|Three-dimensional current structure in the Dutch coastal zone|
de Ruijter, W.P.M.; Borst, J.C.; van der Giessen, A. (1990). Three-dimensional current structure in the Dutch coastal zone. Neth. J. Sea Res. 25(1-2): 45-55
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579, more
|Authors|| || Top |
- de Ruijter, W.P.M.
- Borst, J.C.
- van der Giessen, A.
As part of a more comprehensive programme on the hydrography in the Netherlands coastal zone its complex current structure is investigated. One of the aims is to identify the various dominant factors that control the patterns of the coastal flow. To that end field observations covering a one year period were taken at strategic locations in the Dutch coastal area. One of the main results reported here concerns the long term (i.e. one year) average residual currents. Near the bottom these appear to have a significant onshore directed component, with values of the order 2.5 to 3.5 cm/s. In the upper layer typical average values are between 7 and 11 cm/s. The near surface residual flow is mostly in longshore direction with an onshore component increasing with distance from shore, due to the prevailing southwesterly winds (i.e. close to longshore) over the area. The observed large variability of the three-dimensional current structure on different time-scales is largely induced by variations in wind conditions. If strong winds are accompanied by a high river discharge, a distinct two layer system results with very high residual current speeds in the upper-layer, up to 40 cm/s. The observations also produce evidence for the outflow of Rhine river water to be at least partly responsible for the significant onshore component of residual currents near the bottom, as it determines the density structure in this area. Tidal current ellipses show a marked vertical structure both with respect to shape and sense of rotation. For the region considered the spatial distribution of these parameters clearly illustrates the large influence of bottom friction and coastal boundaries, in combination with earth's rotation. Furthermore the data show that variations due to the spring-neap tidal cycle are substantial.