Gully morphometry and morphology in the Iyi-Ukwu basin, south-east, Nigeria
The characteristics of gullies in the Iyi-Ukwu catchment in Isiala Ngwa, Nigeria were studied and classified as class 2 and 4 gullies using standard classification methods. Mean gully width ranged from 1.07m to 5.17m, while the mean depth ranged from 1.0 to 6.36. Three (3) out of the ten gullies were in the continuous stage of development while others were in their discontinuous stage. All the gullies had a rectangular shape with a gully shape factor of 1.0. Gullies were also found to be long and narrow with the major direction of advancement being southwest wards following the direction of the face of the Enugu-Okigwe-Arochukwu Cuesta. Also morphometric analysis revealed that slope was a major causative factor of gully formation as slope angles ranged between 50 and 140. A statistical analysis of the relationship between gully fall, slope angle and the difference in gully cross sectional areas revealed a significant difference between the cross sectional area of gullies and a significant relationship between gully depth and gully side slope angle implying that as gully channel down-cuts or deepens, the gully side became steeper. This study finally concludes that gullies in the study area were initiated by a combination of steep slopes, high rainfall, soil characteristics, and human activities. Precautionary measures and soft control methods are recommended.
Key words: gully erosion, gully classification, morphometry, morphology, Iyi-Ukwu basin