Transcript View presentation - Landscape Institute

Green Bridges
Findings from Literature Review and
Internal Design Guidance
Project Summary
Drivers for the project:
• Natural England’s statutory role and responsibilities
• Lawton’s ‘Making Space for Nature’ and Natural
Environment White Paper Commitment 32 (NEWP)
• Findings of Natural England’s evidence review of
transport and green infrastructure and resilience,
NECR 169.
• Scarcity of published information on green bridges.
• Inform the design of transport infrastructure and
measures to mitigate for environmental impacts
Definition of a Green Bridge:
An artificial structure over road or rail
infrastructure which is either vegetated or
provides some wildlife function
Project Brief
Literature Review to identify:
a) How effective are green bridges in addressing landscape, access
and ecological severance caused by the road and rail network;
b) How effective are green bridges at providing habitats in their
own right; and
c) How effective are green bridges at delivering wider ecosystem
services?
Project Outputs
Green Bridges Literature Review
Green Bridges Guide
Literature Review Findings
•
Identified 56 Bridges – largely in Europe (Netherlands)
•
Majority of bridges that were identified were over roads
• Bridges in existence appear to have been largely constructed for wildlife
purposes, with the exception of UK
• Examples of bridges found in the UK, include Scotney Castle bridge A21
in Kent, Mile End Bridge in London and Weymouth Green bridges
•
Examples of mixed use bridges found, i.e. for recreation and wildlife
•
Guidance available on design principles from US and Europe
•
Limited information on costs - ranging from £4 million to £10 million
Examples of Green Bridges
•
A21 Scotney Bridge
•
1st Green Bridge in UK
•
Mixed Use Bridge designed for historic landscape purposes
• Built to prevent severance of the historic West Drive (1842) which was
laid out in 1842
•
Main entrance to Scotney Castle.
•
Located within the High Weald AONB.
•
Wider ecological benefits - evidence of dormice using the bridge.
A21 Scotney Bridge
A21 Scotney Bridge
A21 Scotney Bridge
A21 Scotney Bridge
A21 Scotney Bridge
A21 Scotney Bridge
Summary of Design Aspects
•
Hourglass shape
•
Soil depth between 0.6m and 1.5m
•
Planting to create a continuous thicket between 3 and 10m in
width and old tree stumps and banks of moss used to create
habitats
•
Road across bridge is 3.5m wide
•
Arrangement to collect rainwater within a central reservoir within
the bridge structure
Mile End Green Bridge
Mile End Green Bridge
Mile End Green Bridge
• Used to connect fragments of Mile End Park
• Cost £5,800,000
• Recycles rainwater
Weymouth Relief Road
• Four green bridges
• Not built for specific wildlife purpose
• Mixed use
Weymouth Green Bridges
Weymouth Green Bridges
Groene Would, Netherlands
Groene Would, Netherlands
Groene Would, Netherlands
Groene Would, Netherlands
Design Aspects
• 50m wide and 65m long, crosses the motorway at 7m above ground
level.
•
0.5m of topsoil on the bridge and 1m on the access ramps.
•
The topsoil has been taken from immediate surrounds.
• Wetland zone created by a chain of small ponds. Water is pumped up to
the top of the bridge and slowly released through the cascade of small
pools towards bigger pools at the bottom on the access ramp.
• Six amphibian species recorded: common toad, common frog, smooth
newt, great created newt, marsh frog and edible frog.
•
The bridge is closed to the public
• Located within the National Landscape Groene Would, the bridge
connects wetland areas which are bisected by a motorway
Mixed Use Bridges
Zanderji Cariloo
•
300m long, 50m wide
• Vegetated bridge with mosaic planting - shrubs, heath, grassland and
open sandy areas
•
Open to public during daylight hours
• Study compared mammal usage on days with frequent public use with
days with low-level public use and found no strong differences in
mammal use
• At Zanderij Crailoo the mean number of crossings per year of roe deer,
red fox, pine marten, stoat and red squirrel exceeded the national
mean. Daily average recreational use: 500 walkers and cyclists and 5
horse riders.
• 13 species recorded using bridge, including; roe deer, hare, rabbit, fox,
6 species of amphibians and 2 species reptiles.
Zanderji Cariloo
Zanderji Cariloo
Zanderji Cariloo
Mixed Use Bridges
Slabroek
•
100m long, 15m wide
•
Vegetated bridge with mosaic planting - grassland and ruderal
•
Open to public during daylight hours
• Study compared mammal usage on days with frequent public use with
days with low-level public use and found no strong differences in
mammal use
• Data showed crossing frequencies were lower than the national mean
for some species (roe deer, red fox, European hare, rabbit and red
squirrel), but no information given as to why
Slabroek Ecoduct
Slabroek Ecoduct
Ecosystem Services
Ecosystem
service
Bridges
Pollination
Likely that all green bridges planted with vegetation will provide some plants that
can be used by pollinating insects.
Trees, standing
vegetation and
peat
Water cycling
Both trees and standing vegetation are a common feature on green bridges
Mile End –rainwater runs off the bridge into tanks and then is pumped back onto
the bridge and recycled.
