###### Abstract
The researchers showed that even a discharge speed of 10 cm/day can be considered a rapid drawdown in earth-fill dams and can cause failures in the upstream slope. [PERSON] [13] provided stability charts that show the variations in the safety factor with the drawdown level for simple homogeneous slopes. As the reservoir level is lowered, the safety factor decreases provided that no dissipation of the pore pressure occurs during drawdown. Stability charts were presented to facilitate the computation of the safety factor of earth slopes during rapid drawdown. He stated that during the drawdown, two things occurred: (i) the drawdown creates new boundary conditions for the water flow inside the slope and causes the unstable flow, and (ii) the stress variations due to the rapid drawdown create pore pressure. [PERSON] and [PERSON] [14], contrary to earlier researchers who all used limit equilibrium methods (LEM) for estimations of the safety factor of the slope under a range of conditions to produce a series of charts for practicing engineers to utilize, used the finite element method (FEM) to analyze a simple 2:1 slope under different submergence and different drawdown ratios to produce operating charts for such circumstances that should apply to real structures. These researchers then provided a static stability analysis of the dam slopes under a steady-state condition with both slow and rapid drawdowns. The results of the analysis showed that in the early stages of discharge (\(\mathrm{L/H<0.7}\)) the effect of the embankment's weight is greater than the friction, thus reducing the F.S. But, at high discharge levels (\(\mathrm{L/H\geq 0.7}\)), increasing the frictional resistance has a greater effect than increasing the weight, thus increasing the F.S. Therefore, it can be concluded that the dam slope is stable in a dry state or if there is a full reservoir. It will be unstable in a critical condition of drawdown (discharge rate typically 70%). The F.S\({}_{\mathrm{min}}\) obtained for the slope depends on the strength of the materials at different levels of water in the reservoir. [PERSON] [15] mentioned that the earthen dam can be modified versus the downstream slope failures by considering the seepage reduction in the dam mass by supplying a horizontal drainage blanket at the slope's toe. The author provided graphical solutions to estimate the downstream horizontal drain and stability for homogeneous earth-fill dams. [PERSON] [16] presented numerical procedures to evaluate the drawdown ratio, permeability status, transient deformation, seepage analyses, and different loading conditions. In this regard, [PERSON] considered three different discharge modes including slow, fast, and mixed drawdowns which were applied on two 3:1 slopes with two different NWL and two different discharge speeds (R = 0.1 and 1.0 m/day). The results were used to develop the displacement contours for different drawdown ratios and permeability coefficients. [PERSON] et al. [17] provided optimized approaches for homogeneous earth-fill dams with impervious foundations and drains. The optimization was performed with the aim of maintaining safe slopes upstream and downstream and a relevant distance between the normal water levels on both dams' sides. [PERSON] et al. [18] utilized numerical modeling to investigate the rapid drawdown conditions on submerged slopes with changing water levels on the slope upstream. [PERSON] and [PERSON] [19] applied the FEM and LEM to estimate the horizontal drain effects on the upstream slopes of earthen dams to provide a safe status during rapid drawdown. The authors used the GeoStudio package to prepare a comprehensive stability and behavioral analysis. [PERSON] et al. [20] utilized [PERSON]'s [21] LEM-based three-stage procedure to estimate the rapid drawdown conditions for a combined stability and transient flow analysis of earth-fill dams. Using the SEEP-2D finite element computer program, [PERSON] and [PERSON] [22] demonstrated that seepage could cause the weakening of the earth dam's structure in rapid drawdown.