Urban dunes : Towards BwN design principles for dune formation along urbanized shores

Sandy shores worldwide suffer from coastal erosion due to a lack of sediment input and sea-level rise. In response, coastal sand nourishments are executed using ‘Building with Nature’ techniques (BwN), in which the sand balance is amplified and natural dynamics are instrumental in the redistribution of sand, cross- and alongshore. These nourishments contribute to the growth of beaches and dunes, serving various design objectives (such as flood safety, nature, and recreation). Nevertheless, human interference (such as buildings and traffic) along urbanized sandy shores may have significant, yet poorly understood, effects on beach and dune development. Better insight is required into the interplay of morphological, ecological and urban processes to support Aeolian BwN processes for dune formation and contribute to the sustainable design of urbanized coastal zones. This paper aims to bridge the gap between coastal engineering and urban design by formulating design principles for BwN along urbanized sandy shores, combining nourishments, natural dune formation and urban development on a local scale to strengthen the coastal buffer. The first part of the paper analyses sedimentation processes in the (built) sea-land interface and identifies spatial mechanisms that relate coastal occupation to dune formation. Hence a preliminary set of design principles is derived by manipulating wind-driven sediment transport for BwN dune formation after nourishment. In the second part of the paper, these principles are applied and contextualized in two case-studies to compare their capability for BwN in different coastal profiles: the vast, rural, geomorphologically high dynamic profile of a mega-nourishment (Sand Motor); versus the compact, highly urbanized, profile(s) of a coastal resort (Noordwijk). Conclusions reflect on the applicability of BwN design principles within different coastal settings (dynamics, urbanity) and spatial arrangements facilitating BwN dune formation

Analysis of filtering techniques for investigating landslide-induced topographic changes in the Oetz Valley (Tyrol, Austria)

Landslides endanger settlements and infrastructure in mountain areas across the world. Monitoring of landslides is therefore essential in order to understand and possibly predict their behavior and potential danger. Terrestrial laser scanning has proven to be a successful tool in the assessment of changes on landslide surfaces due to its high resolution and accuracy. However, it is necessary to classify the 3D point clouds into vegetation and bare-earth points using filtering algorithms so that changes caused by landslide activity can be quantified. For this study, three classification algorithms are compared on an exemplary landslide study site in the Oetz valley in Tyrol, Austria. An optimal set of parameters is derived for each algorithm and their performances are evaluated using different metrics. The volume changes on the study site between the years 2017 and 2019 are compared after the application of each algorithm. The results show that (i) the tested filter techniques perform differently, (ii) their performance depends on their parameterization and (iii) the best-performing parameterization found over the vegetated test area will yield misclassifications on non-vegetated rough terrain. In particular, if only small changes have occurred the choice of the filtering technique and its parameterization play an important role in estimating volume changes.publishedVersio

Assessing sandy beach width variations on intertidal time scales using permanent laser scanning

[EN] Coastal zones are highly dynamic, and their topography is subject to constant deformation. These deformations are governed by sediment transports that are forced by environmental conditions of waves, tides and wind which result in topographic changes at various spatial and temporal scales. In the view of climate change and intensification of extreme weather events, it is important for coastal management to monitor the deformation and coastal topography with high accuracy. To demonstrate a novel way of deriving these deformations and of analyzing the underlying processes, we use permanent laser scanning (PLS) to monitor part of the typical urban coastal beach in Noordwijk, The Netherlands. A laser scanner permanently installed on a hotel building acquired one 3D point cloud of the sandy beach and dunes every hour, continuously, for a duration of two years. The resulting spatio-temporal data set consists of ~ 15 000 point clouds and contains the evolution of a section of the coast of ~ 1 km length at great detail. The elevation changes are observed at centimeter level, allowing to monitor even small scale and slow processes. However, this information is not readily available from the extensive data set. By deriving digital elevation models (DEMs) from each point cloud and collecting elevation data as time series per spatial grid cell, we structure the data in an efficient way. We use the DEMs to estimate two parameters describing the coastal deformation, beach width and intertidal width. We also extract the shoreline at low and high tide for a part of the data set and estimate beach width and intertidal width from them. We find that heavy storms influence the location of the shoreline and the intertidal width in particular. Ultimately, the estimated beach width and intertidal width at high temporal frequency (monthly) and with high spatial accuracy (meters) helps coastal management to improve the understanding of coastal deformation processes.This research has been supported by the Netherlands Organization for Scientific Research (NWO, grant no. 16352) as part of the Open Technology Programme and by Rijkswaterstaat (Dutch Ministry of Infrastructure and Water Management).Kuschnerus, M.; Lindenbergh, R.; De Vries, S. (2023). Assessing sandy beach width variations on intertidal time scales using permanent laser scanning. Editorial Universitat Politècnica de València. 113-119. https://doi.org/10.4995/JISDM2022.2022.1372911311

CoastScan: Data of daily scans at low tide Kijkduin January 2017

The data set was acquired for the CoastScan project. A Riegl VZ2000 laser scanner was mounted on the roof of a hotel and programmed to perform a scan of the nearby dune and beach area every hour. This data set is a subset, consisting of one scan per day taken in January 2017 of the coast of Kijkduin, the Netherlands. Each file contains a 3D point cloud (x,y,z-coordinates) covering a part of the coast (dunes and beach) of nearly 1 km length. The files were selected to match the lowest tide between 18:00 and 6:00 o'clock, to minimize the presence of people in the area. A few scans are taken during the day, where data at night was not available due to technical problems. One scan was discarded, because of low visibility due to fog (9 January 2017). The files were corrected for a tilt in the scanner, if the tilt exceeded 0.01 degree of the median recorded inclination angle

