· · · Repository Hydraulic Engineering Reports

Memo met samenvatting van de effecten van stormvloed, dijkdoorbraken en overstromingen in Frankrijk door de storm Xynthia op 28 februari 2010. Overzicht schade, slachtoffers, staat van onderhoud waterkeringen en politieke implicaties. In Bijlage korte beschrijving effect Xynthia in Nederland

Samenvattend rapport van de overstromingsramp in Tuindorp Oostrzaan in Amsterdam in 1960 door het doorbreken van een boezemkade van het Zijkaanaal H van de Noorder IJpolder (Barnegat). Deze doorbraak was aanleiding voor de Minister om de Technische Adviescommissie voor de Waterkeringen op te richten.

Uitgebreide uitgave (ca 150 blz) met een beschrijving van de schade door de watersnoodramp 1953 plus een overzicht van de herstelwerkzaamheden. Bevat veel foto's en tekeningen. Deze speciale uitgave is een goede aanvullen naast het verslag van de stormvloed, uitgegeven door Rijkswaterstaat.

Based on an extensive literature study on the most relevant processes associated with dike breaching and the models available, a modelling strategy was developed which consists in the development of a preliminary and a detailed breaching model (LWI Report 910). This progress report aims to address the development and implementation of the preliminary model.

Sea dikes are of crucial importance in the defence systems of low-lying coastal areas in countries such as Germany, The Netherlands or Denmark, etc. Breaches of sea dikes induced by storm surges are regarded as the main cause of coastal flood disasters. Therefore a reliable prediction of both initial conditions for the breach occurrence and the breach development is urgently needed. Depending on the structure of the sea dike and on the hydraulic and morphological boundary conditions, one may distinguish several causes for the initiation and formation of a breach. The main failure mechanisms are (TAW,1999a): • wave overtopping and overflow, which may lead to the erosion of the shoreward slope and finally to breach initiation from the landward side • breaking wave impact including wave run-up and run-down processes which may lead to the erosion of seaward slope (Fig. 1) and finally to breaching from the seaward side The knowledge of the processes of breach initiation and development is crucial for the prediction of the initial conditions at the defence line needed to model the flood wave propagation. For the prediction of a dike breach initiated by the wave overtopping, a PhD research was completed very recently (D'Eliso, 2007). However, as the processes associated with the dike breach initiation from the seaside as well as the breach growth itself are completely different from those related to overtopping, there is also an urgent need for a model to predict the breach growth initiated from the seaside by breaking wave impact on the outer slope

This report provides an overview of the state of the art with regards to embankment breach initiation and formation processes. Basic breach formation processes are explained, including a review of commonly held misconceptions. The different stages of breach initiation and formation are also explained, along with the varying needs of different end users, and hence the significance of the different stages of breach and the importance of understanding uncertainty within the different stages of breach prediction. Different types of breach model, from simple empirical formulae through to complex, predictive physically based models. Current capabilities and research initiatives related to each are summarised, identifying current best practice and current data sets available for model validation. Perceived gaps and priorities for future development supporting the improved reliability of breach prediction are then summarised.

This report describes small-scaled experiments performed at Leichtweiß-Institute for Hydraulic Engineering and Water Resources, Technical University Braunschweig (LWI). The experiments have been conducted to investigate the development of dike breaches in homogeneous sand dikes with and without a clay layer. The used scaling factor was 1:10.The purpose of the tests is to prepare large-scale model tests in the Large Wave Flume of Hannover (GWK) and to learn about required measurement equipment, how to optimally perform the tests and some qualitative difference between tests performed for overflow conditions and wave-induced overtopping conditions.

Based on an extensive literature study on the most relevant processes associated with dike breaching and the models available, a modelling strategy was developed which consists in the development of a preliminary and a detailed breaching model (LWI Report 910, FLOODsite Report ). Results from the preliminary model give an overview of the breaching process, but indicate that improvements into a more process-oriented detailed model are required (LWI Report 927, FLOODsite Internal Report T06-06-01). This progress report aims to address the development and implementation of the detailed model.

This report provides an overview of the technical work undertaken by the partners under FLOODsite Task 6. The research in Task 6 addresses breach initiation and growth. Research was undertaken to (i) investigate and develop preliminary models for predicting wave induced breach initiation (ii) investigate soil processes, review and refine the HR BREACH predictive model (iii) extend the existing model by Visser to predict breach through cohesive materials and develop associated simplified equations for breach prediction.

