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With the use of the process-based geological model Delft3D a base case model is set up to simulate the Brent delta using Gullfaks field conditions as appeared during the Aalenian and Bajocian periods in the Mid-Jurassic. The aim is to visualize and comprehend the morphology and stratigraphy of the base case upon changing both wave conditions and discharge conditions. Wave height and peak period are varied during a first scenario, where discharge and sediment concentration of the river are altered during a second scenario. Nine hydrodynamic and geologically realistic model set-ups were simulated. They represent an outbuilding wave dominated deltaic environment in three dimensions. Within these nine models either the wave height and wave peak period (wave models) or the fluvial discharge and sediment concentration (discharge models) were varied. The wave models with the largest energy, i.e. largest wave height and peak period, show the most assymetrical delta built out towards the wind direction. Sediment is fed to the delta front by distributary channels and further redistributed by longshore currents. Typical wave-dominated lobate structures and an elongated delta built-out are the morphological result. In the low wave energy models the distributaries are concentrated in two channels distributing sediment laterally towards the sides, whereas a more variable distributary channel pattern is encountered in the larger wave energy models. The discharge models feeding the largest amount of sand and clay into the basin show smallest wave influence and most stable formation of the delta front and intertidal-, and supratidal zones. A two way distributary channel system develops from the main fluvial river transporting sediment equally to the deltas sides. Morphologically the delta becomes more river dominated, building out symmetrically and the sedimentation from distributary channels being dominant over wave erosion. The discharge models, having a constant wave climate, show a typical erosional (wave) base with stability or progradation of the delta front and prodelta occurring below this erosional base and erosion of the intertidal-, and supratidal zone above the erosional base. All models typically have an initial mouth bar formation which very rapidly builds out to a sandy stable delta front. Fining upward sequences are the general appearance in abandoned channel fills with relatively more clay content in the lower wave energy models and lower sediment discharge models. Clay is also more abundant in the sediment stack laterally away from the centre delta where sediments are younger. The heterolithic upper part of the channel fill was found to be most susceptible for reworking by waves and (cutting) distributary channels. The cleanest sand stacks were found in the centre delta, in the intertidal zone and delta front. These sand stacks are largest in the larger wave energy models and higher discharge models. The facies description being dependent on three hydrodynamic parameters has partly succeeded. Incorporation of more hydrodynamic or geological parameters could potentially increase the accuracy of facies description.

Introduction Dong Lam Cement Factory is developing a new clinker plant in Thua Thien-Hue Province, Vietnam. The clinker has to be exported towards Ho Chi Minh City, where it is grinded into cement and used for the construction industry. For the clinker production coal is needed and has to be imported. To make the in- and export possible a new dedicated seaport is required to allow for 15,000 dwt clinker vessels and 7,000 dwt coal vessels. Objective The objective is to design a port with sufficient capacity to handle the predicted cargo flow and which offers acceptable conditions for the ships to enter. The effective berth and hinterland capacity have to be determined such, that turnaround times are within limits. To create safe conditions, the vessels need to have enough space for manouevring in the wet port area. These manoeuvres can be seriously disturbed by wind, wave, currents and siltation on the long term. To ensure the workability of the port these effects have to be limited. Analysis To determine the effective berth capacity the queuing theory is applied. In phase 1 and 2 one clinker and one coal berth satisfy with effective capacities of respectively 700 and 175 t/h respectively. In phase 3 two clinker and two coal berths are needed with the same loading/unloading rates. To get insight in the environmental boundary conditions, field data is collected and analysed thoroughly. In Vietnam the wind climate is governed by the South-East Asian monsoon system, with a dominant SE direction and strong NNE winds. The wave climate is directly influenced by the wind climate and shows a similar pattern. With regard to extreme conditions, once a year a tropical storm lands in the vicinity of the port site. These storms are accompanied by strong wave conditions, coming from E to SE direction. Having frequent waves from the NNE and SE, littoral transport is generated in north- and southward direction. Nevertheless, the northward transport is clearly dominant. Currents are heading SE for most of the time. Synthesis Four different layouts are developed for phase 3 of the project. Two of them are dismissed in an early stage, because of unfavourable conditions. The other two layouts – the 'coastal' and 'offshore' alternative, are evaluated with a cost-value approach. In this approach the value of each design is assessed by means of a MCA. Evaluation The following criteria are taken into consideration: navigation, tranquillity at berth, coastal impact, sedimentation, ease of cargo handling, safety and flexibility. Regarding navigation and wind, wave and current hindrance, no significant differences are found. It turns out that the most important difference is found in the coastal impact. The coastal alternative will cause erosion along 7.5 km of coastline with a maximum retreat of 100 m. Instead, the offshore alternative affects 'only' 3 km with maximum retreat of 70 m. The other element of the cost-value approach is the costs. The investment costs for the coastal alternative are 64.1 M$, which include the dredging works, breakwater and quay construction. The costs for the offshore port amount 77.5 M$, which entails the dredging works, breakwater, jetty quay and trestle construction. The relative low costs for the coastal alternative are achieved by applying the cut-and-fill balance; the dredged sand is used as breakwater foundation. Maintenance dredging costs are 1.75 M$ and 0.9 M$ for respectively the coastal and offshore alternative. To finish the cost-value approach the value/costs ratio is taken for both port layouts. The coastal alternative (0.9) turns out to be a better port layout than the offshore alternative (0.77).

