Investigation of the Effects of Land use Change on Flooding and Sedimentation In Honifaqan Watershed

In a natural ecosystem, land exploitation and change in environmental conditions, particularly changes in vegetation and land use effects on hydrological responses such as floods and erosion and sediment and ultimately causing heavy social-economic losses. Then, prediction of effect of land use changes on flood situation in the future decades and sedimentation of watersheds will be the way to deal with this phenomenon. To simulate the hydrological behavior in future decades, HEC-HMS model was calibrated and validated for the previous period, with changes in curve number and percentage of impermeability (as a result of land use changes). Then, predicted hydrograph for coming decades (2020, 2025 and 2030) and last (2004) were compared. The results show that the peak discharge and flood volume in the 2020, 2025 and 2030, will be increased in compared to the decade of 2004 equal to (52.8 and 20/41), (70.29 and 32.51) and (87.78 and 38.05), respectively will increase. Mean peak in the 2020, 2025 and 2030 will be increase (due to land use change), 16, 25 and 38.35 percent, respectively. In the next step, sediment changes in the future was investigated using the sediment rating curve in decades of 2020, 2025 and 2030. The results showed that the amount of sediment for 2020 will be increase 12.01 % compare to 2004, for 2025 compare to 2020, 15.14 % and for 2030 compare to 2025, 36.64 %. According to the results, land use change in future leads to increase in discharge and sediment, which could affect the hydrological and morphological conditions of watershed.