Spatial Variation in Surface Runoff at Catchment Scale, the Case Study of Adigela Catchment, Tigray, Ethiopia

The study was conducted in Adigela catchment with specific objective to examine surface runoff variation in relation to factors affecting runoff processes. Four representative units were selected where runoff data in terms of depth is collected while runoff hydrograph analysis was made to determine runoff volume. The hydroraph at all gauging station was indicated with a trend of rising before the runoff reached peak and started to faill quickly on the recession limb. The discharge in terms of volume at the outlet was then determined using Hydrochan after surveying (Total station) the channel cross section. The study indicated that on average a peak discharge of 0.73, 2.14, 0.47 and 1.53 m 3 /sec from Maykaebo, Mengediweste, Nushteyshintro and Abayshintro were measured respectively. The statistical result has showed that spatial pattern of the origin of runoff is complex and varies significantly between sub catchments. From the field experiments, it was found that the key controls on runoff hydrograph and runoff generation at the catchment scale are shape of the catchment, vegetation cover, and slope gradient, soil type, area coverage and amount of rainfall. It was also found that SCS CN method was efficient and can be used to predict runoff in the catchment. Based on the result, it has been recommended to identify similar hydrological response units in the catchment so as to compare runoff difference among homogenous units. Keywords : Catchment, Runoff, Infiltration and Hydrograph.