The effect of material zones and layers on breach growth and prediction

Morris, M. and Hassan, M. (2018) The effect of material zones and layers on breach growth and prediction. In: Protections 2018 (3rd International Conference on Protection against Overtopping), 6-8 June 2018, Grange-over-Sands, UK.

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Abstract

Breach prediction models have typically focused on the prediction of processes through homogeneous structures (levees and dams), with some allowing for the effects of surface protection layers (such as grass or rock) and in some cases, the effects of simple core structures. Even with these simple models, it can be seen that the effect of surface layers or cores can be significant. The impact of changes in the rate of breach erosion are often magnified by the way in which these changes affect the breach growth timing in relation to the hydraulic load; for example, whether the main breach formation phase occurs as flood levels rise, peak or pass and drop. The EMBREA model was developed to allow breach prediction through levees and dams constructed from zones of material. The model evolved from the earlier HR BREACH model and combines flow, soil erosion and slope stability calculations. Whilst the model can predict both headcut and surface erosion processes, the zoned behaviour is currently limited to the surface erosion simulation process. Simulations using different zoned geometries shows behaviour that is consistent with aspects of different homogenous breach processes, however, as the different zones erode, the characteristics also change. The effect of integrating erosion and breach growth processes through different zones of material gives results which can differ significantly from breach prediction through simple homogenous structures. This emphasises the importance of modelling real, zoned rather than simplified structures. Whilst the significance of zoned breach prediction can be seen, the need to understand, refine and validate the way in which we model these processes remains a top priority. As with earlier models, the rate of erosion depends upon the soil erodibility (Kd) for which we need to confirm the most appropriate erosion relationship(s). With zoned structures, the nature of the soil zones can vary from erosion resistant clay cores to highly porous rockfill material. With macro erosion processes changing from headcut to surface erosion to rockfill slumping, the need to understand why and when the erosion process changes in relation to soil type and grading remains very important. To confirm and validate these processes, large scale laboratory and / or field testing of both homogeneous and zoned structures is required.

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