INVESTIGATION OF SOME FACTORS RESPONSIBLE FOR GULLY EROSION ACTIVITIES ALONG RIVER YASHI, MINNA, NORTH-CENTRAL NIGERIA

Abstract

Investigation of some factors contributing to the propagation of gully erosion along River Yashi, Minna, North-Central Nigeria has been conducted. Field observations of anthropogenic factors and geotechnical properties of soil along River Yashi were determined. The anthropogenic factors observed to contribute to the gully growth include soil excavation along the river bank and on the river bed, building on the flood plain and farm practices. Geotechnical field index properties of soil were determined followed by some laboratory index and performance tests. The outcome of the investigation indicated that; the natural moisture content varies from 8.49 to 18.21% with an average of 12.93%; the uncompacted bulk density (UBD) is between 0.98 to 1.23kg/m3 with an average of 1.10kg/m3 and the compacted bulk density (CBD) is from 1.27 to 1.52kg/m3 with an average of 1.38kg/m3; the specific gravity varies through 2.15 to 2.68 and an average of 2.35; the sieve analysis result shows that coefficient of uniformity (Cu) is from 0 to 20.45 with an average of 7.63 while coefficient of curvature (Cc) is from 0 to 1.01 with an average of 0.64; the plasticity index extend from 0 to 5.63% while the average is 5.54%; the compaction result shows that the optimum moisture content (OMC) varies from 9.90 to 12.39% with an average of 11.39% while the maximum dry density (MDD) ranges from 2.14 to 2.42mg/m3 with an average of 2.28mg/m3; the triaxial shear test result shows that the angle of internal friction (AF) is from 60 to 110 with an average of 9° and the cohesion (C) is from 19 to 32kg/m2 with an average of 26.33kg/m2; The permeability ranges from 1.93 × 10-3 to 2.49 × 10-3cm/sec and the average is 2.14 × 10-3. The results of geotechnical tests show favourable soil condition for gully erosion growth. Slope stability, construction of rip-rap with weeping holes, cultural or vegetation method among others has been suggested as control measures.