1 

Temperature distribution of shallow water FLNG cooling water outfalls
FLNG cooling water outfalls can be characterized as high momentum buoyant jets, relatively close to the surface. The buoyant jet trajectories, spreading rates and surface distribution very much depend on the jet outflow characteristics. A study with the CFD software OpenFOAM has been carried out into the mixing and transport processes of buoyant jets. It is shown that OpenFOAM can be used to model the three dimensional trajectories of buoyant jets and their farfield buoyant plume distribution.
Two dominant mixing processes are the result of the high initial jet momentum. First, the high momentum jet results in large turbulent jet entrainment rates. Second, the relatively shallow high momentum jets result in large horizontal surface currents. These currents horizontally advect the buoyant plume into the farfield and result in steep vertical velocity gradients, which induce vertical mixing of the buoyant plume.
The momentum length scale, Lm proves to be an important parameter to characterize buoyant jets. The momentum length scale represents a distance along the jet trajectory, where buoyancy effects become dominant over initial jet momentum. For these jet characteristics it is found that the dimensionless surface temperature rise follows a logistic distribution function to the momentum length scale, after the point of surface impingement. The relative surface temperature results become constant for increasing values of the momentum length scale. This is the result of increased mixing by the jet turbulent entrainment and steep vertical velocity gradient.
From the logistic distribution an empirical relation is found which can accurately predict the surface temperature rise as a function of the outfall velocity, outfall diameter, outfall temperature, outfall angle and distance from the jet orifice. The outfall depth appears to have no significant influence on the surface temperature rise for the conditions used in this study.
The empirical equation proves to give reliable results for distances larger than 1.5 times the value of the momentum length scale and jet submergence smaller than 7.5 times the jet diameter. The robustness of the equation is also tested for extreme value outfall scenarios. The equation overestimates the temperature rise for small outflow diameters, combined with high initial jet temperatures. For other considered extreme values, the equation proves to give reliable results.
Moreover, it is also demonstrated that the standard kepsilon turbulence closure can be successfully used to model the buoyant jet centerline velocities, jet trajectories, spreading rates and centerline dilution rates of a round turbulent buoyant jet.

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2 

Validation of Swash for wave overtopping
Comparison of measured overtopping data with computations with Swash. The SWASH output discharges are smaller than the 5% lower limit of Eurotop and Neural Network predictions. Nevertheless, they were close values and they have the same order of magnitude, which is very important when comparing overtopping values. No refection analysis was done. The smaller discharges are believed to be explained by the fact that SWASH does not describe splash, and therefore, only overtopping due to waves running up the slope, but not due to “spray” is taken into account. In addition to this, it is thought that SWASH does not model accurately enough wave breaking over abrupt changes in bottom geometry or steep slopes resulting in underestimation of overtopping.
On the other hand, SWASH is not able to predict wave overtopping at rubble mound breakwaters. A breakwater is not well modelled in SWASH, because porous structures are dealt as a numerical dissipation box and not as a physical obstacle for incoming waves. As a result, waves are damped but not diverted upwards, so there is no overtopping. The reasons why this happens and some recommendations are given in this thesis. Besides, some ideas about how to introduce a multilayer structure are explained.

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3 

Modelling the anisotropy of turbulence with the SWASH model: Heterogeneous roughness conditions in open channel flows
In this study the focus is on modelling turbulence anisotropy in open channel flows with the SWASH model. Turbulence anisotropy significantly influences the flow features of: channel flows with heterogeneous roughness conditions, curved open channel flows, compound channel flows with different floodplain depths, etc.
The SWASH model is a nonhydrostatic waveflow model, mainly used to predict the transformation of surface waves from offshore to the beach. For this study, adaptations were made to this SWASH model, in order to model turbulence anisotropy. Two different modelling approaches were used: RANS modelling and Large Eddy Simulation (LES). The SWASH model is extended with a nonlinear kε closure to the RANS equations, since the standard linear closure does not take turbulence anisotropy into account. A 3D subgrid model is implemented to perform LES.
The performance of the LES code and the RANS model with the nonlinear kε closure is tested on two flow geometries: an open channel flow with homogeneous bottom roughness conditions and an open channel flow with parallel smooth to rough bed sections.
Results of the RANS computations, for both horizontal homogeneous and nonhomogeneous open channel flow, show good agreement with laboratory measurements of Muller and Studerus [13], Nezu and Rodi [17] and Wang and Cheng [32]. Although there is a number of closure constants involved with the nonlinear kε model, additional tuning of these coefficients was not necessary for this study: both the homogeneous and nonhomogenous test case were simulated successfully using the standard values proposed by Speziale [25]. With its low computational costs and robustness, the nonlinear kε model appears to be a useful extension to the SWASH waveflow model.
LES results for horizontal uniform flow are validated with DNS data of Moser, Kim and Mansour [12]. Especially near the bed the LES results deviate from the DNS data. The mean velocity, as well as the transverse and vertical turbulence intensities, is seriously underestimated. The deviation from the DNS data is related to the use of non periodic boundary conditions, the coarse grid resolution, the size of the computational domain and the amount of numerical dissipation that is involved.
Since it is the bottom region where secondary currents are generated, the use of the present LES code for problems involving heterogeneous roughness is not appropriate.

