A guide for planners and managers - IUCN

Box II-4. Stabilization of Sand Dunes.
PART II
Protected Areas for Beaches
Relatively inexpensive and available slat-and-wire fencing is used successfully in
artificial, nonvegetative dune construction. Field tests of dune building with sand fences
under a variety of conditions have been conducted in the U.S.A. The following guidelines
are based on these tests (COE, 1984):
1. Fencing with a porosity (ratio of area of open space to total projected area) of about
50 percent should be used. Open and closed areas should be smaller than 5 centimeters
in width.
2. Straight fence alignment is recommended. Zigzag alignment does not increase the
trapping effectiveness enough to be economical. Lateral spurs may be useful for short
fence runs of less than 150 meters (500 feet) where sand may be lost at the ends.
3. Efforts have been most successful when the selected fence line coincided with the
natural vegetation or foredune line prevalent in the area. This distance is usually greater
than 60 meters shoreward of the berm crest.
4. The fence should parallel the shoreline. It need not be perpendicular to the prevailing
wind direction; it will function if placed at an angle to sand-transporting winds.
5. A 1.2 m fence with 50-percent porosity will usually fill to capacity within 1 year. The
dune will be about as high as the fence. The dune slopes will range from about 1:4
to 1:7, depending on the grain size and wind velocity.
6. Dunes are usually built by installing a single fence and following it with additional
single-fence lifts as each fence fills. Succeeding lifts should be parallel to and about
4 times the fence height of the existing fence.
7. The trapping capacity of the 1.2-meter-high fence averages 5 to 8 cubic meters per
linear meter (2-3 cubic yds/linear ft.).
8. Fence-built dunes must be stabilized by planting vegetation or when the fence
deteriorates it will release the sand. The rehabilitation of dunes with fencing should
be only the first step in a two-step operation.
The hardiest species are native beach grasses and creepers, like morning glory
(Ipomoea). In dune planting, plants are often gathered from the wild, trimmed,
sorted, bagged, transported and replanted, as any plant might be. They are planted
according to a design strategy for the dune rehabilitation project (COE, 1984).
A shore protection plan should include regulations to preserve the frontal dune
intact by controlling foot and vehicular traffic (Figure II-47). Access to the beach
should be limited to elevated steps and boardwalks over the dunes that allow
unobstructed movement of sand beneath them and foot traffic should be limited to
these walkways. Exclusion fences should be erected to keep grazing animals off dunes
where this is a problem. Vehicular traffic anywhere on the frontal dune system should
be prohibited. Dune buggies, trail bikes, and other offroad vehicles should be restricted
to the “hard beach” below the berm and to places where traffic will not interfere with
other beach uses.
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