H - Revised Integrated Water Management Plan by Cardno (inc MUSIC file) (13.09.19)

1.3 WSUD in context
of Street Trees
Street trees provide a multiplicity of benefits and are
precious natural assets in urban spaces where green
spaces are limited.
The common scenario for street trees is that they are
planted in confined spaces within the urban streetscape
and provided limited resources needed to remain
healthy and thrive. The soils around street trees are often
compacted during the construction of surrounding paved
surfaces.
Street trees need access to water, adequate soil volume
and a good soil mixture.
To provide the necessary watering requirements for a
healthy street tree, active watering or irrigation is usually
required where the tree can’t access adequate volumes of
water from its surroundings.
Enhanced design, ensuring street trees are configured
for passive watering via stormwater runoff provides many
benefits:
  • Reduced requirements for active watering, ensuring
    tree longevity and resilience subject to drought periods
    and water restrictions;
  • Mitigates many of the impacts of urban stormwater
    runoff. Research has shown that WSUD street trees
    can substantially reduce nitrogen and other pollutant
    loads in stormwater; and
  • Reduced stormwater runoff volumes.

WSUD street trees can be configured as stand alone
bioretention street trees or planted within larger raingardens
and function as biofilters for stormwater.
A WSUD street tree incorporating an adequate soil volume
is ultimately a healthier and more resilient tree, with greater
access to soil, nutrients, and water from the surrounding
environment.
The support provided by Stratacells can therefore play a
crucial role in maintaining a sustainable urban forest. To
obtain an adequate soil volume in a confined streetscape,
Citygreen’s Strataflow systemcan be used under pavements
as a structural support whilst creating a sub-surface space
for uncompacted soils required for trees root expansion. An
adequate soil volume within a Strataflow matrix can provide
tree roots the space they need to grow to full size.




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