Building with Nature is a sustainable approach to design multifunctional flood defences (e.g., accommodating recreational services, nature development, etc.) that harness natural forces as much as possible. Building with Nature therefore extensively involves coastal dunes. These dynamic sandy barriers naturally grow because of aeolian processes. Building with Nature may harness these aeolian processes to build, maintain and reinforce coastal dunes. In that case, aeolian processes are coupled to the variable flood risk of sandy barriers. To facilitate sustainable coastal management, it is crucial to understand the relation between wind speed and aeolian sand transport. Aeolian sand transport can either be capacity- or supply limited. When sand is abundant and available, the transport rate is generally capacity limited; and is determined by the wind speed. However, if the supply of sand is limited (e.g., due to moisture content, vegetation, etc.), the capacity of the wind cannot be reached. In this supply limiting case, the transport rate is not governed by the wind speed anymore. Many models are still based on capacity limited transport; and therefore, overestimate measured coastal transport rates. Additionally, supply limitations are still not fully quantified. Many supply limitations are posed by the bed’s erodibility, i.e., its ability to supply sand grains to the air flow. Exploring the erodibility of the sand surface can improve this situation. To this end, a specialized mobile wind tunnel system was developed. This system is called Mobi-Gust 2 and also includes a wind gauging system. This research involves the design and performance of Mobi-Gust 2; as well as testing its viability to conduct applied aeolian research. In this process Mobi-Gust 2 experimentally verified some supply limitations. The outcomes demonstrate that Mobi-Gust 2 is able to conduct applied aeolian research. The next step concerns the usage of Mobi-Gust 2, so that coastal aeolian sand exchange can be quantified. In this way Mobi-Gust 2 can improve the predictive power of numerical models (e.g., Aeolis).

Coastal areas are sensitive ecosystems, which are important as natural habitat, recreational areas and for protection of the hinterland. Coastal monitoring is essential in the analysis and prediction of coastal development. Coastal monitoring has become more urgent due to climate change and its effects on sea level and frequency of storm events. Permanent laser scanning (PLS) provides a tool to acquire 3-dimensional point clouds of an area nearly continuously over extended periods of time. PLS bridges the gap between incidental, in-situ measurement campaigns with high spatial detail, and frequent monitoring via satellite data at lower spatial resolution. Methods to process the complex high-resolution permanent laser scanning data are needed to find and analyse the effects of geomorphological processes over extended periods of time and with high spatial detail. This dissertation deals with the development of methods for spatio-temporal data mining of large 4D data sets from permanent laser scanning for the application of coastal monitoring on sandy beaches.

Two data sets of hourly 3-dimensional point clouds, acquired over periods of six months and three years at two different locations on the Dutch coast were analysed, to identify and assess geomorphological dynamics at the sediment surface. Each data set contains up to 20 000 epochs capturing the dynamics of the sandy beaches in Kijkduin and Noordwijk.

In this thesis two methods are developed: the application of multiple hypothesis testing for the estimation of minimal detectable bias and the generation of a so-called inventory of trends, and the application of clustering algorithms for grouping elevation time series. The first method using multiple hypothesis testing provides a means to define the minimal detectable bias for an expected model behaviour of time series from permanent laser scanning. This method provides a new way to detect small but persistent and statistically significant changes in longer time series derived from 3-dimensional point clouds. Using multiple hypothesis testing allows to identify linear changes with slopes of 0.032 m/day and sudden changes in elevation of 0.031 m with a given discriminatory power of 80% and significance level of 5% in 24-hour time series.

In an additional step, multiple hypothesis testing is used to reduce the complex permanent laser scanning data set to an inventory of trends, which consists of linear pieces of time series, matching the predefined statistical models and corresponding parameters. This method is applied to find and analyse times and areas where specific processes such as storms, aeolian sand transport or bulldozer works occur. The inventory of trends is particularly effective for the detection of aeolian sand transport, which has been difficult to identify using other coastal observations because it causes small, gradual deformations at the sediment surface.

The second method uses clustering algorithms to identify areas which are subject to similar change patterns. These change patterns are then easily associated with underlying physical and anthropogenic processes, mostly tidal induced changes and bulldozer works.

In summary, the developed methods allow to effectively detect deformations on sandy beaches and establish their origins, such as storms, tides, anthropogenic activities or aeolian sand transport, with a resolution and detail that has not been achieved until now. These results allow further analysis and interpretation of geomorphological coastal processes. For instance, the analysis of bulldozer works in our study area leads to the conclusion, that not only buildings themselves, but also the associated human interventions on the sandy beach around each building have a significant impact on coastal morphology and possibly lead to increased erosion. @en

Dunes often act as the primary line of defence for low-lying hinterland against storm surges with dune erosion in the swash-dune collision regime. In the swash-dune collision regime, an elevated total water level, consisting of tide, surge, and wave setup, temporarily submerges the beach. As a consequence, the incident swash may run up to the dunes and collide with the dune face. The damage to dunes following from these collisions can be severe. In the most extreme of cases, storm surges with dune erosion in the swash-dune collision regime can lead to dune breaching or failure with flooding of the hinterland as a consequence. These floods can have devastating economic effects and potentially lead to loss of life.

The risk assessment of areas protected by dunes is often performed using predictive dune erosion models. Such models first use possible storm conditions as input, then use a set of physics based and empirical equations to model the physical processes based on that input, and finally use a measure of impact to the dunes from the model results to estimate the amount of damage to the dunes. However, not all physical processes are currently fully understood, complicating accurate reproductions in models and the risk assessment of areas protected by dunes.

This dissertation aims to study two such physical processes that are relevant to dune erosion during storm surges in the swash-dune collision regime. The first process is the suspension of sediments in the inner surf zone. The total amount of sediment in the water column affects the sediment transport rates. As a consequence, sediment concentrations can have a substantial impact on the magnitude and speed with which sediments eroded from the dune face are transported offshore, and thus on the total amount of dune erosion.

