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The Zwin tidal inlet and marshland system was nearly doubled in surface in 2019 when a large part of the Willem-Leopold polder was incorporated in the floodable area. The main channel connecting the marshlands to the sea is characterized by a complex 3D morphology with a main channel, sandy bedforms including banks and bars as well as secondary channels. Their presence and movements reflect active sediment transport in the system. The inlet is controlled by hydrodynamics (currents and water level), beach dynamics, tidal prism and sediment supply. This study reports the morpho- and hydrodynamics of the entire tidal channel part from before the opening of the dyke on 04/02/2019 to nearly 3 years after. The results indicate significant morphological changes in the entire channel system where the main channel has become deeper, wider and migrated eastward. Since the opening, the sediment balance is stable in the entrance inlet. In contrast, the inland inlet has lost a significant sediment volume. Short term dynamics in the middle of the entrance and inland inlet unit were studied during field campaigns under calm and energetic conditions. A regime of ebb dominance is found in the center of the channel and to a lower degree at its east side, while the west side of the channel is flood-dominated. In general, the ebb phase lasts about two times the duration of the flood phase. Based on the tidal prism and cross-sectional area analysis, it is concluded that the expansion of the intertidal area in early 2019 meant a very significant increase of tidal prism, which almost quadrupled. The response in the main channel was rapid and strong. A recent sandbank was quickly cleared during the first year after the expansion. As a result, the channel cross-sectional area at the border of the entrance inlet and the inland inlet attained a new equilibrium around 450 m² at the Spring 2020 survey. This section was only reduced by about 10 m² at the Spring 2021 survey. The continued monitoring programme will help to fine tune the insights into the process-response of the Zwin inlet and to estimate the time scales of the expected sanding up in order to guide future management and interventions, Title : FH reports. Flanders Hydraulics: Antwerp. Volume : 16_089_4 Issue : Pagination : VII, 59 + 7 p. app.

The monitoring of the pilot nourishment executed at Raversijde - Mariakerke coastal area for comparing the morphological response to a combined beach and shoreface nourishment and to a beach nourishment took place from the start of the pilot nourishment in 2013 until 2018. Comprehensive data sets containing topographical (LIDAR and beach profiles) and bathymetrical (single and multibeam) measurements carried out at the study zone area have been analysed in order to evaluate the efficiency of the nourishments. Large part of the deployed sand is still in the area three years after the nourishment was carried out. The morphological trends show erosion in the intertidal beach, accumulation on the dry beach and re organization of the shoreface nourishment into one or two submerged sand bar. Numerical modelling proved that this sand bar attenuates the wave height during stormy events both at low and high tide. The large space created south-west from the Ostend port through its extension in 2011 accommodates much of the sand eroding from the two coastal areas of the pilot site. The shoreline advanced towards the sea immediately after the nourishments and it maintains similar position after three years. The dominant process for the beach evolution was the cross-shore transport immediately after execution, but alongshore transport became dominant on the medium and long term and it was calculated to have a net rate of 150 000 to 200 000 m3 in the north-east direction, Title : FH reports. Flanders Hydraulics: Antwerp. Volume : 00_128_16 Issue : Pagination : VII, 65 + 4 p. app.

Title : WL Rapporten. Waterbouwkundig Laboratorium: Antwerpen. Volume : 21_014_1 Issue : Pagination : VIII, 49

