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Modelling SuDS from Device-Scale to Street-Scale
Introduction
As Sustainable Drainage Systems (SuDS) / Low Impact Development (LID) methods are increasingly utilised to manage stormwater in urban areas, it becomes crucial for drainage engineers to accurately represent their hydrological and hydraulic impacts within drainage modelling tools. However, not all tools include explicit SuDS modelling capabilities or their utilisation may be considered too computationally expensive in some practical contexts.
The installation and location of SuDS are often driven by opportunistic factors, such as deteriorating infrastructure or new developments. This retrofitting approach can lead to a fragmented implementation of stormwater management measures. As more SuDS are added to a street, the cumulative effects (retention & detention) must be understood. There exists a distinct lack of monitoring studies that demonstrate the hydraulic impact of SuDS applied across an entire catchment. Consequently, a range of stormwater models have been used to predict performance in these scenarios, the most commonly reported models used are SWMM, MUSIC, InfoWorks ICM and MIKE.
To date, numerous research projects and investigations have focused on the effects and consequences of SuDS devices by modelling, whereas a clear deficit has been identified regarding knowledge on upscaling SuDS. Due to an absence of monitoring data, models that can simulate multiple SuDS at mesoscale or large-scale catchments capturing hydrological behaviour are relatively lacking in validation.
Objectives
(1) establish four alternative modelling approaches for individual SuDS at the device scale in SWMM;
(2) assess the accuracy of outflow predictions from these models using both design storms and real rainfall time series;
(3) assess the performance of the alternative bioretention cell models considering different saturated hydraulic conductivities, outlet control and exfiltration rate conditions;
(4) establish different aggregated modelling approaches for SuDS at the subcatchment scale in SWMM;
(5) assess the accuracy of subcatchment outflow predictions from different aggregated modelling approaches.
Results so far
The study reveals that all approximation approaches have inherent limitations in accurately simulating hydrological dynamics at the device scale. Methods that involve complete disconnection (Disconnect) or transferring catchment areas to pervious surfaces (TransferP) do not effectively capture these dynamics, and underestimated SuDS runoff in all cases considered here. In contrast, approaches utilizing initial losses and storage, particularly those accounting for continuous losses based on evapotranspiration (Cont. Loss), yield more realistic responses compared to those using a daily fixed recharge depth (Daily Loss) in continuous rainfall simulation. Particularly, in a SuDS device with orifice control, the Daily Loss and Cont. Loss models perform reasonably well.
Shuxin Ren | The University of Sheffield | 2024
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