Onderzoeksoutput

The  MOZES-project  (MOrfolgische  interactie  kustnabije  ZEebodem  en  Strand)  investigated  the morphodynamic interaction between the Belgian offshore seabed (shelf and nearshore) and adjacent shoreline aiming to improve regional morphodynamic understanding needed for effective coastal management. The project included data-driven research and numerical modelling.
An impressive bathymetric database spanning the last two centuries of the Belgian shelf in relation to coastal morphodynamics has been assembled. Natural morphodynamics include significant longshore sediment transport to the east, the movement of nearshore sand ridges to the east, and the encroachment of shoreface-connected ridge and tidal channels on the coast. This encroachment is interpreted as ultimately triggered by sea-level rise. Human interaction causes even more intense sediment movements and morphodynamics. Repeated beach nourishments contribute to coastal squeeze, while much of the nourished sand remains in the coastal system but settles in sheltered areas where it is less useful. Dredged fairways to the coastal harbours severed the natural transport paths over the shoreface-connected ridges to the beach and dune belt, depleting the attachment areas. Deep dredged fairways attract sediment from the environment. Dredging of all harbours and access channels means net removal of sediment from the coastal system. Dumping dredged material in nearshore current channels locally plugs them up, diverts the currents and triggers down current channel deepening. Harbour dams extending in the nearshore attract sediment in the alongshore sheltered nearshore areas, while new erosion troughs and channels are created at the offshore side (in addition to downdrift erosion).
Different types of numerical models were applied to better understand the effects of seabed changes on shoreline evolution, as well as the influence of the anthropogenic activities.
The nourishment needs for coastline preservation at the erosional hot-spot of Knokke-Zoute were investigated with 2DH models and a 1D coastline model. Results showed that these models can all reproduce the high erosion rates of beach nourishments at Knokke-Zoute as volumetric losses of the active profile (m³/year) after calibration. Most importantly it was shown that the main driver of this erosion is the combination of wave related cross-shore transport and especially the large gradient of alongshore sand transport in the active zone which is caused by the harbour of Zeebrugge blocking alongshore transport from the southwest coastline. Appelzak channel and local protrusion of the coastline are secondary drivers of erosion of the beaches in Knokke-Zoute.
An idealized coupled shelf-nearshore model (2DH & Quasi2D) was developed to improve fundamental understanding of the impact of shelf ridges and adjacent channels on the decadal nearshore and shoreline morphodynamics. The observed large-scale bathymetric changes over the past 200 years were incorporated in a schematized form. Sea level rise, the hold-the-line strategy to maintain shoreline position and coastal squeeze were also accounted for in the model. Model results using sea-level rise rates from the IPCC scenarios for the next 50 years (>3 mm/yr), combined with a hold-the-line strategy to maintain shoreline position and the associated coastal squeeze, indicate that future annual nourishment volumes in areas where coastline erosion is determined by the channel-ridge morphology may need to be about 2–5 times larger than those under the sea-level rise rates over the last 50 years (~~1.5-3 mm/yr).
Lessons learned for coastal protection from MOZES project demonstrate the importance of considering decadal scale coastal morphological processes to establish sustainable solutions. The channels and ridges closest to the coastline as well as the coastal harbours and fairways are crucial influencing factors to be taken into account in the future nourishment strategies for coastal protection and development.