The CREST project (Monbaliu et al., 2020) showed that topo-bathymetric monitoring carried out in the past 30 years revealed that the amount of sand in the active zone of the Belgian West Coast increased substantially. Correcting for sand works carried out, the rate of natural feeding of the area was estimated to be 10 mm/year, which is significantly more than the local sea level rise rate of 2 to 3 mm/year. One concludes that this coastal zone, with a length of ca. 16 km, has shown a natural resilience against sea level rise. The question remains which processes govern this behavior and where natural input of sand to the system occurs.Using available coastal monitoring data as well as a state of the art sand transport model for the Belgian coast, it was revealed that natural processes drive complex transport patterns in the channel and the nearshore bank, resulting in a cross-shore natural feeding from off-shore to the coastline. The spatial distribution of this cross-shore natural feeding is determined by the existence of a channel – sand bank system.The outcome of this research is a conceptual model for the large scale sand exchange in the study area which is implemented in a 1D coastline model. The most important element in these models is the cross-shore natural feeding of the active zone via a shoreface connected ridge amounting to 95,000 m3/year in the period 2000-2020., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 20_017_1 Issue : Pagination : VIII, 68 + 14 p. app.

In the framework of the Raversijde Living Lab project, an intensive topo-bathymetric monitoring campaign of the soft coastal defences has started from the beginning of 2021. The aim of this report is to provide an overview of all the acquired surveys for topo-bathymetry and driving meteo-marine factors for the period from 2021 to 09/2022 as well as to document the processing on the raw data. Finally, a comparison of the bathy-topographic methods from the beach to the offshore area is presented., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 21_012_1 Issue : Pagination : VII, 34 + 5 app.

Beach erosion occurs along a large part of the Belgian coast, but is often more intense at Knokke. Artificial nourishment of the active beach system is one of the most applied and successful measures to prevent and to cope with erosion. After repeated beach nourishments over the past decades, a major scheme is now being implemented: a combined large beach and shoreface nourishment of a total of approximately 3 million m3 of sand for the Knokke area in the period 2020 – 2025. The aim of this study is to understand the hydrodynamics and morphodynamics of the Knokke area and to evaluate the mega-nourishment. This 2nd year progress report focuses on coastal morphodynamics along the Belgian coast from Zeebrugge harbour to east of the Zwin between 2018-2021. The results clearly indicate the significant effect of the nourishments on the beach and shoreface morphology. Future topographic and bathymetric monitoring and use of digital survey data of the morphology immediately after each nourishment stage will allow to document and understand the ensuing morphological development and efficiency of the nourishments., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 19_118_2 Issue : Pagination : VI, 19 + 9 p. app.

Beach erosion occurs along a large part of the Belgian coast, especially in the Knokke area. One of the most applied and successful measure to prevent and to cope with erosion is the artificial nourishment of the active beach and shoreface system. Under the framework of this project, a combined large beach and shoreface nourishment of a total approximately 3 million m3 of sand is planned for the Knokke area in the period 2020 – 2025. The aim of this project is to understand the hydrodynamics and morphodynamics of the Knokke area and to evaluate the nourishment efficiency. This first year progress report focuses on a literature review of the coastal morphodynamics and processes along the east Belgian coast from Zeebrugge to Zwin, as well as a pilot campaign of measurements at sea. An inventory of the existing topographic and hydrodynamic data as well as an analysis of the wave regime are presented., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 19_118_1 Issue : Pagination : VIII, 59 + 11 app.

The Zwin is a relatively small tidal inlet connected to the North Sea through a tidal channel. The inlet is flooded twice a day and is characterized by the presence of intertidal area with sand banks and salt marshes. From August 2016 until the opening of the dyke in February 2019, large intervention works were carried out to reduce the sediment silting and accretion processes by increasing the amount of water flowing in and out of the inlet (i.e. tidal prism). This project aims to evaluate the success of the intervention work and to improve our understanding on the morphodynamics of the Zwin. Detailed topographic and hydrodynamic measurements were carried out in the entrance and inland inlet units before and after the opening of the dyke. The results indicate significant morphological changes in the entire inlet system where the channel has become deeper and wider. Although a high spatial variability with the onshore mobility of the sandy bedforms occurs in the entrance inlet, the sediment balance is stable there. In contrast, the inland inlet spatially experiences two morphological trends with the dominance of erosion in the middle and east side while accretion takes place westward. Future topographic and hydrodynamic monitoring will allow to monitor further the morphological response and to investigate the contribution of the different driving processes in the Zwin inlet., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 16_089_1 Issue : Pagination : VII, 48 + 19 p. app.

