Year 2 – year 6

Utrecht University

This WP combines (1) the novel field measurements from the Living Lab (WP 1) and (2) existing data and satellite imagery of coastal morphodynamics, to bridge the gap between the processes that drive nourishment-scale morphodynamics and sediment pathways at the scale of the Dutch coast, both for the wet and dry part of the beach-dune system. This is done by two PhD students that work closely together.

The PhD candidate at TU Delft will study morphodynamics on the nourishment-scale, focusing on the redistribution of sediment at a nourished beach and the driving mechanisms. The observations at the Living Lab nourishment (WP 1) will provide key missing data on the initial deformation and sediment dispersal at an individual nourishment. This will be supplemented by examining nourishment performance data in the Netherlands (with RWS) and abroad (a.o. with the USACE and the CSE and CPE firms). The WP 1 data (bed levels, hydrodynamic data and grain-size sampling (with WPs 2.2 & 2.3) will be examined. Moreover, a state-of-the-art Optically Stimulated Luminescence (OSL) sediment tracing tool (Reimann et al., 2015; Pearson et al., 2022) will be used, providing the unique possibility to distinguish the nourished sand from the native sediment and map sediment connectivity (Pearson et al., 2020). Together, this will allow us to unravel the sediment transport fluxes, grain-size distribution, shear stresses, morphological response and, ultimately, sediment pathways at an individual nourishment. Data acquisition will be tailored to test the postulated lee-side and feeder hypotheses and thus build on previous studies.

The PhD candidate at UU will capitalize on existing long-term bathymetric (since 1965; Brand et al., 2022), sedimentological and hydrodynamic datasets of the Dutch coast, a crucial step to expand the scale and map the long-term (10-100 year) response of the coastal zone (10-500 km). Machine learning techniques (Goldstein et al., 2019) will be applied to distil characteristic morphological behavior of multiple nourishments in a range of settings, with varying properties. We will complement this with satellite imagery to investigate the impact of nourishments on adjacent beaches (Vos et al., 2019) and the relative importance of timescales of change. Key areas of persistent sedimentation, such as the foredune (Van IJzendoorn et al., 2021), will be identified for collection of sediment cores, from which changes in grain-size composition through time (vertically in the bed) will indicate long-term changes in bed levels and bed composition related to repeated and large-scale nourishment. Together with the insights on sediment pathways on nourishment-scale from the Living Lab, using the OSL tracing tool, this will allow for conceptual modeling of sediment connectivity within the (future) nourished coastal system.

Furthermore, the analyses in this WP will provide crucial parameters (shear stresses, sedimentation rates, grain-sizes) for quantifying changes in ecological habitats (WP 2.2) and relevant scenarios for numerical modeling predictions (WP 2.4). Our findings and field observations from Netherlands and abroad will be used to generalize and provide input for coastal nourishment strategies (WP 4).

Task 2.1a Quantify nourished sand dispersal at the Living Lab nourishment using OSL techniques
Task 2.1b Exploring lee-side effects in morphology and hydrodynamics at the Living Lab nourishment
Task 2.1c Systematic analysis of nourishment behavior from existing long-term datasets of Dutch coast
Task 2.1d Assessment of shoreline changes beyond nourishment areas from satellite imagery
Task 2.1e Sediment sampling along Dutch coast to reveal long-term changes in grain sizes
Task 2.1f Integration of field data from nourishments abroad for further generalization of findings
Task 2.1g Conceptual modeling to bridge gap between nourishment-scale and coastal-scale morphodynamics
Task 2.1h Distil changes in physical indicators crucial for habitat disturbance and recovery

Long-term analyses and additional field sampling will be co-designed and co-created with RWS. OSL analyses include a 3-month visit to WU, where these techniques have been developed. To further generalize the findings from this WP, a guideline on the impact of nourishment design on the morphological performance will be co-designed and co-created with US Army Corps of Engineers, Flanders Hydraulics Research, University of Aveiro, and US and Dutch engineering companies. This includes a 3-month research visit to the US.

This WP will generate a unique quantitative understanding of coastal sediment pathways, both at nourishment-scale and coastal-scale (Scientific breakthrough; Output). This will be crucial to realize mutual understanding between stakeholders based on shared knowledge of the coastal system, in order to support the development and implementations of coastal policy by RWS and the Dutch Ministry of I&W (Outcomes). Together, this will further allow for the co-creation of nourishment strategies for resilient coastal landscapes with high socio-economic and natural values (Impact).

[Here the key results of this WP will be presented.]