Determination of Physiographic Characteristics of an Ungauged Watershed in North Central Nigeria

Abstract Watershed characteristics such as basin length, shape, area, stream order, drainage density and steam density are some of the factors affecting various aspects of runoff. This research work presents the determination of some physiographic and geological factors of a small catchment in North Central Nigeria. The perimeter of the catchment was delineated with the aid of a Global Positioning System (GPS) using the co-ordinate of the concrete dam located at Elerinjare community and software such as Google Earth and Arc GIS were also utilized. The catchment was found to include some local communities among which are Okanle, Fajeromi, Amodu-Asungbolu, Igberi, Arugbo, Irapa and Basanyin. The total Basin Area for the catchment determined using ArcGIS, was found to be 61.115 km2, with the total length of the catchment as 13.598 km. Other catchment characteristics determined include the catchment drainage density, found to be 0.656; this is an indication of the drainage condition within the catchment; higher drainage densities are expected where the soils are easily eroded, or relatively impermeable, with steep slopes and scanty vegetation. The average length of overland flow within the basin is indirectly proportional to the drainage density within the watershed, it was determined to be 0.62/km for this catchment. The stream density/stream frequency was found to be 0.245/km2. Some of the factors determining the shape of the basin were also determined; these include the circulatory ratio, elongation ratio and compactness coefficient, found to be 0.327, 0.649 and 1.749/km, respectively. This study reveals the physical/hydrological characteristics of this watershed that will lead to hydrological modeling of the watershed for water resource utilization for the communities located within the watershed.