Because river flooding and urban inundation due to extreme rainfall cause the severe damages on the infrastructure, it is necessary to develop an accurate prediction technique and to overcome the disasters. In this study, numerical simulation method was applied to predict urban inundation area with appropriate assumptions and hydrological data in the Lower Var valley region in France. The application site is located in the southeast of France and also geometrically complex with several hydraulic structures, such as weir and bridge piers from the mainstream of a river to the Mediterranean Sea. With complex geometrical consideration, numerical modelling of inundation was conducted separately with two steps. Firstly, the whole area of river reach with the urban area was simulated and analyzed. From the results, the smaller urbanized area was specified with consideration of the capacity of inundation. Two-dimensional hydrodynamic model, MIKE 21 FM (flow model) is applicable to simulations of river hydraulics and flood inundation including the urbanized properties. Upstream discharges for the boundary conditions were set up with based on the Gumbel distribution and SCHADEX method. From the numerical simulation, inundation area and river flow variation were analyzed and compared with respect to the upstream discharge scenarios. Furthermore, the effect of computational mesh resolution was analyzed with the urban model. Calculated flooded areas from the simulation results of the whole area model and urbanized models were compared and verified as a newly proposed and applied procedure of inundation analysis in the riverine area.

The flow around a single circular cylinder with splitter plate was investigated using Computational Fluid Dynamics. The present study investigated the effects of varying splitter plate length and the Reynolds numbers on flow characteristic, such as vortex shedding, drag force, lift force, separation point, pressure, and friction coefficients of the cylinder. It was revealed that the vortex shedding behind cylinder is completely suppressed when the splitter plate length is longer than the critical value, which is proportional to the Reynolds number. The variation of drag and lift coefficients with respect to splitter length can be classified into two patterns of a monotonic decrease and a general decrease but with small increase. We found that the first pattern occurs at Reynolds number ≤ 180 and higher Reynolds number gives the second pattern. When the splitter plate length is similar to the diameter of the cylinder, the vortex frequency, drag, and lift coefficients reach local minimum depending on the Reynolds number. A functional relationship between drag coefficient, length of splitter plate, and Reynolds number was determined.

The Soil and Water Assessment Tool 2012 (SWAT2012) offers four sediment routing methods as optional alternatives to the default simplified Bagnold method. Previous studies compared only one of these alternative sediment routing methods with the default method. The proposed study evaluated the impacts of all four alternative sediment transport methods on sediment predictions: the modified Bagnold equation, the Kodoatie equation, the Molinas and Wu equation, and the Yang equation. The Arroyo Colorado Watershed, Texas, USA, was first calibrated for daily flow. The sediment parameters were then calibrated to monthly sediment loads, using each of the four sediment routing equations. An automatic calibration tool—Integrated Parameter Estimation and Uncertainty Analysis Tool (IPEAT)—was used to fit model parameters. The four sediment routing equations yielded substantially different sediment sources and sinks. The Yang equation performed best, followed by Kodoatie, Bagnold, and Molinas and Wu equations, according to greater model goodness-of-fit (represented by higher Nash–Sutcliffe Efficiency coefficient and percent bias closer to 0) as well as lower model uncertainty (represented by inclusion of observed data within 95% confidence interval). Since the default method (Bagnold) does not guarantee the best results, modelers should carefully evaluate the selection of alternative methods before conducting relevant studies or engineering projects.

Local scour occurs around hydraulic structures such as piers, bed protections, and dikes. In this study, the turbulent flow around a scour hole downstream of a fixed bed protection was investigated. Numerical modeling with OpenFOAM was applied to compute the flow velocity and turbulent kinetic energy with respect to flow conditions by changing water depth. A proper computational grid size and time step for simulations are suggested. Three typical turbulent models, $k-\epsilon$ , $k-\omega$ , and $k-\omega SST$ , were considered for simulating the flow around a scour hole. The performances of the three models were evaluated by comparing them with numerical and laboratory experimental results. Mean flow velocity profiles computed by the three turbulent schemes are generally in good agreement with laboratory measurements. However, $k-\omega$ has a limitation in simulating reversal flow in the scour hole, and the $k-\epsilon$ model does not predict turbulent kinetic energy well near the bottom. Thus, this study found that the most suitable turbulent model for simulating flow around a scour hole downstream of a fixed bed protection is the $k-\omega SST$ model.

Considering fundamental hydraulics, fluid dynamics, and experimental analysis should be analyzed simultaneously with mathematical methods due to the effects of hydraulic properties such as meandering form, sediment, and so on. In this research, to reveal the effects of hydraulic characteristics and longitudinal and transverse coefficients based on the two-dimensional advection-dispersion equation, a laboratory experimental channel has been conducted and analyzed. Additionally, results of experiments have been compared with horizontal two dimensional distributions of flow velocity and concentration fields with respect to the water depth and inlet discharge using two-dimensional depth-averaged numerical models based on FEM (Finite Element Method). SMS and RAMS have been applied with the same experimental conditions and compared. From the analysis of velocity profiles, primary and secondary flows have been visualized. Also the result of pollutant clouds illustrated from the results of tracer tests with an instantaneous and centered injection of solute transport, separation, superposition and stagnation could be deduced outwards of two meandering sections. And same types of characteristics of velocity and pollutant transport could be defined with two-dimensional numerical models.

Local scour at the downstream of the river bed protection is one of the most important parameters for the design criteria and sustainable management of the hydraulic structures. Previously, various researches on its process in the equilibrium state have been suggested with experimental and numerical approaches. In this study, relatively long-term laboratory experiments of local scouring at the downstream of fixed bed in an open channel were conducted with mono-granular sediment bed and analyzed about maximum scour depth and its temporal development. In particular, we conducted experiments with relatively low Froude number (less than 0.5) and their duration of tests was exceeded over 700 hours. We modified the relationship between the dimensionless time and length scales of the maximum scour depth of the local scour hole based on the turbulent shear layer thickness. A new functional relationship between dominant factors and the maximum scour depth in the equilibrium state were suggested and compared with previously suggested formula. Also, from the results by nonlinear regression, Froude number was founded as a dominant factor on the prediction of equilibrium maximum scour depth.