The second process studied is sediment transport due to soil instabilities, i.e. the slumping (or avalanching) of sediments from the dune face. Sediment transport due to soil instabilities leads to dune scarping and a gradual retreat of the dune face. If this type of transport persists for a prolonged period of time, the retreat of the dune face can continue until there is no more dune to erode. As a consequence, the dune breaches and enters the overwash regime, and complete failure of the dune may follow.

To study both processes, a prototype scale field experiment was conducted in the winter of 2021-2022. Two artificial dunes were constructed in close proximity to the high water line on a sandy beach. This increased the probability that the total water level driven by a storm event would result in dune erosion within the swash-dune collision regime. The dunes were monitored for a period of three months and within this period three such events occurred.

The suspension of sediments in the inner surf zone was studied by comparing variability in measured, wave-averaged (i.e. 20 min mean) suspended sediment concentrations. These variations were compared to variability of hydrodynamic drivers that are known from literature to govern sediment suspension during storm conditions. Overall, sediment suspension due to bore turbulence appeared the dominant suspension driver during energetic events representative of storm conditions. During such events, wave energy was saturated in the inner surf zone, and almost all waves were breaking and contributed to the generation of bore turbulence at the free surface. The outcome of the first study suggests that, based on the events analysed, dune erosion models may achieve more accurate results if computations of the magnitude of suspended sediment concentrations were to include a bore-induced turbulence term. If such a term is already included, models should properly address the relative importance of bore-induced turbulence when compared to other drivers.

Sediment transport due to soil instabilities was studied by analysing profile crosssections of the dune face during two storm events. Overall, the morphodynamic behaviour of the upper dune face and dune crest was primarily steered by the morphodynamic behaviour at the dune base. The morphodynamic behaviour (i.e. erosion rate) of the dune base correlated well with the elevation difference between the dune base and the incident total water levels, specifically the square of the total water level that was exceeded for 2% of the time. The slumping events that occurred during both storms likely occurred when sediments from previous slumps at the dune base were nearly depleted by the persisting erosion rate. As a consequence, under similar erosion rates, a new slumping event occurred sooner when the volume of the preceding slump was smaller. A clear relationship could not be established between hydrodynamics seaward of the dune and the volume of individual slumps.

Different model approaches are currently being used to implement sediment transport due to soil instabilities. These different approaches all use the persisting erosion rate of the submerged part of the dune base to steer the erosion of the upper dune face. Therefore, according to the field experiment results, these different approaches may all be able to achieve accurate dune erosion volume magnitudes. Still, depending on the application (e.g. one-dimensional versus two-dimensional modelling), one approach might be more suitable than others.
@en

The Netherlands is a country with a history of human activity along the coast to ensure water safety. In the 1990's a new approach to coastal management was adopted that allowed for more experimentation in the Dutch dunes. Since then a slew of different types of projects have been undertaken, one of which is the construction of foredune blowouts. Foredune blowouts are gaps or indentations in the dunes from which bare sand can erode due to the wind. The motivation for the creation of constructed foredune blowouts can range from wanting to reintroduce gradients back into the landscape to ecological restoration, or water safety.
Over the years different construction methods and designs have been created, however the evaluation of these projects has been difficult in the past due to broadly defined goals and limited monitoring data. The aim of this research is to investigate the potential of constructed foredune blowouts have in achieving water safety and preserving natural values in the Netherlands by modeling constructed foredune blowouts and evaluating the effect of various design aspects.

Insight into the effects of different designs of foredune blowouts is gained through the use of a modeling study that is set up in AeoLiS, a supply-limited aeolian sediment transport model. Different combinations of width, orientation and number of foredune blowouts are simulated in a stretched profile of a section of the Dutch Coast, leading to thirty two simulations. Additionally three alternate methods of implementing foredune blowouts as well as a scenario without a foredune blowout are simulated.

Model results show a pattern of erosion in the intertidal range and deposition along the dunefoot with limited sediment traveling from the beach through the foredune blowout. There is a clear pattern of erosion and deposition along the erosional walls of the foredune blowout and a limited development of a depositional lobe behind the blowout. Simulation of a foredune blowout induced through the removal of top soil and vegetation exhibits similarities with observations in the field.

Constructed foredune blowouts offer a method of creating areas of bare sand which can create space for ecological succession in the vicinity of the blowout. The sand that is removed may also be used to reinforce weaker areas of the dune row. They can offer a diverse looking landscape if that is desirable. However model results do not indicate that constructed foredune blowouts facilitate additional growth of the dunes. The changes in bed level in the model are primarily a redistribution of sediment already situated within the primary dune row.

Along the Dutch coastline, coastal dunes act as the primary sea defence to protect the low-lying areas behind it from flooding. To ensure that these dunes are strong enough to meet national safety standards, models are used to assess their strength. Even though our modelling capabilities have significantly improved over the years, model uncertainties remain because specific processes are not yet fully understood.

One of those uncertainties is the effect of sediment grain size on dune erosion. The relative importance and effect of this parameter differs significantly among dune erosion models. It is however expected that this parameter influences the morphological response of dunes during storm conditions.

Manipulative field experiments to study the effect of sediment grain size on dune erosion were conducted from September 24 until September 27 2022. In total, six experiments were conducted in which four different grain sizes were tested. Two open shipping containers were placed in the intertidal zone and acted as coastal wave flumes. Inside both containers, artificial dunes were built, with median grain sizes ranging from 0.21 to 0.31 mm, and were subjected to wave attack during high water. Cameras were used to calculate erosion volumes at a high sampling frequency. Environmental conditions were measured to capture water levels and wave conditions.

