Page 127 - Oxford City SuDS DESIGN & EVALUATION

9.10.3.4 A place for trees and shrubs in the SuDS landscape

Trees provide a number of functions specific
to the SuDS landscape, as well as providing a using a tree with a light foliage and avoid
great number of other natural benefits. weeping or suckering varieties.

Design criteria: ■ Give preference to a small or pinnate leaf Detailed Design
type that will degrade easily, to avoid
■ Ensure sufficient space for crown spread
and root growth. smothering the vegetation below and to
reduce the risk of blockage to inlets or
■ Allow healthy SuDS vegetation below by outlets.

9.10.3.5 Green & blue roof planting

Green roofs are now a familiar technique for Design criteria:
managing rainfall. The blue roof is a ■ Plant choice should be appropriate for the
development of the green roof whereby it is
proposed depth of growing medium.
used for collecting and storing rainfall ‘at
source’, on the roof. ■ Plant choice should be appropriate for the
proposed use and desired character.
Drainage layers can exacerbate drought
conditions, particularly on a pitched roof. ■ Plant choice should be drought resistant.

Shallow soils of 50-80mm depth are also ■ Plug planting is normally at 20-30 plants 122
prone to plant failure due to drought per square metre.
conditions. A greater depth of soil permits a
stronger plant community and greater

absorption of rainfall. Soil depth should
ideally be nominally 100mm or deeper to
maintain healthy plant growth.

Ruskin Mill Horsely, Glos.
Greenroof with gravel edge and rainchain.

Design Notes:
2
A biodiverse native wildflower mix can be combined with plug planting at between 8-16/m .
A greater depth of soil permits a stronger plant community and greater absorption of rainfall.

Oxford City Council SuDS D & E Guide © 2018 McCloy Consulting & Robert Bray Associates