Techniques to Assess Rain Gardens as Stormwater Best Management Practices

Abstract

Rain gardens are an aesthetically pleasing stormwater best management practice (BMP) that reduce runoff volume and remove stormwater pollutants through the processes of infiltration/filtration, adsorption, evapotranspiration, and plant uptake. Monitoring programs are often used to evaluate the performance of stormwater BMPs such as rain gardens. Monitoring a large number of rain gardens, however, is impractical due to the time and cost requirements. It is of interest, therefore, to develop other techniques to determine the effectiveness of rain gardens. The assessment program is aimed to assist municipalities in evaluating the effectiveness of BMPs for purposes of construction due diligence, NPDES permit requirements, and determining maintenance requirements. The primary process through which runoff volume is reduced in rain gardens is infiltration of water through the soil. Thus, infiltration rate is a key assessment parameter for rain gardens. Two methods for determining the infiltration rates of rain gardens have been developed as part of a tiered four level assessment protocol: 1. visual inspection, 2. capacity testing, 3. synthetic runoff testing , and 4. monitoring.