The classification of landslides in a reservoir of a hydropower project is discussed with focus on height of flood waves that could originate and endanger infrastructure. We did classification before impounding and it was based upon site- and satellite-observations without any drill hole investigations. Consideration of distance to dam, volume, elevation difference to water level, slope inclination and material type are the main classification parameter. In a case study the activation and monitoring of one slide in the impounding phase is described. The observations justified a subdivision of this landslide with different geological models. The highest possible flood waves result from high velocity of failure, therefore the landslide mass was treated like a viscous fluid. The momentum on the water surface revealed the directional consequences and the impact upon the dam is presented.

1 Introduction

Landslide investigations have been carried out in the reservoir of a hydropower project in a mountainous and unpopulated area during impounding phase. The reservoir has a length of ~10 km and water depth is 70 m at dam axis and gradually decreasing towards upstream. Before the reservoir was filled the risk of landslides had to be evaluated in relation to the dam and villages located further downstream on the same river.

The special topic in this project was the danger of high flood waves, which could overtop the dam structure and spread towards downstream because there are no other populated areas in the reservoir itself. However, regardless of the specific consequences of a flood wave in this project the methodology can be applied to other situations at lakes but not to landslides below sea level.

Geological Conditions

The project area is predominantly built up by limestone with locally clay-and sandstone layers. The inclination of slopes in the v-shaped valleys generally varies between 18° - 40°.

The dam area is located in the same geological unit as the reservoir and the foundation conditions in dam zone have been explored intensively. This knowledge of conditions was a small compensation for the lack of investigations in the reservoir zone.

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