Dune erosion was measured with cameras, providing a low-cost and user-friendly method. This method can accurately and continuously capture dune profiles, particularly when there is a distinct color contrast between the dune profile, incoming swash, and backdrop. Analysis of the profile development reveals that the dune toe linearly translates over time in both the cross-shore and vertical directions. The translation in the vertical direction is also correlated with the rising mean water level.

The analytical model derived by Larson et al. (2004) based on wave impact theory was used to relate measured erosion volumes to incoming hydrodynamic conditions and to isolate the relative importance of sediment grain size on dune erosion. The considered time interval used in this study differs from the original approach, as this study focuses on short-term timescales of subsequent events during the experiment rather than the total erosion of an experiment. The application of this newly introduced timescale requires less data and gives more insight into the involved processes for subsequent erosion events. A linear trend is obtained between erosion volume and hydrodynamic forcing but the model cannot be used as an accurate prediction model, it tends to overestimate erosion volumes. The effect of grain size is incorporated in the transport coefficient. The transport gradient decreases when the sediment grain size increases. A negative correlation that converges as grain size increases was found between the two
parameters, demonstrating a non-linear, monotonic dependence.

This study reveals that erosion rates are smaller for dunes composed of coarser grains than finer grains. This is indicated by both the cumulative erosion volumes for identical hydrodynamic conditions and the values of the transport coefficient in the analytical model. Additionally, the formation of steeper
slopes is observed for dunes composed of coarser grains. These findings could be attributed to the fact that coarser grains have larger fall velocities and therefore are less easy transported by the waves and currents. This study enhances our comprehension of the effect of sediment grain size, ranging from 0.21 to 0.31 mm, on dune erosion and can contribute in resolving discrepancies between model predictions and field measurements to improve future assessments of dune erosion with models.

The dunes along the Dutch coast serve as a critical component of flood defense. Storms and a shortage of sediment supply offshore lead to dune and shoreline erosion, posing a hazard to flood safety. To combat coastal erosion, the Dutch government decided in 1990 to proactively nourish the coast. It is expected that as an indirect effect of the sand nourishments, the volume of the dunes will increase. This thesis aims to determine if the influence of the nourishments and storms along the Dutch coast at decadal timescales can be observed.

A conceptual model is presented to address the impact of storms and nourishments. With the model it is argued that storms have little influence whilst nourishments will likely significant influence the long term dune development.

To investigate the impact of storms yearly coastal profile measurements along the entire Dutch coast (JarKus dataset) and storm profile measurements from the storm in 1976 are used. Following the analysis, no correlation is found between the magnitude of the storm impact and the post storm dune development. However, a difference in horizontal dune toe translation (DTT) trend before the storm (1965-1975) and after the storm (1976-1981) is observed. For all coastal regions except the Delta regions, a higher post storm DTT is found.

To investigate the impact of nourishments yearly coastal profile measurements from 1965 to 2022 of more than 1000 transects along the entire Dutch coast are used. Fitting a continuous bi-segmented piecewise linear function showed an average dune volume change (DVC) of 4.5 m3/m/y before the break point year 1993 and 9.3 m3/m/y after 1993 for the entire Dutch coast. These findings align with the fact that large-scale nourishments commenced in 1990.

Furthermore, the nourishment volume is compared to the change in DVC per coastal region to investigate the impact of the nourishments. A Pearson correlation coefficient of r = 0.78 is found between the change in nourishment volume and the change in DVC between the period before and after the breakpoint year. The ratio between nourishment volume and dune growth is 0.24, meaning that if the correlation is causal, 1m³ of nourished volume contributes to 0.24m³ of dune growth.

Based on the data analysis, we conclude that there is no evidence based on the storm measurements in 1976 to suggest that the size of the storm influences dune growth post-storm. However, the measured DTT trend before and after the storm supports the idea that the dune toe tends to return to the pre-storm trend after a storm. Therefore, on a long-term scale, there seems to be no lingering influence of the storm on dune development. Additionally, the data analysis revealed a distinct change in the trend of dune growth in 1993, three years after the start of large-scale nourishments. A strong relationship is found between the amount of nourished sediment and the DVC. These findings supports the idea that nourishments along the Dutch coast have a significant impact on dune development on a decadal timescale.

When two storms quickly succeed one another, it can be called a twin storm. Storm conditions at the coast can lead to higher water levels and waves that can give rise to dune erosion. Therefore, after a storm the dunes are smaller than before the storm. Dune accretion is a much slower process than dune erosion; it can take weeks to months of time for a dune to grow the volume of sand it lost during a storm. If the interval time between two storms is smaller than the time it takes for a dune to gain the same volume of sand it loses during the storm, the second storm can lead to additional impact. So when storms quickly succeed one another, there is not enough time for the dune to significantly grow in between the storms. Due to additive impact, a twin storm might lead to more damage than a single storm with the same return period. In this research it is investigated whether twin storms give more dune erosion than a single storm with the same return period.

To answer this question, the research is divided into two parts. The first part consists of creating representative storm schematisations for single storms and for twin storms using simulated weather data from the European Centre for Medium Range Weather Forecasts (ECMWF). To start with, the storms from the dataset are divided into several clusters. For each cluster, one schematisation is made that represents the storm within that cluster.
In part two, the storm schematisations are used to calculate the dune erosion for each defined storm cluster. The dune erosion is modelled using XBeach, which is a model that is developed to simulate the evolution of the dune profile during extreme storms. The dune erosion will be modelled for two locations along the Dutch coast: Hoek van Holland and Nieuwvliet-Groede.

In this research, it turns out that at Hoek van Holland 25-30% of all storms can be considered a twin storm. At Nieuwvliet-Groede, 15-20% of all storms are twin storms. For Hoek van Holland very few of the constructed twin storms (approximately 10%) give more dune erosion than the constructed single storms. At location Nieuwvliet-Groede approximately 30% of the twin storms cause a larger dune erosion volume than the single storms. In most cases where twin storms result in more erosion than a single storm, this effect can be attributed to deviations in the storm schematisations.

