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Real Time Control (RTC) has become an accepted technique for improving the performance of Urban Drainage Systems (UDS) due to its flexibility and sustainability. Numerous implementations of RTC have been reported during the last decades. At the same time, guideline documents and state-of-the-art reports have been published. Whereas the general aspects and challenges of planning and installation of RTC systems are well covered, there is a lack of information about the adequate equipment for RTC of UDS. After identifying and briefly discussing the basic components of RTC systems for UDS, this paper describes the specific components in detail. This comprises the introduction of available technologies for sensors, actuators, controllers and telemetry systems in the context of RTC and the discussion of their potential and limitations. Lessons learned from the field operational experiences and future trends and challenges are identified.

Combined sewer overflows (CSOs) cause environmental problems and health risks, but poor guidance exists on the use of rainfall data for sizing optimal CSO control solutions. This study first reviews available types of rainfall information as input for CSO modelling and, secondly, assesses the impacts of three rainfall data selection methods (continuous simulation, historical rainstorms selected based on rainfall depth or maximum intensity and IDF-derived storms) on the estimation of CSO volume thresholds to control in order to reach specific seasonal CSO frequency targets. The methodology involves hydrological/hydraulic modelling of an urban catchment in the Province of Québec (Canada). Continuous simulation provides the most accurate volume estimations and shows high sensitivity to the number of simulated *Revised Manuscript with no changes marked Click here to view linked References 2 years. Alternatively, when historical events extracted from rainfall data separated by a minimum inter-event time (MIT) criterion are selected based on their total rainstorm depth, the CSO volumes are underestimated significantly; whereas an analysis based on rainstorm maximum intensities over durations similar to the time of concentration provides more conservative volumes. Finally, synthetic storms constructed from multiple points of an IDF curve tend to underestimate slightly the CSO volumes, but provide acceptable results compared to single point derived storms. It was found that the overflow structures local characteristics had a marginal influence on results obtained from continuous simulation compared to event-based simulation. The use of design rainfall events should thus be restricted to preliminary assessment of CSO volume thresholds, and the final volume estimation for solution sizing should be reviewed under continuous simulation. The innovative contribution lies in the improvement of modelling procedures for solutions design to achieve a maximum CSO frequency, such as specified by many regulating agencies.

Quebec Urban Community (QUC) has selected Global Predictive Real-Time Control (GP-RTC) as the most efficient approach to achieve environmental objectives defined by the Ministry of Environment. QUC wants to reduce combined sewer overflows (CSOs) frequency to the St Lawrence river to two events per summer period in order to reclaim the use of Jacques-Cartier Beach for recreational activities and sports of primary contact. QUC's control scheme is based on the Certainty Equivalent Control Open Loop Feedback (CEOLF) strategy which permits one to introduce, at each control period, updated measurements and meteorological predictions. A non-linear programming package is used to find the flow set points that minimise a multi-objective (cost) function, subjected to linear equality and inequality constraints representing the physical and operational constraints on the sewer network. Implementation of GP-RTC on QUC's westerly network was performed in the summer of 1999 and was operational by mid-August. Reductions in overflow volumes with GP-RTC compared to static control are attributed to the optimal use of two existing tunnels as retention facilities as well as the maximal use of the wastewater treatment plant (WWTP) capacity.

An approach to design and operate real-time control system for combined sewer overflows is proposed. The methodology is based on nonlinear programming with the peculiarity that all the constraints are linear. The problem definition guarantees a non-null optimization space while preserving the physical and dynamical constraints of the state variables. The nonlinear cost function allows standard control objectives to be met and simulation of the behavior associated with storage facilities and actuators. The linear flow dynamic constraints are defined to simulate flow attenuation as well as to reject unknown disturbances.