Innovative Hydraulic Design to Manage Large Supercritical Flow Diversion for CSO Control

摘要

Combined Sewer Overflows (CSO) have a detrimental impact on the quality of receiving waters. Exercising a good level of control on the flows within the collection system is a decisive first step to solve the problem. Although a rather a straightforward task for sewers carrying flow in the subcritical regime, flow control when supercritical conditions prevail can be challenging. This is simply because countermeasures for subcritical flow control do not work as well for the supercritical case (introduction of hydraulic jumps, flow unsteadiness and high energy losses) or because traditional solutions for supercritical flow control, such as leaping weirs, are not applicable (due to financial, constructability or operational concerns). This work proposes a novel structure consisting of an elevated bottom and a wall of varying width - initially expanding and then contracting. A real-life CSO regulator is used as a case study. First, a systematic approach employing a number of analysis techniques is adopted to define the design inputs. Then, a detailed physical model is used to prove the feasibility of the concept and deliver specific design parameters for the regulator. The tests demonstrated that in addition to compliance with regulatory performance criteria, the proposed design effectively controls the flood risk. The results of this study establish the potential of the novel structure to serve as a blueprint to tackle challenging problems of supercritical flow control.