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.

During the fall of 2003, an extensive measurement campaign called the “Nearshore Canyon Experiment” (NCEX) was set up along the coast of La Jolla, California. The project site covered an area in which two submarine canyons are located, respectively La Jolla and Scripps Submarine Canyon. Over 20 institutions collaborated on recording the hydrodynamics and morphological changes. The collective objective of these institutions was to gain more insight into nearshore processes. The canyons are responsible for substantial changes in wave energy distribution over an alongshore distance of a few hundred meters. The irregular wavefield that arises in the direct vicinity of the canyons results in a complex nearshore circulation and in morphological changes in the surfzone. The following research objectives were proposed for this study: 1) “What is the relative contribution to the alongshore current of (i) alongshore water level gradients due to the alongshore variation of wave set-up and (ii) obliquely incident waves?” And 2) “Can the numerical model Delft3D reproduce the order of magnitude and direction of the nearhore currents?” This master thesis describes the hydrodynamic circulation in the nearshore during the measurement campaign and the results of the numerical model Delft3D for two specific cases, respectively a day with wind sea and a day with swell waves. The incident waves drive currents and create wave set-up. Owing to the influence of the submarine canyons, alongshore gradients develop in the wavefield. It is concluded that the influence of the submarine canyons becomes more prominent in case of swell waves and therefore a larger alongshore set-up gradient arises. In both the observations and the model predictions an alongshore current develops strong enough to counteract the wave-driven flow.

Coastal management and engineering rely increasingly on predictions made by computational numerical models of hydrodynamic and morphodynamic processes. However due to the lack of real data from coastal field measurements the models used, are rarely tested. With the COAST3D measuring campaign at a site near the town of Egmond a data set is available with detailed measurements, not only a dense spatial coverage of the modelled area is obtained, but also detailed measurements of boundary conditions, like the wind field and deep water wave height are made. Delft3D-MOR was used to construct a model for the Egmond site. This EGMOND model is validated and calibrated using the data base available from the pilot measuring campaign (data available from April 30 to May 6 1998). Comparison of the model results with measured data show that the model is capable of reproducing the measurements. The validation runs have been carried out using standard parameter settings. These settings enable the hindcasting of measured data but also enables the model to be used for making predictions of future situations. In general the model results give a good approximation of the measurements. For deeper water, where waves have little influence, the results are very good. For the surf-zone, where the details of wave transformations have large influence, the results show less agreement with the measurements. With modifications in the Delft3D-WAVE program and wave schematisations these results could be improved. In the current version of Delft3D-WAVE the Battjes-Janssen theory to take wave breaking into account is applied, including the roller formulation (the roller is defined as a turbulent bore-like mass of water representing a forward momentum flux, which can be seen as an additional sink term in the Battjes-Janssen formulation) could improve the results in the surf zone.

