Keywords: island barrier dune, restoration, artificial
sand dike
Contact: Natuurmonumenten (National Society for
Nature Conservation), 's Graveland, the Netherlands
Location: The Netherlands, Province of Friesland,
Griend
The Wadden Sea island Griend
Griend is a small uninhabited island (appr. 16 ha), lying in the
western part of the Wadden Sea between Harlingen and Terschelling.
In the 13th century the island was inhabited, but in the destructive
stormflood ‘St. Luciavloed’ in 1287 it was nearly drowned. At
present, only during the summer two bird wardens live on the island.
Griend is reknown for its enormous abundance in birds both of
breeding and migrating species. For this reason it is fully protected
by the Nature Conservation Act. The great importance of the island
is due to the availability of large amounts of food at the vast
surrounding intertidal flats, the absence of terrestrial predators
and the absence of disturbance. Furthermore, Griend is of special
interest because of its geomorphological features: it is a curved
sandbar with saltmarshes and mudflats on its leeward side, which
is subject to movement in a southern east direction. Nowadays
Griend is situated approximately 10 km south east of its place
of origin.
For several decades a major threat to Griend has been repeated
erosion of the sandbar along the western side. This may have been
caused by increased water levels especially during storm tides,
due to the construction of the ‘Afsluitdijk’ in 1932. As a consequence
of these changed hydraulic conditions, the natural processes of
erosion at the windward side and accretion at the leeward side
were no longer able to maintain the island. Moreover, due to the
extinction of eelgrass in the western Dutch Wadden Sea, annual
accumulations of large quantities of eelgrass leaves on the shore
of Griend, enhancing the formation of a firm beach ridge, did
no longer occur.
Management
Griend and its surrounding tidal flats, altogether 100 ha, are
managed by Natuurmonumenten (National Society for Nature
Conservation). 
Without
protective measures, the island would probably have already disappeared
in the waves. Several times the sandbar was reinforced by raising
a sandbar in the NW, applying concrete mats, and by construction
of lines of wooden poles to slow down water currents. None of
these measures were able to provide long-term protection. In 1988
Rijkswaterstaat and Delft Hydraulics Laboratory were approached
to investigate alternative solutions for the protection. With
the help of mathematical models, a restoration plan was developed,
for the conservation of Griend for at least 80 years. This plan
is in line with the historical geomorphological development of
the tidal flat area around Griend and is in line with the more
recent tendency of the island to move eastward. Along the northern
and western side of Griend, a 2500 m long and 50-100 m wide dyke
of sand was deposited, as well as a sand depot in front of the
western dyke. The 900.000 m³ of sand needed were extracted
from a large tidal channel some kilometers south of Griend. The
sand dyke was planted with marram (Ammophila arenaria)
and sand couch grass (Elymus farctus).
Results
The restoration project of Griend went well in all respects. Due
to the length of the sand dyke, sand eroding at the western end
is deposited at the eastern end so that Griend continues its slow
move in the eastern direction. Further south of this new salt
marshes could develop.
References
- Essink, K. & J.G. Bosch (1993): On the Conservation of
the Island of Griend in the Dutch Wadden Sea. Wadden Sea Newsletter
1: 5-7. (18.1.3.1).
- Natuurmonumenten (1991): Complete gids met alle natuur- en
wandelgebieden van Nederland. (33KGd91).
- www.waddenzee.nl
