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Measuring Flow Reductions in a Combined Sewer System Using Green Infrastructure
Citation:
Brown, R., Mike Borst, B. Kolze, W. Sydnor, AND J. Dempster. Measuring Flow Reductions in a Combined Sewer System Using Green Infrastructure. Presented at 2015 International Low Impact Development Conference, Houston, TX, January 19 - 21, 2015.
Impact/Purpose:
This presentation quantifies the effect that green infrastructure (GI) had on reducing in-sewer flows and combined sewer overflows (CSOs) in a 17-acre combined sewer system in Louisville, Kentucky.
Description:
A green infrastructure (GI) design approach was used in CSO Basin #130, a 17-acre sewershed in the Butchertown section of Louisville, Kentucky, to reduce combined sewer overflows (CSOs). For the design year, the modeled design was expected to reduce the CSO frequency from 34 to 8 and annual CSO volume by 6.5 million gallons to 0.28 million gallons. The Louisville and Jefferson County Metropolitan Sewer District installed five area-velocity meters in the combined sewer for at least 12 months prior to construction to develop a preconstruction model of in-sewer flows and design the GI controls. InfoWorks CS (Innovyze) was used to develop the preconstruction hydraulic model. The flow meters were installed at the overflow location, in the dry-weather sewer line, and at three locations within the sewershed to separate the sewershed into discrete catchments. The effectiveness of GI in reducing in-sewer flows was evaluated by comparing the measured postconstruction flow volume to the modeled results that use the calibrated preconstruction model with postconstruction rainfall measurements. This presentation highlights the effect of GI on flow volume for the catchment with the strongest calibration results. This catchment was managed entirely with permeable pavement systems. Despite an initial lack of basin-wide maintenance while different maintenance methods were being tested, the paver strips reduced in-sewer flow volumes by about 40%. Performance should improve with the regular maintenance program now in place. A 12-month period with similar distributions of rainfall depth to the design year was identified for both the preconstruction and postconstruction periods to determine the effect of GI on CSO volume. On an annual basis, the CSO volume during the postconstruction period was 33% (2.7 MG) less than during the preconstruction period. During both periods, the partial collapse of the dry-weather sewer limited flow capacity. Since it has been replaced a couple of months ago (November 2014), CSO volume reduction has improved greatly.
URLs/Downloads:
http://content.asce.org/conferences/lid15/program.html
http://submissions.mirasmart.com/ASCE/LID2015/Itinerary/Conferen