Benefiting flood risk, water quality, amenity and biodiversity
What are SuDS?
SuDS aim to regulate water quantity, water quality, amenity and biodiversity. This is known as the “four pillars of SuDS”. SuDS are a new way of managing
surface water in a natural and controlled manner. They slow runoff and provide storage of surface water which mimics pre-development conditions, and minimise the risk of flooding compared to traditional underground piped systems which often provide no improvements to water quality, biodiversity or amenity.
SuDS can discharge to groundwater via infiltration, to a watercourse, surface water sewers or combined sewers.
SuDS and Flood Risk
When a development is proposed, an increase in flood risk is often a worry for local presidents. However, SuDS mimic the existing greenfield conditions and often provide a betterment over the existing scenario.
SuDS hold back flows by attenuating the water on site in designated storage areas, there will be no increase in flood risk either at the site or downstream.
Calculations determine the quantity of storage required at each site. SuDS are designed to accommodate for this volume plus an extra 45/50% which accounts for an increase in future rainfall as a result of climate change.
Examples of SuDS
Detention Basins/ Infiltration Basins
Normally dry outside of storm events. They are designed to store runoff and reduce the volume of surface water.
Attenuation Ponds
As well as storing water from storm events they support native vegetation and provide habitat and amenity places for local wildlife and communities.
Permeable Paving
Pavement made of permeable material that allows water to infiltrate into the ground or be discharged into sewers without overland flow while removing pollutants.
Swales
Shallow, open channels designed to convey, treat and store surface water runoff from rainfall events.
Green Roofs
Multi-layered system that can store water which can be reused for non-potable uses. They also insulate buildings, reduce energy and water costs and have biodiversity benefits.
Soakaways
Excavations that are backfilled with permeable material that allow to water to attenuate and infiltrate into the ground.
The SuDS Treatment Train
SuDS should follow the “treatment train” approach. Where a range of SuDS devices are utilised to treat the runoff prior to discharge. This train begins with
prevention (preventing runoff by reducing impermeable areas) and progresses through local source control to larger downstream site and regional control.
For example, a residential development could use permeable paving (source control) to drain runoff from the driveways, a swale to convey runoff to a detention basin (site control) which could outfall into a regional wetland (regional control).
Design Criteria
- SuDS aim to replicate the greenfield runoff rate. This is the natural flow from the land before development.
- SuDS should store up to the peak flow of a 1 in 100 year storm event +45/50%.
- SuDS features are designed to allow for climate change. A 45/50% Increase in storage volume is required in line with Environment Agency guidance (2016).
Maintenance
Maintenance schedules are a requirement of any planning application containing SuDS in Devon. SuDS are maintained by either DCC highways, South West Water, Parish Councils or a private management company.
Maintenance is crucial to keep SuDS maintained to ensure maximum pollution control, ecological.
Additional Advantages
- Make living spaces more vibrant
- Groundwater recharge
- Improve urban air quality
- Habitat connectivity and diverse ecosystems
- Educational opportunities
- Carbon dioxide reduction
- Multifunctional public and recreational spaces
Devon County Council’s (DCC) Role in Sustainable Drainage
- DCC are a statutory consultee for all major developments in Devon providing comment on the suitability of applicants surface water drainage proposals to the local planning authorities – 9 district councils and 2 national parks.
- DCC review planning applications to ensure there is no increase in runoff rates as a result of the development which is facilitated through the provision of SuDS.
- Applications are reviewed to ensure compliance with national and local guidance.
Useful Contacts and Information
Devon County Council Flood Risk Management Team: 03451551015
Email: floodriskmanagement-mailbox@devon.gov.uk
Webpage: Homepage – Flood Risk Management (devon.gov.uk).
Susdrain: Susdrain – The community for sustainable drainage
The SuDS manual: Item Detail (ciria.org)