· · · Institutional Repository

New Profile for the Amsterdam-Rhinecanal The aim of this thesis is to design a new profile for the Amsterdam-Rhine canal. The new profile needs to be well navigable and requires to have stable bank constructions. Simultaneously several social aspects have to be taken into consideration. The assignment is summarized as follows: Design a new profile of the Amsterdam-Rhine canal with a stable bank protection that takes future developments, durability and recreation into consideration. The history of the Amsterdam-Rhine canal shows that the draft of the vessels that use this canal has increased from 3.30 to 4.00 meters. This four-metre draft has been permitted since 1988 and was based on the dimensions of the push tow units. In the late 90s of the past century, a new generation of inland vessels made its appearance. Around 2002 problems to the bank constructions due to erosion were detected for the first time, possibly caused by the new generation inland vessels. The number of bigger inland vessels, particularly those in the VIa category has strongly increased over the past years together with the engine power and cargo capacity of many vessels (increase in scale). A representative canal section of the Amsterdam-Rhine canal, just north of Breukelen, has been chosen as research site. At this location erosion ranges from 0.20 to 1.70 meters within 15 meters distance of the sheet piles. The possible cause of this erosion has been further investigated in this report. Also research has been done to determine the governing hydraulic load, which is generated by governing vessels overtaking another vessel. The governing situation is defined as follows: a Rijnmaxship (135x17x4.00 m) overtaking a four barge push-towing vessel (198x22.8x4.00 m). In this situation, the return current is governing compared to a situation when loads from the main and bow thrusters are considered. The return current has been calculated with the 1D model DIPRO. DIPRO has also been used to validate the 2D model in Delft3D, to further elaborate the return current in the 2D model. The 2D model in Delft3D has been used to determine the maximum return currents around the two governing vessels. These values have been translated to the bottom of the canal by calculating the erosion. From these results can be concluded that canal profile (2) has twice the amount of erosion compared to canal profile (3). In this report canal profile (3) is recommended as the new normative canal profile for the Amsterdam-Rhine canal. Canal profile (3) is a combination of a box profile with a sloped upper bank and bottom, with in the middle a waterdepth of 7.60 meter. The depth in front of the sheet pile is 6.00 meter. The wet cross section is 751 m2. The bank construction consists of a sheet pile with a slope. The outcome of this thesis is a design for a new representative canal profile in the Amsterdam-Rhine canal. The normative hydraulic load (return current) causes minimum erosion to the canal bottom, which keeps the bank construction stable. Next to this the design proves that environmental and recreational purposes can be well combined in coherence with social developments.

Along the northern coast of Morocco order has been given for the construction of a large transshipment port in the Mediterranean Sea, at a designated project location around the city of Nador. On this green-field coastal stretch a new transhipment port will have to be developed for various types of cargo. Throughputs of the terminals will have to be maximized, a plan for in-phased port development and expansion will have to be provided, cargo transport to the hinterland has to be taken into account and sufficient surface space should be included in the design for additional services. Relevant data regarding the project (location) has been identified and analyzed: hydrodynamic data (wind, waves, currents, water levels) and environmental site data (topography, bathymetry, geology, hydrology and morphology). Besides this, a forecast has been formulated with the expected design ships that will visit the new port. From this, cargo-vessel distributions and vessel-arrival distributions have been defined, resulting in the total amount of shipping traffic for every terminal. Subsequently, the design of the port master plan can commence in which first of all the approach channel, harbor basins and manoeuvring and berth areas have been designed. As a next step the characteristics of the various terminals have been determined, under which the number of berths, quay length and surface areas. After using all port elements listed above jointly, several port masterplan layouts have been drawn up. From these port masterplan layouts, the most promising alternative has been selected after comparison by means of a Multi Criteria Analysis (MCA) on various criteria under which nautical ease, safety, expansion possibilities and costs. Concluding to this, the selected port masterplan layout has been optimized. The resulting harbour layout has been assessed regarding the topic of in-port wave penetration and propagation. Limiting operational wave criteria have been defined and relevant wave processes have been evaluated with the wave simulation model DIFFRAC-2DH. In order to decrease wave reflection due to monolithic breakwaters (and thus the port’s downtime), new simulation runs were carried out with an improved breakwater configuration using low-reflectivity caissons. With these wave-dampening improvements included, the simulation model runs yielded very positive results. The wave study was concluded with an assessment on port oscillations as a result of earthquakes, tsunamis and meteorological forces. After the performed wave study, the port breakwaters have been designed. For this, two typical cross-sections were selected. After including construction constraints and wave damping measures, a rubble mound breakwater was designed with a specific armour layer, and a vertical composite breakwater as a perforated wall caisson on a rubble mound foundation bed. The application of wave energy absorbing measures is a necessity in order to minimize the port’s downtime, and will have to be included in a final design. The designed port masterplan layout meets all specifications and requirements and its breakwaters are adequate in creating calm in-port berthing conditions resulting in high uptimes of the berths.

