Evaluation and development of physically-based embankment breach models

The CEATI Dam Safety Interest Group (DSIG) working group on embankment erosion and breach modelling has evaluated three physically-based numerical models used to simulate embankment erosion and breach development. The three models identified by the group were considered to be good candidates for further development and future integration into flood modelling software. The evaluation utilized 7 case studies comprising three large-scale tests carried out in Norway (5to 6-m high embankments); two large-scale tests from the USA (1.75-m high embankments); and the prototype failures of the Oros (Brazil) and Banqiao (China) dams. The breach models evaluated were SIMBA, HR-BREACH, and FIREBIRD BREACH. Results of the evaluation are presented along with details of the continued development of two of the three models (HR BREACH and SIMBA). The three models included in this evaluation are all physically-based, simulating fundamental erosion processes by relating factors causing erosion to factors resisting erosion. The models utilize quantifiable erodibility parameters that can be directly measured or estimated from other soil properties when measurement is not possible. The models are not calibrated to reproduce observed data from specific dam breach case histories or laboratory tests, but rather rely on verification of the basic erosion process models against laboratory tests designed to study the basic processes. The three models all have the capability to simulate erosion and breach of embankments that are primarily composed of cohesive materials, and some also include erosion models focused on noncohesive soils. The models have varying abilities to analyse embankments with complex internal geometries (i.e., zoned construction). The models all consider erosion caused by overtopping flow, and some have the capability to also consider internal erosion. This evaluation focused only on overtopping. The three models evaluated in this study are: • SIMBA – SIMplified Breach Analysis – Under development at the USDA-ARS Hydraulic Engineering Research Unit, Stillwater, Oklahoma. (Temple et al. 2005, Hanson et al. 2005a). This is a research-focused model used to analyse data from large-scale laboratory tests for the purpose of developing and refining algorithms needed for the creation of an application-focused model, WinDAM B. The focus of SIMBA is headcut erosion in homogeneous cohesive embankments. The version of the model evaluated here had some optional components disabled or restricted. (WinDAM B Version 1.0 was officially released