For further research it’s recommended to investigate how the prediction of the time evolution of the water level can be improved. This is relevant because the dune erosion volume is strongly correlated with the water level. Furthermore, it is advised to do more research into the time scales and modelling of dune growth. Storm groups with interval periods of multiple weeks can be investigated with better predictions of dune growth.

Coastal dunes serve as the primary defence mechanism against coastal storms for many coastal communities around the world. Vegetation plays a role in increasing dune resiliency as it enables dune growth, however not enough is known about its effects during storms. Research has shown that the current climate crisis will increase the intensity of coastal storms as the sea level rises and global temperatures increase. It is therefore of utmost importance to understand the effects of vegetation on coastal dunes. Particularly with current trends of nature-based solutions to plant vegetation in dune restoration projects.

In this master thesis, the impact of Hurricane Ian on two barrier islands is analyzed and modelled. The primary focus of the study was to investigate how dune vegetation influenced the erosional effects of the storm, with a particular emphasis on enhancing the existing methodologies for incorporating vegetation into morphological models such as XBeach. The research findings derived from the data analysis revealed that the most resilient dunes are high, broad and have a dense vegetation coverage. Moreover, the model outcomes highlight the substantial improvement in predictive accuracy achieved by integrating vegetation as a bed roughness coefficient within the XBeach model. Adding vegetation to the model directly influences current velocities, but does not affect water levels, wave heights, or infragravity waves. The primary influence of vegetation becomes pronounced when an island is inundated or breached, significantly reducing the currents and sediment transport caused by water level gradients. An additional effect of vegetation was observed in a comparative analysis between vegetated and unvegetated models. This analysis highlighted a delay in dune crest lowering when vegetation was present, showcasing the importance of vegetation in shaping the response of barrier islands during storm events.

Numerical modelling can help understand the complex processes that shape barrier islands during storms. This research emphasized the necessity of including vegetation in XBeach models to enhance their predictive capabilities. The best predictions occur when high-resolution bathymetric data is combined with land use land cover (LULC) data to include vegetation as a constant bed roughness parameter. Furthermore, reducing the land classes to four different ones based on dune vegetation zones improves the results of the model and facilitates the calibration of bed friction coefficients.

The most effective models applied in this study demonstrated impressive skill, ranging from good to excellent, accurately predicting breaches in the precise areas they occurred for both islands under investigation. This research contributes to the continued improvements of modelling with XBeach and provides a detailed method of analyzing the effects of dune vegetation on dune erosion to determine the impact of Hurricanes in coastal dunes.

Coasts are constantly under the pressure of hydrodynamic conditions such as waves, tides, and storms. In the Netherlands, sand nourishments are executed every few years in order to maintain the country’s sandy beaches for purposes of safety, recreation, and ecology. In order to determine where to carry out these nourishments, the whole sandy coastline of the Netherlands is measured annually by Rijkswaterstaat. This annual survey, called JAarlijkse KUStmetingen (JARKUS), monitors where (increasing) erosive trends appear or persist and, due to its timespan (dating back to 1843), is a valuable dataset to understand the evolution of the Dutch coast. However, this measurement survey is restricted to its annual frequency and is costly. The use of optical satellite imagery for measuring land cover types and geographic features is rapidly becoming more popular due to their high temporal frequency and relatively low costs (due to the public availability of some satellite missions, such as NASA’s Landsat and ESA’s Sentinel-2 missions). This research studied the possibilities of using optical satellite imagery for measuring beach width dynamics in addition to the existing measurement campaigns.

In this study, we derived the Satellite-Derived Beach Width (SDBW) as the cross-shore distance between the Satellite-Derived Shoreline (SDS) and the Satellite-Derived Vegetation line (SDV). We adopted a widely used and validated method for SDS detection and adapted this method to establish the SDV detection method. The SDS and SDV are derived from optical satellites by deriving vectors from the border between two contrasting land cover types that are identified by differences in (sun)light reflectance values. The SDS and is derived from the contrast between water and land, the SDV from the contrast between and sand/sediment and vegetation. The SDBW data was measured from both composite and individual satellite images. The different techniques are suited for different applications, and both have their advantages and disadvantages. A composite image is an image that is composed of a sequence of individual satellite images available within a set window. E.g., a composite is the average image of all those images. Recent research showed that, at the cost of temporal resolution, composite images are suited for analysis of long-term (structural) shoreline trends since they mitigate certain factors influencing image quality (such as clouds and cloud shadows, waves and tides, and satellite instrument errors). Individual images are better suited for analyses of short-term dynamics since they provide instantaneous measurement data. However, they are hampered more by the factors mentioned above, and hence need to be screened before use...

For European Union member states, it is mandatory to assign Natura 2000 areas and regularly monitor them. Currently, vegetation mapping is done mainly manually, which is a time-consuming and expensive practise. Unmanned Aerial Vehicles (UAVs or drones), manoeuvrable vehicles with which high-resolution measurements can be done, could increase automation in this process.
Combining RGB imaging from drones with Machine Learning has already shown promising results. However, RGB imaging has limitations; there should be sufficient daylight, and only the upper layer of vegetation can be monitored. The use of LiDAR could complement the use of RGB imaging due to its ability to penetrate through different layers of vegetation and due to the fact that it does not depend on light conditions. This thesis investigates the contribution that LiDAR point clouds could have in mapping vegetation in typical Dutch Natura 2000 areas, which are typically in coastal dunes.