Viet Nam lies in the region of direct impact of sea level rise and climate change, especially in the East Sea where branches of Me Kong river run off. In the annual report on “Climate change and sea level rise in Viet Nam” MONRE has proposed 3 scenarios of sea level rise in the next 100 years viz. 60 cm (low emission scenario), 75 cm (medium emission scenario), 100 cm (high emission scenario). This study is implemented these 3 scenarios on 2 case studies of 2 sea ports: Nam Du deep sea port with researched structure is jetty structure and Tien Sa sea port with researched structure is breakwater. The thesis focuses on the impact of waves and sea level rise on these two types of structures. The objective of this report is to better understanding of how the hydraulic structure(breakwaters and jetties) be impacted by the rising sea level and waves in that SLR condition in the future; answer the question whether the designed structures are stable and functional enough to sustain with SLR. By the results from study, some conceptual recommendations will be proposed to account SLR in the future design. The results of this report shows that jetty structures are not touched by extreme maximum waves in 3 SLR scenarios. The structures themselves are designed included 30 cm of SLR and high enough for water not to transmit to the deck. However, Tien Sa breakwater is unstable if the sea level rises in next 100 years. The structure was not well designed enough to sustain with rising sea level and higher wave conditions. The solution for repairing is ballasting the caisson breakwater to 1m thickness or another proposing conceptual design is enlarging the caisson toe to 6m length to ensure the stability.

A consortium of DHV, Imares and Alle Hosper proposed the reclamation of tidal marshes in front of the Afsluitdijk. During severe storms the tidal marshes reduce the wave attack and therefore improve the safety assessment of the Afsluitdijk. The construction of the tidal marshes implies the transportation of approximately 50 Mm3 sediment. This study deals with the feasibility of transporting a considerable part of this volume by using the sediment transport processes at the Texel Inlet. The morphological development of the dump of a significant volume of sediment in the deeper parts of the Texel Inlet has been examined. The amount of the dumped volume that sedimentates at the end of the Texel Inlet close to the Afsluitdijk determines the efficiency of the method. The Texel Inlet is a tidal inlet in the western part of the Dutch Wadden Sea. The main hydrodynamic forcing of the Texel Inlet is the tide.

In numerical modelling of water movement wetting and drying is a well known problem. The governing equations are not valid in the dry part of the computational domain which may result in problems with mass conservation, negative water depths and artificially enlarged gradients. A method is proposed that allows for the surface elevation to become negative while strict positivity is demanded from the water depth. In this way mass conservation is guaranteed. It is investigated whether this procedure is mass conservative, efficient and robust. To this end a simple finite element discretization of the inviscid shallow water equations (SWE) is derived. The resulting procedure is validated with several one- and two-dimensional analytical solutions for: 1) a one dimensional dam break, 2) flow over a long crested weir, 3) a one-dimensional oscillating water surface in a parabolic basin, 4) the runup of long waves on a beach, 4) a two-dimensional standing wave in a parabolic basin and 5) the spreading of a parabolic flood wave in two dimensions. In addition two laboratory experiments are used for validation. One experiment with solitary wave runup on a conical island and one experiment with a two dimensional dam break. In general the methods performance is good. However in two-dimensions it can be beneficial, in case of small gradients at the wet/dry interface, to use a lumped mass matrix at partially dry elements too. The wetting and drying iteration converges on average in 2 to 3 iteration steps. In some cases bifurcations and mass errors can occur. However mass errors are caused by rounding errors and can be resolved by using double precision. The occurrence of bifurcations is much less frequent in case of calculations in double precision and can be minimized by adjusting the BiCGSTAB settings.

