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SuDS in London - a guide

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5.14 Goldhawk Road<br />

Location<br />

Shepherd’s Bush<br />

<strong>London</strong> Borough of Hammersmith & Fulham<br />

Extent<br />

0.27ha<br />

Cost<br />

£100,000 (construction only)<br />

Date<br />

2015<br />

Credits<br />

<strong>London</strong> Borough of Hammersmith & Fulham<br />

Robert Bray Associates<br />

McCloy Consult<strong>in</strong>g<br />

GreenBlue Urban<br />

FM Conway<br />

<strong>SuDS</strong> components<br />

Kerb <strong>in</strong>lets<br />

Tree pit attenuation<br />

Flow control<br />

Summary<br />

Tree trench plant<strong>in</strong>g for attenuation.<br />

Project description<br />

Street tree plant<strong>in</strong>g with<strong>in</strong> the pavement<br />

on a busy <strong>London</strong> high street us<strong>in</strong>g a modular<br />

structural tree soil system, comb<strong>in</strong>ed with<br />

kerb <strong>in</strong>lets and flow-control devices.<br />

Objectives<br />

To provide <strong>SuDS</strong> functionality and to<br />

protect the comb<strong>in</strong>ed sewer.<br />

Actions and results<br />

• Each tree is planted with<strong>in</strong> a 1.8m x 1.8m<br />

tree pit with tree grille, located with<strong>in</strong><br />

a much larger soil-filled root<strong>in</strong>g zone<br />

beneath the pavement, aim<strong>in</strong>g to provide<br />

between 10-20m³ of soil per tree<br />

• Dur<strong>in</strong>g heavier ra<strong>in</strong>fall, when the tree<br />

pit fills above the weir level, the water<br />

flows <strong>in</strong>to a sub-base replacement layer<br />

cover<strong>in</strong>g the root<strong>in</strong>g zone just beneath<br />

the pav<strong>in</strong>g build-up. This distributes<br />

the water over the whole root<strong>in</strong>g zone,<br />

allow<strong>in</strong>g it to <strong>in</strong>filtrate <strong>in</strong>to the soil<br />

• Specialist soil with a 25% void<br />

ratio allows ra<strong>in</strong>water storage<br />

• Perforated pipes <strong>in</strong> the base of the<br />

construction collect water and direct<br />

it to a flow control chamber, which<br />

discharges to the comb<strong>in</strong>ed sewer.<br />

The flow control chamber allows<br />

water to build up <strong>in</strong> the root<strong>in</strong>g zone<br />

when it ra<strong>in</strong>s to be released slowly<br />

once the peak <strong>in</strong> runoff has passed<br />

Image courtesy of George Warren<br />

Under construction<br />

• Runoff from the adjacent road and<br />

footpath flows directly <strong>in</strong>to the tree pit<br />

at road level, via a custom kerb <strong>in</strong>let<br />

• The soil level <strong>in</strong> the tree pit is lower than<br />

the road. It is surrounded by a raised<br />

polypropylene weir to allow <strong>in</strong>itial water<br />

storage. This ensures the trees get water<br />

every time it ra<strong>in</strong>s and allows sediments<br />

and litter to drop out of the water<br />

• Integrated protected overflows ensure the<br />

system can discharge freely to the sewer<br />

once storage capacity has been reached.<br />

Flow rates are designed to reduce the<br />

risk of comb<strong>in</strong>ed sewer overflow events<br />

103 5 Case studies

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