The Zwin is a relatively small tidal inlet connected to the North Sea through a tidal channel. The inlet is flooded twice a day and it is characterized by the presence of intertidal area with sand banks and salt marshes. From August 2016 until the opening of the dyke in February 2019, large intervention works were carried out to reduce the sediment silting and accretion processes by increasing the amount of water flowing in and out of the inlet (i.e. tidal prism). On 4 February 2019, the intertidal area was nearly doubled when the International Dijk was cut and a part of the former Willem-Leopold polder was made intertidal. This project aims to evaluate the effects of the intervention work and to improve our understanding on the morphodynamics of the Zwin. Detailed topographic and hydrodynamic measurements were carried out in the entrance and inland inlet units over the period covering the time before the opening of the dyke which was on 04/02/2019 and up to 1.9 years afterwards. The results indicate significant morphological changes in the entire inlet system where the main channel has become deeper and wider. Also, it has experienced an eastward migration along the entire inlet. Although a high spatial variability is noted in the morphological evolution, with a clear onshore mobility of the sandy bedforms in the channel especially in the entrance inlet, the sediment balance is stable there, suggesting that sand bypass dominates there. In contrast, the inland inlet has lost a significant sediment volume over the monitoring period. It has also experienced two clear morphological trends with accretion at the west side with a vertical gain of the sand bank and bars, while erosion dominates in the middle and at the east side. There, the channel has become deeper and wider. Both trend means a migration of the channel toward the east. Since the interventions, the water discharge during the flood and ebb phase has significantly increased. It is linearly related to the geometrical characteristics of the tidal basin and water level. Future topographic and hydrodynamic monitoring will allow to fine tune our insights into the morphological response and to estimate the contribution of the different processes controlling the tidal prism in the Zwin inlet., Title : FHR reports. Flanders Hydraulics Research: Antwerp Volume : 16_089_2 Issue : Pagination : VII, 44 + 2 p. app.

Many sandy beaches around the world bear intertidal bars. These sand bars are a series of parallel troughs and crests on the intertidal part of the beach. The amplitudes, heights, and number of the bars vary greatly between different settings, and their morphodynamics are not fully understood yet. However, these bars may represent a first defense against the erosion of the beach, and their complete understanding is therefore crucial in coastal management. The aim of this study is to identify the key parameters in the determination of the monthly morphodynamics of a multibarred beach. RTK GPS profiles taken along five cross-shore lines at Groenendijk (Koksijde, Belgium) were analyzed to extract the most relevant parameters to study the monthly changes and the evolution of the intertidal bars. The profile points were first tested to determine the best preprocessing method: reprojection of the points onto a fixed profile axis and interpolation techniques were evaluated. Several morphological parameters describing intertidal bars and beach morphology, such as sand volume, bar position, and distance between bars, were calculated using the profile points. Their ranges of monthly change were then used to determine which ones were significant to describe the bar behaviour. Further statistical analysis was then applied to investigate these parameters. Meteo-marine forcings, such as wave and current parameters, were evaluated between studies. Results indicate that sand volume is not an appropriate parameter, at least for this study site and at this time scale: its monthly evolution is lower than the mean measurement error. Also, the number of bars can't be reliably determined due to differences in length between all profiles. However, other parameters such as distance between crests, or bar asymmetry, display significant changes from month to month. The determination of monthly evolution at Groenendijk beach is part of a BELSPO-funded project named Remote Sensing data for investigating the morphodynamics of theBelgian multi-barred macro-tidal beach (RS4MoDy). It combines camera drone surveys and historical airborne LiDAR and orthophotos to assess the morphodynamics of the zone from short-term to long-term. The final goal of this project is to produce a conceptual model of barred beach morphodynamics at many different time scales, from event to yearly evolution.