The effect of constructed structures on time of concentration (Case study: Izeh watershed)

Estimating the time of concentration is one of the most important concepts in physiographic and hydrologic studies in watersheds, and relatively correct estimation of it greatly influences calculation of hydrologic parameters, especially flood peak discharge. Construction of check dams in watersheds leading to residential areas is one of the strategies for changing time of concentration and reducing channel slope, which are substantially effective in controlling floods and reducing flood peak discharge. This research intended to evaluate the effects of corrective structures on hydrologic behavior of watersheds based on flood index. In this study Changes in time of concentration and flood discharge were compared between 1384-1389 years from construction of corrective structures by studying the region, topographic conditions, and protective measures. The return period between 1.25 to 100 years was selected. The parameters of the numbers and heights of the check dams, hydrologic soil groups, channel slopes, time of concentration, regional hydrology, and area of each watershed parcel were studied for this comparison. Results indicated that construction of corrective structures increased time of concentration in I28, I13, I12, I10, I9, I8, I6, I4 parcels amount of 4,8.74,2.68,1.43,1.31,2.01, 0.51 and 11.78 respectively. The lowest percentage increase in the concentration of Parcel No. I13 with a 1 percent. The maximum time to focus on I28, with 11.78 percent.