Uncertainty of Predictions of Embankment Dam Breach Parameters

Abstract

Risk assessment studies considering the failure of embankment dams often require the prediction of basic geometric and temporal parameters of a breach, or the estimation of peak breach outflows. Many of the relations most commonly used to make these predictions were developed from statistical analyses of data collected from historic dam failures. The prediction uncertainties of these methods are widely recognized to be very large, but have never been specifically quantified. This paper presents an analysis of the uncertainty of many of these breach parameter and peak flow prediction methods. Application of the methods and the uncertainty analysis are illustrated through a case study of a risk assessment recently performed by the Bureau of Reclamation for a large embankment dam in North Dakota.

Predicting outflow induced by moraine failure in glacial lakes: the Lake Palcacocha case from an uncertainty perspective

“…Extensive descriptions of the mathematical basis of DAMBRK can be found in Fread (1984,1988,1994). DAMBRK simulates the breach outflow process as an idealized hydraulic process: i.e., one-dimensional open-channel flow over a broad-crested weir that linearly evolves with time (Wahl, 2004;Wurbs, 1987;DHI, 2008). This approach excludes erosion physics and hence does not require geotechnical or structural parameters.…”

“…The empirical model performance is governed by a similar normalized time difference of Table 2. Uncertainty estimates for peak flow predictions using empirical models (adapted from Wahl, 2004;Xu and Zhang, 2009;and Peng and Zhang, 2012 …”

“…However, to take advantage of their simplicity, we must assess their suitability. Although several authors propose empirical models and address uncertainty in dam-breach estimations (Wahl, 2004;Xu and Zhang, 2009;Peng and Zhang, 2012), less attention has been given to developing criteria to use in selecting one empirical model over another. Consequently, assessing whether a model fits the conditions of a particular dam site poses a challenge prior to effective model application.…”

“…Landslide dams, a particular case of natural dams, have received more attention than glacial moraine dams, producing, as a result, empirical estimation methods for peak outflow (Costa and Schuster, 1988;Walder and O'Connor, 1997;Wahl, 2004). The geologic processes behind the formation of each type of dam are different, but failure assessment methods might apply for both types due to common instability issues.…”

“…Herein, we assess the application of empirical models as a calibration tool for hydraulic simulations generating a hydrograph for natural dam-break problems. The approach, applied to nine empirical dam-breach models, evaluates the case of a single natural glacial lake dam, estimating outflow hydrograph predictions and uncertainties (Wahl, 2004;Xu and Zhang, 2009;Peng and Zhang, 2012) to choose the most robust model. In addition, from the uncertainty bands of the empirical models we compute the upper and lower bound potential outflow hydrographs instead of a single expected instance, providing more robust results for flood risk management studies.…”