The influence of soil physical and chemical characteristics on gully development in Nyakach, Kisumu district- Kenya
2003
waruru, B.K.(Kenya Soil Survey, Nairobi, Kenya) | Wanjogu, S.N.(Kenya Soil Survey, Nairobi, Kenya)
Parts of Nyakach division, Kisumu district are seriously affected by severe gully erosion. The soils parent materials are lacustrine and colluviam or alluviam materials deposited in different erosion/depositional episodes resulting in stratified profiles. Stratification has occasioned unstable profiles especially in the deeper subsoils ( 200 em depth). Given the enormous material available for removal, gully advancement has progressed unabated. Headward erosion Ibrough undercutting, slumping and material removal has resulted in gullies 5-10 m deep, 3-7 m wide and 3-5 km long. The objective of this study was to evaluate the influence of some selected soil physical and chemical parameters on gully development and advancement in the area in ocder to provide additional information useful in designing rehabilitation and conservation lhUres appropriate in this area. Soil sampling was done for physical and chemical analysis from selected sites on a longitudinal transect along a gully channel. Results from this study indicate that major parameters that are active include the presence of free carbonates, exchangeable sodium, particle size distribution and the predominance of shrink-swell 2: 1 lattice clays, while processes include tectonic earth movements, soil stratification, and piping. Exchangeable sodium and its consequences on structural stability, parent materials and Tertiary lectooic movements were found to have had a major influence on the development of gullies in !he study area. Once triggered by rainfall, the gullies have sustained their development through cracking, undercutting, slumping, collapsing and crumbling under their own weights. The study also shows that piping phenomena is an important erosional process which has accompanied and fllhanced gully erosion in the area.
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