Sea level rise causes more difficulties for coastal maintenance. Although hard structures were built in the past to prevent for flooding, nature based solutions are preferred more recently. For the application of nature based solutions, a better understanding of the coastal processes is desired. Dry sand is transported towards the dunes by aeolian processes, whose bedform development is understudied while knowledge on this is important. One of the most visually clear bedforms are organised dry sand over a moist beach, referred to as sand strips. In order to improve the knowledge on sand strips, this study focusses on sand strip properties and occurring environmental conditions during their presence at the Noordwijk beach, using data of a terrestrial laser scanning (TLS) device.

Sand strips are detected with the Fourier transform. Since surface moisture can be derived from the reflectance intensity of the TLS-data, and due to the different moisture content of the sand strips compared to the surrounding beach, the Fourier transform is applied on the reflectance intensity. Sand strips are detected based on the energy in the variance density spectrum for a wavenumber-range corresponding to sand strips. The detected sand strips were oriented alongshore to oblique-alongshore with a mean wavelength and height of 13.2 m and 4.0 cm respectively, which is in correspondence with similar sand strip-related studies.

According to sand samples of the beach the grain size varies in transverse direction of the sand strips, comparable with the grain size variation of aeolian sand ripples. The coarser grains were located at the crest and the finer grains at the lee-side. Additionally, the samples also showed a significant difference in gravimetric moisture content between the sand strips and surrounding beach, as expected due to the reflectance-based detection. At the sand strips, the maximum moisture content was 5.3%, while the minimum determined moisture content at the surrounding beach was 6.0%. The mean values were equal to 2.6% and 9.4% for the sand strips and surrounding beach respectively.

In addition, sand strips mainly occurred during (almost) alongshore wind events with a wind velocity in excess of 8 m/s. However, the threshold wind velocity for sand strip formation is determined at 10 m/s. Due to the significant height difference that can remain present during precipitation events, these events are not necessarily restrictive factors for sand strip development, although the reflectance intensity suggests different. Furthermore, sand strips mostly formed during falling tide and they were mostly destroyed during rising tide.

The one life cycle of the sand strips that is analysed showed dynamic sand strip behaviour. The migration rate of the sand strips varied over the width of the beach, causing more inland oriented sand strips. This dynamic behaviour cannot be related to weather conditions since they remained constant, however it could be related to topographic steering caused by the dune. Nevertheless, the results of the dynamic properties are only indicative and encourage further study of dynamic sand strip properties. ... Read more

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. ... Read more

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. ... Read more