A New Framework for Flooding Control in Regulated River Systems

This thesis presents a case study on the application of a dynamic framework for the intelligent control of flooding in the Boise River system in Idaho. This framework couples a robust and numerically efficient hydraulic routing approach with the popular multi-objective, non-dominated Sorting Genetic Algorithm II (NSGA-II). The novelty of this framework is that it allows for controlled flooding when the conveyance capacity of the river system is exceeded or is about to exceed. Controlled flooding is based on weight factors assigned to each reach of the system depending on the amount of damage that would occur should a flood occur. For example, an urban setting would receive a higher weight factor than a rural or agricultural area. The weight factor for a reach doesn’t need to be constant as it can be made a function of the flooding volume (or water stage) in the reach. The optimization algorithm minimizes flood damage by favoring low weighted floodplain areas (e.g., rural areas) rather than high weighted areas (e.g., urban areas) for the overbank flows. The proposed framework has the potential to improve water management and use of flood-prone areas in river systems, especially of those systems subjected to frequent flooding. The Hydraulic Performance Graph (HPG) of a channel reach graphically summarizes the dynamic relation between the flow through and the stages at the ends of the reach under gradually varied flow (GVF) conditions, while the Volume Performance Graph (VPG) summarizes the corresponding storage. The Rating Performance Graph (RPG) summarizes the dynamic relation between the flow through and the stages at the ends of the in-line structure under gradually varied flow or rapidly varied flow conditions. The use of HPGs, VPGs, and RPGs in the proposed approach results in a robust and numerically efficient model because the hydraulics for all river reaches are pre-computed (i.e., any error attained during the computation of the water profiles for each reach-e.g., due to instability-can be detected and therefore corrected before the river system routing) and most of the computations for the system routing involve only interpolation steps. The latter makes this approach highly numerically efficient. The proposed framework is the first model of its kind that uses the HPG/VPG/RPG approach for intelligent control of river flooding and has been applied to the Boise River system of Idaho. In order to test the hydraulic routing approach, a model for unsteady flow routing through dendritic and looped river networks based on performance graphs is presented in this thesis. The application presented in this thesis is limited to subcritical flows; however, it can be extended to supercritical flows. The model builds upon the application of Hydraulic Performance Graph (HPG) to unsteady flow routing introduced by [12] and adopts the Volume Performance Graph (VPG) introduced by [16]. The HPG of a channel reach graphically summarizes the dynamic relation between the flow through and the stages at the ends of the reach under gradually varied flow (GVF) conditions, while the VPG summarizes the corresponding storage. Both, the HPG and VPG are unique to a channel reach with a given geometry and roughness, and can be computed decoupled from unsteady boundary conditions by solving the GVF equation for all feasible conditions in the reach. Hence, in the proposed approach, the performance graphs can be used for different boundary conditions without the need to recompute them. Previous models based on the performance graph concept were formulated for routing through single channels or channels in series. The new approach expands on the use of HPG/VPGs and adds the use of rating performance graphs for unsteady flow routing in dentritic and looped networks. We exemplify the applicability of the proposed model to a looped network and contrast its simulation results with those from the well-known unsteady HEC-RAS model. Our results show that the present extension of application of the HPG/VPGs appears to inherit the robustness of the HPG routing approach in [12]