2016 – Estimating the Probability of Breach for Overtopping of Low to Medium Height Homogenous Earthfill Embankments

Kelly Maslin, Richard Rodd

As an industry there have been many advances in the assessment of the probability of failure associated with a range of failure modes including embankment piping and stability. However, little work has been done on the development of a meaningful tool to assist in the assessment of probabilities of failure for embankment breach due to overtopping.

In the development of this paper a number of embankment overtopping case studies were reviewed and these were used to anchor the suggested probabilities of failure. The case studies assessed were all low to medium height, homogeneous earthfill embankment dams. Consideration has been given to a range of factors including embankment material and construction, embankment geometry, duration of overtopping and the presence and condition of vegetation on the embankment face.

The results of the analysis of the case studies indicate that the probability of breach due to overtopping, particularly for short duration events, is actually relatively low compared to the typical values being adopted within the industry.

It is the intended purpose of this paper that it provides guidance to the industry on the assignment of the probability of embankment breach due to overtopping to allow more consistent, robust and defensible estimates for dam safety risk assessments.

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