Amersham 2020 Affinity Water

This AMP7 WINEP project focused on river restoration on a 1.14 km reach of the Misbourne, west of Amersham.

The chalk stream is failing to meet Good Ecological Status under the Water Framework Directive. Affinity Water commissioned FiveRivers as Principal Contractor to construct and reinstate chalk stream characteristics within the River Misbourne, with a particular focus on fish, invertebrate and flow regimes.

 

 

Project requirements

The problem

This chalk stream was failing to meet Good Ecological Status under the Water Framework Directive and was historically disconnected from the floodplain and low lying sections of the surrounding fields would become inundated frequently in wet weather.

Our approach

The solution

  • Creation of a new re-meandered channel through a grazing field, to reintroduce natural processes and re-connect the River Misbourne to the flood plain.
  • Installation of large wood at the embankment breach at the upstream extent, followed by backfilling of the redundant channel with material from excavations.
  • Reprofiling of the long section by adding additional gravels to improve flow velocities within the new re-meandered channel and existing channel.
  • Construct 2 cattle crossings with four water gates.
  • Stock fencing installed along both banks to prevent livestock poaching within the riparian corridor and the associated increase in fine sediment input.
  • Backwater created using the existing redundant mill leat channel.
  • Installation of 16 brash and 10 gravel berms within existing mill leat to create a more sinuous planform and improve flow velocity and variability.
  • Construction of wetland area.
  • Construction of a 300mm earth flood bund.
Project outcomes

The results

The stretch of the River Misbourne was historically disconnected from the floodplain and low lying sections of the surrounding fields would become inundated frequently in wet weather. Through creation of the wetland, a new re-meandered channel and a new bund downstream, FiveRivers increased the flood storage, and improved floodplain and habitat connectivity in the catchment. Application of   natural flood management techniques achieved added benefits to local fish and invertebrates by reinstating the natural meandering form within the River Misbourne. This was achieved through installation of low-level brash berms

 

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Services implemented.

Martin Whitfield - Managing Director at FiveRivers (5R)

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Martin Whitfield

Managing Director

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