In this thesis, a method is proposed to classify vegetation into herbaceous, shrub, deciduous and coniferous vegetation classes. First, a method is developed to obtain the height of the vegetation.
Using the height of the vegetation, the vegetation is divided into two classes: high vegetation (coniferous and deciduous trees) and low vegetation (herbaceous vegetation and shrubs). In this way, different layers of vegetation can be classified. For the classification of high vegetation, the points from the top of a raster cell to 5 metres below the top are considered. For the classification of the low vegetation, the points in the lower 2 meters of the vegetation are considered. Features are designed that summarise the vertical distribution of points in different ways. These features are used as input to a random forest classifier.

Using this classification method an accuracy of 85% could be reached to classify the higher vegetation into deciduous and coniferous trees. Using the method, spatial patterns in deciduous and coniferous trees are clearly visible; however, when looking at individual tree levels, still improvements can be made. For the lower vegetation, an accuracy of 73% could be reached to divide the vegetation into classes of shrubs, herbaceous vegetation and bare ground. The method generally performed well for the shrubs, but herbaceous vegetation and bare ground still was mixed at some points by the model. For both classification algorithms, the results and behaviour of the model showed high sensitivity to the training data.

This study has shown the potential of the use of LiDAR in the field of vegetation monitoring, especially in areas where cameras cannot reach, where LiDAR could have added value in vegetation monitoring.

Dunes are the primary sea defence along the Dutch coast. This research investigated the development between 1965 and 2021 of the beaches and dunes of the Hoogheemraadschap Hollands Noorderkwartier (HHNK) area which stretches from IJmuiden to northern Texel. This research used an advanced data analysis on the annual coastal elevation data. The coastline of the HHNK area is maintained by several different measures including nourishments, planting and removal of grass, placing reed fences and building regulations. The aim of this research was to relate the investigated developments of the beaches and dunes to these measures and natural processes.
A literature study was performed first, to get acquainted with the research area and the processes that drive the beach and dune development in the area. In four phases, the developments and their relationships with the drivers were investigated for several subsections of the research area that showed similar behaviour. In phase 1, the coastal profile data was collected for multiple transects spanning the research area. Characteristic parameters describing features of the dune and beach were derived from the coastal profile data. In phase 2, the collected profile data was decomposed into spatial and temporal patterns by a principal component analysis. In phase 3, the transects of the research area were categorised on the temporal development of their coastal profile using the results of the spatial and temporal decomposition. This created subsections of the coast that showed a similar morphological behaviour. In phase 4, the morphological behaviour of several subsections was investigated and related to the natural and human drivers. The relationships between the drivers and the developments were investigated for several subsections, varying in morphological behaviour and drivers, to gain insight into these relationships for the entire research area.
The coastal categorisation resulted in 36 subsections which were mainly continuous in space with the exception of four clusters. Seven subsections were studied in more detail, by investigating the development of several characteristic parameters derived from the coastal profiles, like dune volume, beach slope and shoreline location among others. The shoreline location and beach width showed a strong correlation with the nourishments. The beach slope and width were expected to influence the dune volume changes, which was not supported by the results. The beach width is assumed to be larger than the critical fetch length and the variations in beach slope had a marginal effect on the transport capacity. The presence of beach pavilions limited the dune growth in both height and volume, but regularly moving the pavilions did allow for a seaward migration of the dune front. The effect of small beach houses on the dune volume change was found negligible. Maintenance works of HHNK influenced the dune development locally. The placement of reed fences caused seaward migration of the dune front and the creation of blow-outs increased the dune volume behind the most seaward dune. The strongest dune volume increase was found at coastal areas behind shoals that reduced the incoming wave energy.
The coastal categorisation succeeded in grouping transects with a similar development of their modified coastal profiles. Several modifications were proposed to improve the categorisation of the original profiles and to take into account smaller scale processes. Nourishment was distinguished as most important driver for the development of the coastal area, which has maintained the shoreline location and caused a trend break in several other characteristic parameters. Human influences like buildings, coastal structures and reed fences have a strong local effect on the development of the beaches and dunes. Further research could take into account wave and wind climate, water level variations and grain size quantitatively to get a more comprehensive study of the relationships between the development and the drivers.

The Netherlands has 254 km of coastline that is covered with sandy dunes. As these dunes function as primary flood defences, intensive research has been conducted into dune erosion in recent years. This research mainly took place in laboratories, because all boundary conditions could be controlled and measurements could take place very accurately. However, it remains difficult to simulate a natural wave climate in a flume. In addition, there is also the risk of forgetting certain (as yet unknown) natural processes. Partly because of this, the demand for accurate field data and field measurement techniques has increased over the years. This thesis proposes a new experimental method to investigate dune erosion in the field, in which a 40 feet open-top shipping container is used as an in-field wave flume. Two containers are placed in between the low- and high waterline of the Sand Engine, near Kijkduin. The experimental method is validated by looking at the hydrodynamics within the container and by comparing dune erosion within this container with dune erosion from existing field and laboratory studies. This validation consists of four experiments in which several research hypotheses are tested to see if the wave propagation and erosion processes inside the containers work as expected. In general, it can be concluded that the experiments carried out inside the containers were in good agreement with the tested theories. These theories included that: the avalanching process is present, higher dunes have a bigger eroded volume, the dune toe follows the rising water level and the slope of the foredune remains similar during the erosion process. As this was the first time this method has been used, some recommendations are made. One of those findings is that the use of the measurement systems should be the same in both containers. A good reason to use this contained erosion method again is for the investigation of the grain size influence in erosion processes.

