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The Key to Climate Proofing Our Cities

This article explores the use of sustainable drainage systems (Suds) and trees in mitigating urban flooding and improving water quality. It discusses the hydrological properties of trees, how and where to incorporate trees into formal drainage systems, potential barriers and problems, and the importance of Suds in addressing the pressures on existing drainage infrastructure. The article also highlights the need for cross-discipline design and further research to effectively incorporate trees into Suds strategies at various levels.

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The Key to Climate Proofing Our Cities

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  1. The Key to Climate Proofing Our Cities Urban Flooding, Trees & Sustainable Drainage Systems John Young BEng MSc (Eng) CEng MICE MCIWEM

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

  3. 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

  4. 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

  5. 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.

  6. Why Suds? FOUR CROSSES A483 Improvement

  7. Why Suds? • IMPERMEABLE SURFACES • Reduce natural infiltration to ground • Increase volume of surface water run-off • Increase speed of surface water run -off

  8. 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

  9. Suds Components • Attenuation Ponds • Strom Storage Cells • Hydrobrake systems • Filter Drains • Swales

  10. 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

  11. 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

  12. Precipitation Evapotranspiration Stem Flow Leaf Drip Through Fall 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. Sap Flow

  13. 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

  14. 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

  15. Water Quality STREET TREES Bio-retention within a treatment train

  16. 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

  17. 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.

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