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‘RIVERS OF CONCRETE’ (Creating Ecological Value in Concrete Rivers)
PETER WORRALL Technical Director, Penny Anderson Associates
DAVID PALMER Principal Engineer, Black & Veatch
The River Restoration Centre 6th Annual Network Conference 2005
Total channel length lost DoNR 2,224m (989m siphon) LR 2,211m (1,103m siphon)
New Channel DoNR 3,219m (171m siphon) LR 2,560m (171m siphon)
Total Structural Losses (LR + DoNR) • 3138m of concrete lined channel
edge • 1548m of ‘naturalised’ channel edge • 2092m siphon Total Extent of replacement structures (LR + DoNR) • 2309m of ‘naturalised’ channel edge of which 1455m is targeted for water vole habitat • 6100m of ecologically enhanced concrete lined channel edge • 2469m of concrete channel without enhancements • 342m of siphon and culvert (130m being siphon)
Achieving Biodiversity Aspirations - 1
Key Constraints
Low Mean Flows – LR 0.55m3/sec - DoNR 0.78m3/sec
Low flow velocities LR – 0.09m/sec to 0.33m/sec DoNR 0.13m/sec to 0.59m/sec
Conveyance requirements
Concrete channel context
Bird exclusion netting
Shading and temperature regulation
Achieving Biodiversity Aspirations - 2
1. Changes in micro-velocities – by creating sinuous flow path (‘meander’ wavelengths based on 10 to 14 times channel width) - by constricting the channel width at flow cross-over points (increasing flow velocities between 15 and 33%) - by installing larger gravels/cobbles in channel constriction zones
2. Habitat opportunities – different media - stone, gravel, clay, wood and coir, for bed and banks - different levels in relation to mean flow (+100mm, -100mm, -200mm) - backwater and on-line channel features - roughened concrete wall structures
3. Plant diversity – submerged, emergent and marsh plants together with flower rich grasslands
4. Upstream and downstream connectivity within the system – mammal shelves and passage ways
‘Naturalised’ banks for water vole LR 570m DoNR 885m
A berm provides opportunities for growth of
emergent and wet grassland plants, which in
turn provide excellent cover and foraging for
water voles (berm width can be variable)
A bank >0.5-1m in height allows
water voles to construct nest
chambers above water level,
reducing the risk of drowning
during flood events
For illustrative purposes only
Bank height
>0.5-1m
Substrate of bank is
sympathetic to water
vole burrowing (i.e. no
gravely/stony soil or
very loose sand
A shallow profile
(55-60o) to the bank
top will allow
management of
plant growth
A steep bank profile (75-85o)
provides excellent
opportunities for water voles to
construct burrow systems
(subsoil or faced with coir roll)
Marginal shelf planted seeded with
suitable for water voles such as
rushes, sedges and wetland herbs
Minimum requirement for this specification
should be 50m per 150m of naturalised bank
T5 Twin Rivers – Habitat Creation for Water Vole