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Major Restoration on the River Kennet
Posted By: mike on 22/01/2010 01:14

Cain Bio's river engineers are now in the final stage of a major habitat enhancement scheme to restore a 2km reach of the river Kennet near Hungerford in Berkshire.  In 2009 an agreement was reached between EA Thames and two adjoining land owners to permanently remove the historic river impoundments (sluices) and allow the 'linear lake' to return to its natural free-flowing state. The scheme is also supported by Natural England. 

 
 'Before' Upstream view of degraded channel with heavy sediment deposits following removal of sluices.

    'After' Upstream view of same reach showing new channel design with water-vole friendly backwater.


The project presented significant challenges not least of which were technical and logistical issues associated with the removal of huge sediment deposits on the bed of the channel. The work involved implementation of our 'in-house' design using techniques such as marginal pond creation to increase riparian bio-diversity and to protect established water vole habitats. The new meandering river channel  has now been re-designed  to compliment the natural flow regime and deep sediment has been replaced with locally won gravel to form a hard shallow bed.  As shown in the attached images, such was the degree of over-widening that the river had to be reduced in places by as much as 75% of its original width. 

 
Downstream view of Kennet following restoration works   Post-restoration - Upstream view of Kennet showing new riffle.


Desirable aquatic plant species such as Water buttercup (Ranunculus spp) cannot re-colonise unless optimal flow velocities are achieved within the channel. With this in mind variable channel widths and cross sectional profiles have been carefully incorporated into the design to maximise physical conditions and habitat diversity.

The final assignment will involve the translocation and re-planting of Ranunculus, Starwort (Callatriche spp) and other aquatic plants into the newly prepared gravel beds using our snowshoe mattress technique.
 

To follow:
A fully illustrated project case study with fixed point photography will explain in stages how the restoration was conceived from design through to final delivery. Project completion is anticipated towards the end of February 2010 with case study reports and up-dates available during early March and mid-summer 2010.