This thesis describes the development and the characteristics of the coastline along the Dutch coastal zone, managed by Hoogheemraadschap Hollands Noorderkwartier. The coastal zone is a rich environment with multiple stakeholders. These stakeholders use the coastal zone for a range of functions such as safety, nature, business, and recreation. Coastal dunes have been the first line of defense against the sea for many years. On decadal and intercentennial time scale, climate change (e.g. sea level rise) and human intervention (e.g. nourishment), affect the variability of the coastline in different ways. Reports have shown an increase of the mean sea level, which is expected to increase even after the year 2100. Bruun was one of the first researchers, who found a relation between sea level rise and shoreline recession. While Bruuns findings contain the fundamental adaption of the coastline due to sea level rise, the coastline remains a highly complex system. Morphological data has been collected yearly of the Dutch coast as part of the JarKus program. Meanwhile, the data collection and computational power have increased exponentially, while the computational cost has gone down. Combining the newly computational power with the extensive JarKus data set, provides new insight into the complex coastal system. The derived variables from the JarKus data set range from widths, gradients, volumes to heights. These derived variables are combined with nourishment into a high-dimensional data set. Clusters of comparable coastal profiles in the Hoogheemraadschap Hollands Noorderkwartier area, have been made using machine learning techniques. Machine learning techniques such as K-means and the Self-Organizing Map (SOM) contain an intelligence, with the capability of clustering similar high-dimensional objects or data, without knowing the desired output. While both methods have the same goal, K-means moves its centroids inside the data and the SOM moves the data to its centroids (BMU). The advantage of combining both methods, is to keep the topological preservation while having the 'hard' clustering advantage of the K-means, which provides easy interpretation and therefore computations. The coastline of the Noorderkwartier can be broken up into nine clusters. Five of these clusters are classified as main-clusters, having a large number of transects. Four clusters are classified as sub-clusters, having just a few transects. Each of the clusters contains its own characteristic variables. Each of these characteristics originates from its own long-term natural and human-induced causes. The variable dominating the general clustering, is the active profile of the coastline. The lesser dominating variables are the foreshore nourishment, depth of closure and increase in foreshore volume. Meaning that the high-dimensional data set, find their similarities due to these dominant variables. Upon further investigation, the clusters containing the highest active profiles, were also the clusters containing historical larger nourishments. Comparing the yearly change of the standard deviation, shows that the clusters containing larger historical nourishment, have a shifting depth of closure. With respect to the dunes, correlations are found between the dune foot, y-coordinate of the boundary between marine and aeolian transport, dune volume and active width of the dune. While the exact reason for this correlation is still unknown, it shows potential for further research. The results of this research contribute to another step in understanding the complex coastal zone. Hoogheemraadschap Hollands Noorderkwartier can now adjust its policy and approach for each cluster based on the results of this research. For further research, it is now possible to focus on specific clusters with their unique characteristics. Lastly, results highlight the importance of the effect of nourishment on the active profile and with this the future dynamic equilibrium of the coastline.

In future decades, coasts will be exposed to increasing risks because of climate change and sea level rise, which poses an increased threat of coastal inundation, erosion and ecosystem loss. The natural variability of coasts can make it difficult to identify these impacts. Most beaches worldwide show evidence of recent erosion. Sea level rise is currently not necessarily the primary driver, but will become very relevant in the future. Understanding both the short-term and long-term development of a coast is considered essential for coastal managers, in order to maintain safety in the future. For a generic evaluation of the state of the coastal zone, it is also important that not only the coastline changes are examined, but also the behavior of the dunes. The interactions between transport mechanisms should be investigated in order to make a good prediction of the large-scale and long-term development of the coastal zone. Therefore, the adaptation of the dunes and the coastline to interacting cross-shore and longshore sediment transport processes must be studied. To get a comprehensive view on those interactions, a new coupled surfzone-dune model is developed and validated.
This coupled model consists of a combination of coastline model ''Unibest-CL+'' and coastal profile model ''the CS-model''. The coupled model has the capability to simulate beach and dune evolution at decadal to centennial timescales including the relevant sediment transport processes that impact the beach and dune evolution: dune erosion and overwash, aeolian dune build-up, beach erosion and accretion due to gradients in longshore sediment transport, adaptation to sea level rise and response to nourishments. The model is tested quantitatively based on the sediment balance, in a very simple and a more complicated academic case focused on the individual effects of all transport mechanisms included in the coupled model. All test cases in the simple case -- which consist of the smallest scale situation the coupled model is able to simulate -- demonstrate sediment conservation and therewith confirm that the implementation of the different transport equations and their interaction in the coupled model is correct. In the complicated test cases – covering a varying number of cross-shore profiles along a larger stretch of coastline – the accuracy of the predicted sediment fluxes and the subsequent coastline and dune volume changes have been determined. The accuracy of every individual transport mechanism included in the coupled model is found to be sufficient and the different sediment fluxes within the coupled model are balanced.
After model testing, the model is used to hindcast the 22-year long coastal evolution near IJmuiden. The dune evolution in this highly dynamic case is simulated reasonably. Furthermore, the coastline evolution is predicted in accordance with the data. Overall, the coupled model is found to quantitatively and qualitatively perform satisfactory. The model is capable of quantifying the long-term beach and dune evolution with interacting longshore and cross-shore processes. Though coupling the models and therewith simulating the longshore sediment transport gradients instead of deriving them from data induces model uncertainties, the application of the model on the IJmuiden case shows that it is possible to simulate the longshore sediment transport gradients using a schematized wave climate to predict the dune volume evolution sufficiently. Furthermore, the interaction between the cross-shore and longshore sediment transport processes enables the simulation of the redistribution of nourishments, improving the predictive ability of both model components with regard to the coastline evolution as well as the evolution of the dune volume. For future research it is recommended to use the coupled model to look into nourishment strategies and their effectiveness on the long-term, climate change scenarios and their effect on decadal to centennial scale dune and beach evolution and the relative importance of different transport mechanisms on the long-term beach and dune evolution.

