SOIL EROSION PROCESSES AND CONTROL ON RURAL ROADS IN MT. ELGON SUB-COUNTY, TRANS NZOIA AND WEST POKOT COUNTIES, KENYA

Abstract

Roads are essential component to the counties’ economy; they are key agents of economies to thrive, good and well maintained roads imply great and successful economies. Low volume rural roads are facing great challenge and highly deteriorating due to anthropogenic and climatic factors. Low volume rural roads were studied in three varied climatic zones in three counties of western Kenya. The study was carried out to assess the management and the current state of rural roads (Class D and E) in Mt. Elgon Sub County (in Bungoma County), Trans Nzoia and West Pokot counties. Soil loss and deposition on the rural roads, surface runoff rates were determined and the state of soil erosion control works were assessed. Potential areas vulnerable to soil erosion were identified. Catchment characteristics were calculated using Cooks method and the runoff rates coefficient obtained to determine the runoff rates in m3/s. Classification of soils’ drainage potential and soil types in the study areas was determined by using soil data obtained from International Livestock Research Institute. Terrain data was obtained from Shuttle Relief Topography Mission which was used to determine gradients using ARCGIS. Soil movement and deposition was analysed and it was observed that a greater change occurred in the months of November and December 2013 with a deposition change of 11.1 cm compared to 8.80cm for the month of January and February 2014. Highest rate of erosion was recorded at -10.1cm in the rainy months and -6.64 cm in dry months. Total soil volume movement in three months was 8309.75 cm3 where Mt. Elgon Sub County exhibited the highest change of 3284 cm3 .Terrain (gentle/flat and undulating) for West Pokot and Trans Nzoia (Sibanga) roads had a negative correlation while Mt. Elgon (hilly, mountainous and gentle) and Tans Nzoia-Sikulu (gentle/flat) roads had a positive correlation of r=0.530 and r=0.032, respectively. The runoff rates at Mt. Elgon were the highest at 3.7 m3/s, while the mean runoff rate was 1m3/s .Rainfall on the roads catchment ranged between 800-1600 mm3 of rain annually, and this contributed to the most likelihood of roads in upper Mt. Elgon and North of Sibanga getting more eroded than roads in the south and other roads. It was found out that 54.3% of the total road network was made up of gravel and 18.6% of it had been encroached by vegetation which distorted the camber. Culverts’ efficiency was rated at a mean of 40%. Areas most vulnerable to erosion were found to be in Mt. Elgon from 10 km -22 km stretch of the road and Sikulu-Kinyoro road bordering Kapsara tea factory. The research therefore draws recommendations to improve and enhance the management of roads by discouraging road reserve cultivation and creation of cut off drains on upper Mt. Elgon and Sibanga roads, the use of GIS in soil modelling is critical for engineers to avoid vulnerable and unstable areas of the roads.