Seepage and Slope Stability of the Kwandugwa Earthfill Dam in Handeni, Tanzania

Abstract

Earthfill dams are essential for water supply, irrigation, livestock production, and drought mitigation, particularly in semi-arid regions. However, seepage and slope instability remain major causes of embankment deterioration and failure. Therefore, this paper This study evaluated the seepage and slope stability of Kwandugwa Earth Dam in Handeni, Tanzania using appropriate standard methods including field investigation, laboratory testing and numerical modelling with GeoStudio software. Field observations identified localized seepage zones, minor erosion features and surface cracks, while laboratory testing confirmed that the embankment materials possess low permeability and adequate shear strength for seepage control and slope stability. Numerical analysis estimated a seepage rate of 1.26x10^-6m³/s and a downstream factor of safety of 3.26, confirming that the dam is structurally stable under stead-state conditions. The results further indicate that the excessive seepage observed at the dam is more likely associated with the foundation soil than the embankment. The study concludes that the Kwandugwa Earthfill Dam remains hydraulically and structurally stable under the analyzed conditions. Installation of piezometers and periodic inspections are recommended to hence long-term dam safety. This study contributes to knowledge by demonstrating the effectiveness of integrating field investigation, laboratory testing and GeoStudio modelling for evaluating seepage and slope stability of earth dams in Tanzania.