Due to growing human activity in coastal zones, there is an increasing stress on salt marshes all over the world. These intertidal wetlands were often seen as coastal ‘wasteland’ and large areas were reclaimed for urban development and agriculture. In Puget Sound, a system of interconnected marine waterways and basins in the northwest of the United States, this has lead to an 80% loss of marsh area in the last 150 years. In recent years however there has been a growing recognition of their value as habitat for fish, birds and numerous species of plants and as coastal protection. In many countries they are now protected areas and numerous restoration projects are being carried out or planned. One of the largest of these restoration projects takes place in the Nisqually River estuary, in the southern end of Puget Sound. By removing a dike, built in the early 1900s for farming purposes, an area of nearly 405 hectares was reintroduced to the salt water and tides of Puget Sound on November 12, 2009. The goal of this study was to research how this dike removal will affect the estuary in the coming years. A computational model was set up in Delft3D to describe hydrological and morphological processes, with focus on the interaction with vegetation. The vegetation in Delft3D is schematized as cylindrical rods, which add extra source terms to the momentum equation. An external Matlab routine was used to calculate changes in the vegetation field based on the model results. Because this type of vegetation modeling had not been done on this scale before and there were large uncertainties in the required parameters, first a sensitivity analysis was carried out with a schematized model. By doing different runs, changing one parameter at a time, the relative importance of each parameter was examined. The most important parameters were then researched further so that a detailed final model could be set up, with a discharge from the Nisqually River on the southern boundary and tidal forcing on the northern boundary. With the use of a morphological factor a period of 10 years was simulated. Due to limitations in computation time and the lack of some important data, concessions had to be made in the setup of the model. These concessions, combined with the fact that the model could not be validated since there were no post-restoration measurements available at the moment of writing, make it hard to determine the accuracy of the model predictions. Therefore the results should not be seen as an exact prediction, but more as a qualitative impression of how the area is going to develop in the coming years. It was concluded that success of salt marsh restoration mainly depends on elevation. Higher areas are inundated for a shorter amount of time, which makes it easier for pioneer vegetation to establish. During the period in which the restoration area was diked no sediment was brought in, which caused subsidence. As a result, a salt marsh can develop in the eastern part of the estuary but the western part of the estuary is too low to be colonized. However, the dike removal will allow sediment from the Nisqually River to enter the area again, so if enough sediment is provided the elevation will increase, allowing the marsh to expand further. This suggests that sediment discharge from the river is a key factor, and it is therefore recommended to measure this in the future. An alternative scenario, in which the river is forced to flow through the restoration area, was also examined, based on expectations for high river discharges. This increases the amount of sediment that is imported into the area, and could therefore have a positive effect on the salt marsh development. It does however also influence the salinity, which has a large impact on the distribution of vegetation. Further research into these effects is recommended if forcing this change is considered.

Long-term prediction of sediment transport and morphology has become increasingly important. One of the key issues in carrying out long-term modeling is to bridge the gap between short-term hydrodynamics varying from hours to days, and morphological changes, taking place over much longer periods. Lesser et al. (2004) and Roelvink (2006) have introduced the powerful concept of the morphological acceleration factor (Morfac) to coastal morphodynamic modeling, which potentially enables modelers to simulate morphological evolution in coastal areas at the time scales of decades. In this thesis, the effects and limits of the concept of Morfac in coastal morphodynamic modeling are studied from a 1D analytical model with unidirectional flow, and the model with numerical implementation. After linearized and non-dimensionalized, the sensitivity of the Morfac is analyzed based on investigating Froude number, sediment transport facto, friction parameter, Courant number and points per wavelength. The criteria of the Morfac is derived both from stability and accuracy. Forcing parameters such as the flow velocity magnitude is the dominant factor while the model properties like the grid size and time step play a minor role. A necessary stability criteria is derived for this specific 1D case. In the analytical and numerical models, Morfac performs better than in the Delft3D model. A strong recommendation is to further improve the numerical implementation of Delft3D which may extensively increase the value of Morfac we can use.

