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Fen Management Handbook - Scottish Natural Heritage

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238<br />

Case Study 10.1<br />

Monitoring to Inform <strong>Fen</strong> <strong>Management</strong><br />

– Foulden and Gooderstone Commons<br />

Foulden and Gooderstone Commons are a series of groundwater-fed fens overlying<br />

the middle, upper and lower chalk aquifers between Downham Market and Thetford<br />

in north Norfolk (OSGRTF 762002). The chalk is capped with drift deposits that<br />

range from clay to sand and gravel. The fens occur where water can escape from<br />

the aquifer through ‘windows’ in the overlying aquitard, giving rise to springs and<br />

seepages, and to areas of more permanent water in pingos. It is important to<br />

maintain adequate groundwater pressure, and a groundwater table to sustain fen<br />

within the pingoes.<br />

The fens support rich-fen vegetation of the NVC M13 plant community type,<br />

and are designated SSSI and SACs within the Norfolk Valley <strong>Fen</strong>s. The shallowrooting<br />

higher plants such as black-bog rush and bryophytes such as Scorpidium<br />

scorpioides rely on a positive water pressure to maintain their calcium-rich<br />

soil water at close to ground level. The degree of water-level variation found in<br />

monitored examples of these fens, and its relationship with species diversity, is<br />

described by Wheeler & Shaw (2001). Provided such measured values can provide<br />

a reliable index of the required status quo the soil water level, as sustained by<br />

aquifer pressure, should not fall more than about 15 cm below ground level.<br />

Gooderstone Common:<br />

spring and seepage area<br />

North Norfolk is an important area for arable agriculture. Survival of crops and the<br />

meeting of quality criteria means irrigation is often necessary. Water is abstracted<br />

under licence from boreholes sunk into the chalk aquifers. The Environment Agency<br />

has to demonstrate that the licensed abstraction would have no adverse effect on<br />

the SAC.<br />

Hydrological modelling techniques<br />

The only basis on which predictions of drawdown can be made is through<br />

hydrological modelling. Many models are available, each making a set of<br />

assumptions, and each dependent on the quality of the data available to feed into it.<br />

Important factors include the slope of the land relative to the positions of boreholes<br />

and fens, as this determines the direction of flow within the aquifer. For example<br />

applying the THEIS equation to data for Foulden Common predicted a drawdown<br />

of 10-20 cm. Compared with the water fluctuation information provided by Wheeler<br />

& Shaw for NVC community M13, this could cause significant damage.

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