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Spekker, H.. Steuerung von Küstenschutzelementen an Tideflüssen als Grundlage für ein Risikomanagement. In: EUCC - Die Küsten Union Deutschland e.V.. International approaches of coastal research in theory and practice. Coastline Reports (13), pp. 79-94. EUCC - The Coastal Union, Leiden, 2009.


Control of coastal protection elements along tidal rivers as basis for flood and risk management.

Located below mean sea level large parts of coastal hinterlands, especially along tidal rivers, are endangered from inundations during storm surges and extreme floods. Coastal hinterlands are commonly protected by a system of coastal protection elements, e.g. levees or storm surge barriers. Increasing crest heights of these coastal structures is the traditional strategy of coastal defence using deterministic methodologies.

Efficient flood and risk management should reduce risk and mitigate effects of hazards caused by increased water levels due to higher sea level, changes in storm surge frequencies and stronger floods. Apart from sea and river dykes as well as storm surge barriers as major flood protection elements, a variety of additional structures like controllable flood- and spillways or polder areas are feasible structural elements to be established along estuaries and deltas. In combination with innovative control strategies these measures extend the flood storage.

Main objective of the thesis is the analysis of new measures and innovative coastal protection strategies at tidal rivers. In addition to modified regulations of control structures mentioned above, another important focal point is to evaluate the effects of connected polder areas and floodways in order to reduce high water levels and flood risk in the coastal hinterland. Tested on the basis of an idealised estuary the methodology is subsequently applied to real estuaries (Weser River estuary and Mississippi River delta). A high risk potential exists in both regions due to densely populated cities, e. g. Bremen and New Orleans, as well as important businesses and industries along these rivers. This paper presents the results for the Weser River estuary.

Hydrodynamic-numerical models using combinations of characteristic flood and storm surge scenarios are established in order to obtain critical configurations of the hydrodynamic system. Based on that, the probability of failure and the related damage due to flooding of the coastal defence system are calculated for one focal area. Linked models are applied to simulate the process of flooding as a result of failure scenarios of the coastal protection system. Subsequently the risk of the hinterland is calculated as a product of the probability of failure and the flood loss.

Variations of risk control strategies clearly indicate that polder areas as well as artificial floodways along estuaries with controllable inlets are capable to reduce the tidal high water level in estuaries and deltas. Thus, these measures minimise the probability of failure of the coastal protection system also during extreme events. In comparison, changed control strategies of storm surge barriers reduce the tidal high water level only to a limited extent. The results provide a basis for discussion addressing all parties involved within the integrated flood and risk management and may help to find solutions and possible ways for a better communication of risk and the effects of risk mitigation measures.
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