A Green Approach to Combined Sewer Overflow Control: Source Control Implementation on a Watershed Scale

Abstract

A green approach to combined sewer overflow control promotes reduction of stormwater at the source through the application of low impact development and low impact redevelopment techniques. The approach is supported by innovations such as stormwater regulations and other progressive practices like street tree planting and riparian buffer creation and restoration. These practices are designed to improve conditions in both the combined and separate sewered areas and to better manage the water resources, to protect and ensure beneficial uses of water bodies, to restore stream habitat, and to meet the priorities of residents for cleaner and safer streams. The practices are intended to optimize the use of infrastructure planned and constructed in the past for larger populations than those realized today. This paper describes approaches to and benefits expected from low impact development and redevelopment in terms of projected reductions in sewage discharges from a highly urbanized area served by combined sewers.The portion of impervious surfaces in the study area subjected to stormwater control is related to the urban water balance and to combined sewer overflow volume, duration, and frequency. Runoff resulting from small, frequent storms is infiltrated into native soils to the maximum extent possible. Where soil conditions do not allow the full volume to be infiltrated, the volume can be detained and released at a prescribed rate, typically 24 hours or more.Relationships between impervious cover and stormwater management benefits are investigated numerically using the USEPA Storm Water Management Model (SWMM). Model representations such as depression storage, directly connected impervious area, soil properties, combined sewer regulator settings, head loss, and wastewater treatment plant capacity, are validated using observed sewer flow and stream discharge records. Model elements representing stormwater management facilities are added between the hydrologic model representing the precipitationrunoff processes from land surfaces, and the hydraulic model representing the pipes and related appurtenances of the combined sewer collection system. These additional model elements represent physical processes occurring in stormwater management facilities. Infiltration into native soil is represented using soil moisture accounting and a modified Green-Ampt model of infiltration processes. Evaporation of ponded water, storage, and controlled release are simulated as they would occur in facilities meeting the performance requirements of stormwater control regulations. Sustainability 2008714 Hydrologic and hydraulic model simulations indicate that significant reductions in annual combined sewer overflow volume will result from implementation of low impact development and low impact redevelopment on a watershed scale. Estimates are made of annual combined sewer overflow volumes for various levels of implementation of control practices.A detailed analysis of impervious surfaces by type and by ownership leads to conclusions regardi...

Political and Professional Agency Entrapment: An Agenda for Urban Water Research

“…Indeed, similar schemes for new, large sewer tunnels have been identified in many places, including Milwaukee, USA and Auckland, New Zealand and new desalination plants are being developed around Australia. In other places, however, particularly in the United States, there are examples such as in Philadelphia (Smullen et al 2008) and Portland, Oregon where such large infrastructure approaches have been rejected in favour of dispersed, lower impact technologies and stormwater source controls (Natural Resources Defence Council 2006)-even when these have had to be retrofitted into dense existing urban areas (Centre for Watershed Protection 2007). Such large-scale infrastructure projects may be relevant where the degree of uncertainty about future scenarios is low; however, where there is substantial uncertainty, responses require flexibility to utilize a diversity of approaches, including abandonment or significant alteration as a clear option (Evans et al 2004).…”

Optimization of Real‐Time Control With Green and Gray Infrastructure Design for a Cost‐Effective Mitigation of Combined Sewer Overflows

“…In particular, many studies demonstrated CSO volume reductions (Joshi et al., 2020; Mailhot et al., 2014; McGarity et al., 2017; Patwardhan et al., 2005; Radinja et al., 2018; Torres et al., 2018), or both CSO volume and frequency reductions (Alves et al., 2016; Lucas & Sample, 2015). Moreover, CSO control can be improved under high implementation level of GIs (Autixier et al., 2014; Chaosakul et al., 2013; Smullen et al., 2008; Stovin et al., 2013) or when gray infrastructures (i.e., storage tanks) are combined with GIs (Alves et al., 2016; Dong et al., 2017; Fu et al., 2019; Liao et al., 2015; Montalto et al., 2007; Tavakol‐Davani et al., 2015). A few authors also applied various optimization techniques to quantify and locate GI practices at the lowest cost possible while mitigating either peak flows in combined sewer networks (Sebti et al., 2016) or CSO volumes (Fu et al., 2019; Joshi et al., 2020; Torres et al., 2018).…”

The potential to retrofit sustainable drainage systems to address combined sewer overflow discharges in the Thames Tideway catchment

“…Desk‐based feasibility studies relating to the potential usage of retrofit SuDS have suggested that retrofit SuDS could provide cost‐effective components of catchment rehabilitation strategies (Stovin & Swan ; Smullen et al . ; Stratus Consulting ; USEPA ). Preliminary decision‐support tools aimed at identifying opportunities and approaches to SuDS retrofitting have also been proposed (e.g.…”

“…Smullen et al . () and Stratus Consulting () highlight the opportunities provided by urban regeneration to engineer a gradual transformation from conventional piped drainage to SuDS within existing urban cores as part of the City of Philadelphia's long‐term CSO Control Plan. They describe ‘an innovative planning approach [that] promotes control of stormwater at the source through LID and low impact redevelopment retrofit, supported by new stormwater regulations and other progressive practices such as street tree planting and riparian buffer creation and restoration’.…”