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Ranking source areas at sub-watershed outlet will be needed for on-site erosion control. Sub-watershed ranking based on SSY-S can be effectively used in decision making for priority management of critical areas that require conservation measures. Therefore, as can be seen from Table 5, sub-watershed 22 is a critical area in respect of soil degradation, soil compaction, nutrient depletion, loss of soil organic matter, poor seedling emergence, and reduced crop yields. On the other hand, sub-watersheds 25 and 41 produce the lowest SSY-S. Analysis of sub-watershed soil and land cover maps clearly indicates that the first rank of sub-watersheds in soil erosion and sediment yield has clay loam texture and with low vegetation cover. Soils differ in their susceptibility to erosion (erodibility) based on texture; a soil with a high percentage of silt and clay particles has a greater erodibility than other soils under the same conditions. This implies that the amount of clay loam texture soils in the watershed positively affects the soil erosion and therefore, sediment load at watershed outlet. Saghafian et al. (2015) found a relationship between sub-watersheds' ranking based on sediment load and the clay loam contents in their soils. Also, landuse and land cover (LULC) have significant impacts on the generation of runoff, forms of water fluxes, and soil erosion and sediment transport to water bodies. The results showed that with expansion of the low density rangelands in sub-watersheds, the value of the sediment yield index has been increased.

Table 5

Runoff and sediment yield at sub-watershed outlet

Sub-watershedArea (ha)Area (%)Ranking SSY-SRanking SY-WRanking SSY-W
1,564.5 1.75 22 26 26 
2,471.0 2.75 25 16 22 
2,369.2 2.64 12 13 
2,026.4 2.26 18 22 25 
1,980.2 2.20 15 19 18 
829.0 0.92 19 27 
7,276.2 8.11 14 
200.0 0.22 24 37 16 
5,944.2 6.63 16 35 
10 66.3 0.07 38 40 11 
11 2,574.2 2.87 
12 971.2 1.08 17 28 19 
13 2,650.6 2.95 
14 6,138.6 6.84 13 31 
15 4,828.7 5.38 21 13 36 
16 1,331.6 1.48 12 
17 114.3 0.13 38 
18 8.7 0.01 37 41 
19 348.8 0.39 36 36 30 
20 324.1 0.36 31 
21 2,576.4 2.87 20 18 27 
22 3,701.4 4.13 
23 2,490.6 2.78 27 11 12 
24 764.8 0.85 31 33 32 
25 491.7 0.55 39 35 39 
26 3,091.7 3.45 
27 2,304.8 2.57 33 15 17 
28 156.3 0.17 40 39 37 
29 312.7 0.35 23 34 20 
30 1,515.6 1.69 30 32 41 
31 1,563.3 1.74 14 17 10 
32 1,457.1 1.62 10 29 33 
33 5,633.0 6.28 28 21 
34 2,467.1 2.75 35 20 28 
35 1,948.2 2.17 34 30 40 
36 2,799.9 3.12 26 14 23 
37 1,503.2 1.68 29 25 24 
38 2,736.2 3.05 32 23 34 
39 2,640.2 2.94 11 10 15 
40 2,643.8 2.95 21 29 
41 2,896.4 3.23 41 24 38 
Sub-watershedArea (ha)Area (%)Ranking SSY-SRanking SY-WRanking SSY-W
1,564.5 1.75 22 26 26 
2,471.0 2.75 25 16 22 
2,369.2 2.64 12 13 
2,026.4 2.26 18 22 25 
1,980.2 2.20 15 19 18 
829.0 0.92 19 27 
7,276.2 8.11 14 
200.0 0.22 24 37 16 
5,944.2 6.63 16 35 
10 66.3 0.07 38 40 11 
11 2,574.2 2.87 
12 971.2 1.08 17 28 19 
13 2,650.6 2.95 
14 6,138.6 6.84 13 31 
15 4,828.7 5.38 21 13 36 
16 1,331.6 1.48 12 
17 114.3 0.13 38 
18 8.7 0.01 37 41 
19 348.8 0.39 36 36 30 
20 324.1 0.36 31 
21 2,576.4 2.87 20 18 27 
22 3,701.4 4.13 
23 2,490.6 2.78 27 11 12 
24 764.8 0.85 31 33 32 
25 491.7 0.55 39 35 39 
26 3,091.7 3.45 
27 2,304.8 2.57 33 15 17 
28 156.3 0.17 40 39 37 
29 312.7 0.35 23 34 20 
30 1,515.6 1.69 30 32 41 
31 1,563.3 1.74 14 17 10 
32 1,457.1 1.62 10 29 33 
33 5,633.0 6.28 28 21 
34 2,467.1 2.75 35 20 28 
35 1,948.2 2.17 34 30 40 
36 2,799.9 3.12 26 14 23 
37 1,503.2 1.68 29 25 24 
38 2,736.2 3.05 32 23 34 
39 2,640.2 2.94 11 10 15 
40 2,643.8 2.95 21 29 
41 2,896.4 3.23 41 24 38 

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