Effect of check dams on reduction of flood peak (Case study: Manshad watershed)

Watershed management structures are expensive projects that are built with purposes of erosion and sediment reduction and flood control in watersheds. Quantitative assessment of watershed management activities in order to analyze their impacts and making basic decision for implementation of these activities are necessary. As building any structure on bed of dry rivers can affect on river behavior، then، this research was done with aim of investigating the effect of check dams on flooding in Manshad watershed. Therefore، the HEC-HMS model was used for comparison of discharge variations with/without checkdams construction. To determine the effects of check dams، the concentration time (after building the structures) was computed and by changing the input parameters، the flood behavior was simulated. Moreover، model was validated and calibrated by six observed event and flood hydrograph was simulated for return periods of 2 to 100 years before and after the structures operation. To evaluate the effect of checkdams on flooding، the peak discharge and flood volume indices were determined for two conditions (before and after the structures operation). Based on the simulation results، the effect of structures on reduction of peak discharge and flood volume were 9. 82 and 7. 75%، respectively. On the other hand، by increasing the return period of flood، the structures effects on the reduction of peak discharge and flood volume have been decreased as the rate of variations in return periods of 2 to 100 years have been 14. 14 till 6. 95.