Fen Management Handbook - Scottish Natural Heritage

Excavating spoil within the area to be bunded can create an adjacent ‘borrow dyke’
or ditch, which will provide additional habitats for aquatic plants and invertebrates
and facilitate the control and distribution of water around a site. Construction using
a long-reach excavator working on top of the bund allows the machine to make use
of its own weight to consolidate the built-up material. The scraping up of material
for the bund should not breach aquicludes, or create an unsuitable surface for plant
establishment.
Impoundment of large volumes of water above the natural level of the
adjoining land is controlled by legislation. Construction of bunds in the
floodplain will require licensing. (see Appendix V for further details).
Bund creation at Ham Wall
RSPB reserve (RSPB).
Incorporation of a plastic membrane can help make bunds watertight. A facing
apron of geotextile or rock armour may be required to protect against wave action
or erosion. Overflows or sluices should be incorporated at the right points to allow
excess water out, and designed so that the overflow does not erode the bund.
Further details on bund construction can be found in Hawke and Jose (1996) and
White and Gilbert (2003).
Bunding or damming drains to raise water levels may be the most effective method
of re-establishing earlier stages in the natural succession from open water, but it
will not be possible to do this repeatedly. Each time this is done, the water table
within the fen will become increasingly elevated above the regional water table,
increasing the difficulty with which water can be retained due to the increased
hydraulic gradient. The only course of action then would be to lower the fen
surface.
7.4.2 Water-retaining structures – dams
Dams are another mechanism for raising water level on fens. The success of a
dam is measured by the visible build-up of a head of water on the upstream side.
The construction of dams and sluices in reedbeds as described in Hawke and
Jose (1996) and for raised bogs in Brooks & Stoneman, 1997 are equally relevant
to construction of dams in fens. Specifications for dams and sluices are also
provided in the RSPB guide to Water Management Structures.
Dams can be constructed of a range of impervious materials. It is critical that the
dam keys into the material beneath and on either side so that water cannot simply
bypass the structure, or scour out a passage around the dam. Many ditches have
decades of accumulated plant litter which will provide a line of seepage if the dam
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