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This paper describes a simple, physically-based conceptual model utilizing watershed drainage characteristics for rainfall-runoff simulation. This conceptual physiographic model is essentially based on the work of Najafi (2003), which has led to a model compris-ing the main tributary subwatersheds and a single main channel subwatershed. The Ki-nematic Wave (KW) theory is used to describe flow over the subwatershed plans. The dy-namic wave theory is applied for channel flow computations to compute the watershed re-sponses at the outlet. The proposed model was tested on a natural watershed where the results could be compared with the results obtained by Najafi (2003). The results show the proposed physiographic model has advantages over the former in terms of mathematical formulation and input data preparation as well as computation time requirements.

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In this paper, the dam break phenomena has been simulated in curved rivers using 3D numerical model, Flow-3D. It utilizes the finite volume scheme for structured meshes was used for solving the unsteady Reynolds-averaged Navier-Stokes equations in conjunction with the RNG k-ε closure model. In the utilized software, the Fractional Area/Volume Obstacle Representation (FAVOR) method is used to inspect the geometry in the finite volume mesh. FAVOR appoints the obstacles in a calculation cell with a factional value between 0 to 1 as obstacle fills in the cell. Fluid surface shape is illustrated by volume-of-fluid (VOF) function F(x,y,z,t). With the VOF method, grid cells are classified as empty, full, or partially filled with fluid. Cells are allocated in the fluid fraction varying from zero to one, depending on fluid quantity. The pressure and velocity are coupled implicitly by using the time-advanced pressures and time-advanced velocities in the momentum and continuity equations, respectively. FLOW3D solves these semi-implicit equations iteratively using relaxation techniques. In this paper the GMRES technique has been used as pressure implicit solver. A flux surface is a diagnostic feature in FLOW-3D for computing fluid flow rates. It can be used to obtain time-dependent information about the flow in different parts of the domain. A typical flux surface is a 100% porous baffle with no flow losses, so it does not affect the flow in any way. This feature gives the opportunity to determine the flood hydrograph at various stations downstream of the dam. Effects of curve angle and radious of curvature on the flood wave propagation and unsteady flow features along the curved reach, downstream of the dam has been investigated. Results showed that at the initial instants of the dam break in the straight channel, due to the effects of the dynamic wave, flood hydrographs at the dam location and at a distance downstream of the dam have local peak values, while in the curved chnnel cases, the flood wave becomes unstable immediately after the dam break and the local peak occures just at the dam section. The curved reach decelerate the flood wave propagation compared to the straight channel. Effect of channel curvature on the movement of the flood wave along the inner bank is higher than the outer bank and also the centerline of the curved channel. By decreasing the central radious of the bend, slope of the rising limb of the hydrograph and also the peak discharge, attenuates. Furthermore, the peak discharge time reduces. Unlike to effects of the curvature of the bend, increasing the bend angle does not affect the peak discharge. Changing the bend curvature and curve angle has no effect on the falling limb of the flood hydrograph at various stations downstream of the dam.