INFLUENCE OF LAND USE ACTIVITIES ON GEOMORPHIC PROCESSES IN RUPINGAZI WATERSHED, EMBU COUNTY, KENYA

Abstract

Landforms are part of every part of the earth. The study aimed at finding ways by which land use activities contribute substances which effectively influence changes in landform along the Rupingazi watershed in Embu County, Kenya. The main objectives of this study were to assess the influence of agriculture, urban settlements, mining and abstractive activities on landform dynamism in the context of geomorphic parameters of denudation, and to determine their impacts. This was done by considering geomorphic processes such as weathering, erosion, deposition and mass movement. The study was guided by the theoretical framework of the nine-unit slope model suggested by Doornkamp and King; that an initial landform in a climatic and geological region evolves through geomorphic dynamism on varying slope forms. From this notion, the conceptual framework was developed on the assumption that the same denudational processes are operational on Rupingazi watershed and form the relevant variables: Crop farming, livestock rearing, urban settlements, abstractive and mining activities were the independent variables; climate and rocks as the intervening while the geomorphic processes were the dependent variables. Applied Research design, both quantitative and descriptive was adopted for the study. Data was collected from 21 sampling stations (SS) fixed through stratified systematic point sampling. Observations and field measurements on various land uses were used to obtain data. Satellite data and images were also used to compare with field observations. In addition, water and soil samples were collected for further analysis to corroborate field observations. The soil samples were tested for soil pH, porosity, organic contents and main chemical elements. Farming practices influenced geomorphic processes in that there was a very strong positive correlation (coefficient of 0.91) between the angle of farm slope and the distance of soil moved downslope when tilling. On average soils moved the furthest (123 cm) when tilling was done on farms with slope of 260 while tilling on farms with a slope of 6 0 caused soil to move by about 70 cm. Further, use of hand hoe moved about 800 kgs of soils materials in one season per acre. An African mole rat (mainly found where there was farming of napier grass and sweet potatoes) loosened about three kilograms of soil materials. On less steep paths (8 0 ), 1.8 m3 of soil was moved while 9.36 m3 of soil materials on slopes of about 220 was moved as result of livestock. All urban centers are located less than three kilometers from the Rupingazi river. Organic and solid wastes associated with urban settlements were found in sampled waters of the Rupingazi river. An increase of 50% of PO4 and NO3 was observed in sampled waters. The Mg was no increases by 92.3%. Surface run off from these settlements accelerated the impact of erosion and weathering. More than three quarters (76.7%) of the abstractive activities are in the lower reach of the River Rupingazi between SS 16 and 21. Mining and abstractive activities breakdown rocks, thereby accelerating geomorphic processes. Regolith development on any slope plays an important role in the slope evolution because it affects such bedrock characteristics as the strata dip (angle and direction) rock joints, and the effect on the weathering rates and amounts. The study recommends concerted effort and environmental education to control human activities along the watershed to ensure the landform equilibrium in the Rupingazi watershed. Further studies can be carried out to examine and determine the influence ecological zones on the geomorphic processes.