Coastal lagoons are shallow coastal water bodies separated from the ocean by a barrier and they support a range of natural services that are highly valued by society, including but not limited to fisheries productivity, storm protection, and tourism. Songkhla lagoon is the largest lagoonal water resource in Thailand and Southeast Asia. The lagoon is a combined freshwater and estuarine complex of high productivity which represents an extraordinary combination of environmental resources believed to be unique in the region. Climate change, as a response to increased greenhouse gases in the Earth’s atmosphere, is now a widely accepted phenomenon. Sea level rise, temperature, precipitation, and storminess are expected to change significantly with global climate change and to impact coastal lagoons. The nature and magnitude of these impacts are still not very clear. The general objective of the research is to determine the climate change impacts on mixing and circulation at Songkhla lagoon, Thailand. To archive this objective the lagoon was be modeled with Delft 3D, a model developed by Deltares. After the verification with the available data for the region, different scenarios were created to represent the possible changes in mean sea level and riverflow due to global warming. Then, these results were compared to the current conditions to determine the main changes in mixing and circulation in this coastal lagoon. The results suggest an increase in water velocities of the inlet in future scenarios and a decrease of flushing time. Salinity and stratification showed more complex changes in futures scenarios.

The stratigraphic and tectonic framework of the Brent Group and their respective depositional environments is well studied and documented in the literature. The lower progradational Brent deltaic sequence is the response of a high sediment supply rate outpacing the accommodation space rate caused by subsidence and an overall sea level rise stage. These types of systems are typically overfilled basin systems and their facies distribution and stratigraphy are considered be governed by autogenic processes. This implies that the main (fluvial, climatic and basinal) forcing conditions were steady making these formative processes greatly dependent on the geometrical characteristics of the receiving basin and the river delta. While wells and seismic data give a good overview of the stratigraphic sequences, there is still insufficient understanding of the detailed stratigraphic characteristics and facies development within the Brent’s deltaic sequences as response to steady forcing and specific-local scale conditions. This research will focus on the effect of the antecedent bathymetry over which the delta prograded. This antecedent bathymetry is formed by the top of the Oseberg Formation, a coarse grained fan delta. The research objective of this MSc. project is: How the geomorphological evolution, sediment partitioning, facies evolution and stratigraphic response are affected under variable bathymetric conditions by (1) changes in the shoreline direction with respect to the Oseberg´s Fm. pinch out and (2) variable substrate erodability. To address the research objective, a downscaled Brent fluviodeltaic model was created for the Huldra area accounting for the bathymetry generated by the Oseberg Fm. pinch out and also the presumed steady forcing conditions. Published data and data available from STATOIL ASA were used to constrain the basinal and fluvial forcing conditions and the initial bathymetry prevailing in the studied area during Early Jurassic times. Numerical experiments using a hydrodynamic model (Delft3D) show that progradation over the pinch out (shelf edge) can occur under steady sea level condition, producing lobate geometries and basinward sediment sand prone wedge accumulation reaching up to 25 m of thickness. Furthermore they also shows that at, for the anticipated wave climate, no wave induced reworking or transporting of the sand-size grain sediments occurred below 5m water depth because the near-wave orbital velocities are below the threshold transport value. Changing shoreline orientation impacts the wave spreading angle and thereby the affects the interplay between river and basinal forcings. These influence the near coastal reworking pattern as well upstream characteristics of the prograding delta (such as channel avulsion, shifting and abandonment). The numerical experiments including the erodability of the substrate show a large impact on the evolution of the delta. It controls the geometry of the distributary channels. A non-erodible substrate generates wide channels while an erodible substrate produces deeper yet narrower channels since incisions can occur. In addition, it provides a variable but limited sediment source to the delta and the shelf coming from the eroding river bed. While Delft3D is a hydrodynamic model generally applied for engineering scale problems, this study shows it can also be applied to a more geological context. In this aspect we were able to produce new and more geological visualizations not produced before with Delft3D including chronostratigraphic bed level changes, facies model, wheeler diagrams, and reservoir geology maps.

