Abstract

This study attempts to derive the Digital Elevation Models (DEMs) for gullies at Ode-Irele, Lipanu, Akotogbo and Ajagba town in Irele Local Government Area (LGA) of Ondo-State, Nigeria. Gully morphometric attributes such as surface slope, catchments area, average depth and width as well as cross-sectional area and volume of material/ soil excavated were determined. The DEM for each of the study gully catchments was derived from the values of the spot heights and coordinates of each point obtained through the use of GPS and processed using suffer 8.0 soft ware. The values of slopes in the study gully catchments ranged from approximately 0^o58’27 at Lipanu to 4^o51’31” at Ajagba. The DEMs of gullies at Idogun, Ajagba and Ado Quarter displayed slopes that appeared steeper than the gully at Lipanu. Also, the slope shapes as revealed from the DEMs are dominantly convex which implied that overland flow will be generated from all sides of the slope. Therefore, the convexity of most of the gully catchments coupled with the termination of drainage channel constructed half way as well as poor roads and drains maintenance by the community and government have led to the development of large deep gullies at Ode-Irele, Akotogbo and Ajagba in the study area. The development of gully in the area could be minimized by encouraging planting of cover grasses in the building surroundings rather than cement paving of the surface which further make the ground impervious.

Key words: DEM, gully, GPS, accelerated erosion, Irele LGA.