Failure of earth dams can be caused also by seepage problems, foundation instability, deformation, surface sliding, and earthquakes. The most critical conditions that may cause failure of the embankment are: differential settlement, development of shearing within the embankment and foundation, and development of seepage through the embankment and foundation. The stability and factor of safety against Mosul dam embankment sliding are determined considering a possible rapid drawdown and earthquake conditions and using three methods. Unsaturated condition was considered assuming the shear strength parameter (b) to be (0, 0.5, ). GEO-SLOPE OFFICE was used as the analytical tool to simulate both seepage, slope stability, and earthquake. Seepage through dam was analyzed for three period rapid drawdown of water level (30,21,8 day) with the associated saturated-unsaturated transient seepage.
The main results indicated that the minimum slope stability factors of safety were reached using Bishop method and was achieved during 8 day water drawdown and within the second day which indicates the most critical case.

Keywords: Seepage, MOSUL Dam, Finite Element, Slope Stability, Rapid Drawdown, unsaturated soil mechanics.