Evaluating Detention Dam Construction Priority in Tajrish Watershed

Determination of detention dam construction priority is important for selection of optimized method of time schedule for the construction. Since Tajrish watershed is in upstream of populous city of Tehran, its flood control is very important. It is necessary that detention dam priority indices be evaluated for studying the effect of flood control structure construction time scheduling. Therefore, the watershed flood has been simulated using HEC-HMS model and it has been calibrated by recorded rainfall and flood data. The 200 year-return-period flood was used to optimize the outlet of detention dam in according to the recommended water standard of Iran. In this paper, different indices are studied for determining detention dam priority, as follow: area, peak discharge, specific peak discharge, peak discharge reduction percentage due to omitting of a sub basin runoff (FI), specific peak discharge reduction percentage due to omitting of a sub basin runoff (fi), peak discharge reduction due to operation of a detention basin in a sub basin (Fm), specific peak discharge reduction due to operation of a detention basin in a sub basin (fm), total cost and unit flood reduction cost(ΔQC). The detention dam construction priorities have been determined using these indices. Fm and fm are new priority indices proposed in this paper. Furthermore unit flood reduction cost (ΔQC) index was used to rank priority indices. The results show that fm index has the minimum sum of absolute priorities differences (PIMC) with standard index (ΔQC) and the cost index has been the maximum one. fm and cost indices have PIMC equal to 6 and 80, respectively. So, they are the best and the worst indices, respectively.