Effect of Vegetation Cover on Runoff and Soil Loss in Akiriamet-Kimpur Catchment, West Pokot County, Kenya
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Climate and soil characteristics contribute to development of sparse vegetation cover in semi-arid areas. It is recognized that total annual rainfall experienced in such environment is low. However, it is quite infrequent and often erratic causing occurrence of massive runoff. Existing soil and vegetation characteristics favour erosion and movement of large loads of sediment in runoff leading to substantial soil loss. There is need for assessment of environmental factors which influence soil erosion in these areas in order to develop soil conservation policies for proper soil resource management and land use planning. This study aimed at establishing the effect of vegetation cover on runoff and sediment production in Akiriamet-Kimpur catchment. In particular, the study sought to determine the volume of runoff and quantity of sediment generated from runoff plots under natural vegetation cover and rainfall characteristics. Erosion plot experiment was set up based on quasi experimental research design. Two 20m long by 10m wide runoff plots were constructed on gentle slopes, 1.5–2.0% slope grade. Vegetation cover on the soil was measured using the transect line-intercept survey method. The first plot had 25–50% vegetation cover and the second plot had 50–75% vegetation cover. Each plot was replicated twice. Runoff and sediment generated from the plots were collected in cubical tanks at the base of each plot, measured and recorded for fifteen rainfall events during the long rains season. A standard rain gauge was used to measure rainfall. Data was analysed using correlation analysis and linear regression methods. The findings were presented in tables and graphs. The results show that runoff production varied from 1.03% to 1.44% of total rain water. Soil loss was 120.3–155.55 g/m2. Runoff-rainfall correlation analysis showed a significant positive relationship (r =0.9609). Percentage variance in runoff generation (r2) was 92.33%, P<0.05%). Soil loss had significant positive relationship with runoff (r =0.9840). Percentage variance in soil loss (r2) was 96.83%, P<0.05%. The study established that runoff production and soil loss is slow under dense vegetation cover. Hence, the study recommends planting more trees and protection of existing natural vegetation in the study area in order to improve plant cover on the soils. It also recommends development of a soil conservation and management strategy in the study area.