Alongshore variability of the multiple barred coast of Terschelling, The Netherlands

• Published in: Marine geology Vol. 203; no. 1; pp. 23 - 41
• Main Authors: Grunnet, Nicholas M., Hoekstra, Piet
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-01-2004
• Subjects: bar migration; Marine; morphodynamics; multi-bar coast; nearshore bars; ANE, Netherlands, West Frisian Is., Terschelling I; nearshore bars; morphodynamics; bar migration; multi-bar coast
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/S0025-3227(03)00336-0

The alongshore variability of the behaviour of a multiple bar system in the nearshore zone along the barrier island of Terschelling, The Netherlands, is investigated using a bathymetric data set with an alongshore extent of 12 km sampled annually for 28 yr. The spatial and temporal variability of bar behaviour is quantified in terms of bar crest position in relation to morphometric parameters such as bar depth, height, width and volume. Along the entire study area, the bars were generated close to the shore, migrated seaward and eventually degenerated at the outer margin of the nearshore. The interannual migrational patterns of the nearshore sandbars are analysed in terms of time of residence, migration rates and return periods within the life cycle of a bar. The cross-shore nearshore bar behaviour was found to vary alongshore. For instance, cross-shore migration rates gradually increased from 35 to 70 m/yr from one end of the study area to the other. Concurrently, the duration of net seaward migration increased from 9 to 15 yr. The return period and total life span of bars were, however, found to be alongshore uniform on the order of 10–12 yr and 22 yr, respectively. Morphological characteristics of the nearshore bar zone such as slope and width also exhibit gradually alongshore-varying patterns. A strong causal association is established between nearshore slope and both bar migration rates and duration of net seaward migration. It is hypothesised that alongshore-increasing wave heights at the seaward end of the bar zone is coupled with a corresponding increase in nearshore slope. The presence of an important updrift ebb-tidal shoal is identified as key controlling factor in the variability of bar behaviour along the adjacent shoreline of Terschelling.