What are Sustainable Drainage Systems?

Sustainable drainage systems (SuDS) are structures designed to control surface water run off and mimic natural drainage as closely as possible. Sustainable Drainage Systems include soakaways, swales, ponds, etc which are designed to drain or infiltrate surface water in a more sustainable approach to the use of pipes and connections into sewers.

Sustainable Drainage Systems and the Government Planning Practice Guidance (PPG)

The Local Planning Authorities follow the Government Planning Practice Guidance (PPG) when asking for  Sustainable Drainage Systems in developments. The PPG states that:

• New developments should only be considered appropriate in areas at risk of flooding if priority has been given to the use of a sustainable drainage system.

• It also states that Sustainable Drainage Systems should be provided in major developments unless it is demonstrated to be inappropriate. Major developments are considered to be developments which create ten or more dwelling houses or a site of over 0.5 hectares.

How the Local Planning Authority gets to a decision on SuDS?

The Local Planning Authority (LPA) judges whether a development is inappropriate based on the advice of the Lead Local Flood Authority (LLFA) and the relevant flood risk management bodies including their advice on which  Sustainable Drainage System they would consider to be reasonably practicable.

The evaluation on whether it is reasonably practicable is determined by the applicability of the Sustainable Drainage System technical standards published by the Department of Environment, Food and Rural Affairs (DEFRA) in the development and also the applicability of the Sustainable Drainage Standards that the Lead Local Flood Authority has produced for their region. The LLFA evaluation should take into account the design and construction costs of the SuDS.

In regards to the costs of the appropriate Sustainable Drainage Systems, The Planning Policy Guidelines set out that expecting compliance with the SuDS technical standards is “unlikely to be reasonably practicable if more expensive than complying with building regulations”.

If we look at the current Building Regulations, it states that the surface water discharge routes are evaluated and discounted in the following order of priority.

• Discharge using Soakaways

• Discharge to watercourses

• Discharge to sewers

The developer should demonstrate that Sustainable Drainage Systems are not feasible before challenging a decision made by the Local Planning Authority. This is usually achieved by providing a robust Drainage Strategy at pre-planning meetings and at the planning application.  

Sustainable Drainage Systems Approval - Other Consultees

The LPA seeks advice on the following consultees before making a planning decision. It reviews the drainage design submitted:

• Sewerage undertaker where a connection with a public sewer is proposed. The sewerage undertaker most likely recommends a grampian condition for the development. Developers have an absolute right to connect new developments to public sewers once planning permission has been granted, including surface water drainage pursuant to section 106 of the Water Industry Act 1991

• The Environment Agency, if the drainage system directly or indirectly involves the discharge of water into a main river or Source Protection Zones

• The relevant highway authority if there is a connection to the road drainage

• The Canal and River Trust, if the drainage system discharges into or under one of their waterways

• The internal drainage board, the council’s environment or drainage department if the drainage system discharge of water into an ordinary watercourse

The foul water drainage and treatment design does not form part of this approval.

In conclusion

• The Lead Local Flood Authority plays a pivotal role in the approval and evaluation of the Drainage Strategy. In the majority of cases the LLFA can give feedback on the drainage proposals before planning is made. It is recommended that the LLFA is approached for their initial feedback.

• Therefore when making a planning decision the Local Planning Authority will want to be satisfied that the Sustainable Drainage System adheres to the technical standards, there are clear maintenance arrangements and the relevant bodies responsible for the discharge points of the Sustainable Drainage System are consulted and agreements are in place.