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North Shotley and Trimley - use of dredged material
Within the River Orwell two areas have been used experimentally to test the
effectiveness of using dredged material (from the channel excavations to the
port of Felixstow) to build mudflats and/or saltmarshes for flood defence. At
these sites, high
density slurry was used to facilitate the creation of a marsh surface
with variable topography, improving drainage and ecological diversity. The trial
began in 1998 at North Shotley and Trimley and was extended in 2001 at Trimley.
Here channels were excavated onto the existing surface followed by the high
density slurry. The aim was to see if pre-engineering enhances and/or quickens
creek development.
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Guidance: It appears from this site that dredge material can have
both positive and negative effects on the invertebrate fauna. Initially
the deposited material at the Shotley site smothered the existing flats
resulting in a decrease in invertebrates, but increased thereafter (Posford
Duvivier Environment 2000). At the Trimley site there was also
an enhanced invertebrate fauna following recharge when compared with adjacent
control areas (Environment Agency 1999).
For more detailed guidance see (Atkinson
et al. 2001)
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References
Atkinson, P.W., Crooks, S., Grant, A. & Rehfisch, M.M.
2001.
The Success of Creation and Restoration Schemes in Producing Intertidal Habitat for Waterbirds.
English Nature Research Report, 425
English Nature.
Environment Agency
1999.
Monitoring Foreshore Recharge works:Essex 1998 - 2002. Contract 0031. Post-placement monitoring studies.
Environment Agency.
Posford Duvivier Environment
2000.
North Shotley Mud Placement: analysis of effects on benthic invertebrate community.
Harwich Haven Authority, Harwich.
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