INTRODUCTION, FAILURES AND SUCCESSES

Surface water drainage systems developed in line with the ideals of sustainable development and address the consequences of climate change.

They are collectively known as SUDS.

They are being implemented right across the world as the importance of water increases (excluding permafrost regions).

They are designed to:

Manage the environmental risks resulting from Urbanisation

Contribute to environmental enhancement.

Minimisation of the impact from the development on the quality and quantity of the runoff and maximise amenity and biodiversity opportunities. The extent to which this is possible depends on the site, but the ideal is they have equal standing. All SUDS systems needs to have at least 2 of the 3 elements:

Amenity &

Biodiversity

Quality Quantity

What ARE WE TRYING TO ACHIEVE?

Reduce run

off rates

Reduce run off

volumes

Encouraging

groundwater recharge

Reducing pollutant

concentrations and a

buffer mechanism

Enhanced

amenity and

aesthetic value

Enhancing

biodiversity

What does not count as SUDS?

Giant tanks with impermeable liners NO VOLUME REDUCTION – NO GROUNDWATER RECHARGE NO WATER TREATMENT – NO ECOLOGICAL AND NO BIODIVERSITY VALUE MOST DRAINAGE DESIGN PRE 1990

PEAK ATTENUATION REDUCTION

Flow (m3/s)

Time

Without attenuation

With attenuation

EU Water

Framework

Directive 20/60/EC

Buildings

Regulations various

amend.

Flood Water

Management Act

2010

Water Industry Act

1991

Various other Water

Bills

Water Resources

Act 1991

Land Drainage Act

1991

Groundwater

Regulations 1998

Discharge to

groundwater

•Soakaways, Swales, permeable

block paving and other source

control

Discharge to

watercourse • EA or LDA approval and

controls

Discharge to

surface water sewer • Automatic right

removed

Discharge to

combined sewer

Adoptable

standards

2013

Must treat

first 5mm

Located in

accessible

location

Early

engagement

prior to

planning

Minimum

construction

standards

Appointment of experienced Civil Engineer very early in

project

In public highways Or public areas, not back gardens

If you can’t infiltrate at all then harvesting is likely to be necessary

Not onerous, but sensible and practical

Drainage Impact / Drainage Strategy Reports necessary as per Scotland

Problems included:

Very low infiltration

No surface water sewer within 80m

No watercourses within 200m

High groundwater level (seasonal)

Porous Asphalt Permeable block Paved Car Parks Quality Quantity

Rainwater Garden Quantity Amenity Biodiversity Health

Landscaping swale Attenuation Biodiversity

Maximising Source control techniques

and wetted perimeter

RWPS

Small internal courtyard

Attenuation crates

Fountain pump Storm water storage

High level overflow to public sewer

RWPS from roof

Residential flats with underground car park

Basement

Storm water attenuation and separation prior to borehole

Flats

Car park flow To foul sewer

Boundary

Impermeable ground

Stephen Gibson, Director – Wilsham Consulting E stephen@wilsham.co.uk T 01235 529646 M 07449948261 W www.wilsham.co.uk Wilsham provide civil engineering professional services across a very wide spectrum of developments, from hotels, private luxury houses, estate water master-planning, churches, water companies, cathedrals, schools and health facilities. This includes: • FRAs, Residential and commercial estate water master-planning, • Drainage Impact / Strategy Reports to support SAB applications • Highway Design, • Waste water design, • Groundwater and flood mitigation • Engineering advice to water company legal groups