· · · Repository Hydraulic Engineering Reports

This report describes individual flood defence structures of all pilot sites in FLOODsite. For each of the 10 pilot sites the following details are described: Ø the flood prone area Ø the failures observed in the past Ø an overview of all defence structures Ø the flood defence structures in detail together with their potential failure modesThe overall purpose of this report is to give an overview of all flood defence structures of the pilotsites. This information will be needed by Theme 1 to concentrate research efforts on the key flood defence structures and their failure modes. Details of available knowledge on failure modes are then described in a different report so that further needs for research within FLOODsite can be concluded.

It is now accepted that the combination of more intense rainfall, poor planning of built-up areas, rising sea levels, coastal erosion and, in particular, higher storm surges pose a real threat to the UK and many other countries. At a meeting at the Institution of Civil Engineers held on 7 July 2003, the Government Chief Scientist Professor David King asked for 'out-of-the-box' ideas to reduce the cost of future flooding. Here are six ideas, titled as follows. • The Floodsucker • The C-Dam • Pre-emptive Cloud Seeding in Mid-Atlantic • Raising the Water Table Below Arid Regions • Erosion Control with the Great East-Anglian Barrier Reef • Increasing Cloud Albedo

Maps of the Rhine section between Basel and Mainz including the flood defence system.

The report follows the answers to the main goals of the study conducted by CTU. The first part review flood defence structures on the Stropnice River. The second part identifies changes in detention capacity. The detention capacity of the watershed has not change during last century, due to minimal changes in land-use. The third part identifies the flood effects on the river environment. The impact on aquatic biota, especially benthic community, was identified. The evaluation of critical points and potential frictions areas show that they are having local character and the risk may be minimized by following the operational manual.

This report reviews previous investigations on hydraulic loading conditions for different types of flood defence structures such as sea dikes, dunes, beaches and seawalls. For each of these structures the physical processes involved are discussed in some detail and methods are given to either predict relevant input parameters for failure modes of flood defences or the behaviour of the flood defence system under actions from waves or currents.

This report concerns the analysis of flow/discharge measurements obtained from a set of 441 “rigid breach” models constructed between 22/07/1996 and 10/12/1998 at the Agricultural Research Service of the United States Department of Agriculture (USDA) in Stillwater, Oklahoma, US, by G.J. Hanson and colleagues. Each model consisted of a rigid plywood dam cut by a rigid breach. The program of experimental research was aimed at improving models of prediction of discharge through breached embankments, which is the first stage in the prediction of the hydraulic quantities of relevance to embankment erosion and sediment transport in breaches. In contrast with a previous analysis by Temple and Hanson of a subset of the data which consisted in calibrating existing weir discharge prediction equations or a combination of weir equations to obtain a best fit of the measured discharges, the work reported herein concentrates mainly on 1) verifying established weir equations and published guidance on the parameterisation of these equations using the USDA laboratory dataset, 2) testing an approach consisting in combining two weir equations and using the dataset to understand its limitations (the dataset also contains >5000 images which help understanding the physical processes involved in each combination of geometry and flow), 3) using the dataset to understand complex flow patterns observed that are of relevance to embankment breach flow, and 4) suggesting ways in which weir flow equations could be adapted to predict flow in various breach shapes.

Coastal dikes are used as defence structures against flooding in lowland areas and where high tidal ranges occur. The development of a breach induced by wave overtopping has been one of the most frequent causes of dike failure and it is closely related both to the dynamics of a protected coast and to the flood risk assessment and management. At present however, the underlying processes, their simulation and prediction are still not well understood. Due to the urgent need of reliable simulations of the processes, the requirements for a new model were defined. This study, started in 2004 and taking 3 years, is supported by the Joined Doctoral Programme on “Risk Management on Built Environment” (Study University of Florence, Italy and Technical University of Braunschweig, Germany)* and by the European Integrated Research Project FLOODsite (2002- 2006). In this report the processes associated with breaching and the present capability of breach modelling are reviewed. A detailed specification of the new model approach is then proposed.