Real Time Control strategies to reduce expansion of urban drainage systems. Case study: Lyngby-Taarbæk

This article illustrates how real time control (RTCs) strategies can contribute to reduce the expansion of urban drainage infrastructures while maintaining the desired level of service. The Lyngby-Taarbæk catchment is used as case study: based on a static design, a storage expansion of 24,200m3 has been planned to fulfil new environmental requirements.

Two RTC methods are implemented in order to maintain the same combined sewer network performance while reducing the planned basin expansion, and consequently reducing the investment cost. A state-of-the-art global control scheme using a 2-hour weather forecast (the Dynamic Risk Overflow Assessment - DORA) is tested.

Also, a strategy involving predefined “if-then-else” control rules is developed and tested. The performances of both RTC strategies are compared and evaluated by analysing 46 historical rain events with various patterns. According to the simulation results, RTC succeeded in providing similar performance of the drainage system by maximizing use of the available storage.

A storage reduction of 5,220 m3 is accomplished (corresponding to 21% of the proposed basin expansion). The reduced system operated dynamically generates lower combined sewer overflow (CSO) discharges for small to medium rain events; while the desired performance of the system is achieved for big events.

The rule-based strategy reduces significantly CSO, however DORA provides generally better results by using forecasting and riskbased approach. These results show that implementing RTC strategies during the design stages could reduce the elevated cost associated with UDS expansion while offering a similar or even better protection to the environment.