Analysis of the seepage and stability in a non-homogeneous earth dam under transient conditions: a case study

Rapid reservoir drawdown poses a critical condition that can compromise the hydraulic behavior and slope stability of embankment dams. This study evaluates the transient seepage response and upstream slope stability of the Gavoshan Dam in western Iran using two-dimensional numerical analyses with the SEEP/W and SLOPE/W. The models incorporated unsaturated flow and time-dependent boundary conditions to simulate reservoir depletion rates ranging from 0.15 to 1.20 m/day. Findings revealed that under the maximum drawdown rate of 1.20 m/day, the seepage discharge decreased from 6.80 × 10 −5 to 1.77 × 10 −5 m 3 /s/m, while the exit gradient reduced from 0.463 to 0.117 over the 580 day simulation period. Concurrently, the factor of safety (FoS) against sliding decreased from 2.04 to 1.77, remaining within acceptable engineering thresholds. The results highlight the need to consider transient unsaturated flow in dam safety assessments, offering guidance for reservoir operations and risk mitigation to ensure embankment stability during rapid drawdown.