Groene Woud – water is pumped to the top and then cascades down in series of
pools
Kikbeek – pools to collect rainwater, used by wetland species.
Wamback Ecoduct – water management of the bridge is designed with climate
change resilience.
Cultural heritage
A21 Scotney Castle – line of a historic drive maintained
Recreation and
tourism
Mile End, A21 Scotney Bridge, Zanderji Crailoo, Slabroek – all of these bridges are
mixed use bridges.
Aesthetic
experience
A21 Scotney Castle – here the historic drive way was maintained to provide an
aesthetic experience.
Wild species
diversity
Mile End Bridge – links up fragments of the Mile End Park
Many examples world wide
Design Recommendations
Natural
Bridge
Wildlife
Bridge
Mixed
Use
Bridge
Modified
Grey
Bridge
Planning for a green bridge
Key Drivers
Planning for a green bridge
• Develop a communication plan - diverse steering group, including local
authority, local community groups, local wildlife groups, local access groups,
project neighbours, statutory consultees.
•
Information gathering (allow sufficient time for robust surveys)
• Consider the location – consider topography, obstacles present, geology
and geography, maintenance, safety, flood risk and utilities. When siting a
green bridge the landscape context and local landscape character should be
considered.
Specific Design Considerations
Existing and proposed level
of the road
Shape of green bridge, e.g.
hourglass or straight
Width
Suitable vegetation for soil
depth and substrate type
Screening and fencing
Lighting
Ecosystem services benefits
Engineering considerations
Other users (pedestrians,
equestrian, cyclists)
Target species
Ease and cost of
maintenance/management
Length
Drainage and water (for
example, ponds)
Connectivity with
surrounding features in the
wider landscape
Relevant Policy and Wider Benefits
Policies and Guidance
National Policy
Framework (NPPF)
National Networks
National Policy
Statement
Ecosystem Services
Pollination
Water Cycling
Wild species
diversity
Natural
Environment White
Paper
Recreation and
tourism
Natural
Environment and
Rural Communities
(NERC) Act
Aesthetics
Lawton’s Making
Space for Nature
Cultural
heritage
Trees and
vegetation
Alternatives to Green Bridges
Modified grey bridges
Fish passages
Multifunctional overpasses
Amphibian tunnels
Cut and cover tunnels
Pedestrian, cyclist and equestrian bridges
Fences (e.g. where mammal collisions are a key
consideration)
Underpasses for medium-sized and large animals
Warning signs/ warning systems with sensors
Underpasses for small animals
Modified and multifunctional underpasses
Modified culverts
Clearing vegetation/ Planting vegetation
Escape ramps from drains, fauna exits in
waterways
Artificial lighting (e.g. to deter species from
crossing in a certain area)
Natural Bridge
Natural Bridge
• Typical width of 70m to 100m or greater.
• Aim is to provide an ecosystem level of connection i.e. for multi-species
use and use by larger mammals or to provide connection at a larger
landscape scale
• Size allows for the recreation of habitats and ideally the planting should
be designed and integrated so there is habitat continuity from one side
of the bridge to the other.
• Access should be carefully considered, depending on the sensitivity of
the target wildlife
Wildlife Bridge
Wildlife Bridge
• These are very similar in design to a Natural Bridge, but are smaller in
size, ideally 40-50m, minimum 20m.
• This type of bridge is intended primarily to facilitate species crossing the
infrastructure.
• Design specifics may target particular species.
• Ideally an hourglass shape should be used as this is better for wildlife
locating the ramps to cross the bridge.
• Human use should be carefully considered, depending on the sensitivity
of the target wildlife
Mixed Use Bridge
Mixed Use Bridge
•
Principle aim is access
• Species/ wildlife function is an additional benefit rather than a
core aim.
• To determine the width, the minimum width of the natural
zone should be calculated, based on the project aims in terms
of target species. The required width for the recreational
zone should then be added to this to give the total width.
Modified Grey Bridge
Modified Grey Bridge
•
Lower cost option to provide a limited level of mitigation
• May be suitable for forestry and farm tracks across infrastructure or in
an urban setting where it may be possible to modify redundant
infrastructure, for example disused railway
•
It is not recommended for tarmacked roads or roads with heavy usage.
• Less likely to provide any landscape value, but may have wider
biodiversity benefits, such as providing plants for pollinating species
Post construction recommendations
Monitoring Plan
•
Look to establish if the aims have been met
•
The methodology for pre, during and post construction survey should be
consistent to allow data to be compared and used to assess the effectiveness
of the structure
•
Typical monitoring programme may survey the bridge annually for years 1-3,
then year 5 and year 10 following construction – define use and
effectiveness
Maintenance Plan
•
Tie into the monitoring, making changes where necessary if issues are
picked up during the monitoring
•
Detail the management for the first three years after construction
•
Management of the bridge should be tailored to the habitats created on the
structure
Outputs
• Green Bridges Literature Review NECR181, published July 2015.
http://publications.naturalengland.org.uk/publication/6312886965108736
• Green Bridges Guide published by Landscape Institute December
2015
http://www.landscapeinstitute.org/knowledge/documents/TGN9_15GreenB
ridgesGuide_LI.pdf
Further Information
Contact:
Clare Warburton, [email protected]