Title

Evaluating Low Impact Development as a Mitigation Strategy for Alleviating Combined Sewer Overflows

Item Type

Presentation

Location

Elaine Langone Center, Forum

Session

Watersheds and Water Use

Start Date

12-11-2016 1:30 PM

End Date

12-11-2016 4:00 PM

Keywords

combined sewer overflows, stormwater, low impact development, watershed

Description

Combined sewer systems, designed to collect both stormwater and sewage, are present in 700 United States cities, including many in the Susquehanna and Delaware River valleys. These systems were designed to overflow during precipitation events, discharging stormwater, toxins, pathogens, and human and industrial waste to nearby surface waters. We investigated the effectiveness of low impact development (LID), a method of preserving natural watershed hydrology, for reducing combined sewer overflow (CSO) at the watershed scale. An EPA Storm Water Management Model (SWMM) of the Park River Watershed in Hartford, Connecticut is used to evaluate the effect of reducing impervious cover (IC) on CSO. To simulate green infrastructure, simulations were performed for IC reductions up to 30% for storm recurrence intervals from three months through 50 years. Hartford’s target for CSO control in most areas of the city is the elimination of CSO in a “typical” year. When a 5% reduction in IC is simulated, runoff for a 1-year design storm is reduced 13 million gallons (MG) from a base case of 74 MG, and three of 44 initial overflows are eliminated. A hypothetical 30% IC reduction reduces runoff by 58 MG, eliminating 23 CSO locations. Overflow volume reduction continues to increase for all storm sizes; however, the number of CSO eliminated decreases. In a 25-yr storm, no CSO is eliminated with a 5% IC reduction. Results demonstrate that although LID implementation reduces stormwater volume, LID alone cannot eliminate CSO in Hartford for the storm sizes and IC reductions considered. While cost analysis demonstrates the financial benefit of using grey infrastructure in tandem with green infrastructure for stormwater management, the practicality of LID implementation may not exist. Watershed-level modeling, such as that performed in this investigation, can be useful in identifying target areas for LID implementation, avoiding costly individual hydrologic analysis of LID features during each design.

Language

eng

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Nov 12th, 1:30 PM Nov 12th, 4:00 PM

Evaluating Low Impact Development as a Mitigation Strategy for Alleviating Combined Sewer Overflows

Elaine Langone Center, Forum

Combined sewer systems, designed to collect both stormwater and sewage, are present in 700 United States cities, including many in the Susquehanna and Delaware River valleys. These systems were designed to overflow during precipitation events, discharging stormwater, toxins, pathogens, and human and industrial waste to nearby surface waters. We investigated the effectiveness of low impact development (LID), a method of preserving natural watershed hydrology, for reducing combined sewer overflow (CSO) at the watershed scale. An EPA Storm Water Management Model (SWMM) of the Park River Watershed in Hartford, Connecticut is used to evaluate the effect of reducing impervious cover (IC) on CSO. To simulate green infrastructure, simulations were performed for IC reductions up to 30% for storm recurrence intervals from three months through 50 years. Hartford’s target for CSO control in most areas of the city is the elimination of CSO in a “typical” year. When a 5% reduction in IC is simulated, runoff for a 1-year design storm is reduced 13 million gallons (MG) from a base case of 74 MG, and three of 44 initial overflows are eliminated. A hypothetical 30% IC reduction reduces runoff by 58 MG, eliminating 23 CSO locations. Overflow volume reduction continues to increase for all storm sizes; however, the number of CSO eliminated decreases. In a 25-yr storm, no CSO is eliminated with a 5% IC reduction. Results demonstrate that although LID implementation reduces stormwater volume, LID alone cannot eliminate CSO in Hartford for the storm sizes and IC reductions considered. While cost analysis demonstrates the financial benefit of using grey infrastructure in tandem with green infrastructure for stormwater management, the practicality of LID implementation may not exist. Watershed-level modeling, such as that performed in this investigation, can be useful in identifying target areas for LID implementation, avoiding costly individual hydrologic analysis of LID features during each design.