Context and objectives
The intertidal beach is a dynamic environment, characterized by morphological changes driven by several meteo-marine processes such as wind, waves, currents. In numerous sandy intertidal beaches around the world, sand bars are present. They are a key component of beach systems, as they are a primary source of sediment supply and storage for the beach. Most studies on intertidal bar morphodynamics have focused on short-term: daily, weekly, and sometimes monthly changes of the morphology of the intertidal bars. Due to the numerous challenges associated with a dynamic environment where the morphological response influences the driving factors, limited studies have tried to compare bar morphodynamics at different time scales. Besides, the long-term evolution of the bars is also rarely studied. The RS4MoDy study aims to investigate the morphodynamics of a macro-tidal barred beach from short (storm event) to long-term (>20-years), and to address the relative roles of meteorological‐marine forcing factors in driving bar behaviour and evolution. Specifically, the main objectives of the work packages have been:
WP1: To survey the barred beach system using high resolution orthophotos, digicam images and DTMs from new (short-term) and historical (long-term) data.
WP2: To determine the morphodynamic components of the model of barred beach.
WP3: To determine hydrodynamic and sedimentary components of the 3D model of barred beach.
WP4: To develop a conceptual model of intertidal bar morphodynamics incorporating forcing factors and sediment characteristics from short to long-term (>25 years).
Results of the bar morphology, based on the automatic bar extraction using LiDAR and UAV surveys developed in Python, indicate that the multiple intertidal bars are permanent but dynamic features at Groenendijk beach. They experience temporally and spatially variability from season to years. A homogenous distribution of these features across the intertidal beach is observed with an abundance just above the mean sea level. Also, higher and steeper bars are present on the upper-beach, while a decrease in height and slope is observed in the seaward direction. Although marine forcing is characterized by a seasonal variability, a low degree of seasonal coherence is found between marine forcings and bar morphological response.In addition, the internal sedimentary structures of the inner bars indicate that a clear vertical accretion which in agreement with the longer-term beach morphological evolution.Spatial and temporal variograms were generated to describe the spatial and temporal dynamics of beach elevation for multibarred beach environment. The developed space-time stochastic model based on spatial and temporal variograms successfully predicts the average distribution of sand volume change over time. Thismodel makes possible to predict over time the evolution of integrated beach morphological characteristics.
Societal (including environmental) relevance
Bar morphological results have revealed how intertidal bars behave at Groenendijk after storm and over the long term. This provides useful insights for the authority that manages the coast and coastal safety, i.e. Coastal Division. Also public awareness of the natural dynamics was raised using the Coastsnap stand and application.
Products and services
Developed an automatic bar extraction Python toolbox will be published and made open-access to scientists.
Coastal Division, VLIZ, Flanders Hydraulic Research scientists will be immediate potential users. The developed automatic bar extraction tool will be made open-access to scientists. In addition, data could be further use for future MSc and BSc dissertations.