In 2010, a realignment of the main channel of the Maumusson inlet, France, is observed. This breach of the ebb-delta is observed not long after a severe storm that afflicted the Charente-Maritime region in February 2010; Xynthia. A strong link between the breach and the Xynthia storm is expected: a storm event driven breach. In order to assess this hypothesis the impact of the Xynthia storm and the breaching process is investigated by use of a process-based numerical model, Delft3D. Two possible options for the breach are initiated, namely event-driven or a long-term development where the flow through the inlet becomes inefficient. In order to assess the two time scales, two scenarios are introduced for the numerical model; long (10 years) and short term (Xynthia storm). Hardly any input reduction is applied to the short-term scenario while the long-term scenario suffers extensive wave input reduction and the use of a morphological acceleration factor in the view of computational efficiency. Following the qualitative analysis; the results are in the line of expectations. The impact of the Xynthia storm turns out to be rather limited. During the long-term development of the ebb-delta (deflection of the main channel and elongation of the bypassing bar) the impact of the Xynthia storm event increases. When spill channels form and the ebb-delta is tending to breach, the impact of the Xynthia storm drops relatively rapid. In the long-term scenario, deflection of the main channel southwards is observed and simultaneously the bypassing bar elongated in the same direction. Finally, the flow through the inlet becomes inefficient and spill channels start to develop. The location of the new main channel is betrayed by the ebb and flood-tidal flows, making the bypassing bar relatively narrow on a specific location. Breaching of the ebb-delta at the Maumusson inlet is not caused by the 2010 storm driven event but was part of cyclic behaviour with an expected turnaround time in the order of decades. As a result, the littoral drift is significantly reduced by the new orientation of the main channel.

This is a numerical modelling study on the impact of dredging and disposal activities on the long-term morphological development of the Columbia River mouth (MCR). Dredging activities removed 120 Mm3 of sand from the MCR during the studied interval between 1958 and 1999. Only one-third of this volume was disposed in the active littoral zone. Therefore, dredging activities might be an important factor for recent erosion trend at the coasts directly adjacent to the MCR. The net influence of both dredging and disposal activities is analyzed by making use of a Delft3D model. Morphological acceleration techniques and wave climate reduction are used to bridge the gap between hydrodynamic and morphological time scales. The model performance is assessed with simulations for the 1926-1958 interval. These simulations indicate that the model captures the large-scale morphological changes that occurred in the study area. Simulations for the 1958-1999 interval are then used for the analysis of the impact of dredging and disposal activities. Based on the model results, dredging activities led to significant volume losses in the inlet itself and in the area west of the river entrance. On the Peacock Spit shoal directly north of the inlet, the volume losses due to dredging are almost completely reversed by disposal of dredged material on the shoal itself. Dredging and disposal activities did not have significant effects for the littoral drift at coastal stretches adjacent to the MCR. In the studied period, the Peacock Spit shoal did absorb the negative effects of dredging and the additional supply due to disposal activities, without reducing its sediment supply function to the adjacent coastal cell. Other effects of dredging and disposal activities were the formation of distinct sand mounds at the locations of some disposal sites and maintaining the southern orientation of the MCR channel at the estuary side of the inlet. Main implication of the model results for disposal strategies is that the sand volume of the Peacock Spit shoal should be maintained to avoid further erosion of the shoal and prevent undermining of the North Jetty and to maintain the sediment supply function of the shoal for the updrift coastal cell.

