Effect of Exclosure on Runoff, Sediment Concentration and Soil Loss in Erosion Plots in Khamsan Representative Watershed of Kurdistan Province

Nowadays performing the watershed and rangeland management projects play the important role in water resources and soil management worldwide. Although watershed and rangeland management projects have the considerable importance as approaches to rural areas development and natural resources management, more studies have been focused on their effects on sediment and their effects on soil erosion have rarely been considered. While, knowing the integrated effectiveness of watershed and rangeland management projects is necessary for their performance analysis to achieve the project goals. The present research was therefore conducted to study the effect of exclosure on runoff volume and coefficient, sediment concentration and soil loss in erosion plots at the scale of individual rainfall events.
The present study was conducted in two treated and control sub-watersheds with exclosure treatment and under grazing with area of 107.54 and 110.15 ha in southwest respectively, in Khamsan representative watershed with an area of 4337.27 ha in south of Kurdistan Province, Iran. Three plots with dimension of 22.13 × 1.83 m were installed in each western, northern and eastern slopes for the runoff volume and coefficient, sediment concentration and soil loss measurement. The exclosure treatment was operated for installed plots in treated subwatershed from 2007. Then, all the data of runoff volume and coefficient, sediment concentration and soil loss from USLE standard plots in both control and treated sub-watersheds for 52 rainfall events over the years 2009 to 2014 were measured.
The results showed the significant (p≤0.05) decreasing effect of exclosure treatment on runoff volume, sediment concentration and soil loss in erosion plots at the scale of individual rainfall events. Finally, decreasing rates of 15.68, 6.13, 16.67, 24.37 and 21.43 % due to exclosure respectively for runoff volume and coefficient, sediment concentration, soil loss and sediment yield were observed. The variables of runoff volume, soil loss and sediment yield had statistically significant differences (p≤0.05) in treated and control sub-watersheds. The sediment concentration variable had p value of 0.058 and therefore the effect of exclosure treatment on sediment concentration was also significant (p≤0.06). In other words, the variables of runoff volume, sediment concentration, soil loss and sediment yield were significantly decreased in treated plots and sub-watershed due to exclosure.
Based on the results, it can be revealed that the exclosure treatment, because of increasing vegetation density, caused the increasing infiltration and the decreasing runoff, sediment concentration and soil loss at plot scale.