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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.

For local protection of coastal stretches where buildings are situated in or form part of the coastal defense line the deep water reef concept has been developed. Two reef concepts were designed; a shore-parallel breakwater (of 3 km length) and a segmented breakwater (three blinds of 1 km length), both located in 10 m water depth at 1.5 km off the coast of Scheveningen. In the present research the hydrodynamics and long term morphodynamics of the two deep water reefs are analyzed with the physics-based numerical model Delft3D. The two reef concepts are modeled in 2DH mode with the Parallel Online morphological approach. The hydrodynamic processes at submerged breakwaters are different from those operating at emerged breakwaters. Wave transmission by the submerged breakwater crest creates two additional effects; 1) a water level set-up with a discharge over the reef and 2) reduced wave action at the landward area of the reef. The water level set-up drives two large-scale circulation cells off the reef tips, with velocities up to 1 m/s. In the surf zone the longshore currents are directed towards the shadow zone, where the second effect creates a sheltered area. The magnitude of these effects is for the parallel reef concept amongst other parameters dependent on the wave height and wave transmission, whereas for the blinds reef concept this is also dependent on the wave direction due to the orientation of the blinds. The longshore varying currents and reduced waves in the surf zone cause the coastline to development into a salient form. At the lee of the reef accretion occurs, whereas at the southward and northward sides of the sheltered area erosion occurs. The morphological development is similar for the two reef concepts and of the same order of magnitude. The blinds reef is the preferred alternative for construction, as less severe erosion is modeled to occur. Equilibrium will likely be attained in 15 to 25 years after construction.

This research has focussed on the identification of the relevant processes behind the long-term fine sediment dynamics. Three main influences were considered: the tide, wind waves and biological stabilization/destabilization. The study was performed by means of computational modelling, within the process-based model, Delft3D. By modelling several different scenarios, the separate influences of the tide, wind waves and biology were investigated. The results showed that the tidal asymmetry, entering the basin from the sea, was the main contributor to the import of fine sediments. In general, the tide promoted a large import towards the intertidal areas below the MSL line, and only a very small import towards higher elevations, due to the limited transport capacity of the tidal currents in these areas. Waves were the main contributor to the export-flux of fine sediments by the model, by increasing the bed shear stress in the intertidal areas and causing a relatively larger distribution of sediment towards the deeper areas. Waves were also the main contributor to the high suspended sediment concentrations inside the modelled basin, causing a substantial increase in the basin-average SPM concentrations. In case of a combined influence of waves and biology, particularly the interaction between the seasonal variations appeared to be of importance, which further enhanced the export flux from the modelled basin during late autumn and early winter. With respect to the distribution of sediment, the biological influences caused a landward shift in the deposition and the sediment was distributed much more evenly than if no biological effects were included in the model.

The potential ecological effects of the sand mining activities for Maasvlakte 2 have been identified in an Environmental Impact Assessment (EIA). One of the identified effects in this EIA was an impact on the number of sea ducks in the Natura 2000 area 'Voordelta'. The sand mining activities will cause an increase of the silt concentration along the North Sea coast. Subsequently the light intensity in the water column decreases. A change of the light intensity can affect the growth of phytoplankton. An impact on the growth of phytoplankton can finally affect higher-order species in the food chain: phytoplankton is eaten by bivalves and bivalves form the main food of sea ducks like eiders. Within this so-called impact-effect chain from sand mining to sea ducks, a large number of uncertainties play a role. In the EIA safe assumptions were used for a lot of these uncertainties. The final predicted impact is a result of the accumulation of several safe assumptions. Therefore, the probability of occurrence of this predicted impact will be small. Information on this probability of occurrence will be useful in the discussion about the necessity of mitigating and compensating measures. The main objective of this thesis is to give insight in the probability of occurrence of the possible effects of sand mining on sea ducks in the Voordelta. The research started by analysing which uncertain factors and processes have a large influence on the final result. A Monte Carlo analysis was used to take the uncertainties of these factors into account in the modelling of the ecological effects. Probability density functions were estimated for the relevant variables and were finally combined in the Monte Carlo analysis. From the results of the Monte Carlo analysis probability distribution functions for the impact of sand mining on eiders are derived. These probability distribution functions show that the probability that the sand mining activities for Maasvlakte 2 have a significant effect on eiders in the Voordelta is very small and can be considered negligible. In this thesis is shown that giving insight in the probability of occurrence of significant ecological effects by using a probabilistic analysis is possible. The methodology that is used in this thesis is also expected to be applicable for the assessment of ecological effects of other human activities.

This thesis is an exploratory research into the maintenance of the Slijkgat, by analysing the morphological behaviour of the Slijkgat and the Haringvliet. The Slijkgat is the approach channel for the fishery harbour of Stellendam. The delta area west of the Haringvliet Dam started to accrete after the construction of the dam around 1970, therefore maintenance dredging became necessary. Recently it was decided to deepen the channel over a width of 100 m from -5.00 NAP to -5.50 NAP and to maintain this depth. Based on the Stakeholder Agreement for Maasvlakte 2 the municipality of Rotterdam will become responsible for this deepening and maintenance. The responsibility for the implementation is transferred to Project Organisation Maasvlakte 2 of the Port of Rotterdam. This study investigates the possibilities for maintaining the Slijkgat; the possible maintenance scenarios are based on future morphological developments. These future developments are derived from a historical morphological analysis. This analysis is based on bed level measurements and Delft3D Flow calculations. Data sets of 1986, 1992, 1998 and 2003 were used and these data were compared. From this analysis it can be concluded that the sediment volume in the total study area is approximately stable, but that the sediment volume is shifted within the area. The Inner Area has become shallower, while the Outer Area has eroded. The Delft3D Flow calculations show that the amount of water that is discharged through the Slijkgat has increased in the period 1986 -2003. In the future the Slijkgat will most likely remain open as a result of river discharges. The dimensions of the cross-sectional area of the Slijkgat depend on these high river discharges, since these move sediment from the channel. As a result the Slijkgat is in a dynamic equilibrium since these high river discharges only occur a few times per year. The rest of the year the Slijkgat is accreting. The past ten years ebb and flood channels have developed in the Slijkgat. As a result the bed level in the Slijkgat is varying. Although the dimensions of the cross-sections increase in general due to the increase of tidal volume, some locations will remain around -4.5 to -5 m NAP due to ebb and flood channels. To utilise the system dynamics, the dependency of the cross-sections on river discharge is used as base for the scenarios. During high river discharge current velocities are high in the Slijkgat and sediment is transported, which makes that the channel dimensions increase. This principle is used for the formulation of different scenarios, which are all evaluated based on the increase of current velocities in the Slijkgat. In general it can be concluded that velocities in the Slijkgat can increase by opening the sluices during a shorter period. For the shallow areas near the sluices these effects are significant. Where the Slijkgat meets the Outer Area velocities decrease and the effects of the change in discharge regime is less noticeable. A permanent change in closing policy can reduce the maintenance activities at the locations closest to the sluices. A new closing policy that will be implemented is 'de Kier'; the sluices will opened during high water and salt water will enter the fresh water reservoir. If this new policy is implemented current velocities will increase in the Slijkgat, since the total amount of water will increase. Furthermore discharging though only the southern or the northern sluices does not make a difference for the current velocities.