In almost every coastal engineering problem, morphological changes play an important role. To understand and predict morphological changes, numerical models such as Delft3D are often used. In the last couple of years the time scale of interest has increased considerably. Due to the large calibration effort and especially the large computational time a full three-dimensional (3D) simulation is generally not very practical. Therefore most of these morphological studies are carried out in the depth-averaged (2DH) mode. Several projects showed that especially in depth-averaged mode the present possibilities to adjust the cross-shore transport in the nearshore area, and the associated cross-shore profile developments, are inadequate. Based on these drawbacks it was decided to implement, validate and evaluate a new approach in Delft3D which represents the 3D results in the nearshore zone, but with less computational time. A quasi-three dimensional (Q3D) model based on the concepts of Reniers et al. (2004) was implemented into the Delft3D model. This model computes the vertical velocity distribution at every grid point accounting for tidal forcing, wave breaking, wind and dissipation due to bottom friction. Validation and evaluation cases showed good agreement between the 3D and Q3D hydrodynamic and morphodynamic model results. The computational time (relative to 2DH) was increased with only a factor 1.2 for Q3D model against an increase up to a factor 7.1 for 3D modelling. The Q3D model reproduces the 3D model results very well with significant more time efficiency and seems therefore a good additional mode to the Delft3D modelling software.

A process-based numerical model was applied to investigate wave reworking in the deltaic environment. The two main objectives were (1) to develop this model and (2) consequently apply it to study the effects of wave reworking on the morphology and stratigraphy of a delta. A depth-average Delft3D model with two sediment fractions (fine silt and fine sand) was developed. The initial condition was the morphology and stratigraphy of a pre-defined fluvial-dominated delta. This initial condition was first subjected to gentle perpendicular waves for a period of 44 months, for a situation with no active river discharge, to resemble a degrading delta. Next, the reference model was subjected to waves for the same period and varying riverine water and sediment discharges were added to the model. The results of these simulations gave a realistic representation of sediment reworking by waves in the deltaic environment. The deltaic environment rapidly adjusted to changes in the forcing. The base case showed the effects of delta front erosion, channel infill and sediment sorting. Due to the difference in energy required for stirring up and transport of sediments, sand sediments remained in the deltaic environment while silt sediments were transported. This process of sediment sorting is dominant in wave reworking and is adequately represented by the model. Sand sediments are deposited on the edges of the delta front and thereby shield the underlying fine sediments. The results for the fluvial input case showed similar realistic behaviour and exhibited a switch towards wave-influenced delta morphology and behaviour, as defined by classical delta classifications. Also deposition of sand-ridges around the river mouth was observed. Sand deposits prevented further erosion of fine sediments of the delta front and sand-ridges shield the deltaic environment behind the ridge. This study also demonstrated that the influence of riverine sediment discharge is a steering factor for delta development. The model proved to be robust in the sensitivity analysis and provides greater insight in the coupling of morphology and stratigraphy of deltas and delta behaviour. The model therefore contributes to the understanding of the response to changes of processes in the deltaic environment, which is of increasing importance to help to sustain deltas for future generations.

Groins are old and intuitive means of reducing erosion and are found along the coast worldwide, although according to CEM (Coastal Engineering Manual 2003), “they are probably the most misused and improperly designed of all coastal structures”. The original purpose of groins was to reduce local erosion, that is, to hold the width of beach in their vicinities. Despite the simplicity of groins, their interaction with the beach is complex, and existing functional design guidance is limited. On the other hand, over the past decade there have been significant advances in understanding of coastal sediment processes, predictive modeling capability, and field measurements. Therefore, with the existing numerical tools the current study will be conducted in order to achieve better insight into this specific topic, to find some design criteria for normal groins and T-shape groins. The first step in this research is to do a wide literature review to find some reliable data regarding wave height and current velocities in a groin field. An irregular wave field must be studied, since regular wave fields concentrate energy around a single frequency, so they produce exaggerated offshore bar and strong rip currents (Hulsbergen et al 1978). On the other hand, the abilities of Delft3D numerical model must be validated for modeling currents and morphological interaction of littoral zone and structures for the case. Once we comprehend the current models are capable of modeling different phenomena, a sensitivity analysis will be carried out to find some design rules for these structures.

Dune evolution on natural and nourished beaches on an engineering timescale is not well understood. Using a study of both literature, and data which has been gathered of the Dutch coast, a new hypothesis regarding the causes of variability in dune evolution is proposed. Following this hypothesis assumptions are made on the basis of which a conceptual model is developed that includes both the accretive and erosive processes that govern dune evolution.

