Geomorphological changes of natural and engineered vegetated foredunes since completion of Kustwerk Katwijk

For centuries, vegetation has been utilized to enhance dune stability and provide coastal protection. Marram grass (Calamagrostis arenaria) is the most commonly transplanted species on engineered coastal dunes in the Netherlands. However, the geomorphic behavior of engineered foredunes relative to neighboring natural foredunes remains unknown. This study utilizes historical airborne laser surveys, multispectral satellite data, and 2023 field surveys to compare the spatial and temporal patterns of sand accretion and vegetation health of the dike-in-dune in Katwijk, NL, with those of the southern neighboring Berkheide from 2015 to 2023. Results show that average annual sand accretion at the Berkheide foredune was about 1.5 times as much as at the dike-in-dune. Average annual increases in vegetation health, as represented by normalized difference vegetation indices, are roughly equal and less than 0.1 at both the dike-in-dune and Berkheide foredunes. This study observed a generally positive correlation between average annual accretion and vegetation health for each foredune. However, in areas of permanent and temporary beach structures, the Berkheide dune appeared to be the most adversely impacted. This information suggests that the foredunes are growing similarly-although the dike-in-dune is engineered-which is promising for urban coastal communities with coastlines visible leeward.