It is strongly advised that that any club appoints a suitably qualified and experienced consultant in
planning and executing any work of this type. Planning permission may be required – consult with
your local authority. Furthermore, the club should consult the Environment Agency and the local
Water Company for any necessary permissions. Design must be as per BS EN 752:2008 / BRE
Digest 365.
What is a Soakaway?
A soakaway is a form of ‘infiltration drainage’ that allows storm water to infiltrate into the ground rather
than discharge directly into a sewer. The advantage of this approach is that it helps reduce flooding risk
by preventing ‘flash’ discharges of storm water into sewers and surface water systems that are a
common problem during flooding events.
Soakaways and other forms of infiltration drainage are traditionally found
where clubs are too far from a public sewer but they can also be used as
a form of reducing discharge to sewers. This can have economic benefits
where your water company is charging you for stormwater drainage.
Soakaways also provide a sustainable overflow to rainwater harvesting
systems.
Soakaways can take a number of forms – the simplest are rubble/aggregate filled pits at the end of the
drainage pipe. More complex designs could include dry jointed brickwork or pre-cast perforated
concrete ring units that are surrounded by a granular backfill and an outer geotextile membrane. Longer
soakaway trenches are effective because they have a greater infiltrating surface to volume ratio. Modern
soakaway systems also include load bearing reinforced plastic structures known as geocellular systems.
Designing and Installing a Soakaway
Soil infiltration rates in soils will generally be lower than peak discharge rates during long or intense
storms. The purpose of the soakaway is to provide a buffer store for the storm water so that it can
infiltrate into the soil and bedrock over time.
The size of the soakaway is dependent upon the inflow of water (the size of the area being drained and
the frequency, intensity and duration of large rainfall events) and the outflow of water (dependent on the
soil/rock type, soil infiltration rate, the shape and depth of the soakaway, the storm duration and the
water table).
The design will need to consider the:
1. rainfall events in your area;
2. size and type of surface draining to the soakaway;
3. nature, stability and variability of the soils on site;
4. location in relation to building foundations, groundwater abstraction and the water table.
5. incorporation of sediment traps and inspection chambers/wells to reduce the effect of silts and
other fine particles which can reduce infiltration over time.
Like all aspects of drainage, design is critical and we would advise that you engage a suitably
experienced drainage consultant/engineer – particularly in the design stage.
Guidance written by Dr Iain James, Cranfield University on behalf of ECB 2012
Page 1
Clubs should speak to their local planning authority to determine whether planning permission is
required. Clubs should also contact their regional environment agency office at the planning stage as
their approval will be required in the planning permission process.
You can find advice on the design and construction of soakaways in the following:
1. BRE Digest 365 ‘Soakaway design’, published by the Building Research Establishment,
Watford. www.bre.co.uk ;
2. CIRIA Report 156 and the CIRIA SUDS Handbook both published by the CIRIA, London
www.ciria.org ;
3. BS EN 752:2008, contact your local library for a loan copy.
4. The Environment Agency’s GP3 document, available to download here (Part 4/Section 4 is
relevant to soakaways).
The Environment Agency does not approve of direct discharge of surface water into groundwater and
require a maximum acceptable depth of 2 m for a soakaway and at least 1.2 metres above the highest
seasonal groundwater table.
It will be necessary to dig trial pits to determine soil infiltration rates and ground suitability prior to the full
design and installation of the soakaway. Bear in mind that infiltration rates and groundwater levels vary
through the year, particularly in shrinking clay soils – it is important to test infiltration in the winter months,
not just in summer. During this exploration phase and during construction it is essential that nobody
enters the excavation/pit as there is a significant risk of subsidence/wall failure that could result in death.
Make sure that personnel involved in the design and construction are competent and experienced
because the hazards and risks are significant.
When and where are soakaways not suitable?
There are a number of situations where soakaways are not appropriate or their design will need to be
modified/approved by a geotechnical engineer:
1. Where runoff/drainage water could pollute groundwater – this could be from car park areas,
where a hydrocarbon trap will be required. It also includes areas where maintenance machinery
is washed down;
2. Where soils are contaminated and could leach into groundwater;
3. Where soils are so slowly permeable that infiltration will be very low;
4. Where groundwater levels are high;
5. In Groundwater Source Protection Zone 1 (SPZ1) to find out whether your club is in this zone
visit the Environment Agency’s ‘What’s in Your Backyard?’ website.
6. Where building foundations might be at risk due to collapsible soils and adverse shrink and
swell.
The soakaway should be installed above the groundwater table – not within it, to reduce the risk of
groundwater pollution and to maintain the effectiveness of the soakaway (infiltration into saturated rock
and soil could be very slow).
It is important to consider slopes to ensure downslope areas do not become continuously saturated.
Also soakaways should not be sited on heavy traffic routes – an example would be the route of the roller
from the grounds shed to the square, or outfield and training areas.
Soakaway pits should not be located within 5 m of building foundations and when on chalk, shrinking
clay soil or collapsible soils, the advice of a geotechnical engineer should be sought.
Benefits of Soakaways

Soakaways can help to reduce the risk of flooding in built up areas.
Guidance written by Dr Iain James, Cranfield University on behalf of ECB 2012
Page 2

They also help to reduce surface water drainage charges.
Disadvantages of Soakaways



Soakaways need to be designed carefully – this shouldn’t be seen as a dig a hole in the ground,
backfill it and don’t worry about it solution to drainage.
There are certain soil and groundwater situations where soakaways are unsuitable.
It is necessary to seek approval from your local authority and the Environment Agency
Guidance written by Dr Iain James, Cranfield University on behalf of ECB 2012
Page 3