Retrofitting Stormwater BMPs in a Supercritical Flow Regime: A Hydraulic Perspective

A computational hydraulic model toolkit was required to facilitate designs that would permit retrofitting stormwater Best Management Practices (BMPs) and flow diversion structures on covered and open channels. This paper outlines the development of the computational hydraulic model toolkit. The paper addresses: 1). The computational hydraulic modeling of the base case — pre installation of the BMP, 2). The use of a Diversion Channel to divert the treatable flow from the Main Channel to the BMP via a weir or gate, 3). The transitioning of the flow regime from supercritical to subcritical immediately upstream of the BMP and wholly within the Inlet Diversion Channel to optimize the settlement of sediments in the BMP and limit sediment drop out in the Inlet Diversion Channel, 4). The transitioning of the flow regime from subcritical to supercritical immediately downstream of the BMP and wholly within the Outlet Diversion Channel to minimize flow depths, 5). The strategic positioning of the hydraulic jump outside of the Main Channel to prevent overtopping and the likely flooding of adjacent residences, 6). The design of flood mitigation works and the mitigation of sediment drop out upstream of the weir in the Main Channel, and 7). Retaining Main Channel capacity.