Citation:

Brown, R., Mike Borst, K. Mackenbach, AND J. Gray. Measuring Flow Reductions in a Combined Sewer System using Green Infrastructure - abstract. Presented at 2015 International Low Impact Development Conference, Houston, TX, January 19 - 21, 2015.

Impact/Purpose:

In 2009, the Louisville and Jefferson County Metropolitan Sewer District (MSD) submitted an Integrated Overflow Abatement Plan (IOAP) addressing combined sewer overflows (CSOs) and sanitary sewer overflows. Many of the solutions involve gray infrastructure, such as large, end-of-pipe storage basins that capture and store overflows until it can be pumped to the system for treatment. In an effort to reduce the size and cost of gray infrastructure projects and to add other benefits, MSD included plans to incorporate green infrastructure (GI). The first sewershed to use GI to meet the IOAP objectives was CSO Basin #130, a 17-acre sewershed in the Butchertown section of Louisville. The effectiveness of GI in reducing in-sewer flows will be evaluated by comparing the measured postconstruction flow volume and peak flow rates to the modeled results that use the calibrated preconstruction model with postconstruction rainfall measurements. This presentation will focus on the change in flow volume and peak flow rate in the subbasins after GI installation. Preconstruction and postconstruction CSO volume and frequency will also be presented.

Description:

In 2009, the Louisville and Jefferson County Metropolitan Sewer District (MSD) submitted an Integrated Overflow Abatement Plan (IOAP) addressing combined sewer overflows (CSOs) and sanitary sewer overflows. Many of the solutions involve gray infrastructure, such as large, end-of-pipe storage basins that capture and store overflows until it can be pumped to the system for treatment. In an effort to reduce the size and cost of gray infrastructure projects and to add other benefits, MSD included plans to incorporate green infrastructure (GI). The first sewershed to use GI to meet the IOAP objectives was CSO Basin #130, a 17-acre sewershed in the Butchertown section of Louisville. The planning used InfoWorks, a combined sewer hydraulic model, to determine a cost-effective design to meet the regulatory targets outlined in the IOAP. The resulting solution for this basin used a GI design. The design included 14 permeable pavement strips (permeable articulating concrete block/mat), 28 tree boxes, and four infiltration planters installed upstream of existing catch basins to intercept and infiltrate runoff before it entered the combined sewer system. These controls were installed in parking lanes and sidewalks within the public right-of-way. For the typical rainfall 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. To develop a preconstruction model of in-sewer flows, MSD installed four area-velocity meters in the combined sewer in January 2011. The locations included the overflow location, the outlet to the wastewater treatment plant, and two locations within the sewershed. In July 2011, an area-velocity meter within the sewershed was moved and another added to separate the sewershed into three discrete subbasins. Each subbasin is dominated by one GI type. The northern subbasin includes 12 permeable pavement strips, the eastern subbasin includes 28 tree boxes, and the western subbasin includes a permeable pavement strip and an infiltration planter. The first two permeable pavement strips were constructed in December 2011 in the northern subbasin. The remaining controls were installed in 2013. Most have been in place and infiltrating stormwater for more than one year. The effectiveness of GI in reducing in-sewer flows will be evaluated by comparing the measured postconstruction flow volume and peak flow rates to the modeled results that use the calibrated preconstruction model with postconstruction rainfall measurements. This presentation will focus on the change in flow volume and peak flow rate in the subbasins after GI installation. The first scheduled basin-wide maintenance of all the permeable pavement strips occurred in June 2014, so this presentation will also evaluate if permeable pavement strip maintenance had a measureable effect on the in-sewer flow volume and peak flow rate. Preconstruction and postconstruction CSO volume and frequency will also be presented.

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