The workability of floating construction equipment is one of the elements in the construction phasing of the design of the Ashdod port extension in the south of Israel by DHV Consultancy and Engineering. Waves play an important role in the workability of floating equipment, since they induce motions to floating equipment with the possibility of adverse effects on the workability. For the purpose of assessing the workability of this equipment in relation to the wave climate during several critical phases of the construction, wave modelling should provide insight. A recent development is the availability of Boussinesq-type models for this type of studies. Boussinesq-type models are phase-resolving, which means that they describe the individual wave behaviour. This gives Boussinesq-type wave models the capability of describing wave propagation in relatively shallow regions (e.g. harbours and foreshores), where nonlinear effects and dispersion play an important role. Boussinesq-type wave models are suited to deal with complex harbour geometries, including modelling of diffraction, partial reflection and wave-wave interactions. In this study, it is investigated whether TRITON, an experimental Boussinesq-type wave model currently under development at Deltares, is suitable for the purpose of workability assessment of floating equipment. The suitability of TRITON depends on aspects like the applicability of Boussinesq-type models in general, the correctness of results and the computational effort for TRITON. As part of this study, the results of TRITON are compared with measurement data from a physical scale model of Ashdod port, which was mainly set-up for measuring moored vessel motions. For the validation of TRITON for the purpose of workability assessments, the Ashdod port extension is used as a case study. The plausible floating equipment scenario for the construction phasing of the Ashdod port extension (consisting of typical dredgers, stone dumpers and crane barges) is sensitive for primary waves within a peak period range of 5-12s. The estimation of the workability limits of the plausible equipment is based on a combination of ship motion theory, information from contractors and personal communication with experts. Based on the present study, TRITON is considered technically capable for the purpose of workability assessments in port applications. The appropriateness for using TRITON in this type of application is however limited by the application range of TRITON – due to the mathematical background of Boussinesq-type models – and by computation times.

The storm surge early-warning system that is going to be established in the Netherlands, combines the accurate weather forecast with the hydrodynamic and morphodynamic models in an operational mode, in order to estimate the potential impact on the coasts. This study focuses on the morphodynamic validity of the operational model system, by studying two historical storm surge events on prototype scale. Due to the lack of warning, the 1953 storm surge left behind thousands of casualties and extensive wreckage of the Dutch coastline. In order to reduce the probability of experiencing again such a devastating storm surge, the coastal defense policy in the Netherlands had been reorganized on national level and more effective countermeasures had been received. When the 1976 storm surge attacked the country, the civil awareness and the reinforced coastal defense abate the impact and the fatalities. The degradation of the coastline has been recorded as part of the Jarkus coastline monitoring programme, and after the conducted analysis the non-uniform impact along the North Holland province became evident. Two numerical models form the operational model schematization; the deformation and the propagation of the storm surge are simulated with the Delft3D model and the nearshore hydrodynamic and morphodynamic processes by the XBeach model. The available storm surge level records attest that the model underestimates the storm surge level for both of the events, up to 0.70m and the phase lag up to 45 minutes. In the studied site of Bergen, the performed sensitivity analysis of the XBeach model proves that the water level underestimation is an important parameter for the deviations between the coastal profile records as a result of the 1976 storm surge and the computed post storm profile, as higher computational skill is obtained when imposing the measured storm surge level record instead of the computed one. Furthermore, the XBeach model reacts as expected at the changes concerning the waves' asymmetry and the slumping of the water area through its avalanching mechanism, reflecting a higher computational skill. In contrast, the model is insensitive to the long waves' sediment stirring and to the additional imposed wind setup. Concerning the model performance in the area of Castricum, the model skill is excellent and very good convergence is obtained on estimating the volume change and the estimated dune retreat. In Julianadorp, while the influence of the groins is not accounted, due to the significant scouring that is observed in the backshore zone, the model performance is bad. The geological features and the bed profile of the studied areas present a different pattern of the energy distribution, which may indicate a possible reason for the longshore erosion variability during the 1976 storm surge. The operational model needs to be further verified with the 2DH simulations in order to account for the longshore profile development and the effects of the hard non-erodible structures, while it is also recommended to further investigate the extensive scour development in the backshore zone.

