Effects of slope length on erosion of some alfisols in Western Nigeria

Erosion was monitored for erosive rainstorms received during 1977 and 1978 from an Alfisol at Ibadan in western Nigeria on bare plowed soil using field runoff plots on natural slopes of 1, 5, 10 and 15% and with 5, 10, 15 and 20 m slope lengths. Equations of the type A = αLb were computed relating soil erosion (A) to slope length (L). Erosion was affected more by slope gradient than by slope length and was in the order of 1, 17.6, 31.3 and 22.8 for 1977 and 1, 25.5, 53.0 and 62.4 for 1978 for 5, 10 and 15% slope gradients, respectively. For gentle slope gradients of 1 and 5%, slope length had little effect on erosion. During 1978, erosion for 10% slopes was in the order of 1, 1.05, and 1.08 for 5, 10 and 15 m slope lengths, respectively. For 15% slope, however, the soil erosion was in the order of 1, 1.11, 1.51 and 1.60 for 5, 10, 15 and 20 m slope lengths. The mean sediment concentration (averaged over all slope gradients), was 1, 1.27, 1.50, 1.99 for 1977 and 1, 1.61, 2.71, 2.73 for 1978 for 5, 10, 15 and 20 m slope lengths, respectively.