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4 

Resistance of submerged groynes
Groynes are commonly used in the major rivers in the Netherlands. They confine the flow of the river to a main channel but also act as resistance element once submerged and in that way influence the stage discharge relationship of the river. Several formulas exist describing groynes as a drag resistance. Another possible way of determining their resistance is by using a weir formula and fitting the up and downstream water levels to the water level slope of the river.
In this thesis a schematized model of the river Waal is set up and progressively expanded. At first seven different drag and weir formulas are compared. There is no consensus for resistance is between them. They are therefor compared to a 2DV computer model of flow over a highly submerged weir in the SWASH software package. Drag resistance, expressed as a function of water depth to groyne height ratio has the same scaling as two weir formulas though they do not match in absolute terms.
A 2DH computer model is then used to determine the magnitude of the lateral turbulent momentum exchange between the main channel, groyne fields and flood plain.
Finally a 3D computer model is used to determine groyne resistance and the distribution of discharge and momentum around the groyne. Treating groynes as weirs is found to be an acceptable assumption.
The schematized model is used to simulate a high discharge of 13.550 m3 s1. Groynes, when seen as a weir, would be responsible for a 36 cm water level increase. Lateral turbulent momentum exchange increases this by another 34 cm, while using the groyne resistance found in the 3D model added only another 7 cm.

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5 

Crossshore Velocity Moments in the Nearshore: Validating SWASH
The crossshore sediment transport is of great importance in the coastal water since it may lead to significant change of coastal profile. Many researches have proved that the sediment transport is proportional to velocity moments. In this study, the velocity moments under wave action in the perpendicular direction to the coastline are studied by means of a nonhydrostatic model SWASH and a decomposition technique.
The purpose of this project is to perform the velocity moments which contribute to the crossshore sediment transport with a numerical analysis and the most significant components can be found through the comparisons. These contributed flows to the velocity moments, namely the asymmetric oscillatory flow, wave groupinginduced flow and undertow, are the major objects to be studied.
A set of measurements of wave flume experiment are adopted to evaluate the feasibility of the method developed in this study. Firstly, a series of sensitivity analysis of wave decay and mean velocity are presented to investigate the influence of varied settings in SWASH, including the vertical resolution, boundary imposition, bottom friction, discretization schemes for advection terms and water depth in velocity points. The results indicate that predictions of SWASH with proper settings are in good agreement with measurements in terms of wave decay and vertical velocity. Furthermore, a detailed analysis is subsequently conducted with regard to surface elevation, wave decay and undertow. Most of the SWASH predictions are in relatively good agreement with the measurements, but some deviations occurred after wave breaking. This is probably associated to the absence of the production of turbulent energy due to surface roller.
A signal decomposition technique is applied to separate the signals with different frequencies. Through the decomposition process, the long and short wave flows are separated by means of filtering out the other part. The SWASH predicted central odd moments of long wave flows is relatively underestimated while the long wave flow variances and the central odd moments of asymmetric flows agree well to the observations. This may correspond to the loss of signal information after decomposition.
By summing up the contributions of undertow, wave groupinginduced long wave flow and asymmetric oscillatory flow, the total odd flow moment is easily acquired.
Generally, the offshoredirected undertow is the dominant component, the shoreward asymmetric flow is of secondary importance and the contribution of long wave flow is relatively small. As a consequence, the resulted total flow carries the sediment transporting seaward. In overall, SWASH is capable of simulating the wave decay and vertical flow structure correctly.
However, some deviations near the breaking point implies that, the implementation of breakinginduced turbulence in SWASH is of great importance.

