Haxey Grange Fen - Water Level Management Plan

  Haxey Grange Fen was declared a site of specific scientific interest in 1981.  It is considered to be the best example of primary fen habitat known in South Humberside and is particularly important for its invertebrate communities.  Four species of national note have been recorded on the site, including the rare Mire Pill Beetle.  In 2009, Natural England assessed the site to be “unfavourable declining”, with low water levels identified as a primary cause.  This highlighted the need for a review of the existing water level management plan, produced in the year 2000.

 

Left: Site map showing active water level monitoring network.  Pink circle (dipwell); orange circle (gaugeboard); blue circle (stilling well) Right: The rare Mire Pill Beetle

 

In August 2015, Phoenix Adam was commissioned by the Doncaster East Internal Drainage Board (DEIDB) to review and, if necessary, update the existing water level management plan, with reference to Natural England’s target water levels for the site:

  • Raising of water in the central part of the site to above ground level in mid-winter
  • Maintain and regulate water at ground level to 150mm BGL from March to end of July and ground level to 300mm BGL for August and September.
  • Ensure that areas not identified as requiring raised water levels remain dry

 

Left: The central pond area (August 2015).  Habitat for the rare Mire Pill Beetle

Right: Model results:  Light blue squares are flooded.  Dark green and blue squares are the drains

 

Phoenix Adam undertook the following tasks in the delivery of an updated water level management plan:

- collating data on the history of water management and monitoring on the site from two key stakeholders: the IDB and Natural England.

- site visit to undertake basic levelling of adjacent drains and water level measurements within the drains.

- creation of a groundwater model of the site in Groundwater Vistas

- calibration of the model to historic gauged water level data

- modelling a number of options to raise water level to within Natural England’s targets for the site.

- provision of un updated report, providing recommendations for further work

 

Left: Calibration of the model against observed data (time in days). 

Right: Plan view of model showing topographic variation (higher ground to lower ground: red to yellow to green to blue).

 

Preferred options for water level management included solar and wind-powered recharge to the centre of the site from the southern boundary drain and installation of a bund in the drain to encourage water retention.

The project was delivered on time and received good feedback from both Natural England and the Internal Drainage Board.  As a consequence, the scope has been extended to include additional monitoring and updating the model with the new data to increase confidence in the results.

 

 

Phoenix Adam Ltd operates under ISO9001 UKAS accreditation. Outputs were subject to our ISO9001 Check, Review, Approval and Verification process.  

Above: a rare sighting of the lesser-spotted Genn at work.  Adult males can reach 40cm in height.

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