Introduction

When an earth embankment has retained a reservoir with a fairly constant water surface elevation for a long time, the seepage conditions within the embankment will likely reached a steady-state. If it is necessary to drain the reservoir quickly, the pore-water pressures within the embankment may remain relatively high while the stabilizing effect of the reservoir’s weight along the upstream side of the embankment is removed. This process is typically referred to as ‘rapid drawdown’ and can cause instability of the upstream face of the embankment.

A SEEP/W water transfer analysis can be used to evaluate changing pore-water pressure conditions after the reservoir has been drained. In the worst case, it is assumed that the reservoir has been drained instantaneously. More realistically, the reservoir will be drained over a period of time. 

This example illustrates how these conditions, modeled with a water transfer analysis, can be used in SLOPE/W to determine the influence of instantaneous or gradual drawdown on slope stability.