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6 

Assessment of the application of permeable pile groins as coastal protection
Permeable wooden pile groins have a long tradition as being part of the coastal protection in the Netherlands, as well as in Germany and the United Kingdom. They are built to protect beaches from eroding by reducing the current velocity along the beach and thus its ability to transport beach material. This type of groin is most popular among the population; in Zeeland (NL), they are incorporated into the national heritage. In scientific research however, they lack attention. More focus is set on beach processes themselves and on the (supposedly) more stable impermeable rubble mound groins. As several researches stress their potential as soft methods and their advantages over impermeable groins, this thesis intends to put their usage more into focus. By means of generic numerical research and a comparison to available laboratory data and analytical approaches, the understanding of this type of groins is enhanced. This thesis explores the usage of permeable wooden pile groins in coastal waters under the influence of current and wave forcing.
Both impermeable and permeable groins are able to reduce the sediment transport capacity and yield sediment accumulation. Impermeable groin are researched on reasonable well, as they are supposed to be more stable and their effects easier predictable. Important disadvantages are also originating from their impermeable structure: they deflect the approaching current causing strong offshore directed flows and large scale eddies between neighbouring groins. The paths of the sediment transportation will lead to a zigzag profile of the shoreline, eventually causing erosion landward of the original shoreline and outflanking of the groin. Permeable groins reduce the original current velocity originating from the tide or breaking waves while not changing the general flow field. As a consequence, the sediment transport capacity reduces and dangerous ripcurrents are prevented to a great extent.
The thesis provides insight into the theoretical behaviour of the flow field around groins based on available laboratory experiments and theoretical considerations. This is enriched by a numerical research. For the forcing by a current, an analytical model is developed which provides the global change in the water level upstream and downstream of a stream. Further, the change in the velocity behind the groin and next to the groin can be obtained.
In numerical models available for hydraulic engineering and research, the direct implementation of permeable pile groins is not explicitly provided. For most large scale hydrodynamic and morphology models the flow around a groin is on a too small spatial scale to be of interest compared to the whole flow domain. However, there are tools available to approximate the effects of permeable groins. The effect of the groins on the hydrodynamics is evaluated by means of the numerical model SWASH (Simulating WAves til SHore). This relatively new model is developed with the intention to reproduce both small and large scale flows in shallow water. In SWASH, two possible tools are available of which one on basis of a Morison equation proved to be suitable for the representation of groins on a laboratory scale.
The numerical research evaluates the effect of permeable pile groins on the flow field when subject to a forcing by either a constant current originating from the tide, or the like, or from breaking waves. It is evaluated that many effects caused by the presence of groins on the flow field can be reproduced on a flat and an inclined (beach) bottom, both under a current or a wave forcing. For the wave forcing at a beach profile, a more detailed analysis is done on the effect on the flow field and bottom shear stresses under variations in the physical parameters. This study gives the range of boundaries under which permeable groins are applicable and their consequent effect on the flow field.

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7 

Thermally destratifying lakes against blue algae with rising air bubbles
Mixing systems are used in deep lakes to prevent blue algae from rapidly growing. Air bubbles rise from the bed, dragging water from below upwards. The resulting vertical circulation suppresses blue algae growth. However, these systems demand electricity of about €25,000 per km2 per year. The airlift promises to mix the water more efficiently, using a vertical tube wherein the bubbles rise.
Smallscale laboratory experiments presented in this thesis show that the airlift is slightly slower in completely removing stratification than a single bubble plume with the same air flow. 3D schematisations hereof using Delft3D are indifferent. A case study using 3D schematisations of Lake Haarlemmermeerse Bos also shows that the airlift is not more efficient. Hence generally the airlift is not better for lake destratification than a bubble plume system.

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8 

Wenselijkheid en haalbaarheid van verwijdering van de Rozenburgse sluis: deelstudie 1  nut en noodzaak

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9 

Swell propagation in a natural coastal channel in the SWAN model
Compare the 1D spectrum computed in SWAN (Svasek, 2007) with it measured by buoy OS4 in the Oosterschelde Estuary, serious underestimation of wave energy can be found on lowfrequency band. Investigation has been performed to find the possible reasons for the missing energy on low frequency part. In this study, diffraction is hypothesized as the reason owing to 1) the model constructed by Svasek has no diffraction; 2) diffraction does redistribute the wave energy from areas with rapid spatial variation in amplitude to areas with low amplitudes.
Before the diffraction is added to the Oosterschelde Estuary in the SWAN model, two subtests have been studied beforehand.
1. A ray tracing model (REFRAC model) is applied to the Oosterschelde Estuary for two purposes: 1) to find the existence of diffraction in the Oosterschelde Estuary; 2) to validate the refraction effects in the SWAN model. A parallel case called Canyon case is applied to the REFRAC model first to provide a reference.
The results show that areas with rapid variations in amplitudes exist in the Oosterschelde Estuary. It is necessary to take diffraction into consideration. The effects of refraction in the SWAN model work well.
2. Three academic cases have been performed in advance to validate the diffraction implementation in the SWAN model. They are the Semiinfinite Breakwater Case, the Gap in Infinite Breakwater Case and the Ridge Case, respectively.
The results show that diffraction has apparent effects in the SWAN model. The underestimation of wave energy in the lee of the breakwaters has been improved. Diffraction in SWAN compensates the refraction over irregular bottom albeit it is not accurate enough. Model in SWAN with diffraction, under certain spatial resolution and with smaller number of smoothing steps is suggested.
By performing the Oosterschelde Estuary in the SWAN model with diffraction, the results show that diffraction has apparent effects when the incoming waves at the boundaries are unidirectional. However, when the incoming waves have broader directional spreading, diffraction cannot solve the underestimation which can be resulted from the fact that diffraction effects of the wave components may cancel each other.
Therefore, further investigations with respect to local wind sea and the ambient currents are suggested as future work since these two processes induce the wave energy on lowfrequency band flow. In addition, the effects of the directional spreading of the incoming waves at the boundaries are suggested to be further studied since the value of the directional spreading is critical to the diffraction implementation in the SWAN model.

