Modellierung der Flutwelle nach Versagen einer Hochwasserschutzeinrichtung
Final Report Abstract
The failure of flood protection measures (e.g. dikes, mobile walls) releases a wave into the hinterland which may cause extensive damage in the floodplain. In contrast to the flood wave propagation initiated by dam breaks the knowledge of so-called dike-break induced flows can not be called satisfactory. By means of literature research the most influencing variables are identified. A combination of physical (theme A) and numerical (theme B) modelling is used to quantify the impact of the determining factors as regards a reasonable forecast of discharges, water depths and flow velocities of flood waves initiated by dike breaks. An idealised physical model was constructed to examine experimentally dike-break induced flows taking into account the specific boundary conditions of that type of flow. Initial water levels and discharges in the channel as well as the breach width are systematically varied in the scale model test (theme A). A novel semi-analytical formula was developed via measured data to predict the water levels on the main axis rectangular to the breach. It is based on the assumption that the lateral propagation of a dike-break wave can be described as a superposition of well-known sub-processes, namely positive and negative dam-break waves. The approach is applicable in engineering practice and accords well to the measured data. Moreover, the shape of the wave front from top view is approximated. The remaining differences coming from the underlying assumptions are broadly discussed. Altogether, the scale model tests yield an overall picture, which can be used to effectively forecast the flood wave propagation. Special attention so far is paid on the first transient phase as regards the propagation and arrival times of the wave front. Furthermore, water levels, horizontal velocities over depth in the body of the wave as well as discharges through the breach are detected for the final steady state. Once again, the hydrodynamic and geometric boundary conditions are methodically changed. The measured data provides a worthwhile basis for establishing, validating and improving numerical models and simulations, which is the objective of the second project part (theme B). Modelling a Hood wave due to failure of flood protection measures: According the experimental configurations the flow is computed via two different depthintegrated shallow water models and a fully 3D free surface code based on the RANS. The basic flow pattern is reproduced well by all three simulation results. In addition to the hydraulic and geometric conditions several numerical parameters are examined. It was possible to compute the whole flood event when releasing the dike-break induced wave from the initial open channel flow with a closed flap gate up to the final steady state in a single stable run without oscillations. The resulting deviations from the performed measurements are analysed focussing - like in the parallel literature review - on the simplifications of the mathematical model or the numerical approach. The latter has to deal with complex free surface structures, steep gradients, flow over initially dry bed, and friction at the wave front. As regards the mathematical models the different simulations enable direct comparisons between the assumptions of the SWE and the less simplified RANS in relation to the collected experimental data. In consistency with theoretical hypothesis the 3D results fit better the scale model data. By identifying the significant weak points of the SWE concerning that type of flow the priorities of developing and implementing enhanced approaches in shallow water models are elaborated. The relevance of an optimisation is evaluated by the influence of the analysed effect on the experimental flow. The large-scale and longterm inundation of a floodplain in practical applications is strongly affected by the steadystate discharge through the breach. Thus, its correct calculation is the decisive parameter to evaluate model modifications. Comparative simulations including realistic scenarios with complex topography are used to demonstrate the accuracy, feasibility, robustness, and practical applicability of the numerical approaches. The research findings expand into risk assessment studies especially into the calculation of potential damage and vulnerability. Application and exploitation potential can be found in cost estimations used by the insurance industry, evacuation mapping for civil protection, disaster control, emergency management, flood hazard and inundation mapping, set-up of flood protection conceptions, and in the designing and dimensioning of protective structures. Hence, reliable simulation results are eagerly required to fulfil legal and economic demands.
Publications
- BRIECHLE, S. (2006J: Die flächenhafte Ausbreitung der Flutwelle nach Versagen von Hochwasserschutzeinrichtungen an Fließgewässern. (in German) Aachen: Shaker. - ISBN 978-3-8322-6674-5
- NiEMEYER, M. (2007): Einfluss der Breschenbildung auf die Flutwellenausbreitung bei Damm- und Deichbrüchen, (in German) Aachen: Shaker. - ISBN 978-3-8322-7132-9
- HUBER, N.P., NIEMEYER, M, KÖNGETER, J., POLCZYK, H. (2005): Risikoaspekte in der DIN 19700: Eine exemplarische Betrachtung der Rurtalsperre. (in German) In: Die Wasserwirtschaft, Jg. 95, H. 1/2, pp. 24-30. - ISSN 0043-0978
- KUTSCHERA, G.; BACHMANN, D.; HUBER, N.P.; NIEMEYER, M; KÖNGETER, J. (2008): RAPID - Ein Risk-Assessment-Verfahren für den technischen Hochwasserschutz, (in German) In: Wasserwirtschaft, Jg. 98, H. 1-2, pp. 43-48. - ISSN 0043-0978
- KÖNGETER, J.; BRIECHLE, S., HUBER, N.P. (2005): Contributions in Mobile Hochwasserschutzsysteme: Grundlagen für Planung und Einsatz, (in German) Bund der Ingenieure für Wasserwirtschaft, Abfallwirtschaft und Kulturbau (BWK) e.V., Bulletin 6. - ISBN 3-936015-19-8
- NIEMEYER, M.; HUBER, N.P.; BRIECHLE, S.; KÖNGETER, J. (2005); Simulation dämm- und deichbruchinduzierter Flutwellen, (in German) In: Österreichische Wasser- und Abfall- Wirtschaft, Heft 1-2 Jänner/Februar 2005, 57. Jahrgang, Springer: Wien, NewYork, Verlagspostamt 1201 Wien, Zulassungsnummer: 02Z031194M
- ROGER, S.; BÜSSE, E.; KÖNGETER, J. (2006): Dike-break induced flood wave propagation. Proc. of the 7th Int. Conf. on Hydroinformatics, 4-8 September 2006, Acropolis, Nice, France, Vol. 2, pp. 1131-1138, Research Publishing Services. - ISBN 81-903170-1-6
- ROGER, S.; DEWALS, B.J.; SCHÜTTRUMPF, H.; PIROTTON, M. (2008): Simulating dike-break induced flows: Model tests vs. 2D-numerics. Accepted for FLOODrisk Conference, 30 September - 2 October 2008, Oxford, UK
- SCHÜTTRUMPF, H.; GEISENHAINER, P.; POHL, M. (2008): Analysis of dike failures at the coast and in estuaries. Accepted for 31st Int. Conf. on Coastal Engineering, 31 August - 5 September 2008, Hamburg, Germany