Due to the planned construction of Maasvlakte 2 the E.ON power plant on the Maasvlakte will not discharge its heated water into the North Sea anymore, but in the harbour basins itself. This together with a planned increase of the total amount of thermal discharges in the Maasvlakte area (power plants of EnecoGen and Electrabel, chemical industry etc.) will most probably lead to an increase of the water temperature within the harbour basins, which can lead to economical, legal and ecological consequences. In cooperation with the Port of Rotterdam and Deltares, this master thesis aimed to give an answer to the amount of increase of water temperature due to the planned thermal discharges, its consequences and measures to reduce this increase of temperature. With the use of some first estimates and a heat-balance there could be concluded that the increase of temperature is significant and that the movement of the tide together with the freshwater flux is the main mechanism for the netto heat flux out of the Maasvlakte area. Stratification has an important influence on the spreading of the heat plumes in the harbours. To give a more accurate prediction of the increase of water temperature at the mixing zone borders and at the intake locations (recirculation), the numerical hydrostatic model Delft3D-FLOW and the near-field model CORMIX are used. It is shown that the regulations will not be exceeded if the borders of the mixing zones are chosen close to the Beerkanaal. The predicted increase of temperature at the E.ON-intake will cause some economical losses. Replacing the intake at a greater depth or (even better) a variable intake near the water surface and bottom could be effective measures to reduce these losses. For a more drastic reduction of the increase of temperature in the harbour basins, relative expensive measures are needed. It is recommended to the Port of Rotterdam to place future thermal discharges as close as possible near the Beerkanaal or North Sea, and to study the ecological effects of the temperature rise in the Eastern Yangtzehaven.

De Westerschelde is een complex estuarium waarin natuurlijke ontwikkelingen, menselijk ingrijpen en hydrodynamica elkaar beinvloeden. Voor het beheer van dit gebied worden o.a. numerieke rekenmodellen toegepast om de water- en sedimentbeweging in de Westerschelde te simuleren. Met behulp van het softwarepakket FINEL is een horizontaal twee dimensionaal model van de Westerschelde gebouwd (FINWES96). De resultaten van dit model komen goed overeen met metingen van waterstanden en snelheden en de resultaten van het reeds bestaande WAQUA-model SCALDIS100. Op basis van het stroommodel FINWES96 zjjn zandtransporten berekend. Deze berekeningen zijn gebaseerd op de evenwichtstransport-formules van Engelund/Hansen en Van Rijn. De resultaten van deze berekeningen zjjn redelijk in overeenstemming met gemeten zandconcentraties, beddingvormen en bodemveranderingen. Het model FINWES96 kan op verschillende manieren bij morfologisch onderzoek gebruikt worden. Als illustratie is de invloed van de verdieping van de drempel van Hansweert bestudeerd. De belangrijkste conclusies van het afstudeerproject zijn: - Het gebruik van numerieke modellen is een relatief goedkope en veelbelovende methode voor morfologisch onderzoek (onder andere in de Westerschelde). - Het softwarepakket FINEL is flexibel en betrouwbaar. - Bij de verdere ontwikkeling van morfologische modellen voor de Westerschelde zal men onder andere aandacht moeten besteden aan de naijling en onder- en oververzadiging van de zandconcentratie. - Een verdieping van de drempel van Hansweert tot NAP - 16 m doet de jaarlijkse baggerhoeveelheid met 0.5 - 1.0 Mm3 toenemen. - Storten van het t.b.v. de verdieping gebaggerde zandvolume in de Schaar van Waarde of het Zuidergat beinvloedt de grootschalige water- en zandbeweging. M.n. ter plekke van de overgang tussen verschillende geulen (drempels) verandert het erosie/sedimentatiepatroon.