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10 

Typhooninduced extreme water levels near Singapore: a numerical model investigation
Due to the diminishing Coriolis force towards the equator, the equatorial zone is known to be cyclonefree. However, on 27th December 2001, a tropical cyclone Vamei was formed near Singapore; 1.4 degrees latitude North from the equator, and made a landfall about 60 km northeast of Singapore. Although this event did not cause any major destruction to Singapore, the neighbouring areas such as states of Johor and Pahang of Malaysia had suffered inland flooding and landslide caused by the heavy precipitation of the storm.
Chang et al. (2003) has suggested that the return frequency of a typhoon similar to Vamei is approximately 1 in 400 years, thus the possibility of a tropical storm occurring in Singapore could not be ignored. With the population density of over 7000 per square kilometer, the consequences of flooding due to storm surge can be devastating for Singapore.
This study aims to provide a quantitative assessment to estimate the possible storm surge induced by typhoon near Singapore using numerical hydrodynamic modeling tool Delft3D. In order to simulate the hydrodynamic condition of both the tide and the storm surge in the Singapore Strait, the socalled Singapore Regional Model (SRM) will coupled offline with the cyclone model; Wind Enhanced Scheme (WES), both developed by DeltaresDelft Hydraulics (2004 and 2009b). The hindcast of the typhoon Vamei event has been attempted in this report to examine the applicability of the model in Singapore waters. Then the sensitivity of different typhoon’s tracks, forward speeds and radii of maximum winds on the storm surge will be examined closely to estimate the worst case scenario in terms of surge that could cause by a typhoon in this region.
This report also acts as a preliminary study of the possible extreme high water levels which includes storm surge, tide and sea level anomaly that could occur along the coast of Singapore. According to the result of this study, the extreme event with an estimated return frequency of 1 in 400 years can cause the water level to reach as high as 2.0 to 2.8 depending on location.

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11 

Impact of access channel geometry on wave penetration in harbours
Access channels (entrance channels) to ports are a relevant part of port facilities, and they have a strong influence on the port operations as well. However, little information is available about their analysis and design regarding the wave interaction with access channels.
This study is focused on the interaction of waves with entrance channels regarding wave propagation. This report has three parts: i) a qualitatively assessment of diffraction effects carried out with SWAN; ii) a comparison between SWAN (phase averaged wave model) and SWASH (phase resolving model) results, regarding refraction and diffraction effects; and ii) a systematic analysis of the results in SWAN on several wave conditions and a few access channel geometries (slopes).
SWASH is used to test SWAN capabilities in an environment where significant refraction and diffraction is expected. The results of the comparison are analyzed and recommendations for future comparison are presented.
The systematic analysis of conditions provides information about performance of SWAN and its ability to correctly represent physical phenomena particularly regarding refraction and diffraction. Additionally, recommendations for wave propagation analysis for entrance channels are presented.
Finally, based on the results, engineering recommendations and considerations are presented regarding operations of ports and the design of related structures such as breakwaters.

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12 

Luwtemaatregelen Hoornse Hop
De ecologische kwaliteit van het Markermeer is de laatste decennia sterk achteruit gegaan. De oorzaak hiervan is dat door de afsluiting van het Markermeer met de Houtribdijk een ondiep meer is ontstaan met een bodem van klei waarin een dynamische sliblaag aanwezig is. Al bij lage windsnelheden ontstaan golven die erosie van deze sliblaag veroorzaken. De slibconcentratie in het water is hoog, waardoor het water troebel is en er nog maar weinig waterplanten in het Markermeer groeien. Dit heeft nadelige gevolgen voor de rest van het ecosysteem van het Markermeer.
Dit afstudeeronderzoek richt zich op een luwtemaatregel in het Hoornse Hop. De lokale effecten op golven en stroming in het Hoornse Hop wordt onderzocht. De studie is gericht op een damwand als lijnvormige luwtemaatregel voor de kust van NoordHolland. Hierbij wordt de effectiviteit van verschillende varianten onderzocht. De hoofdvraag van dit onderzoek is:
“Op welke manier kunnen lijnvormige luwtestructuren langs de NoordHollandse kust de golven en stroming in het Hoornse Hop zodanig beïnvloeden, dat daarmee een bijdrage wordt geleverd aan het oplossen van het slibprobleem van het Markermeer?”
Om de lokale effecten van de luwtemaatregel in het Hoornse Hop te onderzoeken, is een hydrodynamisch model van het Markermeer opgezet in Delft3D. Het model simuleert de golven en stroming die door de wind worden opgewekt en berekent hiermee de bodemschuifspanning die optreedt in het Hoornse Hop. Hiermee worden vervolgens gebieden bepaald waar erosie van de sliblaag door de luwtemaatregel wordt voorkomen.
In dit onderzoek zijn een aantal varianten ontwikkeld met een verschillende ligging en vormgeving, waarbij de effectiviteit in het reduceren van de golfhoogte en het afbuigen van stroming is onderzocht. Als zoekgebieden voor de luwtemaatregel zijn drie gebieden langs de kust van NoordHolland, tussen Hoorn en Edam, aangewezen.
Uit dit onderzoek kan worden geconcludeerd dat lijnvormige luwtestructuren in het Hoornse Hop een bijdrage kunnen leveren aan het oplossen van het slibprobleem van het Markermeer. De aanleghoogte is hierbij een belangrijke ontwerpparameter, die groot genoeg moet worden gekozen om transmissie van golfenergie over de luwtestructuur te voorkomen.
Daarnaast dient de ligging van de luwtestructuur bij te dragen aan afbuiging van stroming naar het Markermeer. Hiermee wordt instroom van slibrijk water achter de structuur naar het luwe gebied beperkt. Om dit te bereiken dient de luwtestructuur zich voldoende ver uit te strekken richting de kust van NoordHolland.
Tot slot wordt aanbevolen om in plaats van een damwand een ander type constructie als een dam of golfbreker toe te passen.

