sustainable drainage for schools.pdf - Public Architecture

Sustainable drainage
(SUDS) for schools
7
Robert Bray describes a sustainable approach to
schools drainage.
Sustainable Drainage Systems or SUDS are a new
way of managing rainfall that avoids the problems
caused by conventional pipe and gully drainage.
Conventional drainage can cause flooding, pollute
and damage watercourses with the consequent loss
of valuable wetland habitat. SUDS mimics natural
drainage, using the landscape and simple structural
techniques to collect, clean, store and release runoff
slowly into the environment.
SUDS techniques include:
• filter strips and swales (flat bottomed ditches) -
vegetated surface features which collect, convey
and sometimes store runoff, trapping silt and
beginning the natural cleaning process.
• filter drains and permeable surfaces - allow water
to percolate into below ground storage structures,
cleaning the runoff as it passes through the stone fill.
• infiltration devices - encourage water to percolate
directly into the ground and include soakaways,
trenches and basins as well as many of the other
SUDS structures.
• basins, ponds and wetlands - temporary or
permanently wet features that also collect, treat
and store runoff before release to the environment.
SUDS techniques are usually used in series in a
‘management train’ with runoff being dealt with as
soon as possible in the sequence of stages ‘at
source’. The jargon surrounding the SUDS approach
belies a very straightforward and logical discipline,
which is based on the way nature controls rainfall, and
this ideal is the guide for all SUDS design.
Although SUDS has been recommended by the
Environment Agency for nearly 10 years now and is
considered ‘best practice’ in PPG25 - Development
and Flood Risk, there have been remarkably few
examples of Sustainable Drainage on Local Authority
properties. There have been many concerns raised in
recent consultations about the SUDS Framework
Agreement document, particularly issues of cost,
maintenance and who will take responsibility for
SUDS features and these doubts have resulted in a
poor uptake of SUDS in public places. There is no
clear national legislative requirement for sustainability,
so initiatives like SUDS must offer distinct advantages
to Local Authorities, and reservations dispelled by
example and demonstration sites. Worcestershire
County Council has recently implemented two school
SUDS schemes, which demonstrate the benefits of
this new drainage approach to the Local Authority, the
School and the Community.
The first example, Waseley Hills High School and
Holywell’s Primary School at Rubery near Bromsgrove
have suffered flooding, saturation of playing fields and
the blocking of drains by silt due to the runoff from an
adjacent Country Park. The existing drainage system
is inadequate, difficult to modify and cannot deal with
exceptionally heavy rain which is increasingly frequent
due to climate change.
Swale to wetland feature
The SUDS design took advantage of primary school
improvement works to create a new sports area which
will also act as water storage feature during exceptional
heavy rain. A silt control basin and interceptor swale,
constructed at the top of the site, collect overland flows
from the Country Park and trap silt which used to block
drains in the High School playground. Water flows
slowly through a new wildlife pond and then along
conveyance swales to a cascade falling to a wetland
feature in front of the school. The water continues
under an ornamental bridge in a low flow channel
around the sports area and into a local watercourse.
Low flow channel
Robert Bray is a
landscape architect
who has been at the
forefront of sustainable
drainage systems
development for over
ten years. He is the
Principal of Robert Bray
Associates which
specialises in SUDS
T: 01453 764885
F: 01453 765545
E: bob@robertbray
associates.co.uk
W: www.sustainable
drainage.co.uk

8 Sustainable drainage (SUDS) for schools
The SUDS system provides a number of benefits:
“The capital costs
for the project were
reasonable and
provided incidental
benefits not usually
associated with
drainage.”
• SUDS creates a new robust natural drainage system.
• SUDS controls overland flows and retrieves playing
fields for the schools.
• SUDS traps silt and controls pollution.
• SUDS protect the schools and adjacent properties
from flooding.
• SUDS provides a visual, educational and
wildlife resource.
The capital costs for the project were reasonable and
provided incidental benefits not usually associated
with drainage. There is also an opportunity to reduce
charges by the Water Company as all the runoff from
the Primary School now flows to the watercourse
without entering the storm sewer.
Maintenance of the SUDS features will be done by
existing landscape contractors who are familiar with
the basic requirements of litter collection, grass cutting,
inlet-outlet inspections and wetland management.
This should be cheaper than cleaning gullies and
pipes, as it is part of everyday site care, and is visible
for inspection and enjoyment by the school.
The second SUDS scheme is for a new primary school
at Matchborough in Redditch. This new project was
underway when problems with the conventional
drainage design became apparent. Water was to be
collected in gullies and pipes into a pumping station
and then pumped up to the storm sewer. This would
have resulted in a £3000 p.a. service charge to the
Water Company and an annual maintenance bill for
the pumping station of £800. This scheme was
expensive and could not accommodate runoff from
the school playground, as this is located behind the
school at the lowest part of the development.
A SUDS scheme collects runoff in attractive wetland
basins at the front of the school draining both the
main drive and the car parks. Water flows through a
long swale following the western boundary hedge,
picking up roof runoff where it is surplus to the
requirements of a rain harvesting system and leading
to a storage wetland. Playground runoff is collected in
a swale which travels between the playground and the
playing field also flowing to the wetland. Runoff from
existing adjacent housing is intercepted in another
boundary swale which discharges directly to the Ipsley
Brook, again protecting playing fields from winter
saturation caused by sheet water flow across the site.
Collector basin for school entrance
The Head Teacher at Matchborough is eager to
integrate the SUDS scheme with the ‘Forest Schools’
approach to primary education being pioneered by
Worcestershire County Council, and incorporate
curriculum studies with the wetland resource. Careful
SUDS design and a measured consideration of Health
and Safety are allowing children to experience water
in a controlled way.
The SUDS approach to drainage delivers a holistic
and cost effective solution to the management of
rainfall on school sites which can be easily managed
using current landscape maintenance practices.
Storage wetland
SUDS schemes are simple, robust and easily
understood by all school stakeholders with
opportunities for educational and wildlife benefits.
Capital and management costs for SUDS are usually
less than conventional drainage and where water can
infiltrate or flow to watercourses then schools can avoid
connection fees and annual storm sewer charges.
The benefits of SUDS to the school campus
situation are now being understood at Waseley
and Matchborough with more exciting SUDS
designs now being designed for schools in Devon
and Milton Keynes.
The future looks bright for SUDS in a school
environment!