Abstract
Seepage and slope instability are major causes of embankment dam failure, often leading to loss of life, property damage, and socio-economic disruption. The Goronyo Dam, commissioned in 1984 on River Rima in Sokoto State, Nigeria, has a storage capacity of 942 × 10⁶ m³ and serves over 80,000 ha of irrigated land. However, persistent water loss has raised concerns about seepage-induced deterioration and structural safety. This study investigated seepage behaviour, identified possible failure mechanisms, and assessed potential downstream impacts. Soil samples from failed and unfailed embankment sections were tested for particle size distribution, Atterberg limits, compaction, permeability, and shear strength. Results show predominantly fine-grained soils classified as low- to medium-plasticity clay (CL). The average liquid limit, plastic limit, and plasticity index were 31.8%, 19.5%, and 12.3%, respectively. Failed sections exhibited higher optimum moisture content (22.81%) and lower maximum dry density (1.67 Mg/m³) compared to unfailed sections (17.05% and 1.73 Mg/m³). Permeability values were 8.42 × 10⁻⁶ m/s and 5.30 × 10⁻⁶ m/s, respectively. Shear strength parameters indicated cohesion of 24.73 kPa and friction angle of 28° for failed sections, and 18.97 kPa and 37° for unfailed sections. Seepage and slope stability analyses using GeoSlope, 2007 yielded seepage discharges between 2.87–3.29 m³/day/km (failed) and 1.35–3.15 m³/day/km (unfailed). Factors of safety for upstream slopes were 2.50 and 3.08, and for downstream slopes 1.97 and 2.39, respectively. A survey of 100 downstream households revealed significant socio-economic impacts, with 87% reporting high flood intensity, loss of livelihoods, reduced irrigation, and decline in fishing activities. Pearson correlation analysis (r < 0.5, p < 0.01) confirmed a significant relationship between dam failure and socio-economic variables. The study highlights seepage as a key factor in embankment performance and underscores the need for improved seepage control and monitoring to ensure long-term dam safety.