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13 

Effectiveness of Floating Breakwaters: Wave attenuating floating structures
From previous engineering projects it turned out that it is difficult to determine the transmitted wave height of floating breakwaters without performing physical models or using numerical models. In this thesis it is investigated which steps should be taken during the preliminary design process in order to predict the effectiveness (wave transmission) of floating breakwaters more accurately. Existing formulas which can be used to determine the transmission coefficient of floating breakwaters are compared with data of physical models. A numerical model (AQWA) is used to generate additional data for the areas of interest where physical model data is missing. Based on physical and numerical model data conclusions are drawn regarding to the applicability of the existing formulas for wave transmission. The final product of this thesis is a flowchart which can be used as a design tool during the preliminary design stage in order to predict the wave transmission of floating breakwaters more accurately.

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14 

Golfrandvoorwaarden in havens: Bruikbaarheidsgrenzen voor (numerieke) modellen
Volgens de Waterwet dienen elke zes jaar de Hydraulische Randvoorwaarden (HR) te worden vastgesteld. De HR bestaan uit hoogwaterstanden en golfrandvoorwaarden voor de toetsing van waterkeringen gegeven overschrijdingskansen welke in de wet zijn vastgesteld. Ook voor waterkeringen in havens en afgeschermde gebieden dienen de HR vastgesteld te worden, maar mag er rekening worden gehouden met een reducerende invloed als gevolg van de geometrie en de bathymetrie op de belasting door golfrandvoorwaarden. Voor het bepalen van de reductie van de golfrandvoorwaarden schrijven het Voorschrift Toetsen op Veiligheid (VTV, onderdeel van het wettelijk toetsinstrumentarium) en RIKZ (2004) een driestappenschema voor waarbij van grof naar fijn wordt gewerkt. In het schema moet worden overgegaan op een volgende stap als blijkt dat de te toetsen kering niet voldoet aan de gestelde veiligheidseisen bij de belasting uit de betreffende stap. Elke volgende stap levert een nauwkeuriger, betrouwbaarder en scherpere golfrandvoorwaarde op ten opzichte van de vorige stap.
De eerste stap voor havens en afgeschermde gebieden wordt gevormd door het toepassen van ongereduceerde golfcondities en is het meest conservatief. De tweede stap bestaat uit het toepassen van het eenvoudige spreadsheetmodel ‘Golfbelasting in havens en afgeschermde gebieden’. De laatste stap in het bovengenoemde schema is de toepassing van numerieke modellen.
Het spreadsheetmodel uit de tweede stap is vooral ontwikkeld voor simpele havengeometrieën en het gebruik is alleen toegestaan wanneer aan een aantal voorwaarden wordt voldaan. Een probleem is dat deze voorwaarden tot nu toe zijn gebaseerd op theorie en nog niet zijn geverifieerd aan de hand van metingen. Hierdoor is het niet duidelijk waar de werkelijke bruikbaarheidsgrenzen liggen van dit model en wanneer moet over worden gegaan op de derde meest gedetailleerde stap.
De keuze welk numeriek model moet worden toegepast in de derde stap wordt overgelaten aan de gebruiker. Maar doordat modellen verschillende eigenschappen hebben, is een model niet altijd voor alle situaties geschikt voor het correct bepalen van de gereduceerde golfrandvoorwaarden. Door bruikbaarheidsgrenzen te formuleren voor numerieke modellen welke aangeven in welke situatie de modellen correcte antwoorden geven, zou deze keuze veilig en gefundeerd gemaakt kunnen worden.
Onderliggend onderzoek is uitgevoerd om te bepalen binnen welke grenzen het spreadsheetmodel, SWAN (spectraal energiemodel) en Pharos (mildslope model) geschikt zijn voor het modelleren van de indringing van golven in havens en afgeschermde gebieden en leiden tot conservatieve antwoorden. Hierbij is gefocust op havens waarvan de geometrie op het grensvlak van complex dan wel nietcomplex ligt. Het effect van wind op golven niet beschouwd voor een zuivere vergelijking van de modellen. De modellen zijn toegepast op diverse cases en de resultaten zijn vergeleken met schaalmodelmetingen en resultaten van een meer gedetailleerd numeriek model. Ook zijn tests uitgevoerd waarmee de gevoeligheid van de modellen voor enkele hydraulische en numerieke aspecten is onderzocht. Op basis van de cases en de gevoeligheidstests is een oordeel gegeven over de prestaties van de modellen en zijn bruikbaarheidsgrenzen opgesteld.
Met het onderzoek is aangetoond dat het spreadsheetmodel waarschijnlijk breder ingezet kan worden dan de huidige richtlijnen doen voorkomen. De resultaten van het model blijken conservatief ten opzichte van gemeten waardes of numerieke modellen in situaties waarvoor het spreadsheetmodel is ontwikkeld. Echter ook in situaties waar het model oorspronkelijk niet voor ontwikkeld is, zoals havens met sterk reflecterende randen en/of veel afgeschermde gebieden, blijkt het spreadsheetmodel conservatief. Door het breder in kunnen zetten van het spreadsheetmodel kan tijd en geld bespaard worden op het gebruik van rekentechnisch duurdere en arbeidsintensievere numerieke modellen.
Voor SWAN en Pharos is vanuit de opgestelde bruikbaarheidsgrenzen een schema afgeleid waarmee een onderbouwde keuze kan worden gemaakt uit de twee modellen. Pharos blijkt hierbij het breedst inzetbaar en SWAN vooral in een haven met een open geometrie welke belast wordt met een kortkammig golfspectrum. In dit laatste geval is het in SWAN missende golfproces diffractie van minder belang en komen de berekende golfpatronen van SWAN en Pharos sterk met elkaar overeen. SWAN geeft in dit geval over het algemeen wel conservatievere antwoorden. In alle andere gevallen zijn de prestaties van SWAN matig tot slecht door de afwezigheid van diffractie. Zo zijn de prestaties van SWAN matig in havens met veel afgeschermde gebieden welke belast worden met een kortkammig spectrum. Voor dit type haven wordt het aangeraden SWAN alleen te gebruiken om een eerste impressie te krijgen van het lokale golfpatroon. In havens welke belast worden met een langkammig spectrum levert SWAN slecht en wordt de toepassing van het model afgeraden.
Bovenstaande conclusies zijn gebaseerd op een beperkt aantal cases. Aanbevolen wordt in een vervolgstudie de huidige dataset uit te breiden om de opgestelde bruikbaarheidsgrenzen nader te onderbouwen.

