Multiple lines of evidence to decrease drainage to surface area ratio for effective bioinfiltration stormwater control - Franklin Township, NJ
Citation:
Oconnor, T. Multiple lines of evidence to decrease drainage to surface area ratio for effective bioinfiltration stormwater control - Franklin Township, NJ. Association of Environmental and Engineering Geologists (AEG) New York-Philadelphia Chapter, Franklin Township, NJ, May 11, 2023.
Impact/Purpose:
This is an invited presentation for the local chapter of AEG on May 11. It is comprised of three previously cleared presentations. STICS (ORD-025440, ORD-030396) and recently cleared Rapid Subproduct SSWR 410.1.1.6 (STICS ORD-047593) of same title. All slides remain same from SSWR 410.1.1.6 - Adding 1 slide from ORD-025440 and 21 from ORD-030396; this is all background information to give audience more context for the study. Audience may not be as familiar with stormwater regulations and practices. Clearance by 4/13/2023 would be appreciated, as this night of next AEG meeting and they would like to announce next presentation for 5/11/2023.
Description:
Bioinfiltration units were constructed at USEPA’s Edison Environmental Center to evaluate drainage to surface runoff ratio for sizing of bioinfiltration stormwater controls. Three sizes of hydraulically isolated bioinfiltration units were tested in duplicate with changes in aspect ratio of length from inlet wall by doubling successive length from smallest (3.7 m) to largest (14.9 m) while width remained the same (7.1 m). The watershed areas were nominally the same resulting in watershed to surface area ratios of 5.5:1 for largest duplicate units, 11:1 for the middle units and 22:1 for the smallest. Each unit was instrumented for continuous monitoring with water content reflectometers (WCR) and thermistors with data collected since November 2009. The bioinfiltration units were filled with planting media initially comprised of 90% sand and 10% sphagnum peat moss by volume and approximately 99% and 1%, respectively, by weight. These units were then planted between May and November of 2010 with a variety of native grasses, perennials, shrubs and trees that were tolerant to inundation, drought and salt. In late 2012, a survey of shrubs planted in these bioinfiltration units was performed. The published results of the combined analyses of moisture content, rainfall and size of shrubs indicated the smaller units had superior shrub growth due to the more frequent saturation of the root zone as measured by WCR, while the plants in the largest units, particularly away from front wall where runoff entered, potentially relied on direct rainfall only. Starting in 2017 additional monitoring was performed in these units including chemistry analysis by loss on ignition and total phosphorous of the engineered planting media and an additional survey of plants. As in the previous study, plants did better in the medium (11:1) and small (22:1) bioinfiltration units compared to largest units (5.5:1), and there was greater buildup of carbon and phosphorous in the smaller units. One species of grass that dominated the two largest bioinfiltration units away from the inlet was drought tolerant which was indicative that plants in these units relied on rainfall rather than stormwater runoff. Oversized units do not completely use the control volume and many of the other original plantings grew slower or were less widespread in comparison to plantings in that smaller units that flooded more frequently and achieved greater growth.