This project focuses on studying and modelling the flow in the sailing area of the 2012 Olympic Sailing Competition, located partly in Portland Harbour and partly in Weymouth Bay, in order to provide accurate and reliable current forecasts for the Dutch Olympic Sailing Team. From literature it follows that the main flow in the area is the tidal flow. Wind- and wave-induced currents may have a significant influence on the flow as well. Since the available current data is considered outdated, sailed current measurements have been performed to obtain reliable current data. To provide for current forecasts, the two-dimensional depth-averaged numerical flow model FINEL2D, which has the finite element method (FEM) as numerical basis, has been used. FINEL2D adopts the discontinuous Galerkin method to solve the shallow water equations, complemented by a Riemann solver according to Roe to account for the fluxes trough the element boundaries. The TPXO model has been used to enforce boundary conditions on the model. A Nikuradse roughness of 0.035 m has led to model results which deviate least from the measured current. To overcome the phase shift that is still visible, the roughness around Portland Bill and the Shambles Bank has been increased to 0.25 m. By investigating the influence of wind and waves on the flow, it appeared that the wave-induced current in the area of interest is negligible. Wind does however have a significant influence on the flow. Since it is difficult to obtain accurate and reliable wind predictions, accounting for the wind in the current forecasts is difficult. In conclusion it can be stated that the flow in the sailing area of the 2012 Olympic Sailing Competition can be modelled well by means of the two-dimensional depth-averaged numerical flow model FINEL2D. The model results correspond well to the during the survey measured flow velocities and flow directions.

It is common practice to protect subsea pipelines by embedding them into the soil. Trenches can be made before or after the pipelines have been laid. In the latter case, the excavation process is called post-trenching. The essence of post-trenching, as handled in this thesis, is erosion of sand by a water-jet. The literature study focused on the processes of jets and erosion. A lot of research has been done in the field of water jets and useful information is widely available. Nevertheless the available information on the subject of impinging jets is rather limited and the validity remains questionable. Water jets used for post-trenching create high flow velocities for which the traditional erosion equations are not valid. Therefore use is made of a special set of equations for high speed erosion. With the information provided by the literature study a description of jetting in sand was made. The known processes were arranged resulting in a set of equations. Following the rules for scaling the set of equations was converted into a properly scaled model. Preliminary model tests were conducted to observe the jet-process and narrow down the possible jet angles. These preliminary tests were followed by scale model tests to determine the erosion depth for different nozzle angles, flow velocities etcetera. A numerical model was developed to simulate jet-induced erosion. Since the erosion equations, making use of the average flow velocity, could not model the erosion behaviour of a jet, a turbulence term was introduced. The results of the simulations were compared with the model tests. Though the numerical erosion model showed promising results, it could not be validated due to a lack of data. The most important conclusions are that soil can be eroded to the desired depth, a data-set has been created and much insight is gained with respect to the post-trenching process. Last but not least, a numerical model was made that can prove to be useful after better validation.

New developments in the design of off-shore harbours, involving land reclamation and the use of large vessels (draughts larger than 10 meter) have made it necessary for breakwaters to be constructed in deeper water. In deep water, vertical caisson breakwaters have been found to provide better economical solutions than rubble mound breakwaters, because they use less material per cross-section. These vertical caisson breakwaters lead to a high level of wave reflection, a phenomenon that causes unfavourable disturbance and which creates a threat to safe navigation of vessels. Because ofthis high wave reflection factor the wave loads on a vertical breakwater are also become high. To reduce the high reflection of waves and the wave loads on the vertical breakwater the search for innovative breakwater designs, which dissipate the wave energy effectively, is necessary. New existing innovative breakwaters like perforated and slit-type caissons are effective in reducing wave reflection and wave loads, but only in a narrow range of wave frequencies. The main question of this study is whether it is possible to dissipate wave energy in a dynamical way by transferring the wave energy to a movable element, which is able to dissipate wave energy effectively in a wide range of wave frequencies? New innovative dynamic breakwaters with movable elements are presented in this report. The wave damping characteristics of the dynamic breakwater with a horizontally translating flap are analysed. A simple mass-spring-dashpot model has been derived and this can be used to describe the dynamic behaviour of the movable flap. The damping characteristics of a dynamic breakwater with movable flap depend entirely on the hydraulic boundaries (wave height, wave period and water depth) and the characteristics of the movable flap (mass, spring stiffness and damping). The hydraulic performance of the dynamic breakwater is described by the reflection of the waves in front of the movable flap. To study the hydraulic performance of the dynamic breakwater with movable flap the analytic solution is obtained and a computer model is used. The analytical solution is derived to describe the wave reflection for waves that are assumed to be long waves, so vertical accelerations are not simulated in the analytical solution. From the analytical solution it can be concluded that, in theory, the dynamic breakwater with movable flap can damp waves totally for one specific wave period if the characteristics of the flap are tuned to this wave period. The main conclusion drawn from this study is that a dynamic breakwater with a movable flap is able to reduce the wave heights in a wider range of frequencies than a static breakwater. For a dynamic breakwater with movable flap with characteristics that are tuned to certain target wave conditions it is possible to reduce the wave reflection by 50 % for a wide range of wave frequencies.