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15 

The Mekong Deltaic Coast: Past, Present and Future Morphology
According to the future development plan, discharge sluices will be constructed at three main branches of Tien River to prevent salinity intrusion. To evaluate the consequences of these constructions to the Mekong Delta Estuaries, the empirical relationship between tidal prism and river crosssection is estimated in this study. It is found that the two open branches of Tien River will deepen by more than 10 meters when all three other branches are closed.
Due to the need of land for agriculture and other economic sectors, sea dikes are always built close to the mangroves forest. Along the Southern Coast of Viet Nam there are many places where mangrove degradations and coastline erosions are observed on a large scale when sea dikes are built too close to the mangroves forests. Based on the relationship found for mangroves width and coastline evolution, it is concluded that the critical value of 300 to 400 meters of mangroves width is necessary for the stability of the East Coast of Viet Nam. Results from the SWAN model also show that mangroves have a significant effect on wave height attenuation only at crossshore widths greater than 300 to 400 m and that an increase in width beyond 1000 m does not make much of difference.

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16 

Feasibility study of an artificial sandy beach at Batumi, Georgia
This master thesis aims to determine the best design option and the feasibility of an artificial sandy beach along the Old Boulevard of Batumi, Georgia. The coastline south of Batumi is affected by erosion problems. The coastal stretch between the port in the north and the Chorokhi River south of Batumi should be protected. In 2010 Alkyon/ARCADIS proposed a detailed design to protect this coastal stretch. The beaches of Batumi originally consist of pebble. In the northern part of the coastal stretch, the so called Old Boulevard, a lot of tourist activities takes place. For this reason sandy beaches where requested by the client along this part of the coast. In the design proposed in 2010, pocket beaches have been envisaged here. In this thesis an alternative design for the pocket beaches are proposed. This design should contain more sand and less visual structures, opposed to the pocket beaches proposed in the 2010 study.
In order to determine suitable measures and alternatives, the morphological impact of the measures and the corresponding sediment transports have been considered. The sediment transport rates have been computed using numerical models. For the longshore transports the model UNIBESTLT is used and the crossshore losses are determined with the use of the XBeach model.
With the use of gained information of the behaviour of a sandy beach and possible measures to optimise the design of an artificial sandy beach, 7 alternatives are proposed. The 7 alternatives are compared and assessed with the use of a MultiCriteria analysis (MCA). From the MCA can be concluded that a perched beach with a beach placed parallel to the boulevard is the most promising alternative. A preliminary design has been prepared for this alternative. The perched beach consist of a sandy beach with a width of 135 meter. At approximately 180 meter from the shoreline a submerged breakwater is present with a submergence of 0.5 meter.
The pocket beaches as designed in the 2010 study and the preliminary design of the perched beach as designed in this study are finally compared. The pocket beaches have a partly sandy beach and contain some undesirable visual structures. The perched beach fulfils the wish of a fully sandy beach with almost no visual structures, the costs are however considerably higher than for the pocket beaches, 25.5 M€ versus 56.6 M€. It can be concluded that the two options have their own benefits and drawbacks. The preference depends on which aspect is valued as most important and/or which aspect is valued as least important.

