CASE STUDIES OF FAILURE AND DAMAGE OF SOME DAMS DUE TO RESERVOIR EFFECTS

Abstract

The construction of a dam across the river modifies the existing fluvial environment to a lacustrine environment. This causes many impacts on the existing environmental balance of the area. It is essential that all these impacts are evaluated carefully not only for the safety of the engineering structure, but also to adopt environmentally sound mitigation measures. The major impacts of dam construction' include leakage, reservoir rim instability, earthquake hazards, siltation and subsidence. Leakage occurs below the reservoir, through ridges bordering the reservoir as well as through the dam foundation, and piping through the dam foundation has been a major cause of failures_ The important factors responsible for leakages have been discussed in addition to giving suitable examples. Reservoir rim instability is associated with the fluctuation of water level between maximum reservoir .level (MRL) and dead storage level (DSL). The unfavourable topographical and geological conditions which cause instability of slope have been discussed in detail. Earthquake' hazards in the form of reservoir induced seismicity (RIS) is a major factor for dam failures especially in complex tectonic environments. The RIS which iv occurs in the initial phases of reservoir operations is more influenced by the geologic and tectonic setting of the area. In addition to analysing the unfavourable conditions which influence RIS, regulated reservoir operations to keep RIS to a minimum have been suggested...