Controlling surface water runoff from works near water
What you must do
Protecting watercourses
You must not discharge or allow water contaminated with silt to enter a watercourse or drain as it can cause pollution.
Channel run-off away from watercourses and surface water drains when dewatering a site.
Protect all surface water drains and watercourses with cut-off ditches or earth bunds. These should be at least 10 metres from the watercourse.
General Binding Rules (GBRs) for discharges of run-off water (GBR 10 and 11)
GBR 10 - Discharging water from a surface water drainage system
In Scotland, GBR 10 details the rules relating to discharging water from a surface water drainage system.
GBR 10 has been updated to cover surface water discharge from:
- land used for residential purposes (up to 60 hectares).
- land used for non-residential premises or yards (excluding industrial estates).
- car parks with up to 1,000 spaces.
- metalled roads (excluding motorways and A roads).
- waterbound roads.
and
- construction sites, where the site, including any constructed access tracks, do not:
- exceed 4 hectares.
- contain a road or track longer than 5km.
- include any area more than 1 hectare, or any length of more than 500m on ground with a slope of more than 25°.
If your site exceeds these thresholds then you will require authorisation from SEPA: Construction site licences.
GBR 10 specifies that all reasonable steps must be taken to ensure pollution does not occur.
The discharge must not:
- contain trade effluent/sewage.
- result in discolouration, iridescence, foaming or growth sewage fungus.
- destabilise banks or bed of the receiving surface water.
- contain run-off from fuel delivery areas, vehicle loading/unloading bays where potentially polluting matter is handled or oil and chemical storage, delivery and handling areas. if constructed on or after 1st April 2007.
All parts of the surface water drainage system must be maintained in good working order and repair and steps must be taken to ensure that matters liable to block or obstruct the drainage system are prevented from entering.
Construction specific rules:
Sites must be drained to a Sustainable Urban Drainage System (SUDS) unless the discharge is from a single dwelling or to coastal waters.
All parts of the construction site which began operations on or after 01 June 2018, on which works are to be undertaken or any vehicles are to be operated or parked on, must be drained by a surface water drainage system with the capacity to accommodate the maximum volume of run-off expected to occur from the land during the period of construction.
Good practice
Protecting watercourses
Do not strip soil up to the edges of any watercourse, stream or drainage ditch because loose soil can be washed into the watercourse. This can silt-up the riverbed and harm wildlife. You can be liable for causing pollution even if the pollution was only caused by your indirect actions.
When you plan your works, think about where surface water will run once the vegetation is cleared.
Identify any watercourses, surfaces, foul drains, or field drains in or next to your site that your work may affect.
Existing field drains can provide a route for the discharge of polluted water to watercourses. It is essential that you know where they are and do not allow polluted run-offs to enter them. This is particularly important where you choose to discharge silty water over the ground.
Plan ahead to manage silt run-off so that it does not pollute watercourses or ruin any Sustainable Urban Drainage Systems (SUDS) designed for the completed phase.
Guidance for Pollution Prevention (GPP) 5 contains guidance on measures you can take to avoid causing pollution during building and engineering work.
GPP 5 Works and maintenance in or near water (Adobe PDF – 782KB)
Phasing your works
Produce a method statement to address how the amount of silty water you produce will be minimised and how you will stop it directly or indirectly entering watercourses or drains.
Your method statement should consider the phasing of the works. Large areas of cleared vegetation will increase the risk of run-off causing pollution.
Strip vegetation and topsoil in sequence, clearing only the areas where you need to work.
Minimise the amount of exposed ground and stockpiles of soil on your site. This will reduce the amount of silty water that you have to deal with.
Phase your works to ensure that mud from vehicles, roads or surface water run-offs from areas under construction does not enter surface water drainage of areas already completed.
If the completed phase has Sustainable Drainage Systems (SUDS), include details of how these will be protected during the construction phase in your method statements.
If the site is on a slope, consider whether the up-slope works can be completed first to prevent silty water running down-slope into completed works and drainage.
For projects that require open trenches, plan your work so that the length of trenches needed at any one time is kept to a minimum. Open trenches will produce silty water.
See our pages
Northern Ireland:Construction site Permits, Authorisations and Licences. (Know your PALs)
Scotland: Construction site Permits, Authorisations and Licences. (Know your PALs)