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17 

Feasibility study on the use of a floating breakwater to protect a new artificial beach in Balchik, Bulgaria
The coast of Bulgaria is subject to erosion. Because of this fact, around the town of Balchik, which is situated on the Black Sea coast, almost no sandy beaches are present. Last years there have been vast tourist developments in and around Balchik. Because of these developments, the province demands solutions to adapt coastal protection structures to become more attractive regarding recreation. In this study, a small pilot project on the creation of an artificial beach will be described. One possible source of nourishment sand is to dredge it from the local bottom. However, this sand is too fine to form a stable beach without a breakwater in front of it for protection.
In this study is investigated whether it is technically feasible to use a floating breakwater to protect the new proposed beach in Balchik. In order to do this, the following approach is followed. A description of the current situation as well as boundary conditions regarding wind, waves, water level, bathymetry and sediment properties is given. Next, the maximum allowed wave height to form a stable beach is determined by means of sediment transport calculations in crossshore and longshore direction and several possible nourishment sand sizes are considered. In order to lower the incoming waves (boundary conditions) to the maximum allowed wave conditions, a floating breakwater with a certain transmission coefficient is necessary. An investigation on possible types of floating breakwaters is made and the possibilities to produce the floating breakwater are described. From the types of breakwaters found, the most suitable type is selected. The last step is to determine the required dimensions and offshore distance of the floating breakwater in order to achieve the required transmission coefficient. If the required dimensions stay within reasonable limits, it can be concluded that it is technically feasible to use a floating breakwater as beach protection.
It is chosen to use concrete caissons to create the floating breakwater, because of the fact that in the vicinity of the project location a company is located which can produce floating concrete structures. Regarding beach nourishment materials, the equilibrium beach profiles with mean grain diameters 0.1, 0.2 and 1.0 mm are considered. It is chosen to further elaborate the case of the locally available sand with a mean grain diameter of 0.1 mm, because for this sand a floating breakwater is necessary in order to stabilize the nourishment. The other two sediment sizes may form a stable beach without a breakwater in place.
In order to determine the required dimensions of the floating breakwater, a distance of 200 m between the floating breakwater and the coastline is chosen. With the aid of a literature study on floating breakwater dimensions it is found that for this particular location and governing wave conditions, the draft of the floating breakwater is the governing parameter which determines the transmission coefficient. The breadth of the structure is determined by stability requirements. In this design, it is assumed that the breakwater is fixed in space, which is, regarding the main outline of the design, a reasonable assumption.
The result of the study is a preliminary design of a beach nourishment with a volume of 91,000 m3 which is protected by a 240 m long floating breakwater consisting of three elements. The final conclusion of this study is that it is technically feasible to use a floating breakwater as beach protection measure.

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18 

Stability of a Crown Wall on a Breakwater: A refinement of existing design formulae
This thesis investigates the stability of a crown wall situated above SWL (Still Water Level) on top of a rubble mound breakwater. Crown walls are concrete super structures implemented commonly to provide a flat surface for pipelines and to make the breakwater accessible for vehicles.
The vertical distance between SWL and the bottom of the crown wall is referred to as the freeboard in this thesis. Current design formulae do not take the freeboard into account when calculating the uplift force on the crown wall. Furthermore design formulae assume that the maximum of the horizontal and vertical force occur at the same time. Previous research noticed that these two maxima might not occur simultaneously. The time difference between both maxima is referred to as phase lag.
The first goal of this research is to gain insight in the influence of the freeboard on the uplift force and the uplift pressure distribution. The second goal is to quantify the phase lag. A dataset is needed to achieve both study goals. Two approaches are investigated to obtain a dataset. The first is a numerical model, the second is a physical scale model. The research question is: to determine in what way a numerical model or a physical scale model can be used in order to gather a reliable dataset to realise the project goals.
The selected numerical model is the IH2VOFmodel. Currently the VOFmodel is only validated when the crown wall is (partly) situated below SWL. An experimental dataset was acquired to validate the model. Because the dataset did not provide the exact water depth, it cannot be used to validate the model.
For this research physical scale model tests are conducted, in which wave pressures were measured. The recorded pressure data contain a significant amount of noise. Therefore the data are unsuitable to obtain the actual wave force and the exact pressure distribution on the crown wall. It is concluded that the data are only suitable to partially reach the project goals.
Current design formulae assume that the uplift pressure reaches the rear end of the crown wall. However, the measured pressure data indicate that the uplift pressure does not reach the rear end. A correlation is found between the relative freeboard and the location at which the uplift pressure becomes 0. A conceptual model is proposed which explains what part of the crown wall experiences an uplift pressure.
Furthermore the pressure data are analysed to gain insight in the phase lag. The phase lag appears to be dependent on the relative freeboard and seems to increase with a higher relative freeboard. This finding is explained by a conceptual model which assesses the vertical distance the water travels through the breakwater.
This study shows that current design formulae appear to overestimate the uplift force on a crown wall for situations with a freeboard. It also indicates the presence of a phase lag. Furthermore it points out that there are uncertainties about the uplift force on a crown wall. Hence, it is recommended to perform scale model tests whenever a crown wall is designed to gain insight in its stability. Based on investigated articles the VOFmodel seems to be a promising tool to perform a stability analysis. However a phase lag was not present in the results of the VOF simulations. Furthermore, options to reduce computation time should be investigated.

