Building for nature:Preserving threatened bird habitat in port design

The fast economic development of the People's Republic of China has created an increasing demand for usable land, resulting in large-scale land reclamations along the coastal zone. One of these regions is Tongzhou Bay (Jiangsu coast), a region characterized by large intertidal mudflats and deep tidal channels with potential for the development of agri-aquaculture and the construction of a deep-sea port. However, these intertidal mudflats also provide vital ecosystem services and support many wildlife species, including several endangered migratory shorebirds within the East Asian-Australasian Flyway. With increasing realization of the importance of maintaining such ecological values, a more integrated coastal development strategy is needed. This study aims to develop a sustainable integrated design for the Tongzhou Bay port, following a "Building with Nature" approach. We use a morphodynamic model to compute habitat suitability for two shorebird species (Great KnotCalidris tenuirostrisand Bar-tailed GodwitLimosa lapponica). Several port configurations were developed on the basis of three design criteria: (1) create area for future port development, whilst (2) preserving existing high-value ecotopes for shorebirds and (3) enhance the natural accretion rate of such ecotopes. Simulation results showed a clear difference in siltation patterns, preservation and enhancement of preferred ecotopes. This work therefore demonstrates the potential and importance of morphological and habitat suitability modelling when designing large-scale reclamations and port constructions, especially in dynamic areas such as Tongzhou Bay

Ecological impact of land reclamation on Jiangsu coast (China):A novel ecotope assessment for Tongzhou Bay

China's continuous and rapid economic growth has led to the reclamation of large sections of the intertidal mud coast in combination with port construction, such as that of the proposed Tongzhou Bay port on the Jiangsu coast. These reclamations threaten the local ecosystem services. An ecotope distribution map was created and a hydrodynamic numerical model of Tongzhou Bay was set up to quantify the impacts of reclamation on the ecosystem. Based on the field data and model results, several abiotic features were classified into 11 ecotopes and visualized in an ecotope map of the Tongzhou Bay ecosystem. Validation with spatial distributions of two threatened shorebird species (bar-tailed godwit and great knot) showed confirmation with the mid-range and low-range littoral zones (inundated from 40% to 100% of a tidal cycle), indicating the importance of the areas with these conditions to these populations. Overlaying the ecotope map with recent and proposed land reclamation schemes revealed a loss of ecotopes, composed of the high-range (42%), mid-range (48%), and low-range (38%) littoral habitats, corresponding to a 44%–45% loss of the most important ecotopes for bar-tailed godwit and great knot (mid-range and low-range littoral zones). These results confirm the applicability of the novel ecotope assessment approach in practice

Nearshore Monitoring with X-Band Radar: Maximising Utility in Dynamic and Complex Environments

Coastal management and engineering applications require data that quantify the nature and magnitude of changes in nearshore bathymetry. However, bathymetric surveys are usually infrequent due to high costs and complex logistics. This study demonstrates that ground‐based X‐band radar offers a cost‐effective means to monitor nearshore changes at relatively high frequency and over large areas. A new data quality and processing framework was developed to reduce uncertainties in the estimates of radar‐derived bathymetry and tested using data from an 18‐month installation at Thorpeness (UK). In addition to data calibration and validation, two new elements are integrated to reduce the influence of data scatter and outliers: (a) an automated selection of periods of ‘good data’ and (b) the application of a depth‐memory stabilisation. For conditions when the wave height is >1 m, the accuracy of the radar‐derived depths is shown to be ±0.5 m (95% confidence interval) at 40x40 m spatial resolution. At Thorpeness, radar‐derived bathymetry changes exceeding this error were observed at timescales ranging from three weeks to six months. These data enabled quantification of changes in nearshore sediment volume at frequencies and spatial cover that would be difficult and/or expensive to obtain by other methods. It is shown that the volume of nearshore sediment movement occurring at timescale as short as few weeks are comparable with the annual longshore transport rates reported in this area. The use of radar can provide an early warning of changes in offshore bathymetry likely to impact vulnerable coastal locations

Measurements of morphodynamics of a sheltered beach along the Dutch Wadden Sea

A field campaign was carried out at a sheltered sandy beach with the aim of gaining new insights into the driving processes behind sheltered beach morphodynamics. Detailed measurements of the local hydrodynamics, bed-level changes and sediment composition were collected at a man-made beach on the leeside of the barrier island Texel, bordering the Marsdiep basin that is part of the Dutch Wadden Sea. The dataset consists of (1) current, wave and turbidity measurements from a dense cross-shore array and a 3 km alongshore array; (2) sediment composition data from beach surface samples; (3) high-temporal-resolution RTK-GNSS beach profile measurements; (4) a pre-campaign spatially covering topobathy map; and (5) meteorological data. This paper outlines how these measurements were set up and how the data have been processed, stored and can be accessed. The novelty of this dataset lies in the detailed approach to resolve forcing conditions on a sheltered beach, where morphological evolution is governed by a subtle interplay between tidal and wind-driven currents, waves and bed composition, primarily due to the low-energy (near-threshold) forcing. The data are publicly available at 4TU Centre for Research Data at: https://doi.org/10.4121/19c5676c-9cea-49d0-b7a3-7c627e436541 (Van der Lugt et al., 2023).</p