Statistically assessing vertical change on a sandy beach from permanent laser scanning time series

In the view of climate change, understanding and managing effects on coastal areas and adjacent cities is essential. Permanent Laser Scanning (PLS) is a successful technique to not only observe notably sandy coasts incidentally or once every year, but (nearly) continuously over extended periods of time. The collected point cloud observations form a 4D point cloud data set representing the evolution of the coast provide the opportunity to assess change processes at high level of detail. For an exemplary location in Noordwijk, The Netherlands, three years of hourly point clouds were acquired on a 1 km long section of a typical Dutch urban sandy beach. Often, the so-called level of detection is used to assess point cloud differences from two epochs. To explicitly incorporate the temporal dimension of the height estimates from the point cloud data set, we revisit statistical testing theory. We apply multiple hypothesis testing on elevation time series in order to identify different coastal processes, like aeolian sand transport or bulldozer works. We then estimate the minimal detectable bias for different alternative hypotheses, to quantify the minimal elevation change that can be estimated from the PLS observations over a certain period of time. Additionally, we analyse potential error sources and influences on the elevation estimations and provide orders of magnitudes and possible ways to deal with them. Finally we conclude that elevation time series from a long term PLS data set are a suitable input to identify aeolian sand transport with the help of multiple hypothesis testing. In our example case, slopes of 0.032 m/day and sudden changes of 0.031 m can be identified with statistical power of 80% and with 95% significance in 24-h time series on the upper beach. In the intertidal area the presented method allows to classify daily elevation time series over one month according to the dominating model (sudden change or linear trend) in either eroding or accreting behaviour

A six month high resolution 4D geospatial stationiary laser scan dataset of the Kijkduin beach dune system, The Netherlands

In Kijkduin (The Netherlands) a Riegl terrestial laserscanner on top of a building has surveyed a kilometer of beach and dune from November 2016 to May 2017. More than 4000 hourly and daily scans were obtained during this period containing between 1 and 10 million points per epoch with a decimeter order point spacing and centimeter order vertical accuracy. The dataset was collected within the CoastScan project (Vos et al., 2017) which aims to study the natural variability and resilience of the coast and the use of near-continuous laserscanning to study various spatiotemporal processes simultaneously. The dataset contains 4082 individual scans with supporting files to obtain georeferenced and time corrected point clouds in the Dutch national coordinate system

4D spatio-temporal laser scan dataset of the beach-dune system in Noordwijk, NL

From July 2019 to June 2022 a stationary laser scanner, installed on top of the balcony of Grand Hotel Huis ter Duin was used to survey the beach-dune system at the coast in Noordwijk, The Netherlands. The observed area is about 1000 m long and, depending on the tides, about 350 m wide and includes dunes and a sandy beach.A total of 21812 hourly scans were obtained from July 11th 2019, 14:00 until June 21st 2022, 12:00. Each scan produces a 3D point cloud containing about 4 million points depending on atmospheric conditions and the tide-dependent width of the beach. Additional attributes such as the laser return intensity are available for each individual 3D point record.</p

The Copernicus Sentinel-6 mission: Enhanced continuity of satellite sea level measurements from space

International audienceGiven the considerable range of applications within the European Union Copernicus system, sustained satellite altimetry missions are required to address operational, science and societal needs. This article describes the Copernicus Sentinel-6 mission that is designed to provide precision sea level, sea surface height, significant wave height, inland water heights and other products tailored to operational services in the ocean, climate, atmospheric and land Copernicus Services. Sentinel-6 provides enhanced continuity to the very stable time series of mean sea level measurements and ocean sea state started in 1992 by the TOPEX/Poseidon mission and follow-on Jason-1, Jason-2 and Jason-3 satellite missions. The mission is implemented through a unique international partnership with contributions from NASA, NOAA, ESA, EUMETSAT, and the European Union (EU). It includes two satellites that will fly sequentially (separated in time by 5 years). The first satellite, named Sentinel-6 Michael Freilich, launched from Vandenburg Air Force Base, USA on 21st November 2020. The satellite and payload elements are explained including required performance and their operation. The main payload is the Poseidon-4 dual frequency (C/Ku-band) nadir-pointing radar altimeter that uses an innovative interleaved mode. This enables radar data processing on two parallel chains the first provides synthetic aperture radar (SAR) processing in Ku-band to improve the received altimeter echoes through better along-track sampling and reduced measurement noise; the second provides a Low Resolution Mode that is fully backward-compatible with the historical reference altimetry measurements, allowing a complete inter-calibration between the state-of-the-art data and the historical record. A three-channel Advanced Microwave Radiometer for Climate (AMRsingle bondC) provides measurements of atmospheric water vapour to mitigate degradation of the radar altimeter measurements. The main data products are explained and preliminary in-orbit Poseidon-4 altimeter data performance data are presented that demonstrate the altimeter to be performing within expectations