The Key to Climate Proofing Our Cities

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The Key to Climate Proofing Our Cities

• Urban Flooding, Trees
• Sustainable Drainage Systems
• John Young BEng MSc (Eng) CEng MICE MCIWEM

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Introduction

1. Why and what are Sustainable Drainage Systems
   (Suds)
2. Hydrological properties of trees
3. How can we introduce trees into formal drainage
   systems
4. How and where we can use trees at a source, site
   and regional level
5. Potential barriers and problems

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Why Suds?
In the mid 1990s there was a growing recognition
that continuing urban development would place
significant pressure on existing drainage
infrastructure
WHAT WOULD HAPPEN? pressure on our drainage
infrastructure much of it aging Victorian
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Why Suds?
FLOODING Increases in frequency and magnitude of
flooding from urban storm water systems

• THEN CLIMATE CHANGE
• More intense frequent rainfall
• Economic loss
• Social health impacts

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Why Suds?

• WATER FRAMEWORK DIRECTIVE
• Degradation of existing rivers and diffuse
  pollution first flush from roads and other
  impermeable surfaces
• BOD
• Heavy metals
• Chemicals, pesticides etc
• Suspended sediments

Suds used to mitigate problems with diffuse
pollution.
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Why Suds?
FOUR CROSSES A483 Improvement
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Why Suds?

• IMPERMEABLE SURFACES
• Reduce natural infiltration to ground
• Increase volume of surface water run-off
• Increase speed of surface water run -off

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How we do Suds?

• OBJECTIVE OF SUDS
• Replicate closely the response of a natural
  catchment.
• Limit discharge rates to the equivalent green
  field rates of run-off
• Improve water quality

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Suds Components

• Attenuation Ponds
• Strom Storage Cells
• Hydrobrake systems
• Filter Drains
• Swales

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Suds Components

• Green Roofs
• Filter strips
• Filter drains
• Swales
• Soakaways
• Permeable paving
• Bio-retention systems

• WHAT DO THEY DO?
• Intercept rainfall at source
• Temporally store water
• Attenuate discharge
• Allow infiltration to ground
• Improve Water Quality

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Hydrology Trees

• WHAT DO TREES DO?
• Intercept rainfall at source
• Temporally store water
• Attenuate discharge
• Allow infiltration to ground
• Improve Water Quality

IS A TREE CANOPY A GREEN ROOF? Probably
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Hydrology Trees

• WHAT DO DESIGN ENGINEERS WANT?
• Canopy interception rates
• Storage volumes
• Retention times
• for individual and groups of trees and for
  different species throughout the growth life of
  the tree.

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Source Site
VISITOR CENTRE DEVELOPMENT Run-off from Visitor
centre roof Public squares Car Parks
POSSIBLE USE OF TREES Interception Storage
Delay of discharge to stormwater system Water
quality improvements
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Regional
POSSIBLE USE OF TREES Shading of impermeable
surfaces Interception storage Delay of
discharge to stormwater system Water quality
improvements
STREET TREES Run-off from roads Car Parks
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Water Quality
STREET TREES Bio-retention within a treatment
train
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Potential Difficulties

• Flooding is more prevalent in winter than summer.
  Loss of leaf during winter effectively removes
  the benefit associated with the canopy.
• Space within the urban environment to incorporate
  trees.
• Rate of tree growth and canopy development
• Potential clashes with utilities including foul
  sewers, gas, telephone and electricity.
• Structural damage associated with tree roots and
  perception associated with the risk of collapse
• Adoptability by the Local Authority or Water
  Company

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Conclusions

• Trees can be used effectively within a Suds
  strategy at source, site and regional level
• Research is required to establish the engineering
  design parameters
• Codes of Practice and design guides must be
  developed to give Suds designers the tools to
  incorporate trees into a formal drainage systems
  at site and regional level
• Cross discipline design is essential including
  architects, landscape architects,
  aboriculturalists and engineers are involved in
  urban design.