Assessing impacts of green infrastructure at the watershed scale for suburban streets in Parma, Ohio

Next week, the Watershed Hydrology Lab will be well represented at the CUAHSI 2014 Biennial Colloquium. We’ll be presenting four posters, so here come the abstracts…

Assessing impacts of green infrastructure at the watershed scale for suburban streets in Parma, Ohio

Kimberly Jarden, Anne Jefferson, Jennifer Grieser, and Derek Schaefer

High levels of 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. The West Creek Watershed is a 36 km2 subwatershed of the Cuyahoga River that contains ~35% impervious surface. We seek to evaluate the hydrologic impacts and pollution reduction of street scale investments using green infrastructure best management practices (BMPs), such as rain gardens, bioretention, and rain barrels. Before-after-control-impact design will pair 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-construction. Runoff data has been preliminarily analyzed to determine if peak discharge for large (> 10 mm) and small (<10 mm) 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 ensure no outside hydrological impacts are having an effect on the flow. Initial analysis of total flow volume for each event, pre- and post-construction, show that total volume has increased on the street with green infrastructure treatments. Possible explanation for the increase on flow volume could be attributed to under drains from bioretention creating a more connected flow path to the storm drain or an upstream leak in the control street storm drain. Each scenario will be investigated further to confirm results. Further research will include analysis of the total effect of street-scale BMPs on storm hydrograph characteristics including, hydrograph regression behavior and lag time. Analysis on the accumulation of metals in the bioswales and the reduction of metals in street runoff will also be conducted to determine if the BMP treatments are capturing pollutants associated with storm water. After studying the effect of each individual treatment, we will define the level of disconnected impervious surfaces needed in order to achieve a natural hydrologic regime in this watershed.

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