Fen Management Handbook - Scottish Natural Heritage

Explanation of abbreviations: S2 = Cladium mariscus swamp, S4 = reedbed,
M13 = Schoenus nigricans – Juncus subnodulosus mire, M24 = Molinia caerulea
– Cirsium dissectum fen meadow, S24 = Phragmites australis – Peucedanum
palustre tall-herb fen, ‡ = more details for individual sub-communities in the ecohydrological
guidelines (Wheeler et al. 2004).
Plant community
Mean
Summer
Maximum Minimum Mean
Winter
Maximum Minimum
M13 -10 5 -30 1 -5
M24 -25 -10 -53
S2 -15 40
S24 ‡ -15 4 -78
S4 -10 50 -80 50 150 0
Small, shallow areas of open water are preferable to large, deep areas because of
the increased risk of erosion around the margins where large waves build up over
large areas of exposed water. Aligning the longest length of a scrape perpendicular
to the prevailing winds can help reduce wave erosion.
9.8.2 Controlling water level
Water levels on any site are controlled by the rate at which water enters and leaves.
Some form of control structure(s) may be needed to control water inflow and outfall,
or on larger sites, to control and manipulate water movement between different
hydrological blocks. On many sites, simple structures such as pipe dams and drop
board sluices will be sufficient.
Water control structures
Flexi pipe sluices: Cheap, easy to install, and an effective method of precise water
level control, but only capable of moving low volumes of water. They consist of
flexible, ribbed plastic pipe e.g. 300mm single wall aquapipe, incorporated in to an
earth bund or dam. Alternatively, rigid pipe may be used, with a right angled ‘turner’
section installed, which can be rotated to differing positions to allow water to be
retained or let out.
Drop board sluices: simple structures comprising a series of boards that drop in
to a grooved spillway. Water levels are adjusted by inserting or removing boards.
There are many different types of materials that can be used to construct the
retaining walls of the sluice including plastic sheet piling, wooden boards and
welded metal frames.
See RSPB Water management techniques for conservation – technical case study
series (N Droy) for further information. www.rspb.org.uk/sluices
9.8.3 Bunds and borrow dykes
Bunds, or low earth banks, keyed in to an impermeable substrate can be used to
retain water above the level of the water table in the surrounding land, and may also
help to retain winter floodwater, where this is desirable. Further details of bunds are
included in Section 7: Fen Water Management.
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