Hydraulic Design and Evaluation of Small Earth Dams for Agricultural Water Storage in Sokoto State

This study examines the hydraulic design and performance evaluation of small earth dams constructed for agricultural water storage in Sokoto State, North West Nigeria. Small earth dams provide critical water storage for supplemental irrigation, livestock watering, and dry season farming in semi-arid northern Nigeria, where surface water availability is highly seasonal. Sokoto State has invested in a programme of small dam construction, but systematic hydraulic performance evaluation is absent. This study applies hydraulic design analysis to 12 existing small earth dams in Tambuwal, Gwadabawa, and Isa local government areas, using field measurement and hydrological data to assess design adequacy and performance. Design assessment covers spillway capacity, embankment stability, seepage control, and sedimentation rate. Dam water balance analysis estimates annual water yield and irrigation supply reliability. Sedimentation surveys quantify storage loss from catchment erosion. Beneficiary farmer surveys assess water use patterns and agricultural production outcomes. Findings reveal that spillway capacity is inadequate for the estimated 100-year return period flood in 4 of 12 dams, posing overtopping risk. Sedimentation rates average 3.2 percent of initial capacity per year, significantly above the design assumption of 1.5 percent, attributable to deforestation in dam catchments. Despite these deficiencies, dam-irrigated farmers achieve dry season crop revenues averaging 145,000 naira per household. The study recommends dam safety rehabilitation, catchment reforestation, and annual sedimentation monitoring as priority management actions.

Keywords: earth dams, hydraulic design, agricultural water storage, Sokoto State, sedimentation.