Ho Chi Minh City (HCMC) is one of the most important cities in Vietnam; it is the largest city and the economic centre of the country. Currently HCMC is facing two main problems: frequent flooding of the city and salt intrusion in the Dong Thap Muoi region. Most floods are the result of monthly high tides that hinder the discharge of rain and river discharge water. Floods as a result of solely high river discharge or storm surge are less probable. It is expected that the flood problem will increase in the future due to urban and industrial developments in low lying areas, climate change and land subsidence. A possible solution for, or contribution in solving, these problems is controlling the in- and outflow in the estuary mouth to a feasible extent with a barrier downstream of HCMC. In this study the feasibility of different barrier options is determined and compared using a simple multi criteria analysis, taken the main interest of five stakeholders into account.

The research objective of this thesis is to determine the new hydrodynamic and morphodynamic situation in case the Oosterschelde storm surge barrier is removed, with emphasis on the development of the intertidal area. To reach the objectives of this study a literature study is performed which describes the impact of the Deltaworks. An analytical model is developed to evaluate the effect of the Philipsdam and Oesterdam on the hydrodynamics in the Oosterschelde when the barrier is removed. Besides that a Delft3D model, the Kustzuid model, is used to determine the effect of bathymetric changes, removal of the barrier and realignment of the basin. Several adaptations have been made to the Kustzuid model to improve the performance. A theory by [Friedrichs and Aubrey, 1988] is used to analyse the distortion of the water level and discharge signal. The applied theory uses the relative phase of the M2 and M4 component to indicate the asymmetry. Removal of the barrier causes an increase of the tidal range by 10 to 20%. This is indicated both by the analytical model as by the Delft3D model. The tidal range will not get as large as it was before the Deltaworks. Removal of the barrier will cause an increase of the tidal prism and strengthen the ebb dominance of the basin. Besides that shoal build up will be enforced by the higher current velocities. Simulations with different bathymetries dating from 1983, 2008 and 2100 indicate that the loss of sediment from the shoals to the channels leads to a less ebb dominant system. A sligthly less ebb-dominant system is found in 2008 compared to the 1983 scenario. Ongoing loss of sediment from the intertidal area leads to a scenario without intertidal flats in 2100. In the 2100 scenario without barrier the system gets flood dominant in the eastern parts of the basin. Flood dominance throughout the entire basin is found when the barrier is still in place in 2100. Large scale realignment of the Oosterschelde is simulated by adding intertidal area to the Oosterschelde without increasing the channel volume. These simulations show increased ebbdominance, leading to export of sediment. The set back of part of the dikes will increase the flow velocities inside the basin, however not enough to cause shoal build up. When the barrier is removed in combination with realignment, shoal build up will occur. Based on empirical relations, realignment of the Oosterschelde is not expected to have a large effect on the relative flat area.

The Wash estuary is situated at the English east coast. Covering an area of approximately 615 km2, the estuary is among the largest estuaries in the United Kingdom. Adjacent to the Wash estuary, the Fenlands are situated, a low lying area covering almost 3900 km2. Within the last century several coastal flood disasters and near flood disasters have occurred in the area. In view of the predicted climate changes it is proposed to construct a privately funded storm surge barrier across the estuary, including a tidal power plant to generate marine power. The thesis focuses on establishing the technical and economical feasibility of such combined structure, taking into account the effect of the barrier on the tidal amplitude within the basin by means of a storage basin approach. Furthermore both the present values of the investment costs and the revenues from generating energy and reducing the flood risk are computed over the structure’s lifetime. The main conclusions are that technically it is feasible to construct a tidal power plant and a storm surge barrier within the Wash estuary. However, presently the computed break-even energy price is too high for the project to be competitive with other low carbon energy sources. Hence, the project is considered to be not economical viable. In the performed economical analysis possible financial incentives from both the UK Government and the European Committee, such as: carbon pricing, buy-out price and Feed-in-Tariffs are not included. Depending on global developments, the project may become feasible on the medium and long term (2020-2050).

