Slope Stability Analysis of The Nipah Dam Embankment in Madura, Indonesia

Abstract

Dam safety is essential for sustaining water supply, irrigation, flood control, and downstream community protection. Operational changes in reservoir levels may alter hydrostatic pressure, seepage conditions, and embankment stability, requiring comprehensive safety assessments. This study aimed to evaluate the slope stability and seepage safety of the Nipah Dam embankment under normal operation, raised reservoir level, rapid drawdown, and seismic loading conditions. A quantitative approach was applied using hydrological records, dam specifications, reservoir data, geotechnical parameters, and field observations. Reservoir inflow was modeled using HEC-HMS, while seepage behavior and pore-water pressure were analyzed using SEEP/W. Slope stability was evaluated using SLOPE/W based on the Bishop limit equilibrium method under static loading, Operating Basis Earthquake (OBE), and Safety Evaluation Earthquake (SEE) conditions. Under static loading, the factors of safety ranged from 2.302 to 3.209, exceeding the required criteria of 1.5 for steady-state seepage and 1.3 for rapid drawdown conditions. Under OBE loading, the factors of safety ranged from 1.623 to 2.111, while SEE loading produced values ranging from 1.001 to 1.398, satisfying the minimum criteria of 1.2 and 1.0, respectively. The piping safety factor was 5.9, exceeding the recommended value of 4.0. Therefore, Nipah Dam remained stable and safe under both existing operating conditions and the proposed 1.5-m increase in normal water level during normal operation and seismic events.