ADEQUACY OF DRAINAGE CHANNELS IN A SMALL URBAN WATERSHED IN NIGERIA

Abstract

This research presents an analysis for the adequacy of drainage channels. Topographical and location map was used as a guide to locate the drainage channels. Rainfall records for a period of four years (2008-2011) were used to develop the intensity –duration   frequency of the study area . Field survey and geometrical measurement of the drainage channels were carried out and data obtained from the measurement were used for the analysis of runoff from drainage channels. The time of concentration was determined using the Kirpich equation and modified version of Kirpich equation (new equation of  time of concentration). The peak flow and maximum flow velocity from the drainage channels were determined using the rational model and manning’s equation.  Analysis of the results showed that most of the drainage channels had lesser runoff when the modified Kirpich equation was used. All the drainage channels of basin A had velocities ranging from 1 to 2m/s and the drain capacities are okay. All the drainage channels of basin B had velocities ranging from 2 to 4m/s and the drain capacities are okay. Channels 2 and 9 of basin C had drain capacity less than the actual discharge this makes the drain inadequate. Basin C revealed that, channels 1, 4, 5, 7, 8, 10, 12 and 13 have flow velocities less than 1m/s and this will cause deposition of sediment, a redesign of inadequate drainage channels with velocity less than 1m/s  was done and their velocities ranges from 1.21m/s to 1.54m/s. A redesign of drainage channels 2 and 9 of basin C showed that the drain capacity were greater than the actual discharge and this makes the drain adequate .This study suggests that; proper design, analysis, construction and maintenance of drainage channels be made.

http://dx.doi.org/10.4314/njt.v33i4.20