2014 – Review of Embankment Dam Breach Parameter Prediction Methodologies

Sam J. F. Knight and David C. Froehlich 

Breaching of embankment dams can result in significant flood hazards, placing people and property downstream of the dam at risk. The consequences associated with the failure of a dam need to be assessed to determine appropriate design parameters, operational procedures, and maintenance requirements necessary to reduce the risks that the dam poses to an acceptable level. Adequacy of dam failure impact assessments can be affected significantly by the accuracy of the predicted breach hydrograph used when modelling dam failures.
This paper compares various methods for estimating parameters of a commonly used embankment dam breach model that considers the breach to form in the shape of a trapezoidal opening in the dam. Model parameters include measures of the breach shape and formation time. Parameter estimation methods are evaluated in terms of the reliability of their results for a range of dam heights and volumes.
The comparison includes the method proposed by MacDonald and Langridge-Monopolis (1984), which has been adopted in regulatory guidelines in the USA, the approach proposed by Von Thun and Gillette (1990), the method proposed by Allen (1994), which has been adopted in Queensland’s regulatory dam failure impact assessment guideline, and the method developed by Froehlich (2008), which has also been adopted in regulatory guidelines in the USA. The reliability of the different methods has been evaluated based on their accuracy in reproducing dam breach parameters for actual dam failures where well documented measurements are available. An example is given that demonstrates how the predicted breach hydrograph could vary with the use of the different breach parameter estimation methods, and with how the breach is assumed to develop.