Coastal aeolian sediment transport is influenced by supply-limiting factors such as sediment sorting by grain size. Sorting processes can cause a coarsening of the bed surface and influence the formation of aeolian ripples. However, it is not fully understood what influence sorting processes have on the magnitude of this transport. In this study, sorting processes of different grain sizes when interacting with wind and their influence on the magnitude of aeolian transport are investigated by performing a tracer study and developing a conceptual model. Sand grains were painted in different colors according to particle size and placed on Noordwijk beach, Netherlands. Several experiments were conducted with varying wind speeds. Surface sampling and cameras tracked the sand color movement on the bed surface, and wind speed and direction were measured. The tracer experiments show that for moderate wind conditions, ripples developed. Once the ripples have formed, the supply of finer tracer grains in downwind direction decreased over time, while the supply of coarser grains remained constant. A strong linear relationship between ripple speed and wind speed was found. For higher wind velocities, no ripples or differences in transport of grain size fractions were observed. Alternating phases of erosion and deposition of upwind sand were observed which could not be related to local variations in wind speed. Based on these results and literature, a conceptual model for an Active Bed Surface Layer (ABSL) with two regimes corresponding to moderate (I), and high (II) wind speeds was developed. The concept enables to estimate the magnitude of aeolian sediment transport as a function of wind speed, bed characteristics, and upwind sediment supply. For Regime I, a linear relationship between sediment transport and wind speed is suggested and for Regime II a third power relationship in combination with a process-based model accounting for supply limitations is suggested.

In this paper we introduce a setup to investigate aeolian saltation and surface dynamics on a centimetre spatial resolution and a sub second temporal resolution. We develop a Lagrangian saltation model and a high-resolution surface model, which we couple to each other and to a turbulence resolving large eddy simulation model. The simulated transport takes place primarily in the form of aeolian streamers, bursts of elongated transport structures parallel to the wind field, which result in a mass flux signal that is highly heterogeneous both in space and time. The temporal frequency responses up to 1 Hz of the mass flux and wind field share the same characteristics, which indicates a coupling between the two. The system can be in equilibrium, during which the stress profiles induced by the particles, the turbulent fluxes and the imposed large scale pressure gradient balance each other. A bimodal shape is found in the mass flux profile, in which we can distinguish an upper and lower saltation layer. The upper layer is associated with a transitional phase between transport by saltation and suspension that exists in the aeolian streamers. Furthermore, The setup is able to simulate ripples, although future research is needed to investigate the mechanisms that influence the final shape of the ripples.

The United States Army Corps of Engineers (USACE) is scheduled to present their solution for a storm surge barrier on Galveston Island in 2021 to congress for approval. A solution for an engineered dune system on the Galveston Island West End has been proposed, but storm surge models have shown that protection from this engineered dune only goes so far, moreover the search for a proper alternative that fulfills technical requirements and social political influences have proven to be challenging. This study aimsto assess different dune alternatives, proposed in different reports, with a range of multi disciplinary criteria. The assessment of dune alternatives will also result in guidelines that should be considered for design, maintenance and governance aspects for an engineered dune barrier on Galveston Island, TX. Using a multi disciplinary approach for the evaluation of the different dune alternatives, the following research question was formulated: To what extent do the various dune alternatives fit the requirements for a land barrier at the West End of Galveston Island, looking at both technical and sociopolitical aspects? In this context, technical requirements are defined as the storm surge-and rainfall coping capacities of the dune, i.e. against what kind of storm is the dune resistant. Social political influences are a combination of the perception by local residents that are directly influenced by the construction of a dune system, governmental forms of collaboration, and in provide an analysis of the maintainability of the dune alternatives using the storm surge capacities. The different dune alternatives that have been assessed consist of the dune system proposed by the USACE and GLO (2018), the big dune system proposed by Galvez (2019) and the hybrid dune system as proposed by Muller (2017) and will hereafter be called alternative 1, 2 and 3 respectively. In this report a fourth alternative was introduced which is based on the hybrid dune system by Muller (2017) and consists of a clay core instead of a concrete core. Alternative 4 was chosen in order to simulate the difference between a concrete core and a clay core. Based on XBeach calculations, the storm surge coping capability of each dune was determined by projecting 10 year-, 50 year- and 100 year storms onto the dune alternatives. ArcGIS maps from the Galveston Island allowed for projection of flow patterns on the island in order to determine the rainfall coping capacity. An evaluation of sociopolitical aspects was based on a review of the literature on dune systems, forms of collaboration between governmental and private entities, and interviews with various respondents consisting of private individuals and companies, as well as governmental agencies involved in the process. Analysis of the various dune alternatives, based on multi disciplinary criteria, demonstrated that alternative 1 is completely flattened in 50 year storm events, whereas alternatives 2, 3 and 4 show a good storm surge capacity. All alternatives aggravate the current rainfall capacity at Galveston Island West End, because each dune system poses an obstruction that is not there currently. Alternatives 2 through 4 show a good enough storm resilience, requiring post-storm recovery maintenance while still providing a reduced but fair storm surge capacity. The sociopolitical results indicate that Galveston Island West End residents wishes are only safeguarded for alternative 1. On this basis, the main recommendations are to perform tests upon the dune system alternatives regarding storm events occurring in succession, which is not unusual in the Gulf of Mexico. A combination of alongshore erosion rates from the Galveston Island and the effect of dune vegetation should be determined for the dune alternatives, since these aspects were not considered in this research. Further research is needed to identify the combined effects of rainfall and storm surge in order to get insights into the performances of a certain alternatives. Furthermore, the exact role including the desired storm surge capability should be well defined in order to determine which stakeholder wishes and influences are to be fully considered for the dune system design.

