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Flow Dynamics and Nutrient Reduction in Rain Gardens
Citation:
Gilchrist, S., E. STANDER, M. BORST, T. P. OCONNOR, AND A. Rowe. Flow Dynamics and Nutrient Reduction in Rain Gardens . Presented at Philadelphia Low Impact Development Symposium, Lowes Philadelphia Hotel, Philadelphia, PA, September 25 - 28, 2011.
Impact/Purpose:
To inform the public.
Description:
The hydrological dynamics and changes in stormwater nutrient concentrations within rain gardens were studied by introducing captured stormwater runoff to rain gardens at EPA’s Urban Water Research Facility in Edison, New Jersey. The runoff used in these experiments was collected from a 9-acre watershed dominated by a student parking lot and high-density residential housing. Water was pumped into eight pilot-scale non-vegetated outdoor mesocosms. The results of these experiments prepares for the next phase of the research work which includes plants in the rain gardens to determine the effects of vegetation on the same objectives. The mesocosms vary by size, presence or absence of anaerobic zone, and addition of internal hardwood mulch layers. The statistically-considered factorial design uses rain gardens befitting backyard and urban landscape scales. Water balance measurements are collected to understand stormwater flow dynamics through rain gardens. Time domain reflectometers are used to measure: temperature-corrected soil moisture content; sub-surface infiltration rates using timing of wetting front passing two reflectometers embedded at different depths; percentage return to antecedent levels before next rain event; and elapsed time before breakthrough under a range of antecedent moisture conditions and influent volumes. Effluent samples are collected for laboratory analysis at initial breakthrough and at two later times before influent feed is discontinued. Quantitative assessments are also being collected for total nitrogen and nitrogen species (nitrate, nitrite, and ammonium) for determination of nitrogen removal, pH, total suspended solids and particle size distributions for both influent and effluent volumes. These pilot-scale tests will determine whether a sandy, fast-draining media can promote nitrate removal under varying factors such as media saturation, organic matter content, and rain garden size.