Improving the accuracy of breach modelling: why are we not progressing faster?

Abstract

Flood risk assessment and management often requires the prediction of potential breaching of a flood defence embankment or dam in order to either assess potential impacts or provide information to assist emergency planning, evacuation, repair strategies and improve alternative future design strategies. There are many different aspects of the overall breaching process, which are more, or less, relevant to the wide range of potential end users of such information. Consequently, the prediction of breach growth is an area where research has been undertaken for many decades in an attempt to provide more reliable models and predictions. However, despite many initiatives providing observations and recommendations as to processes observed and how research might progress, more detailed literature searches will often uncover conclusions and observations noted a decade or two or three earlier that are similar to those being made today. In particular, observations relating to material type, state (such as water content and compaction) and properties are relevant here. This prompts the obvious question as to why our ability to predict breach initiation and growth has not progressed further over this period. Why are so many studies identifying similar issues and, in effect, 'reinventing the wheel'? With a programme of research into breach initiation and growth under the EC FLOODsite Project and continued pressure to improve tools and techniques following events such as those seen at New Orleans in August 2005, this paper considers this question of apparent slow progress and offers some suggestions as to why this may have occurred and what direction might prove more effective in the future.

On the importance of analyzing flood defense failures

“…These stages have been observed in several large-and small-scale breach experiments [17]. However, differences in breach behavior have been found in the rate, and manner of breach formation.…”

“…The performance of breach models is thereby often misinterpreted. Morris [17] mentions that models are usually developed and calibrated against a single dataset because of the lack of high quality datasets available for calibration purposes, hence the ability of the model to reproduce the results of the dataset is inherently quite good. It is partially for this reason that under the SAFElevee project an extensive database will be constructed for the purpose of better validating breach models.…”

Numerical modelling of glacial lake outburst floods using physically based dam-breach models

“…This simulation tool predicts the progressive growth of a dam breach initiated by either the overtopping or piping of non-cohesive and cohesive embankment materials (Morris et al, 2008;Westoby, 2013;Westoby et al, 2014b). The model employs physically based hydraulic, sediment-erosion and discrete embankment stability modules to calculate the evolving breach geometry and associated drainage outflow hydrograph (Morris et al, 2008). This approach offers a significant advance over simplified, empirically derived breaching models or analytical methods that fit the pattern of breach expansion to user-defined final breach dimensions and formation time.…”

Coastal Flooding in the Solent: An Integrated Analysis of Defences and Inundation

“…Topographic profile surveys were used for analysis of shingle beaches (which are important natural and managed defences in many areas of the Solent). Methods exist to calculate progression of breaching, and subsequent release of water onto the floodplain but any deterministic prediction remains highly uncertain [80,81]. Hence the modelling results in this paper take a simplified approach with breaches assumed to be broken down to floodplain level and water flowing through for the entire tidal cycle.…”