Abstract: When reservoir water level drops sharply and rapidly from long  time high-level storage, the falling velocity of reservoir water level and soil property will exert adverse impact on the stability of upstream slope soil mass. The hazard of seepage on the upstream slope surface is demonstrated by seepage analysis softwares (Geoslope and unsst2). Fitted curves between k/μv and critical descent altitude of reservoir levels when flow with free surface does not appear are presented. Moreover, both the influence of soil anisotropy caused by various factors and the impact of substrate suction internal frictional angleφ^b on the stability of upstream slope seepage are also considered. The study reveals that all possible factors in practical projects and the results of seepage field calculation should be considered in the analysis of the seepage stability of upstream slope during the drawdown of reservoir level.

Key words: drawdown of reservoir water level , seepage stability , critical gradient of seepage from slope surface