Local geometrical perturbations in alluvial channels can generate a pattern of alternate bars. Each bar is accompanied by a pool at the other side of the channel. This pool can decrease the strength of the bank, which can result in bank failure and bars can hinder navigation. Furthermore, non-migrating alternate bars are considered to be a possible cause of meandering. Previous linear analyses and laboratory experiments showed that these bars arise downstream of perturbations in the relatively narrow and deep channels corresponding to subresonant conditions, but both upstream and downstream of perturbations in the relatively wide and shallow channels corresponding to superresonant conditions. Previous numerical computations reproduced alternate bars under subresonant conditions, but failed to do so under superresonant conditions until the recent 2D depth-averaged computations using Delft3D. This study is an advance on the former modelling work of van der Meer et al. and has the objective to assess to what extent the numerical results agree with linear theory and experimental observations and to investigate the development of bars upstream of a bend under superresonant conditions. The model is validated by reproducing the few available superresonant experiments in a U-curved flume. Downstream of the bend, the numerical model and experimental observations clearly matched. The numerical model, however, was not able to reproduce the development of non-migrating alternate bars upstream of the bend at the experimental conditions. It appeared that the point of resonance was over-predicted by the numerical model. The observed wave lengths and bed-topography spectra complied with the literature. The numerical simulations were unstable for realistic values of the horizontal eddy viscosity (O(10-5 m2/s) for small-scale models). The latter was therefore increased to stabilize the simulations. This increase was the cause of overpredicting the point of resonance by the numerical model. For the bedload transport procedure Delft3D offers two options, the ‘upwind’ procedure and the ‘central’ procedure. The former introduces numerical diffusion, whereas the latter is less stable. The shortening of bars for large width-to-depth ratios, as observed by former numerical simulations, is probably the result of numerical diffusion. The ‘upwind’ procedure causes sediment deposits and scour to be concentrated near the banks, because the higher modes (for example the central mode) within the alternate-bar spectrum were damped. Therefore ‘upwind’ bar peaks are higher and can become inactive, because these bars run dry before they are fully developed and consequently have a smaller wave length. The alternate-bar pattern upstream of the bend under superresonant conditions was found to develop from downstream to upstream, in accordance with linear theory, only if no perturbation was applied at the upstream boundary. A development from upstream to downstream dominated in case of a perturbed upstream boundary. The computed alternate bars migrated invariably downstream, under both superresonant and subresonant conditions. I ascribe this to nonlinear effects, since the bars did migrate upstream under superresonant conditions, in accordance with linear theory, as long as their amplitudes were very small. This study has shown that alternate-bar formation cannot be solely understood from linear equations. It seems therefore recommendable to investigate the contribution of non-linear effects in a more quantitative way. The numerical model can become more accurate by improving the transverse bed slope effect formulation.

