Not all SuDS are created equal: Impact of different approaches on combined sewer overflows

Prabhat Joshi,Joao Paulo Leitão,Peter Marcus Bach,Max Maurer

doi:10.1016/j.watres.2020.116780

Prabhat Joshi, Joao Paulo Leitão + Show 2 more

Open Access

https://doi.org/10.1016/j.watres.2020.116780

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Abstract

Sustainable urban drainage systems (SuDS) help in stormwater management by reducing runoff volume, increasing runoff concentration time and thereby improving the drainage system capacity. This study investigated the potential and cost-effectiveness of SuDS in reducing combined sewer overflows (CSOs). We simulated the performance of four SuDS techniques (bioretention cell, permeable pavement, rain barrel and green roof) at incremental levels of spatial coverage for a small urban catchment with a combined sewer system. We also used an Analytic Hierarchy Process (AHP) considering end-point CSO, land use, imperviousness, slope and elevation criteria to identify priority areas for SuDS deployment. Results showed that CSO volume attenuation ranged a maximum of 50–99% for the catchment, depending on the deployment strategy and underlying mechanisms of each technology. We also found that deployment of SuDS in AHP-selected sub-catchments improved CSO reduction only for rain barrels and green roofs, but not for bioretention cells and permeable pavements. SuDS were also a cost-effective retrofit option: for a 40% volume reduction, the SuDS cost, at most, 25% of the equivalent cost required for a large CSO tank. Outcomes of this study demonstrate the efficacy of SuDS in controlling CSOs, adding yet another tangible benefit to their increasingly recognised multi-functionality.

Highlights

Combined sewer systems capture and convey both stormwater and municipal sewage through a single sewer line towards a central treatment facility
We address the aforementioned knowledge gaps through three specific objectives: i Elicit the long-term efficacy (35 years) of Sustainable urban drainage systems (SuDS) in reducing combined sewer overflows (CSOs) encompassing events with varying rainfall patterns, ii Assess the impact of spatial deployment strategies for SuDS, and iii Understand the cost-effectiveness of SuDS from a life-cycle costing perspective, in particular, we adapt the methodology of Montalto et al (2007), Tavakol-Davani et al (2016) and Johnson and Geisendorf (2019), to compare different types of SuDS
We investigated if targeting selected few sub-catchments for SuDS implementation was more effective than distributing them uniformly all over the study site

Summary

Introduction

Combined sewer systems capture and convey both stormwater and municipal sewage through a single sewer line towards a central treatment facility. Only a limited amount of stormwater is processed in the treatment plant. Anything that exceeds this capacity is directly released to the receiving water body through designated storage and overflow structures, a process referred to as combined sewer overflows (CSOs). CSOs have garnered much interest around the world since many cities have combined sewer systems in place (Komínková et al, 2016; Llopart-Mascaró et al, 2015; Xu et al, 2018). Exceeded drainage capacity can lead to urban floods, which might cause traffic disruption, economic damage, and jeopardise human health (Qin et al, 2013).

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