The erosion problem in Hai Hau coastal district (Vietnam) is the subject of this thesis. The exact processes that drive this ongoing erosion however are not well defined yet, and therefore two main goals are defined. The first goal is to gain more insight into the processes that drive the ongoing erosion in Hai Hau. The second goal is to predict the future developments of the nearshore area with following consequences for the coastal defense system. The most important results are: 1. Large amounts of wave energy coming from north-eastern directions are blocked by the Ba Lat delta. The only waves reaching the northern part of the Hai Hau coast refract around the delta. These refracted waves are lower than the waves in the other parts of Hai Hau. 2. Modeling south-western currents along the Ba Lat delta showed that the flow is restored at a distance of approximately 13 km south of the southern spit of the Ba Lat delta. Due to the asymmetrical shape of the Ba Lat delta this reattachment point is expected to be located more south in reality. 3. Alongshore sediment transport modeling by waves only, resulted in southward directed transport in winter, with increasing transport capacities in southern direction. Summer transport directions are north. In the annual transport a point of diverging transport direction has been observed near Van Ly. 4. Lowering of the seabed in front of the dikes resulted in a reduction of sediment transport capacities for all locations. The transport gradients, and hence the eroded volumes, decrease as well. These results lead to the following conclusions: a) The sheltering effect of the Ba Lat delta on the sediment transport in Hai Hau is a reduction in sediment transport capacities in the northern parts during winter monsoon periods. This transport increases in southern direction. During summer monsoon periods waves are not hindered to reach the shore and transport capacities are more constant. b) conclusions regarding the annual erosion were based on the assumption that the large scale residual currents reattach in the middle of Hai Hau. Currents along the coast are expected to increase in southern direction from 0 m/s in the North to 0.2 m/s in the South. c) The present annual eroding volume is approximated at 546.000 m3/year. 4) Lowering of the seabed in front of dikes over the width of the surfzone due to ongoing erosion, reduces the width over which sediment is transported in longshore direction. This also leads to lowering of alongshore sediment transports rates and eroded volumes. An equilibrium situation is not to be expected in the near future.

Recent study has shown that 3D computations of the morphological development of a coast shows irregularities compared with the 2DH (depth-averaged) computations. Therefore a validation of the surf zone currents computed using the 2DH (depth-averaged) and 3D approach in Delft3D is made. The 2DH and 3D approach are compared using an idealized case and validated using data from the laboratory experiment performed by Reniers and Battjes and data from SandyDuck97 field measurements. The 3D approach underestimates the wave-driven longshore current compared with the 2DH approach. The longshore current computations in the 3D approach are dependent on the thickness of the computational layer just above the bed. In the 3D approach the bed shear stress is computed using the quadratic friction law and the velocity in the computational layer just above the bed as input, and the assumption of a logarithmic distribution of the longshore current. The dependency is caused by the assumption of a logarithmic velocity distribution in the computation of the bed shear stress. Due to wave breaking enhanced turbulence this assumption is not valid. Computing the bed shear stress using the velocity in the computational layer just above the edge of the wave boundary layer solves the layer dependency. This new method of computing the bed shear stress in particular and the longshore current computations by Delft3D in general are extensively validated. The 2DH and 3D approach agree well with the measurements for both the laboratory and the field data. For the laboratory experiments the longshore currents are underestimated in the bar trough. The wave height is the bar trough is overestimated, which might causes the underestimation of the longshore current since too little wave energy is dissipated. It is recommended to further examine the translation of wave forces to a current. For the field experiments the longshore currents are generally overestimated near the coast. The wave height computation showed a reasonable agreement with the measurements but also a systematically overestimation. More attention should be paid into accurately modelling the wave height and the wave height decay. Also the vertical distribution of the current velocity is compared with data from the SandyDuck97 measurements and showed a reasonable agreement.

