Fen Management Handbook - Scottish Natural Heritage

Case Study 7.4
Fen Water Management
– The Anglesey Fens
The Anglesey Fens SAC is a complex of six basin and valley-head rich-fen systems
located in the Carboniferous Limestone Region of central Anglesey. The component
sites range in size from a few ha to over 250 ha and support a range of plant
communities referable to the Annex I types alkaline fen and calcareous fen with
Cladium mariscus and species of the Caricion davallianae, as well as areas of
base-enriched fen meadow referable to the Eu-Molinion (NVC community M24)
and other calcareous types (notably M22).
Management objectives
To restore fen features across the site to favourable condition. Hydrology figures as
a key factor influencing feature condition.
Management rationale
The Anglesey Fens mainly comprise valley-head and basin wetlands with
groundwater inflow confined to the mire margins as a result on low conductivity
peat infill (including lacustrine clay, marl and peat). Management of axial and other
main drainage features needs to result in maintenance of year round high waterlevels
and the restoration of shallow hydraulic gradients, whilst avoiding significant
overbanking. This is an important issue given that some of the main drainage
features arise upstream and outside the sites in intensively farmed catchments.
Management of marginal hydrology aims to allow the uninterrupted movement of
water from marginal springs and seepages across the mire surface.
Historical Management
Extensive drainage has been a feature of most of the Anglesey Fens. Most was
undertaken in an attempt to improve agricultural productivity and included deep
arterial main drains as well as numerous smaller ‘foot-of-slope’ drains to aid
drainage off surrounding agricultural land. A key aspect of the latter concerns its
role in severing key water supply pathways between groundwater discharge zones
and the fen surface.
Hydrological restoration – techniques and outcomes
Hydrological restoration has followed two dominant themes: (i) work to restore
high year-round water levels either by installing dams and other control structures
in main and other key drains or preventing/minimising further ditch clearance and
maintenance, and (ii) restoration of key water pathways between groundwater
source areas and the fen surface, either by damming drains or their complete infill.
A significant associated benefit of the latter technique has been the creation of
shallow open water pools and scrapes suitable for colonisation by Charophytes and
other early successional specialists.
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