Andreas Kortenhaus

CLASSIFICATION OF WAVE LOADING ON MONOLITHIC COASTAL STRUCTURES

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

FAILURE MODE AND FAULT TREE ANALYSIS FOR SEA AND ESTUARY DIKES

Abstract: A detailed analysis of failure modes for seadikes has been performed and was used to derive a complete set of limit state equations for the description of failure scenarios of seadikes. These models and scenarios were then used to calculate the respective failure probabilities and the overall failure probability by a fault tree approach. A simple example of a non-existing seadike was used to illustrate the procedure. Details of parameters, model uncertainties and their influences on the results as well as further information required for the aforementioned procedure are also discussed.

RISK-BASED DESIGN OF COASTAL FLOOD DEFENCES: A SUGGESTION FOR A CONCEPTUAL FRAMEWORK

A conceptual framework based on probabilistic risk analysis (PRA) is proposed for the design of coastal flood defences which meets the sustainability requirements. The overall framework includes the management of the remaining risk as an integral part of the design process. The implementation of the risk analysis requires (i) the prediction of the flood risk, (ii) the evaluation of the acceptable flood risk and (iii) the evaluation of the flood risk level which is obtained through comparison of the predicted and acceptable flood risk. NECESSITY OF NEW DESIGN APPROACH FOR COASTAL FLOOD DEFENCES Coastal areas are among the most densely populated areas worldwide so that there is a large and increasing demand for housing, recreation and further socio-economic activities in these areas. Today almost 40% of the world population are living within a 100 km wide coastal strip and almost 70 % of the large cities with more than 2.5 million inhabitants are located in coastal areas (Fig. 1). Generally, this tendency implies more infrastructure to be provided and more coastal defence structures to be built in this area. In fact, this development has already resulted in a dramatic conversion of the natural coastal zones to a built (artificial) environment protected by an almost artificial defence line. 1 University Professor, Joint Research Centre for Coastal Engineering (FZK) of the University of Hannover and the Technical University of Braunschweig, Leichtweiss-Institut (LWI), TU Braunschweig, Beethovenstr. 51a, D-38106 Braunschweig, Germany, h.oumeraci@tubs.de 2 Senior research engineer, Leichtweiss-Institut (LWI), TU Braunschweig, Beethovenstr. 51a, D-38106 Braunschweig, Germany, a.kortenhaus@tu-bs.de

APPLICATION OF OVERTOPPING MODELS TO VERTICAL WALLS AGAINST STORM SURGES

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

RELIABILITY ASSESSMENT OF A COASTAL DIKE AND DUNE SYSTEM AT THE SOUTH OF FALSTER, DENMARK

The ‘Falster dike’ is a system of a coastal vegetated dunes with a grass-covered sand dike protecting a low-lying area of about 7,000 summer houses, many of which being inhabited during winter, and therefore in danger of any storm surge induced flooding. The paper discusses (i) the assessment and uncertainties of relevant data such as bathymetry, topography, wind and wave data, water levels; (ii) deterministic calculations of wave run-up and overtopping of the dike without dunes; (iii) the calculations of dune erosion; and (iv) a reliability assessment of a dune and dike system. Results suggest that the dunes in front of the dikes lead to a significantly increased safety of the flood defences and will therefore withstand present and future conditions, including climate change scenarios.

Wave run-up and wave overtopping on a rubble mound breakwater - Comparison of prototype and laboratory investigations

Hydraulic model tests were performed within the European CLASH project at two different sites in Europe to hindcast measured overtopping rates during storm events from prototype measurements at the Zeebrugge rubble mound breakwater. This paper describes the general methodology behind this comparison and results regarding uncertainties in measurements of both waves and mean overtopping rates. Quantification of uncertainties is shown to be the first step in being able to quantify model and scale effects and therefore need to be properly assessed. First plots of available model tests showing considerable scatter in wave overtopping results are also given together with initial data points from prototype measurements.

Probabilistic Design of Caisson Breakwaters and Sea Walls: Present Status and Perspectives

Probabilistic design tools for vertical breakwaters (PROVERBS) was a major European research project within the 4 th framework programme of the European Union and was finished in 1999. The overall objective of the project was to develop and implement a reliability based framework and associated probabilistic tools for the design of vertical breakwaters. 23 research organisations from 8 European countries and from disciplines such as fluid and soil mechanics, structural dynamics, applied mathematics, coastal and harbour engineering have contributed to the project. The paper discusses PROVERBS results and shows applications to representative breakwaters as well as their implementation within a risk analysis framework. The advantages and restrictions of probabilistic design will be summarised and conclusions will be drawn towards extending future research to risk analysis approaches.