ASSESSING HYDROLOGIC IMPACTS OF STREET-SCALE GREEN INFRASTRUCTURE INVESTMENTS FOR SUBURBAN PARMA, OHIO

Impervious surfaces in urban environments can lead to greater levels of runoff from storm events and overwhelm storm sewer systems. Disconnecting impervious surfaces from storm water systems and redirecting the flow to decentralized green infrastructure treatments can help lessen the detrimental effects on watersheds. Most research on green infrastructure has focused on the performance of individual elements, whereas this project addresses the question of hydrologic impacts and pollution reduction of street scale investments using green infrastructure best management practices (BMPs), such as front yard rain gardens, street side bioretention, and rain barrels. The West Creek Watershed is a 36 km² subwatershed of the Cuyahoga River that contains ~35% impervious surface. Before-after-control-impact design pairs two streets with 0.001-0.002 ha. lots and two streets with 0.005-0.0075 ha. lots. Flow meters have been installed to measure total discharge, velocity, and stage pre– and post-BMP construction. Runoff data have been analyzed to determine if peak discharge for storm events has been reduced after installation of BMPs on the street with 0.001-0.002 ha. lots. Initial results show that the peak flows have not been reduced for most storm events on the street with the green infrastructure. However, several larger events show that peak flows have been reduced on the treatment street and need to be further investigated to determine what conditions led to flow reductions from these storms but not other events. Initial results for centroid lag-to-peak, centroid lag, lag-to-peak, and peak lag-to-peak show that lag times have increased on the treatment street. Additional research will include analysis of the total effect of street-scale BMPs on storm hydrograph characteristics including, hydrograph recession behavior and total runoff volume. Water samples are being collected at the end of each street during storm events to evaluate the ability of the BMPs to remove heavy metal pollutants from stormwater runoff. After studying the effect of each treatment street, we will define the level of disconnected impervious surfaces needed in order to reduce peak flows within the West Creek watershed.