Fen Management Handbook - Scottish Natural Heritage

9.7 Site assessment
Planning and design of any wetland creation project requires a great deal of site
information and data. The following section highlights some of the more important
aspects to understand and investigate during the early planning phases, and
their relationship with target fen types and creation methods. Section 5: Fen
Management and Restoration includes further guidance on site assessment.
9.7.1 Water quantity
Sufficient water of the right quality and quantity is fundamental to any fen. The first
essential prerequisite in assessment of the suitability of any potential site for fen
creation, or restoration, is therefore to establish the quantity of water supply to the
site. Obtaining reliable information on the amount of water entering the proposed
fen, and amounts potentially lost via various routes, for each quarter of the year is
essential. Ideally records for several years at least should be examined to identify
annual as well as seasonal variations.
The water available at a site can be estimated using the following
calculation:
Water available = rainfall – evapo transpiration (ET) – seepage losses +
seepage inputs
Climate data
The Met Office hold rainfall and evapotranspiration data from which they
can produce daily, weekly or monthly estimates for a specific location.
MORECS is a nationwide service giving real time assessments of
rainfall, evaporation and soil moisture. (www.metoffice.gov.uk). EA, SEPA
and NIEA may also hold relevant information.
MAFF technical bulletin No.34: Climate and drainage (1976), also
contains useful information on rainfall and evaporation values.
Information on rainfall and other climatic variables is relatively easy to obtain
(see above) but climate change predictions suggest that the pattern of rainfall
and evapo-transpiration is likely to change across the UK in the future, and
such changes will need to be incorporated into any calculations. The difficulty in
accurately calculating water budgets is further complicated by the hydrological
complexity of most fens, and the variations in seepage on individual sites depending
on soil type, soil structure, and variations in the height of the water table between
one location and another (the hydraulic gradient). Expert advice from a professional
hydrologist should therefore be sought at an early stage.
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