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Improving habitat

Improving the River Glaven habitat to encourage an increase in eel numbers

Introduction of six new eel passes

Manmade structures on rivers, such as sluice gates, dams, weirs, mills and flow gauging stations, have been identified as major impediments to movement of eels and elvers into the river, along the river and to suitable habitat, and back out to sea, with significant impact on their ability to reach maturity and to breed.

This issue was recognised at a national government, and European, level when a European Council Regulation was transposed into English law through the Eels (England and Wales) Regulations 2009, implemented from January 2010. In summary, the key part of these regulations required that new or existing structures should be adapted to allow the free passage of eels. The Environment Agency surveyed rivers and identified a list of potential barriers to eel passage, ranked in priority for passage and for legal compliance with the regulations. On the River Glaven, 35 structures were identified, 7 in the tidal area of the fresh and salt water marshes and 28 spread through-out the length of the river. However, only four were prioritised as requiring remedy, or further analysis, under the requirements of the legislation.

This left 31 structures owned by a variety of individuals, which were undoubtedly inhibiting eel passage - but with no legal requirement for improvement in the foreseeable future.

Examples of restrictions to eel access

Examples of restrictions to eel access

With the aim of identifying, prioritising and improving 6 of these remaining structures, the project:

  • Conducted a survey to ground truth the Environment Agency list of suitable structures.
  • Prioritise these structures according to defined audit criteria.
  • Liaised with prioritised structure owners to identify those willing to take part in improvement works.
  • Signed formal agreements with these participants to define ways of working, outcomes and requirements for continued future maintenance of the improved structures by them.
  • Implemented work to adapt the agreed priority structures.

Some structures were ruled out as increased ease of passage for eels would also allow invasive signal crayfish better access to protected sites for our native white-clawed crayfish.

Finally, six structures were selected for improvement, located at:

  • Blakeney Freshes.
  • Bayfield weir.
  • Bayfield bridge.
  • Selbrigg Pond.
  • Gunthorpe.
  • Glandford – addition to pre-existing pass to improve its function.
Design drawing of an eel pass

Design drawing of an eel pass

Example of the eel pass at Glandford Mill

Example of the eel pass at Glandford Mill

New eel refuges

Felled trees create new riverine habitat

Felled trees create new riverine habitat

It is important to have refuges in a river for eels, and other river species, to shelter and to feed safely.  One of the easiest ways to create these refuges is to fell selected trees into the river at appropriate sites.  River-based diversity of habitat also leads to variations in flow speed and volume, creating a more diverse and rich ecological habitat. Many rivers have been cleared of this sort of debris in the past, with the belief that this was speeding flow and reducing risk of flooding. However, this thinking has been reversed and now we aim for a varied riverine habitat.

This project felled thirteen trees into the river, seven at Natural Surroundings and six at Thornage Common, creating a wealth of new, improved habitat for eels.

New ponds and backwaters

Use of satellite imagery to survey sites

Use of satellite imagery to survey sites

Eels live for many years in the river, but also in its ponds and backwaters.

With the aim of creating at least two new ponds and/or backwaters, the project:

  • Conducted a survey to identify potential sites.
  • Liaised with site owners to identify those willing to take part in improvement works.
  • Signed formal agreements with these participants to define ways of working, outcomes and requirements for continued future maintenance of the improvements by them.
  • Implemented work at the agreed sites.

The work on Bayfield Lower Meadow created extensive areas of scrapes, ponds and backwaters. The funding for this work formed part of the match funding for this project and was provided by the Environment Agency from the Catchment Restoration Fund for the Nine Chalk Rivers Project (http://norfolkriverstrust.org/trust_project/9-chalk-rivers).

The work on Blount's Meadow created a new pond and reinstated the remnants of two ditches, which were no longer functioning as good habitat.

In all, we achieved:

  • Four new connected backwaters at Bayfield Lower Meadow, Bayfield New River and Blount's Meadow.
  • Four new accessible ponds at Bayfield Lower Meadow and Blount's Meadow.
Preliminary ideas for Bount's Meadow

Preliminary ideas for Bount's Meadow

Pond creation

Pond creation