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Development of a scenario-based stormwater management planning support system for reducing combined sewer overflows (CSOs) - Buffalo, NY
Citation:
Fu, X., X. Wang, AND M. Hopton. Development of a scenario-based stormwater management planning support system for reducing combined sewer overflows (CSOs) - Buffalo, NY. Association of Collegiate Schools of Planning, Buffalo, NY, October 25 - 28, 2018.
Impact/Purpose:
We developed a scenario-based Stormwater Management Planning Support System for CSOs to provide a platform for coordinating the installation of GI and GrayI to eliminate/reduce CSOs of a specific watershed or sewershed. Combined sewer systems are designed to discharge excess untreated water to natural water ways when the combined flow exceeds the capacity of the wastewater treatment system that still serves as a common urban conveyance method in many cities around the world, especially in old towns. Combined Sewer Overflows (CSOs) contain pollutants that can cause serious environmental problems and public-health risks. Green Infrastructure (GI), which can infiltrate, store, and/or detain stormwater at different levels, has been integrated with existing Gray Infrastructure (GrayI, such as gutters, pipes, and drains conveyance and storage facilities) to overcome CSO problem in urban areas. However, there lacks an objective-oriented planning framework from the angle of whole watershed or sewershed aiming at eliminating CSOs. Although the GIs present many advantages on managing runoff, the combination of GIs and GrayIs for solving CSO problems cannot be overlooked. Moreover, the existing spatial units in stormwater simulation, such as catchment areas, place barriers in GI implementation and public participation. Variations within a catchment for spatial distribution, attribution, ownership, and management of GIs are not clearly informed. To address the aforementioned gaps, we developed a scenario-based Stormwater Management Planning Support System for CSOs (SWPSS-CSO). The goal of the SWPSS-CSO is to provide a platform for coordinating the installation of GI and GrayI to eliminate/reduce CSOs of a specific watershed or sewershed. The analysis is parcel-based and provides GI’s exact amount (retention volume or pervious area), location, associated ownership, costs of construction, and maintenance. Researchers, planners, utility managers, community leaders, and the general can use the SWPSS-CSO to participate in GI planning process to address runoff control and enhance community quality. The SWPSS-CSO was developed using CommunityViz (v5.0), a planning support extension of ArcGIS, and applied to CSO #488 sewershed in Cincinnati, Ohio as a case study. It consists of three components: scenario generation, scenario modeling, and scenario comparison. One baseline scenario and three alternative scenarios are developed. The baseline scenario presents a sewershed with existing CSS without any GI installation. The three alternative scenarios represent an increasing use of GI by adding practices to the preceding scenario: 1) installation of rain barrels and green roofs on private parcels; 2) installation of porous pavement on private driveways and paved parking; and 3) installation of porous pavement on sidewalks and retention basins on public-owned land. The suitability analysis of each type of GI is based on drainage area, slope, hydrologic soil group, stream buffer, and roof type. Runoff, time of concentration, and peak flow rate are simulated using USDA TR55---Urban Hydrology for Small Watersheds. Results show the third alternative scenario has the best performance among four scenarios by mobilizing 97.25% private parcels and 27.59% public parcels to attend GI installation, reducing almost 41% runoff comparing to the baseline scenario, and dropping the peak flow rate to 226.19 cfs, under rainfall event of 5-year recurrence interval. However, to eliminate the CSO problem, tanks (GrayI) are needed with 22.57 ac-ft storage capacity.
Description:
Combined sewer systems are designed to discharge excess untreated water to natural water ways when the combined flow exceeds the capacity of the wastewater treatment system that still serves as a common urban conveyance method in many cities around the world, especially in old towns. Combined Sewer Overflows (CSOs) contain pollutants that can cause serious environmental problems and public-health risks. Green Infrastructure (GI), which can infiltrate, store, and/or detain stormwater at different levels, has been integrated with existing Gray Infrastructure (GrayI, such as gutters, pipes, and drains conveyance and storage facilities) to overcome CSO problem in urban areas. However, there lacks an objective-oriented planning framework from the angle of whole watershed or sewershed aiming at eliminating CSOs. Although the GIs present many advantages on managing runoff, the combination of GIs and GrayIs for solving CSO problems cannot be overlooked. Moreover, the existing spatial units in stormwater simulation, such as catchment areas, place barriers in GI implementation and public participation. Variations within a catchment for spatial distribution, attribution, ownership, and management of GIs are not clearly informed. To address the aforementioned gaps, we developed a scenario-based Stormwater Management Planning Support System for CSOs (SWPSS-CSO). The goal of the SWPSS-CSO is to provide a platform for coordinating the installation of GI and GrayI to eliminate/reduce CSOs of a specific watershed or sewershed. The analysis is parcel-based and provides GI’s exact amount (retention volume or pervious area), location, associated ownership, costs of construction, and maintenance. Researchers, planners, utility managers, community leaders, and the general can use the SWPSS-CSO to participate in GI planning process to address runoff control and enhance community quality. The SWPSS-CSO was developed using CommunityViz (v5.0), a planning support extension of ArcGIS, and applied to CSO #488 sewershed in Cincinnati, Ohio as a case study. It consists of three components: scenario generation, scenario modeling, and scenario comparison. One baseline scenario and three alternative scenarios are developed. The baseline scenario presents a sewershed with existing CSS without any GI installation. The three alternative scenarios represent an increasing use of GI by adding practices to the preceding scenario: 1) installation of rain barrels and green roofs on private parcels; 2) installation of porous pavement on private driveways and paved parking; and 3) installation of porous pavement on sidewalks and retention basins on public-owned land. The suitability analysis of each type of GI is based on drainage area, slope, hydrologic soil group, stream buffer, and roof type. Runoff, time of concentration, and peak flow rate are simulated using USDA TR55---Urban Hydrology for Small Watersheds. Results show the third alternative scenario has the best performance among four scenarios by mobilizing 97.25% private parcels and 27.59% public parcels to attend GI installation, reducing almost 41% runoff comparing to the baseline scenario, and dropping the peak flow rate to 226.19 cfs, under rainfall event of 5-year recurrence interval. However, to eliminate the CSO problem, tanks (GrayI) are needed with 22.57 ac-ft storage capacity. Although GrayIs still play important roles in controlling CSOs, GIs can add meaningful capacity to the stormwater system. The SWPSS-CSO can further be applied to test more scenarios for other watershed or sewershed, such as scenarios for extreme rainfall event related with climate change, future land cover change, and new types of GI. In addition, the SWPSS-CSO is an open system that allows users to customize objectives, models, indicators, and parameters for runoff-related decision-making needs.