting, March 23, 2010.