Coastal dunes habitats are in the transition zone of marine and terrestrial ecosystems and therefore have high biodiversity in terms of animal and vegetation species. These species provide important ecosystem services to the human kind. Due to the development and operation of Maasvlakte 2, an increase of nitrogen emission is expected in the province Zuid-Holland of the Netherlands. When this is taken up by the vegetation and soil in the dunes, encroachment by shrubs will dominate. This will lead to a decrease in species diversity of dune habitats in protected areas of the Natura 2000 network, which is an unfavourable situation conforming to the Nature Protection Law (Wet Natuurbescherming). The main loss is expected to be in grey dunes and humid dune slacks of the Natura 2000 areas nearby Maasvlakte 2. This research focuses on the classification of grey dunes, white dunes, humid dune slacks, woody vegetation, water and their sub-classes in the Natura 2000 areas Solleveld & Kapittelduinen, Voornes Duin and Goeree & Kwade Hoek. Remote sensing in combination with machine learning have been proven to be useful in the monitoring of dune habitats. Open access satellite data provide high temporal and geographic coverage, but are often limited in their spatial resolution. Contrarily, high spatial resolution products are limited in their spectral resolution. In this thesis, the effects of spatial resolution, spectral features and feature combinations on the classification of dune habitats using aerial images and a Landsat-7 image (2012) are analysed. The classifications are performed with a Random Forest classifier, using both a pixel-based and region-based approach. In contrast to the traditional pixel-based method, the region-based method incorporates spectral and statistical information of neighbouring pixels. The best performance is achieved with the region-based approach on a 4m resolution aerial image with an accuracy of 87%. The 10m region-based classification is the second best with an accuracy of 83%. The misclassified pixels are mostly classified as the other sub-class of the same main-class. The region-based method should not be applied to satellite images with low spatial resolution as it causes more loss of detail. More spectral bands contribute to a better classification performance, but they contribute less than the spectral bands that were already used. Also, Landsat-7 images were used to create yearly habitat maps for 2012 and 2019 to subsequently analyse the habitat changes between those years, although the accuracies of the Landsat-7 maps are an issue. The main changes in habitat are found in the woody vegetation (shrubs, trees) and humid dune slacks. The woody vegetation decreased in area, causing an increase in grey dunes area in Voornes Duin and Goeree & Kwade Hoek, whereas the opposite has happened in Solleveld & Kapittelduinen. Loss of area in humid dune slacks is detected in all three regions of interest. The local dune manager confirmed that the detected changes in woody vegetation are mostly correct and caused by dune management activities. The perceived changes in humid dune slacks are less reliable. Finally, a modified training dataset is used to classify Sentinel-2 images in 2019. These results compared reasonably well with the few locations we visited during our fieldwork campaign.

Today's coastal zones are densely inhabited as the majority of the world's population lives in these attractive areas. The shorelines in coastal zones are shaped by complex spatial and temporal variable interactions between natural forcings like changes in mean sea-level, tides, wave and wind conditions, and storm surges. Besides, natural hazards such as coastal erosion, tropical cyclones, hurricanes, typhoons, floods, salt intrusion and tidal surges threaten a major part of the world's population. Furthermore, climate change is likely to increase the risk of natural hazards. As a response, humans changed the world's shorelines and the forcing-driven processes that work on them, to increase protection against hazards and keep supporting their activities. These human interventions are deployed discontinued in time, disperse spatially and might result in negative consequences leading to human-induced hazards. This research focuses on one particular hazard to coastal communities, coastal erosion, which is extended to a term referred to as shoreline evolution by incorporating coastal accretion as well. Up till now, detailed local-scale studies are able to expose human and natural drivers of shoreline evolution and provide a possibility to make a step towards intentional rather than accidental coastal engineering. Digital imaging and, more recently introduced, satellite imagery proved to be a promising new technology to measure and monitor shoreline evolution at bigger temporal and spatial scales. Nevertheless, the opportunity to develop a model that exposes the drivers of shoreline evolution on a planetary scale remains unexplored. This is due to the required computational effort as well as the large variability in coastal systems around the world. With an ever-increasing data availability, data-driven models incorporating Machine Learning (ML) proved to be an efficient alternative approach to heavy computing classical process-driven models in civil engineering practice. Next to this, a coastal classification can be used as a means to inventory the aforementioned variability. Therefore, the research objective in this study is to explore the possibility of exposing and classifying the drivers of shoreline evolution on a planetary scale, by employing ML on satellite imagery. Approximately 390.000 km of shoreline is analyzed for the past 33 years. This resulted in a statistically derived classification of natural and human-induced sandy shoreline evolution. By elaborating on this classification, it is found that natural and human-induced shoreline evolution accounts for approximately 16 and 25% of the total of globally exposed and classified shoreline evolution signals respectively. All outcomes in this research can support detailed local scale investigations and therefore provide an enhanced opportunity to make a step towards intentional rather than accidental coastal engineering. Hence, it is concluded that the developed and applied methods that employ ML on satellite imagery can be used to expose and classify (in)direct human and natural influences on sandy shoreline evolution using spatial and temporal characteristics on a planetary scale. 57% of the shoreline evolution signals is present in a regime with complex and combined (compound) influences, which still requires (rather than supports) local scale investigations to determine the correct influence or driver. More research is required to elaborate on the opportunities that can enhance insight in the compound regime, to improve the obtained results and advance the applicability of this study.

Galveston Bay is an area in the Upper Texas Coast (USA) historically suffering from the impact of several large magnitude hurricanes. In 2008 hurricane Ike, one of the most devastating natural disasters in Unites States recent past, raised awareness of the flood vulnerability problem of the area and triggered the beginning of different proposals, studies and designs to tackle this issue. The main action plan to be taken in the future consists on the construction of a series of interconnected dikes and storm surge barriers along the barrier islands, called Coastal Spine or Ike Dike. In this thesis, an alternative to the dike as land barrier is proposed, designed and evaluated. The concept consists of using a dune system that can serve as a flood defence structure in case of hurricane while being integrated into the coastal system in daily conditions. The dune is firstly parametrized, later its performance during design storm scenario is evaluated via numerical modelling, and lastly it is compared to the default Coastal Spine dike proposal to assess its feasibility and obtain final conclusions.