Evaluating the effect of formation of flow pattern on the outflow hydrograph in the HEC-HMS simulator (case study: Roudzard basin)

Achieving basin runoff estimation requires a more realistic simulation of the precipitation process. Simulation closer to the reality of the process has always been the goal of the researchers. How the first starting point of runoff at the basin level is, leads to different patterns, therefore, is effective in the accuracy of the process simulation. The lagged pattern of flow formation in the catchment area, due to the assumption of the formation of the flow from the center of the surface, is closer to the current flow reality than the conventional pattern in simulation, such as HEC-HMS. The present study was designed to evaluate the latent pattern in the catchment area of the Roudzard River, comparing it with the conventional model in the HEC-HMS simulator. The results showed that the lagged pattern, in contrast to the conventional model, increased the number of parameters for the three rainfall events, the values of the Nash and PWRMS were 0.13, -37.0, -0.08 and 2.49, 8.35, 6.41 respectively Which had a lower accuracy in comparison with the values of them such as 0.57, 0.68, 0.43 and 1.03, 6.96, 3.87 in the conventional pattern. However, sensitivity analysis of the parameters indicated the type of pattern is different in the relative sensitivity of the parameters. As in the delay pattern, the K parameter is more sensitive than the conventional pattern compared to the CN parameter. Comparison of two selected patterns in estimating flood volume showed that the delay pattern has a better performance than conventional pattern.