Development of Improved Drainage System for Storm Water flow at Isale koko Ilorin, Kwara State, Nigeria

Abstract

Among areas prone to flood disaster yearly in Ilorin is Isale koko. The study involved the reconnaissance survey to ascertain the current capacity of the existing drainage in the flood disaster prone area of Isale Koko, Ilorin, Kwara State, Nigeria. The dimension of the drainage network of the area was taken at eight (8) various points and the average area of the drainage was obtained to be 0.44m². The already existing drainage in the area was divided into 3 sections for easy computations of flow value, length, depth and width. The rainfall intensity for the study area was found to be 98.49mm/hr. The rational method and Manning’s equation were used for the surface runoff and the proposed drainage respectively. The peak flow of the area and maximum flow velocity in the drains were determined to be 48.46mᶟ/s and 2.21mᶟ/s respectively. The best hydraulic section method was employed to obtain new drainage dimensions for both rectangular and trapezoidal channels. The new designed rectangular channel had dimensions of 1.16m × 0.812m while the trapezoidal channel had dimensions of 1.43m×0.72m×0.87m. The area of both channels was obtained to be 0.67m². A comparative analysis was carried against the average area of the pre-existing drainage that showed a 53.3% increase in drainage area; proving that the current drainage infrastructure of the area is grossly inadequate. Sequel to the analysis, the trapezoidal shaped drainage was recommended for the study area. Keywords—Drainage, Flood, Infrastructure, Runoff, Storm water