Songu G. A.^1,, Oyatayo K. T.¹, Iorkua S.A.²

This study examined gully development in Demekpe drainage basin, Makurdi Local Government Area of Benue State of Nigeria; with a view to determine the volume and amount of sediment loss from a 3^rd order gully system. The systematic sampling technique was used to segment the gully which measured 220m long at intervals of 20m. Parameters measured include among others gully length, gully depth, gully shoulder and bed widths, slope gradient, cross sectional area, stream density, stream frequency and stream intensity. Cartesian coordinates, spot heights and core soil values were also determined. Digital Elevation Model was used to model gully form, direction of runoff and sediment delivery ratio in the gully system. The result showed that the volume of sediment loss from the gully system with a cross sectional area of 91.7m² is 931.5m³ using the End Area method of soil loss determination. The amount or weight of sediment loss from the gully system is estimated to be 12,575.28 tonnes. The Digital Elevation Model of the gully system indicates a trapezoidal form and slopes with summital convexity. The convexity of the slope shape implies that runoff is generated from all sides of the slopes, influencing a considerate amount of sediment loss at the gully sides and floor. It is therefore recommended that planting of cover crops should be intensified to enhance infiltration and concreted surfaces should be minimised to reduce surface runoff and sediment loss along slopes.

gully, sediment loss, digital elevation model, Demekpe drainage basin, Makurdi local government area