Nearshore subtidal bathymetry from time-exposure video images

Time-averaged (over many wave periods) nearshore video observations show the process of wave breaking as one or more white alongshore bands of high intensity. Across a known depth profile, similar bands of dissipation can be predicted with a model describing the time-averaged cross-shore evolution of organized wave and roller energy. This close correspondence between observed and modeled dissipation proxies is used to develop a new remote sensing technique, termed Subtidal Beach Mapper (SBM), to estimate nearshore bathymetry. SBM operates on a time series of cross-shore intensity profiles to resolve the pattern in depth change on a morphological timescale (including overall gain or loss of sediment) rather than to focus on the particular change induced by a single intensity profile. From each intensity profile, the breaking-induced component is isolated by removing the contribution of background illumination and persistent foam. The depth profile is updated based on a comparison between this video-derived dissipation proxy and a cross-shore profile of the dissipation of the roller energy. This updating is implemented through time-dependent mass balance equations for the seabed and a buffer layer above the bed. SBM was tested using 1 year of hourly video data collected at Egmond aan Zee, Netherlands. The dominant morphological changes observed from ground truth data were reproduced reasonably well, including the shoreward migration of the outer bar and the net sediment gain in the profile. Root-mean square differences between surveyed and SBM derived depth after 1 year of video-based depth updating with an average of about 70 intensity profiles per month were smallest (~0.2 m) on the inner bar and largest (~0.6 m) in the outer bar trough, with a profile average value of about 0.4 m. Despite the many processes included in SBM, the implementation of a heuristic scaling function in the mass balance equations to spatially adjust morphological growth rates was essential to these results, in particular near the shoreline, where otherwise the profile is prone to an unrealistic deepening.Hydraulic EngineeringCivil Engineering and Geoscience

Morphological development of a mega-nourishment; first observations at the sand engine

Large (mega-scale) nourishments have been proposed as a promising alternative for traditional beach and shoreface nourishments, especially for locations with large structural erosion and sucient sediment to dredge. This paper examines the initial bathymetric evolution of the Sand Engine, a mega-nourishment of 17 million m3 protruding almost 1 km seaward from its surrounding coast. Topographic surveys show that, despite the blunt initial shape of the nourishment, the sediment is reworked into a nearly symmetrical (bell curve like) shape in less than 1.5 years. The cross-shore extent decreased by 150 m in this period which is a reduction of 15%of its original extent. Simultaneously, the alongshore size of the nourishment increased by 60 % as the sediment is redistributed to the adjacent coasts. This is also reflected in the large 1.6 million m3 loss of sediment on the peninsula. Almost 70 % of this volume is found to accrete in adjacent coastal sections. Although not all sediment loss from the peninsula could be relocated, the findings reveal that the Sand Engine mega nourishment is feeding its surrounding coast substantially

Application of remote sensing video system to coastline management problems.

This contribution evaluates the application of coastal video systems to monitoring and management of coastal stability problems of sandy coastlines. Specifically, video-derived parameters (coastal state indicators or CSIs) are developed which facilitate the measurement of shoreline evolution (erosion/accretion) and response to storms, seasonal cycles and anthropogenic interventions like beach/shoreline nourishment and dredging. The primary variable which forms the basis for all the CSIs discussed in this contribution is the shoreline position derived from time-averaged video images. These waterlines are used to generate secondary products including shoreline contours at a constant pre-defined level, (intertidal) beach volumes, and momentary shoreline positions which reflect the sand volume in a meter wide section of the intertidal coast. Video-derived coastal state indicators were verified via comparisons with traditional topographical/bathymetric surveying techniques and a good agreement was found in all cases. CSIs were computed for three contrasting sandy coastal environments including an unprotected natural beach, a protected beach and a spit. Firstly, results are presented which demonstrate the advantages of coastal video systems over and above infrequent traditional topographic/bathymetric surveying methods. Namely, the ability of video-derived CSIs to quantify the magnitude, accurate location, precise timing and rates of change associated with indi8vidual extreme events and seasonal variability of wave climate. Secondly, video-derived coastal state indicators were used to monitor two different types of human intervention, including beach nourishments and a dredged spit in a navigation channel. The video-derived datasets of coastal state indicators offered significant improvement to current CZM practices, facilitating better timing of management interventions as well as more effective monitoring of the spatial impact and longevity of these actions

Morphological Development of a Mega-Nourishment: First Observations at the Sand Engine

Large (mega-scale) nourishments have been proposed as a promising alternative for traditional beach and shoreface nourishments, especially for locations with large structural erosion and sufficient sediment to dredge. This paper examines the initial bathymetric evolution of the Sand Engine, a mega-nourishment of 17 million m3 protruding almost 1 km seaward from its surrounding coast. Topographic surveys show that, despite the blunt initial shape of the nourishment, the sediment is reworked into a nearly symmetrical (bell curve like) shape in less than 1.5 years. The cross-shore extent decreased by 150 m in this period which is a reduction of 15 % of its original extent. Simultaneously, the alongshore size of the nourishment increased by 60 % as the sediment is redistributed to the adjacent coasts. This is also reflected in the large 1.6 million m3 loss of sediment on the peninsula. Almost 70 % of this volume is found to accrete in adjacent coastal sections. Although not all sediment loss from the peninsula could be relocated, the findings reveal that the Sand Engine mega nourishment is feeding its surrounding coast substantially.Hydraulic EngineeringCivil Engineering and Geoscience

A new alternative to saving our beaches from sea-level rise: The sand engine

A boldly innovative soft engineering intervention, comprising an unprecedented 21.5 Mm3 sand nourishment known as the Sand Engine, has recently been implemented in the Netherlands. The Sand Engine nourishment is a pilot project to test the efficacy of lo