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Abstract: This study aims to develop a simulation-based optimization model applicable to mitigate hazardous floods in storm events in a watershed which consists of a complex channel network and irregular topography. A well-established model, CCHE1D, is used as the simulation model to predict water stages and discharges of unsteady flood flows in a channel network, in which irregular (i.e. non-rectangular and non-prismatic) cross-sections are taken into account. Based on the variational principle, the adjoint equations are derived from the nonlinear hydrodynamic equations of CCHE1D, which are to establish a unique relationship between flood control variables and hydrodynamic variables. The internal conditions at the confluence in channel network for solving the adjoint equations in a watershed are obtained. An implicit numerical scheme (i.e. Preissman’s scheme) is implemented for discretizing and solving the adjoint equations with the derived internal conditions and boundary conditions. The applicability of this integrated optimization model is demonstrated by searching for the optimal diversion hydrographs for withdrawing flood waters through a single floodgate and multiple floodgates into detention basins. Numerical optimization results show that this integrated model is efficient and robust. It is found that the single-floodgate control leads to an unfavorable speed-up in river flow which may create extra erosions in the channel bed; and multiple-floodgates diversion control diverts less flood waters, therefore can be a cost-effective control action. This simulation-based optimization model is capable of determining the optimal schedules of diversion discharge, optimal floodgate locations, minimum capacities of flood water detention basins in rivers and watersheds. [Copyright &y& Elsevier]

A depth-integrated two-dimensional hydrodynamic and sediment transport model, CCHE2D, has been developed for analyzing free surface flows for general applications to hydraulic engineering problems. Mixed schemes of finite element method (Efficient Element Method) and finite volume method are adopted for solving momentum and continuity equations. A unique velocity correction method was developed to couple the governing equations. Pressure (free surface) field is discretized on a staggered grid. Two zero equation turbulence closure schemes: a depth averaged parabolic, a depth averaged mixing length eddy viscosity model, and a two-equation k-∈ model for depth-averaged flows are included for different application needs. Algebraic systems of equations are solved implicitly by using SIP method. This model can be used for simulating steady and unsteady near field and natural river flows with relatively shallow water depth. Validation tests for this model show good agreements between the model prediction and data of physical models and field measurements. [ABSTRACT FROM AUTHOR]

Focuses on a study which proposed a method for the prediction of a movable roughness coefficient by relating the roughness parameter. Details on the relationship of bed roughness coefficient; Parameter ranger of flume and field data used in calibration; Data collection and analysis; Results.

Abstract: This study numerically investigates effects of cutting riparian vegetation on flow characteristics by using a two-dimensional numerical model. The numerical model is based on depth-averaging the time- and volume-averaged Navier–Stokes equation with turbulent effects determined by the standard k–ε turbulence model. Drag forces exerted by the flow on vegetation are considered by adding source terms into momentum equations. In a rectangular channel and compound channel with vegetation along one side, numerical predictions show are in good agreement with those of previous studies. Five cutting scenarios, including the original, cutting along the main channel side, cutting along the bank side, alternative cutting, and reducing vegetative density, are analyzed in this study. The influences of the cutting scenarios on hydrodynamic behaviors are evaluated via numerical simulations. Simulation results suggest that cutting along the main channel side is the most effective scenario for reducing water depth and flow velocities. [Copyright &y& Elsevier]

Abstract: It was observed that in some closed inland lakes sediment transport was dominated by wind-induced currents, and the sediment resuspension was primarily driven by wind-induced waves. This paper presents the development and application of a three-dimensional numerical model for simulating cohesive sediment transport in water bodies where wind-induced currents and waves are important. In the model, the bottom shear stresses induced by currents and waves were calculated, and the processes of resuspension (erosion), deposition, settling, etc. were considered. This model was first verified by a simple test case consisting of the movement of a non-conservative tracer in a prismatic channel with uniform flow, and the model output agreed well with the analytical solution. Then it was applied to Deep Hollow Lake, a small oxbow lake in Mississippi. Simulated sediment concentrations were compared with available field observations, with generally good agreement. The transport and resuspension processes of cohesive sediment due to wind-induced current and wave in Deep Hollow Lake were also discussed. [Copyright &y& Elsevier]