The design of source control techniques is covered in 'The SUDS Manual', CIRIA C753, 2015. See also
for further details of SUDS techniques.
Several source control techniques are outlined below.
A soakaway is a special manhole, plastic 'crate' or rubble filled pit designed to temporarily store run-off and to allow it to percolate into the soil. When
designing a soakaway it is important to know the capacity of the soil to accept water and this can be determined by carrying out a percolation test
to BRE365. The Building Regulations require that soakaways should be positioned no closer than 5m from buildings or roads.
Rainwater Harvesting Systems
Rainwater harvesting systems allow the water from a building roof to be collected in a storage tank and used for domestic purposes such as flushing
toilets or watering gardens. In the dryer parts of the country rainwater harvesting can utilise a significant proportion of the rain falling onto a
house's roof and so can contribute to reducing the total run-off from a site.
Some run-off will remain however, since an overflow is always required
to cater for the case of a severe storm occurring when the tank is already full. In addition the 'first flush', which is likely to contain most of the pollutants,
is often diverted away from the tank. The design of rainwater harvesting systems is covered in BS EN 16941-1:2018
A green roof is a specially designed covering system which supports low growing vegetation on a roof to provide some measure of reduction and
attenuation of the rainfall run-off, see photograph. The roofs should have a slope of between 1 in 80 and 1 in 3. Depending on the type of vegetation to be used, the overall
depth of the growing medium and the underlying drainage layer would typically be a minimum of 100mm.
Green roofs are best incorporated into a building from new although they can be retrofitted to existing ones but this can be a complex operation.
Pervious pavements allow rainfall to pass through the surfacing to ideally eventually soak into the underlying soil. This
can be a very efficient way of preventing surface water run-off since it requires little or no additional space or pipework, etc.
Pervious pavements fall into three main categories, the first being where the water soaks into the underlying soil and the lower layers of the construction
depth of the pavement allows temporary storage of water while this takes place. The second is where the soil has a relativity low
permeability and so rainfall can only partially infiltrate into the soil and a secondary drainage system within the pavement construction has to
be provided to cope with the excess water. The third case is where the soil is impermeable or where there are problems with contaminated land. In this
case the sides and base of the pavement construction are wrapped within an impermeable membrane so that the pavement temporarily stores the water and
so acts as an attenuation tank. The outflow from the pavement then flows at a reduced rate into a drainage system.