THE EFFECT OF GULLY EROSION IN ILARA-MOKIN, ONDO STATE, NIGERIA

Soil erosion has been a serious concern to the formation and development of gully sites. The study was centered on the causes, effects and control to stabilize this recurrent menace. The gully classification based on shape in this study area is described in terms of V-shaped and U-shaped, the gully classification based on size ranges from medium to large gully. The findings garnered from different sites revealed that the factor that influence gully formation along the flood prone areas are the amount of heavy rainfall, the overland flow, the soil properties and also as a result of human intervention by the burning of bushes and felling of trees owing to the fact that Ilara-Mokin the study area is an agrarian community. The soil samples were subjected to laboratory and data analyses which include the Particle size analysis, liquid limit, plastic limit, direct shear test, organic matter content, exchangeable bases, soil pH and its conductivity. The uniformity index, U.I of the particle size analysis carried out revealed that the soil along the gully bed has more of coarse sand in the ratio 5:3:2 of the soil sample which hasten gully formation. The values obtained for the liquid limit and plastic limit are 27.00 and 6.67 of the soil sample which falls below the standard limit for low compression (<35) that hasten the process of gully formation. The result for direct shear shows that the soil strength is not well compacted as obtained in the experiment carried-out based on the fact that the shear stress is considered weak and subjected to failure, owing to the fact that the soil samples are cohesion less thereby causing it to be easily eroded. The result shows that soil organic matter contents on the surface of the gully erosion sites are very high with values ranges from 6.90 - 19.30. This thereby increased the extent of surface run-off encroaching deeply into the sub-soil; the cation exchangeable capacity contributes to this course as well as a result of their higher and lower concentration in the soil properties at the gully erosion sites. The gully erosion can be stemmed through the construction of checkdam, re-vegetation of trees and plants on the gully floor and side walls and also by diverting surface water above the gully head.