Sound flood risk management decision making is underpinned by flood risk analysis. Current methods applied at regional and local scales are often limited in their consideration of the potential for defences to fail. Ultimately this can lead to underestimates of the true risk and subsequent difficulties in justifying mitigation measures such as maintenance and replacement of defences. A methodology has been developed for assessing flood risk arising from fluvial and coastal sources that explicitly considers defence failures represented through fragility curves. This method requires consideration of flooding scenarios involving multiple defence section failures and flood events ranging in severity. It has therefore been necessary to develop a purpose-specific flood spreading method that is capable of simulating many flood events in practical timescales. The method has been applied to the Thames Estuary, where outputs including spatial maps of flood risk and defences attributed with residual risk have been used to support decisions relating to strategic flood risk management over the coming century.

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Recession of high-mountain glaciers in response to climatic change frequently results in the development of morainedammed glacial lakes. Moraine dam failure is often accompanied by the release of large volumes of water and sediment, termed a Glacial Lake Outburst Flood (GLOF). Chukhung Glacier is a small (~3 km 2 ) receding valley glacier in Mt. Everest (Sagarmatha) National Park, Nepal. Unlike many Himalayan glaciers, which possess a thick mantle of supraglacial debris, its surface is relatively clean. The glacier terminus has receded 1.3 km from its maximum Holocene position, and in doing so provided the space for an icecontact moraine-dammed lake to develop. The lake had a maximum volume of 5.5 × 10 5 m 3 and drained as a result of breaching of the terminal moraine. An estimated 1.3 × 10 5 m 3 of material was removed from the terminal moraine during breach development. Numerical dam-breach modelling, implemented within a Generalised Likelihood Uncertainty Estimation (GLUE) framework, was used to investigate a range of moraine-dam failure scenarios. Reconstructed outflow peak discharges, including failure via overtopping and piping mechanisms, are in the range 146-2200 m 3 s -1 . Results from two-dimensional hydrodynamic GLOF modelling indicate that maximum local flow depths may have exceeded 9 m, with maximum flow velocities exceeding 20 m s -1 within 700 m of the breach. The floodwaters mobilised a significant amount of material, sourced mostly from the expanding breach, forming a 300 m long and 100 m wide debris fan originating at the breach exit. moraine-dam. These results also suggest that inundation of the entire floodplain may have been achieved within ten minutes of initial breach development, suggesting that debris fan development was rapid. We discuss the key glaciological and geomorphological factors that have determined the evolution of a hazardous moraine-dammed lake complex and the subsequent generation of a GLOF and its geomorphological impact.

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.