Fen Management Handbook - Scottish Natural Heritage

Increase flooding frequency and duration through
management of embankments / change in operation of
water control structures, or change in flood management
of the catchment. Make sure that the flood water does not
contain too much silt and/or nutrients that can affect the
desired fen type
Lower the land surface of the fen. In some situations the
top layer of the fen can be scraped off; this is particularly
beneficial where the surface has become nutrient
enriched and when the land level needs to be reduced.
Problem: Too much surface water
Remedy: Decrease topogenous supply
Change management of ditches / drains so that water
drains out more rapidly. Care should be taken to ensure
that the fen will not become too dry; It is good practise
that ditch outflows are fitted with water control structures
(flood boards, weirs).
Decrease flooding to the fen by altering flood
embankments.
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This kind of management will need consent from
environmental regulators and is likely to affect adjoining
landowners
Care must be taken that excavated spoil does not
contaminate the new fen surface (see below for further
guidance)
This kind of management might need consent from
environmental regulators and can affect adjoining
landowners
This kind of management is likely to need consent
from environmental regulators and affect adjoining
landowners
Strategies to restore target hydrological regimes should aim to mimic the natural
hydrological functioning of the site in as many ways as possible. For example:
– use the same water source, i.e. groundwater or surface water, to restore
appropriate water quality conditions.
– if a site was naturally dependent on continuous groundwater discharge to
maintain high soil water levels, remediation through creation of downstream
dams or sluices, might give high soil water levels, but could result in undesirable
‘stagnant’ water with associated low levels of dissolved oxygen.
For sites with relatively uniform land levels, excavations or structures such as bunds
(see below) may be required to contain the water and prevent flooding of adjacent
land, though care is needed to make sure that any bunds do not isolate the fen from
its source of water, such as a stream or river. Past drainage of fen peat may have
caused significant shrinkage and the formation of hollows. On sites with varying
land level, ensuring sufficient depth of water on the areas of higher ground may
result in areas too deep for fen creation where there are hollows or areas of lower
ground.
Reversing past management on topogenous fens (i.e. those dependent on ponding
up of surface water originating from groundwater, rainfall or surface flow - see
Section 2: Understanding Fen Hydrology) is more difficult.
Provided the source (aquifer) is not contaminated (for example by nitrate),
groundwater is a preferable source for fens, to water from streams and rivers,
particularly those with elevated levels of nutrients and suspended solids. Clay and
silt particles in the water column hold nutrients such as phosphates and increase
the nutrient holding capacity of fen soils through cation exchange capacity (see
Section 4: Understanding Fen Nutrients). Section 8: Managing Fen Nutrient
Enrichment goes into more detail about reedbed filtration and other techniques
which can be used to improve water quality.
Past land management may have caused fundamental changes to the soil/peat
chemistry. Experience in Holland shows that deep drainage of previously unfertilised
fen meadows caused the reduced forms of iron and other minerals to oxidise