Active Flood Hazard Mitigation.?I: Bidirectional Wave Control

Active mitigation of unimodal flood waves is achieved by selective lateral flow withdrawal. This is shown to create depression waves that reduce the impact of hazardous flood waves in rivers. Lateral outflow is induced by a deliberate levee breach or through an emergency side channel spillway generating bidirectional wave action in the main channel. An adjoint sensitivity method founded on 1D shallow-water equations is used to identify the optimal locations and timing for the lateral outflow. The efficiency of the adjoint sensitivity method allows flood hazards to be mitigated in real time by rapidly providing the flow sensitivity to changes in lateral outflow. The spatial and temporal coordinates associated with the peak values of the sensitivities are examined as indicators of optimal locations and timing for active control. The sensitivities are found to be good indicators of optimal control points even in cases where the magnitude and duration of the lateral outflow exceeds the small perturbation assumption.