Assessing the effects of four SUDS scenarios on combined sewer overflows in Oslo, Norway: evaluating the low-impact development module of the Mike Urban model

Abstract

Paved surfaces, increased precipitation intensities in addition to limited capacity in the sewer systems, cause a higher risk of combined sewer overflows (CSOs). Sustainable drainage systems (SUDS) offer an alternative approach to mitigate CSO by managing the stormwater locally. Seven SUDS scenarios, developed based on the concept of effective impervious area reduction, have been implemented in the Grefsen catchment using the Mike Urban model. This study evaluated the hydrological performance of two SUDS controls (i.e. green roof (GR) and rain garden (RG)) modules of the model and the effect of the SUDS scenarios on the CSOs using event-based and continuous simulations. The Nash–Sutcliffe efficiency (NSE) along with flow duration curves (FDCs) has been used for evaluating the model performance. Event-based evaluations revealed the superior performance of the RG in reducing CSOs for larger precipitation events, while GRs were proven to have beneficial outcomes during smaller events. The study illustrated another way of assessing the continuous simulations by employing the FDCs. The FDCs were assessed against a discharge threshold at the outlet (which authorities can set as design criteria) of the catchment in terms of the extent, each scenario reduced occurrence and duration of outflow that invokes flow in the overflow pipe. HIGHLIGHTS This paper demonstrates merits of the SUDS concept for mitigating the challenges climate change pose on combined sewer systems using two SUDS controls and seven SUDS scenarios.; It illustrates how the flow duration curve (FDC) based evaluation approach can be of great practical significance, thereby contributing to the discussion on adaptation of such design criteria in the future.; It evaluates efficiency of the implemented SUDS measures extensively by employing a range of performance evaluation techniques.; The use of Mike Urban model's low-impact-development module for implementing SUDS controls makes this manuscript a pioneering research work, as this is the model of choice among many practitioners across the world.;

Keywords

• bioretention cell
• flow duration curve
• green roof
• rain garden
• sustainable urban drainage system