Flood protection of the land around an estuary has been important for the Netherlands since the floodings of 1953. There are several types of possible solutions. For example; levee heightening, construction of a dam or a storm surge barrier. All these solutions have certain disadvantages, like costs or environmental impact. Another option is a reduction barrier. This was one of the options for the Eastern Scheldt barrier, but at that time a storm surge barrier turned out to be better. A reduction barrier can provide safety by introducing additional resistance in the estuary. This can reduce the amplitude of the tide in the estuary. The reduction barrier itself can be described as a dam with some openings in it. Water can still flow in and out of the estuary which is important for both the environment and shipping traffic. The design water level consists of a combination of regular tide and a storm surge. The tidal wave has a smaller timescale than a storm surge wave. This makes the tidal wave much easier to reduce than the storm surge wave, since slow motions are more difficult to dampen. The reduction barrier is more effective on reducing the tidal wave in estuaries where this wave is amplified due to the shape of the estuary. The tidal wave reduction means that the reduction of the water level maximum is limited, since the storm surge wave is not reduced. The analysis revealed that the Western Scheldt is a suitable location for a reduction barrier. The Western Scheldt requires a relatively small reduction in water level maximum, due to the relatively high quality of the levees. Belgium requires a reduction of the water level maximum of 0.5 metre in the current situation near Antwerp. The reduction barrier can be adapted for up to 1 metre sea level rise by installing moveable gates. The shipping traffic through the barrier is an important aspect for the feasibility of the barrier, since there are four ports located along the Western Scheldt. The barrier is located just east of the line Vlissingen - Breskens. The reduction barrier has two shipping channels. The main shipping channel is located near Vlissingen and the secondary shipping channel is located near Breskens. Vessels are able to pass through the barrier during normal conditions. It is assumed that the environment is not harmed since 80% of the original tidal prism can be maintained. The barrier is mainly composed of concrete caissons and rubble mound. The construction costs of the reduction barrier are an estimated 4 billion euros, this is comparable with the costs of the Eastern Scheldt barrier and also comparable with the costs of levee heightening. A reduction barrier in the Western Scheldt is technically feasible. For further research is recommended to make models of the water motion and sediment transport in 3-D. Fast and real-time shipping simulations can be used to optimize the shipping openings.

In the southeast of the city of New Orleans, in St. Bernard Parish lies a coastal defensive area, which is formed by a primary dike, a secondary dike and a transitory wetland area in the middle. During Hurricane Katrina on the 29th of August 2005, a huge storm surge from the east overtopped and destroyed large sections of the primary dike. The surge continued through the wetland overtopping the secondary dikes and flooded large parts of St. Bernard Parish. The flooding killed over a hundred people and made many homeless. The coastal defensive system at St. Bernard Parish is very well comparable with the concept of ComCoast COMbined functions in coastal defence zones. This is a European project, which develops and demonstrates alternative solutions for flood protection in coastal areas. One of its main solutions is to use a wide coastal defence zone, containing a transitional area between an overtopping resistant primary dike and a lower protective secondary dike. The transitional zone will be a buffer for the storm surge and will be an area suitable for multipurpose use, with great opportunities for both man and nature. This Master Thesis analyses the failure of the St. Bernard Parish coastal defence system. Subsequently, it develops spatial integrated solutions for the coastal defence zone, using the coastal defensive strategies, which follow from the ComCoast-concept. Additionally, the effects of wetlands on a storm surge are investigated by means of an analytical analysis and a numerical model. It was concluded that catastrophic failure of the coastal defence system could have been prevented if the primary dike was not partly constructed of poorly non cohesive materials. Some basic constructional calculations and a quick study on environmental impacts made clear that the ComCoast alternatives; Overtopping resistant dike and Foreshore recharge, offer the most suitable solutions for the St. Bernard Parish area. The study on the effect of wetlands on a storm surge showed that it can both lead to a decrease, as an increase of the eventual storm surge height at the dike. The analytical and numerical approach has increased the understanding of the hydraulic behaviour of the system.

In a consortium Iv-Infra has made a proposal for a storm surge barrier to protect the city of New Orleans against hurricanes like Katrina. The design is a pile supported concrete structure with a considerable complex superstructure. The superstructure of the reference design consists of a perforated inclined wall and a vertical back wall. Since the hydraulic processes and variable wave pressures on the superstructure are not trivial and hard to predict more research is required to design similar structures in the future. The objective of this study is to get an understanding of the hydraulic processes and variable wave pressures on the reference structure. The research is divided in an analytical part and a part of physical model tests. The near shore wave conditions are calculated with SWAN. The design conditions are a storm surge of 6m, a wave height of 2,2m and a wave period of 5,25s. In order to obtain an understanding of the hydraulic processes and wave pressures on the reference structure first a simple and impermeable sloping structure is considered. It is found that for the local conditions in combination with steep sloping structures non-breaking wave conditions occur. Therefore it is assumed that the linear wave theory can be applied for determining the variable wave pressures. A model is made for the influence of a gap at the bottom of an inclined wall on wave reflection; wave run-up and wave transmission. In the physical model tests different experimental set-ups are tested. The expectations drawn on the basis of the results of the analytical part are verified by the results from the model tests.