effect of check dams on time of concentration and reduction of flood peak (case study: gash watershed)

check dams, are small dams in the watershed. these dams are constructed in susceptible areas to erosion due to reduce of flow velocity and erosion, control of sediment and flood in upstream of reservoir dams. these structures are made using wood, stone and cement, and gabion. these structures change the hydrological response of the watershed by reducing flow velocity, the channel slope and storage of flow. analyzed the effects of these dams before making can be deciding on the correct and efficient implementation of the project as well as better management in order to achieve various objectives effectively. since the constructions of these dams are effective on flood behavior, this research aims to impact of check dams on time of concentration and reduction of flood peak discharge in the gash watershed. in this research are used from puls method for flood routing in reservoir and muskingum method for flood routing in river due to evaluate the impact of dams, and also flood hydrograph with 25 to 100 year return period was simulated the situation before and after construction of dams. the results showed that the proposed check dams are reduced peak of flow between 75 to 97 percent and flood volume from 73 to 98 percent that shows the positive effects of the construction of these dams in reducing the peak of flow and flood volume. in addition, in different return period with increasing peak of flow and flood volume, reservoir role in reducing peak of flood discharge and flood volume will be decreased. also time of concentration will be increased between 0.26 to 0.98 hours by construction of check dams.