Assessment of Drainage Infrastructure Adequacy in Selected Towns of Adamawa State

Urban flooding attributable to inadequate drainage infrastructure is a recurring problem in the rapidly urbanising towns of Adamawa State, North East Nigeria. This study assesses the adequacy of surface drainage infrastructure in Yola, Numan, and Mubi towns through field inspection and hydraulic analysis. A descriptive engineering assessment methodology was applied, involving measurement of drain cross-sections, slopes, and inlet spacing at 80 locations across the three towns. Hydraulic capacity calculations using Manning's equation were performed using design rainfall intensities for 2-year and 10-year return period storms. Blockage levels were assessed by visual inspection and classified on a four-point scale. Results indicate that 64 percent of measured drain cross-sections are hydraulically undersized for the 2-year return period storm under current levels of blockage. Average blockage level across the three towns is 45 percent of cross-sectional area. The Yola GRA area records the most severe inadequacy, with 78 percent of drains failing the 2-year storm capacity test. Mubi shows the worst blockage rates at 58 percent average cross-section obstruction. Only 22 percent of the inspected drainage network has functional inlet structures to intercept surface runoff from adjacent roads. The study recommends an emergency desilting programme for all existing drains, enlargement of undersized primary channels to accommodate a 5-year design storm, and adoption of a community drain maintenance model with local government oversight.

Keywords: drainage infrastructure, urban flooding, hydraulic capacity, Adamawa State, North East Nigeria