Evolving Tools for Prediction of Earth Dam Breach

Abstract Only -
Over the past several years, research has advanced the understanding of the erosion processes associated with earth dam breach. Embankments have been constructed at various scales in the US and Europe (Hanson et al., 2005) and breached under controlled conditions. This has allowed the failure processes to be observed and documented. To date, the research conducted by the Agricultural Research Service has focused on failure of homogeneous embankments by overtopping. Additional large-scale tests have allowed the ability of vegetation to delay or prevent failure of embankments subjected to low levels of overtopping to be quantified (Temple and Hanson, 2002). Research focusing on understanding the failure initiated by internal erosion along defined flow paths is presently being undertaken.
Computational models of the breach processes are being used in analyzing the data from the controlled breach tests to further extend the understanding of earth embankment breach. As these models mature, they are being incorporated into software intended for field application. The Windows Dam Analysis Modules (WINDAM) software is being developed by the USDA and its partners with the first component (WINDAMa) presently being tested and expected to be made available in the near future (Temple et al., 2006). This first component is a level surface reservoir routing model that focuses on evaluating the ability of vegetation or riprap on the downstream face of an embankment to withstand attack associated with overtopping flow
(Temple and Irwin, 2006).
A research oriented model, Simplified Breach Analysis (SIMBA) is being developed and used to simulate homogeneous embankment breach (Hanson et al., 2005; Temple et al., 2005) and evaluate algorithms describing the breach processes. This model is based on the four stages of breach observed in the controlled breach tests. These stages are: 1) surface erosion on the face of the embankment resulting in formation of a headcut, 2) advance of the headcut through the crest of the embankment, 3) breach development as the headcut enters the reservoir, and 4) breach expansion resulting from the release of the stored water. The components of SIMBA are presently undergoing validation testing using available data from actual dam breaches as well as the data from controlled tests.
Work has begun on incorporating algorithms from the SIMBA model into the WINDAM software. As the algorithms describing the erosion process for each of the breach stages are refined and validated, they will be integrated into WINDAM. Following additional testing, this software will be made available for general use.
Initially, the WINDAM software with breach analysis capabilities will be applicable only to homogeneous embankments subjected to overtopping. It is intended that the capabilities later be expanded to include zoned embankments and breach initiated by internal erosion. A limited number of tests have been conducted which include multiple materials (Hunt et al. 2006) in the embankment and controlled testing of homogeneous embankments subjected to erosion along an initially well defined flow path has begun.