Abstract
Dam breach width significantly influences peak breach outflow, inundation levels, and flood arrival time, but uncertainties inherent in the prediction of its value for embankment dams make its accurate estimation a challenging task in dam risk assessments. The key focus of this paper is to provide a fuzzy logic (FL) model for estimating the average breach width of embankment dams as an alternative to regression equations (RE). The FL approach is capable of handling nonlinear behavior, imprecision in discrete measurements, and parameter uncertainty. Historical data from 69 embankment dam failures are used in the development and testing of the FL model. Application of the FL model is also presented for estimating average breach widths of two case studies that have adequately documented data. The accuracy of the FL rule-based model is investigated using uncertainty analysis: the mean prediction error between the FL estimates and the observed average breach widths is very small (=0.03) and comparable to that achieved using the best available RE. Moreover, the FL uncertainty band is found to be approximately ±0.51 order of magnitude smaller than the ±0.56 order of magnitude achieved with the best available RE. The simulation results indicate the potential of the FL model to be used as a predictive tool for estimating the average breach width of embankment dams.
Highlights
IntroductionEmbankment dams (earthfill or rockfill) are the most commonly built type of dams in many countries
Embankment dams are the most commonly built type of dams in many countries
The results suggest that the Fuzzy logic (FL) model could be a good tool for estimating average breach width, not replacing the best available regression equation of Froehlich (1995), but complementing it with extra information that may help the modeler
Summary
Embankment dams (earthfill or rockfill) are the most commonly built type of dams in many countries. Many of the available RE assumed the breach width as a linear function of only the dam (or the breach) height and/or the reservoir volume This assumption may be valid for small embankments having similar geometry and soil characteristics. This general objective includes: (1) developing a Mamdani’s FL inference system for predicting Bav, (2) comparing the results of the FL model with those of the best RE for predicting Bav, (3) performing an uncertainty analysis for the results of the FL model and the RE, and (4) applying the FL model on some of the available case studies that have adequate data. The available case studies of embankment dam failures presented by Froehlich (2008) constitute the basis for the development of this FL rule-based model. The construction of the conditional statements ‘IF– rules’ and the membership functions, based on the observed measurements and the relation between the input and the output variables, are the things that make FL useful and capable of representing the actual system behavior
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