The IMPACT Project (www.impact-project.net) provided valuable data on breach formation processes. Five large scale field tests were performed in Norway, and a further 22 laboratory tests were performed in the UK. A review of this data has been undertaken to support breach model testing and development under Task 6.

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.

Erosion of surface vegetation of fluvial and coastal embankments is the first step in the breach initiation process for an embankment. Detailed knowledge of the driving forces, factors and erosion mechanisms is required to understand and manage the failure risk. Past and present research on the erosion of surface vegetation has been reviewed and is summarised in this report to provide a summary of the current state of knowledge. Based upon these findings, gaps in knowledge and research needs have been identified.

Based on an extensive literature study on the most relevant processes associated with dike breaching and the models available, a modelling strategy was developed which consists in the development of a preliminary and a detailed breaching model (LWI Report 910, FLOODsite Report ). Results from the preliminary model give an overview of the breaching process, but indicate that improvements into a more process-oriented detailed model are required (LWI Report 927, FLOODsite Internal Report T06-06-01). Results from the detailed model, where new processes have been included, provide a first step toward a complete process-oriented description of the breaching process (LWI Report 937, FLOODsite Internal Report T07-06). This progress report aims to quantify the uncertainties start validating the model.

Sea dikes are of crucial importance in the defence systems of low-lying coastal areas in Germany as well as in other countries such as The Netherlands and Denmark. Breaches of sea dikes due to storm surges are regarded as the main cause of flood disasters, so that a reliable prediction of both breach initiation, breach formation and breach development is urgently needed. One may distinguish several causes of dike breaching, depending on the structure of the dike as well as on the morphologic, geotechnical and on hydraulic boundary conditions. A breach may be initiated either from the landside by wave overtopping and overflow or from the seaside by repeated breaking wave impacts on a dike slope. For a dike breach initiated by wave overtopping, a PhD research has been completed (D’Eliso, 2007). Because the processes associated with the dike breach initiation from the seaside as well as the breach growth itself are completely different, there is an urgent need to investigate the dike breaching initiated from the seaside. The knowledge of the process of breach initiation and development is crucial for the prediction of the initial conditions at the defence line needed to model the flood wave propagation. In order to satisfy those needs, a tiered and modular strategy similar to that adopted by D'Eliso (2007) is applied. Similarly, the complete model consists of a simplified preliminary model and a more process-oriented detailed model. In this report the assumptions of the preliminary model, its implementation, example application and discussion on the limitations and capabilities is presented.

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.

During the IMPACT Project a number of large scale field tests were undertaken in Norway to collect data, including extensive video footage, recording the physical processes that occured during the initiation and growth of breach through the test embankments. The video footage has been carefully analysed and key processes identified, to support the development of new and improved numerical models. This report presents the findings of this analysis

Description of the performance of the large-scale experiments in the GWK in Hannover in 2008

Sea dikes are of crucial importance in the defence systems of low-lying coastal areas in Germany as well as in other countries such as The Netherlands and Denmark. Breaches of sea dikes due to storm surges are regarded as the main cause of flood disasters, so that a reliable prediction of both breach initiation, breach formation and breach development is urgently needed. One may distinguish several causes of dike breaching, depending on the structure of the dike as well as on the morphologic, geotechnical and on hydraulic boundary conditions. A breach may be initiated either from the landside by wave overtopping and overflow or from the seaside by repeated breaking wave impacts on a dike slope. For a dike breach initiated by wave overtopping, a PhD research has been completed (D’Eliso, 2007). Because the processes associated with the dike breach initiation from the seaside as well as the breach growth itself are completely different, there is an urgent need to investigate the dike breaching initiated from the seaside. The knowledge of the process of breach initiation and development is crucial for the prediction of the initial conditions at the defence line needed to model the flood wave propagation. In order to satisfy those needs, a tiered and modular strategy similar to that adopted by D'Eliso (2007) is applied. Similarly, the complete model consists of a simplified preliminary model and a more process-oriented detailed model. In this report the assumptions of the preliminary model, its implementation, example application and discussion on the limitations and capabilities is presented.