Active Flood Hazard Mitigation. II: Omnidirectional Wave Control

Active mitigation of unimodal flood waves is achieved by selective boundary flow withdrawal. This is shown to create omnidirectional depression waves that can reduce the impact of hazardous flood waves in wide rivers, harbors, and reservoirs. Boundary outflow is induced by a deliberate levee breach or through an emergency side channel spillway generating disturbances that reflect on the banks of the channel further complicating the wave pattern. An adjoint sensitivity method based on the 2D shallow-water equations is presented to aid in the mitigation of an extreme flooding event by identifying optimal locations and times for the selective withdrawal of flood waters. The efficiency of the method allows adaptive flood control to proceed in real time. It is shown that wave reflections from solid boundaries create a complex pattern of sensitivity waves and multiple options for control. The adjoint sensitivity results become less accurate as the magnitude and duration of the perturbation become large. However, the adjoint sensitivities provide reliable information for identifying optimal locations and times for a selective withdrawal of large magnitude and a fair indication of the spatial dependence of the objective function sensitivity to large changes in flow.