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19 

A modelling study on the residual circulation in the North Sea, with the focus on water fluxes through the Strait of Dover
In this master thesis the residual circulation in the North Sea is investigated. It has been shown that the numerical models used in this thesis (DCSMv5 and DCSMv6) give a rather low representation of the actual circulation pattern in the North Sea. The dominating forces which cause residual currents in the North Sea are the tidal forcings, meteorological forcings and density variations. Their variability over the whole domain, as well as their interaction with bottom topography and the earth’s rotation, leads to a variety of different processes. Since it is difficult to quantify to total transport over the whole North Sea, the focus in this thesis lies on the transports through the Strait of Dover.
Studies on fluxes through the Strait of Dover date back to the late 1920’s, where in situ velocity profiles were measured and integrated over the crosssection to make an estimate on residual flows. In later studies different methods were used to obtain valuable information on transports. Use was made of electric potentials through a telephone cable, high frequency radars and modelling studies. Because the magnitude of residual transports is an order of magnitude smaller than short scale movements like tidal oscillations, the estimated trans ports lack accuracy. They vary between 87000 to 235000 m3/s. Dutch ecologists suggests an annual inflow in the order of 100000 m3/s.
In this thesis the stateoftheart numerical DCSM models of Deltares have been com puted in Delft3DFLOW to investigate the dominant processes in the Strait of Dover. The models cover the complete northwest European continental shelf and calculate depth aver aged barotropic flow. The representation of the general North Sea circulation is qualitatively well, except for some highly stratified and density driven areas. However, the in and outflow of water at the North Sea boundaries is considerably low. The leakage of the radioactive nuclide Antimony125 from La Hague in 1985 till 1994 has been simulated to give an in dication of the spatial varying transit time of the current model. It is shown that in the southern region transit times are simulated to be two times larger than other modelling studies and measurements suggest.
The daily varying residual flow through the Strait of Dover has been investigated by applying a LowPass frequency filter to the modelled fluxes. The contribution of tidal residuals are found to be very significant with an average annual flow of 45000 m3/s. When meteorological forcings are also taken into account the annual inflow for the year of 2007 equals 56000 m3/s. Since meteorological forcings vary throughout the years, a quasilinear approximation is formulated where the daily residual flow is a function of the wind induced shear stress and wind direction. A correlation of 0.79 is found for this linear approximation. For rapidly varying surface elevations differences between the North Sea and English Channel the approximation fails to give proper estimates.
During the research, model adjustments were made to (1) assess the sensitivity of the fluxes and (2) look for candidate solutions to improve the amount of transport through the Strait of Dover. Physical adjustments have been made by implementing density differences, residual surface level boundaries and a varying bottom roughness. The numerical adjust ments were for the largest part based on different discretization methods. In addition, a preliminary computation has been performed in DFlowFM; a recently developed simulation package which computes on an unstructured grid. Although there are notable differences for each adjustment, the effects are small in comparison with tide and wind induced residuals.

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20 

Calibrating a rainfallrunoff model in a data scarce catchment in Mozambique
Rainfall runoff modeling is a major task of many hydrologist. Therefore always a lot of research is done to modeling. One of the problems of modeling is often the lack of data. Most of the world is data scarce, in the sense that no discharge is being measured. Although this is the case, it is often preferable to make a model of a catchment in such an area.
Therefore a lot of research is carried out in calibrating a rainfall runoff model without discharge data. This research is also focusing in this. With a fieldwork of 3 weeks and knowledge of the local fishermen, the catchment is being investigated. The catchment is in the south of Mozambique, and is the catchment of the Lumane river. This is the last tributary of the Limpopo river. Upstream of the Lumane is a fresh water lake, which feeds the river. The yearly fluctuating of this lake is used for the calibration of the rainfall runoff model.
With information of the local fishermen, a hydraulic model of the river and the yearly precipitation pattern; a Fourier series is made, describing the lake’s water level. This Fourier series is used for the calibration of the rainfall runoff model. Next to this, also GIS data of actual evaporation is compared with the outcome of the model. This is also used for the calibration.
In order to validate the model is looked at how well the model is following the Fourier series of the lake’s water level. Furthermore is checked if the fluctuating of the reservoirs is reliable, as well as how reliable the calibrated parameters are. Since the rainfall runoff model is a lumped model, but based on an hydrological classification, the parameters really mean something. Therefore can be seen if the model is acting as suspected.
From the results it becomes clear that the model is mimicking the level of the lake. Also the discharge data seems to be in the right order of magnitude compared to historical data and local measurements. Only the evaporation outcome differs a lot from the GIS data during summer time. The reliability of this GIS data will therefore be discussed as well as the shortcomings of the model structure.
After all one can conclude that it is possible to calibrate a rainfall runoff model without discharge data. However, to validate the model, discharge data is necessary. Else, it is hard to know how good the model really is.

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