Keywords:
Atlantic region
mainland barrier island
erosion
dune dynamics
Contact: M. Schulze Dieckhoff. NLWK. Jahnstr. 1.
26506 Norden. Germany.
Location: Wadden Sea, Germany, Lower Saxony
The East Frysian Islands
The dune chains on the East Frysian Islands form the storm surge
protection for the islands. Since 1986 the dunes are part of the
National Park, Niedersächsisches Wattenmeer. Sand is transported
along the northern side in an eastern direction by littoral drift
and sea currents. The inlets between the islands are deep and
wide with a tidal range of 2.5 m allowing enormous amounts of
water and sediment in and out of the inlets. This mass transport
is influenced by tides at the tidal inlets thus forming tidal
flats. Westward where the sandbars of the tidal flats reach the
beach, erosion of the edge dunes occurs. To the east, the continuous
sand supply causes the formation of new dunes.
Management
In the middle of the 18th century, groins and seawalls were built
to stop erosion. At present these structures are maintained and
secured by beach replenishment. In areas where no structures have
been built, dunes can erode as long as an efficient second dune
row is strengthened. These measures have recently been taken to
ensure an adequate protection from floods. Three profile types
are distinguished: the well-supplied beach with the creation of
fore-dunes, the balanced-supplied beach with erosion and accretion
periods, the eroding beach with a considerable retreat of the
coast . On beaches with a neutral sand balance sand trap fences
of marram grass are constructed to make the lower dunes higher.
In areas with a long term positive sand balance, no measures are
taken.
Protection measures
An important task for dune managers is to protect the vegetation
from destruction. In the inner dunes, the danger of blow outs
is great. By continuous monitoring, planting of marram grass and
the building of sand trap fences of natural materials like brushwood,
vegetation is prevented from damage. Indirect measures are the
construction of foot- and cycle-paths and the enclosure of endangered
dune areas. Long term erosion of frontal dunes can be reduced
by beach replenishment.
Dune reinforcement
In the Northern beach area of the island of Langeoog, a peripheral
dune wich protects the village and the public water supply, is
subject to dune erosion. To reinforce the dune, sand was deposited
behind the dunes in the form of a natural dune. Tertiairy dune
areas were avoided as far as possible. The newly built dune was
first protected by hay and then planted with marram grass. Various
possibilities to secure the area are still investigated.
References:
- Erchinger, H.F., Conservation of barrier dunes as smooth,
natural method of coastal protection on the East frysian Islands,
Germany, Coastal Dunes, Carter, Curtis & Sheehy-Skeftington
(eds), Balkema Rotterdam, 1992.
- Thorenz,F.& Martin Schulze Diechoff, Dune protection
in Lower Saxony, Coastline 1998-4, 20-21.