The most densely populated and economical most valuable areas in The Netherlands lie below mean sea level. These areas are protected against the sea by a joint coastal dune system. The vital importance of this dune system is reflected in the extensive collection of Dutch legal regulations that ensure the safety level of the dunes. The assessment methods currently prescribed by these regulations are developed in the early eighties. These methods are strictly speaking only valid for infinitely long, uniform and straight coasts. The Dutch coast with its curvatures, islands and estuaries does not meet these prerequisites. The wide application of these assessment methods is mainly justified due to intentional overestimation of the expected dune erosion. In virtue of the expected climate change and corresponding sea level rise, an effective and reliable coastal management becomes increasingly important. Dutch water management authorities therefore commissioned the development of a renewed probabilistic assessment method for dunes. Such method will provide a more accurate and elegant way of dealing with the large number of uncertainties involved in the dune erosion process. The original assessment methods for dunes along the Dutch coast are extended with a computational method for additional erosion along convex coastlines. This method is based on a limited data analysis, which resulted in a cautious guideline. It is therefore expected that current regulations underestimate the influence of coastal curvatures on the amount of dune erosion. In context of the development of a probabilistic assessment method for dunes, little is known about the relevance of coastal curvatures. It is questioned if longshore phenomena in general and coastal curvatures in particular should be incorporated in the newly developed assessment methods. A probabilistic model set-up is created using the numerical semi-two-dimensional dune erosion model DurosTA and a Monte Carlo routine. The dune erosion model is developed especially to investigate the influence of coastal curvatures. Using this probabilistic model set-up, series of computations with varying coastal curvatures and incident wave angles are made for different types of relevant probabilistic hydraulic conditions. From the results the influence of coastal curvatures on the erosion volumes, and thus the retreat distances and probability of failure, is obtained. The results are compared to current regulations. Furthermore the aspects of the dune erosion process that are particulary interesting for curved coastlines are determined. The physical and location independent importance of different model parameters is investigated by conducting a traditional sensitivity analysis. The probabilistic and location dependent importance of the model parameters is investigated by a probabilistic analysis using, amongst others, the design point. Results show that curvatures found along the Dutch coast can increase the 1/4,000 year retreat distance over 100%. Also coastal stretches with curvatures that are neglected in the current regulations still appear to suffer from a larger retreat distance up to 15%. In comparison, the maximum additional retreat distance to account for coastal curvatures is according to current regulations less than 20% in the observed situations. Furthermore the physical importance with respect to the amount of dune erosion of the sediment diameter increases along curved coastlines due to the more efficient transport of suspended sediments. From a probabilistic perspective the storm surge level gains importance due to the common formulation of the correlation between the storm surge level, the significant wave height and peak wave period.

In September and October of the year 2009, three sandgroyne nourishments have been executed at the Delfland Coast near the village of Ter Heijde. The nourishments have been executed to restore the sediment buffer in the upper part of the coastal profile. A sandgroyne is a concentrated amount of sediment (200.000m3) artificially nourished from the beach into the sea, appearing in the formation of peninsulas. It was anticipated that the three sandgroynes would be absorbed into the coastal system by the impact of waves and currents, nourishing the upper shoreface from the shoreline until a depth of about -5m NAP over a coastal stretch of about 2.5km. The construction and evolution of the sandgroynes have been monitored intensively. The following research objectives were proposed: 1) Assess the morphological evolution and practical aspects of the sandgroynes constructed at the Ter Heijde coast and 2) Use the site specific knowledge from the Ter Heijde pilot project to create a future perspective of sandgroyne nourishments as a common applied method to nourish the shoreface. This master thesis describes the process of the monitoring campaign, the results of a morhpological data analysis, the results of an initial model simulation set-up and a practical analysis. The sandgroynes have been absorbed in the coastal system, dominantly between the shoreline and the -5m depth contour. However the spatial scale of longshore sediment redistribution was larger than accounted for, driven by the intense wave climate. It is concluded that the sandgroynes can be an effective method for nourishing the shoreface, under flexible contract requirements that acknowledge the dynamics of the natural system.