| چکیده انگلیسی مقاله |
Recently, inappropriate land and water resources in watersheds increased surface runoff and soil erosion and decreased the infiltration rate and groundwater level. Eroding fertile upstream soil causes sedimentation downstream of the rivers. Watershed management projects are prepared and implemented to ensure soil and water conservation, flood control, and reducing their destructive consequences. Evaluation of watershed management projects is essential to identify their effects and make the optimum decisions in various conditions. In the present study, the effectiveness of watershed management measures was carried out in the Nekarood Watershed, Northern Iran. The watershed with a total area of 121046.32 ha has 15 sub-watersheds, six of which were studied in detail. Different types of mechanical projects, including 44 stone-mortar check dams, nine sidewalls, and one branch strap dam, have been implemented during 2005-2020. The results showed that 72.4% of the structures are stable, 22.2% need to be repaired, and 5.6% have been destroyed. Some 75% of the volume of check dam reservoirs was filled with sediments, and 3.4% of the volume of constructed structures is filled with sediments, which implicitly indicates the high sediment trap efficiency of the structures. Determination of peak flood discharge using the precipitation-runoff model showed that peak flood discharge has significantly decreased after watershed management measures in all studied sub-watersheds. In order to evaluate the stored water through applying biological projects in each sub-watershed, the SCS method was used. The results approved a significant decrease in runoff control after the implementation of biological projects. The results also showed that the specific erosion rate in six studied sub-watersheds with erosion-sensitive formations before watershed management measures varied between 804.75 and 921.10 m3 km-2, while it ranged from 754.17 to 843.73 m3 km-2 after watershed management measures. This decrease can be attributed to reducing peak flood discharge, increasing runoff time of concentration, and decreasing erosion intensity coefficient. |
