The cause of failure of an earth dam is usually either overtopping or piping, and in both cases the mechanism is the earth dam breaching process. In order to reduce the threat of earth dams failing, simulations of earth dam breach events are crucial. Techniques for modelling dam breaching are therefore a fundamental part of every dam safety programme.

In accordance with general worldwide tendencies to increase dam safety, and as part of the Czech programme to re-examine dam safety, selected existing earth dams in the Czech Republic have been recently re-examined and analysed from the point of view of the potential failures due to breaching. The selected dams are located upstream of significant urban areas or industrial zones. The scope of this paper is to introduce and compare several earth-dam breach modelling techniques and to present their practical application to Slusovice, an existing category I dam in the Czech Republic.

A dam breach due to overtopping or piping generates a flood wave that propagates downstream into the valley below the dam. The flood wave usually has disastrous consequences and causes damage to human life and financial losses greatly exceeding the cost of the dam breached. In order to create emergency and alarm systems, knowledge of the dam breaching mechanism is necessary.

The key results of earth dam breach modelling are a flood hydrograph (time-dependent breach outflow discharge Q(t)) and development over time of the breach characteristics (shape, size etc) and its routing through the downstream valley. Based on knowledge of the flood hydrograph, flood protection and management plans can be compiled.

This paper deals with the maximum outflow discharge Qmax and flood hydrograph Q(t) prediction only.

Detailed reviews and analysis of various earth dam modelling techniques can be found in [4] and [8]. Within the scope of the analysis presented in this paper, methods of earth dam breaching were analysed, tested and compared, and consequently applied to a simulation of a hypothetical Slusovice dam failure. The following were compared:

Preliminary estimate of peak discharge, using statistical evaluation of real dam failures.

Simplified calculation of the process of breaching using an analytical solution ([3] and [4]).

Method based on a modification of the computer code Breach [1].

Analogy with the Teton dam failure.

The first part of the investigation focused on the identification of the most probable types of failure of the Slusovice dam. Based on long-term observations of the dam behaviour (deformation, seepage), estimates of probable maximum N-year flood events, hydraulic analysis of the spillway capacity and evaluation of the dam foundation and sub-base geological structure, it was concluded that piping was the most probable mechanism of the hypothetical Slusovice dam failure.

It is assumed that two possible locations of piping channel can be identified:

Variant I. The end of the sealing membrane at the right bank.

Variant II. The lowest part of the valley, where the bottom outlets are located.

For this reason, all calculations were carried out for these two variants of the dam failure.

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