Real-Time Control Strategies of the Outflow from Stormwater Basins from a River’s Perspective

Dirk Muschalla, Marc B. Neumann and Peter A. Vanrolleghem

ABSTRACT

The objective of this contribution is to integrate real-time control (RTC) in stormwater management to reduce the impact on local aquatic ecosystems. This is achieved by managing stormwater from urban catchments by equipping existing stormwater basins with a dynamic sluice gate. The goals are to increase the water retention time in the basin and to decrease the hydraulic peaks to the receiving water. The aim of the first objective is to increase sedimentation and thus removal of fine particles, on which the majority of contaminants are agglomerated, whereas the second objective focuses on reducing the hydraulic stress in the receiving water by avoiding hydraulic peak impacts. Hence, the aims are ecohydraulic in nature.

Starting from a real case study consisting of a small urban catchment with one stormwater basin at the outlet of its stormwater drainage system, the proposed RTC concept is evaluated by a simulation study with accompanying measuring campaign. Flow and water quality are modeled by applying a hydrodynamic model for runoff and a quality model for TSS. The runoff model is based on the full St. Venant equations. The quality model for TSS is based on build-up and wash-off equations for the surface runoff phase. For the stormwater basin, sedimentation theory with particle-size specific settling velocity distributions is used. As simulation software EPA’s SWMM 5 is used.

The developed RTC strategies are based on the mentioned objectives and constraints – decreasing TSS and agglomerated contaminant loads by increasing the time for sedimentation, decreasing hydraulics peak impacts and avoiding overflows of the basin. Multi-objective Evolutionary Algorithms are applied to support the development of the RTC strategies. First, the best performing static operation of the basin is searched for by adjusting the maximum outflow of the basin. Second, the theoretically best performing RTC strategy is developed by direct optimization of the sluice gate set points over time with the assumption that forthcoming precipitation is perfectly known in advance, i.e. using perfect weather forecast. Based on these two approaches a more general rule-based control strategy is derived. Finally, all developed approaches are compared with the current system setup (no control scenario).

Based on modeling water quality and quantity and implementing dedicated control algorithms for the sluice gate, real-time control proved to be an effective solution for reducing the suspended solids discharge and hydraulic stress in the urban river. In all studied cases, the controlled basin offered sedimentation efficiency that is significantly higher than the current basin solely controlled by a static device. In addition, the developed dynamic RTC strategies allow a considerable reduction of the hydraulic peak loads. This study showed that the proposed solution to integrate real-time control in stormwater basins has the potential to significantly reduce the hydraulic stress and the load of contaminants released into the receiving waters, improving water quality in urban rivers and improving aquatic ecosystems in urbanized catchments.


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