Sustainable Drainage Systems (SuDS)
Complete Surface Water Management from Planning to Construction
Holistic Approach to Managing Surface Water
Our chartered engineers help to create sustainable developments by effectively managing surface water using a holistic approach. This inclusive approach delivers water quality and flood risk management alongside the amenity benefits. We have worked with architects, developers and contractors to integrate water within the design to adapt developments to climate change.
Our design are cost effective for our developers. We produce designs fully adoptable by the water companies. We use the latest software to design 3D network, SuDS structures and MICRO drainage to provide the hydraulic modelling of our systems. Our sustainable drainage system design includes the design of permeable surfaces, ponds, soakaway etc.
Our Products on Surface Water Drainage Design
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Sustainable Drainage Systems (SuDS) Design Methodology
Our projects integrate the full management of surface water run-off with flood control. We take special care when selecting the location of our structures to ensure full integration with landscape design to create spaces where water is part of the development.
We obtain your development’s drawings and levels in mAOD.
We consult the Sewerage Undertaker, the Environment Agency and local council to get their agreement on the capacity of their network and the specific requirements for approval.
We scope CCTV surveys, holes, topographical surveys, connectivity surveys and soakaway tests to confirm the basic information necessary to complete our sustainable surface water drainage design (SuDS).
We work together with trial architects and landscape architects to create hydraulic models to design our SuDS networks and produce detailed construction drawings.
Frequently Asked Questions
What are SuDS?
SuDS are surface water drainage methods which take into account quantity, quality and amenity issues. Sustainable storm water management techniques control and manage the quantity and quality of urban runoff.
These techniques involve a re-evaluation of conventional storm water management, moving away from traditional piped surface water drainage systems to softer engineering solutions that are closer to their natural drainage regimes and help to promote wider environmental objectives.
What does SuDS stand for in drainage?
The minimum permitted depths for unprotected drains are:
- 0.35m for domestic gardens or pathways without car loading.
- 0.50m for domestic driveways and areas where the gross vehicle weight is less than 7.5 tonnes.
- 0.9m for domestic driveways, parking areas and narrow roads with limited access to gross weight higher than 7.5 Tonnes. 0.9m for agricultural land and public space.
- 1.2m for other highways and parking areas with unrestricted vehicle access.
What is drainage structure?
A drainage structure is a structure that aids the movement and management of water. These structures can be manholes, pipes or any sustainable drainage system and outfall.
What surveys and investigations are required for the drainage design?
SuDS stands for Sustainable Drainage Systems. The term SUDS was first introduced to the UK by the Sustainable Drainage Scottish Working Party (SUDSWP) in the mid-1990s to advocate an integrated approach towards urban runoff management.
Until recently, the uptake of SUDS has been limited in England and Wales due to a lack of supporting legislation combined with the ongoing issue of who should be responsible for adoption and maintenance.
However, the situation has adapted to the need to meet the requirements of the EC Water Framework Directive (WFD) and the Floods Directive.
SUDS are now also included in national planning policy in both England and Wales.
What is the purpose of SuDS?
The purpose of SUDS is to replicate the natural drainage system by managing the water as close to its source as possible, therefore allowing opportunities to manage flood risk, water quality and create amenity/biodiversity benefits including habitat for wildlife.
SUDS can therefore be summarised as an integrated solution to surface water management rather than just a collection and disposal facility.
Thus, whether it be primarily used for flood risk management, pollution control, or simply to provide an amenity feature, the design should be undertaken to maximise all possible benefits.
How do SuDS and piped systems differ?
Traditional piped systems are primarily designed for ‘conveyance’ and often have minimal storage capacity. Given the requirements of the Water Framework Directive, the recommendations of the Pitt Review (following the floods of Summer 2007) and the EC Floods Directive, sustainable drainage systems need to do more than just ‘convey water.’
For an urban drainage system to be sustainable it needs to be able to:
- Effectively drain developments to control flooding from moderately intense rainfall events.
- Control pollution.
- Manage extreme events.
The key principles associated with the design of the Sustainable Urban Drainage Systems (SuDS) are given by the SuDS Manual (C753) 2015 produced by CIRIA. SUDS should provide the same or greater level of hydraulic capacity than traditional pipe systems, while additionally offering multiple benefits.
How do SuDS work?
In order for SUDS to mimic natural drainage in an urban environment, a ‘management train approach’ should be adopted. This is fundamental in achieving a successful SUDS scheme, as it uses drainage components in sequence to incrementally reduce pollution, flow rates and volumes.
The management train has two main objectives. Firstly, to provide an integrated and balanced approach to mitigate the changes in runoff that occur as land is urbanised. Secondly, to help mitigate the impact of water quality on receiving systems.
This is achieved by providing controls and using SuDS at four levels:
- Level 1: Prevention. Site design to prevent runoff and pollution.
- Level 2: Source Control. Runoff controlled using systems as close to the source as possible. For example: green roofs, permeable paving, filter drains, swales and filter strips.
- Level 3: Site Control. Management of water in local areas by using swales and detention basins.
- Level 4: Regional Control. Management of run-off from a whole site or catchment by using retention ponds or wetlands.
What are the water quality benefits of using SuDS?
The SUDS philosophy of using a ‘management train approach’ with sustainable drainage components in series as opposed to traditional pipework can result in runoff water quality that is similar to good quality river water.
Properly designed, constructed and maintained, SUDS can effectively remove wide range of pollutants from urban runoff by reducing the impact of suspended solids. There are 2 basic mechanisms for the removal of pollutants in SUDS:
- Sedimentation/ filtration;
What are the flood risk benefits of using SuDS?
The design of SUDS components is generally volume based whereas pipe systems are conveyance based.
SUDS components therefore provide larger storage volumes, meaning that these systems will only become overloaded by events occurring over a longer duration, so that failure will result in less impact.
SUDS also retain and attenuate runoff for longer than pipe systems which immediately pass all of the flow downstream.
Utilising SUDS manages the flood risk by reducing the volume, frequency and flow rate of surface water runoff, as well as managing exceedance.
Managing exceedance is managing the flows in an extreme event between the major system (above ground) and the minor system (below ground, i.e. drainage system).
In an extreme event the minor system will often surcharge, only accepting part of the total runoff, the rest will be conveyed by the above ground ‘major’ system e.g. summer floods 2007.
Options for managing exceedance will generally be above ground. This requires the management of excess flows in an extreme event through design of above ground features to minimise flooding of properties by providing flow pathways.
This can be done through designing highways, raising kerbs and by creating sacrificial areas that allow storage of excess flows.
SUDS are more easily designed for managing exceedance flows than piped drainage, mainly because traditional drainage systems are minor systems.
What are the Amenity & Biodiversity benefits of using SuDS?
SUDS can provide recreational and ecological benefits, provided these are considered during the design process.
Landscaped SUDS and more natural looking SUDS in particular can contribute to the amenity value of an area and the quality of life for the users.
What are the benefits of using SuDS for water companies?
Large scale disconnection of surface water from combined sewers is an effective way of reducing flooding and discharges from Combined Sewer Overflows.
SuDS can be used in the following ways when disconnecting surface water:
- Directly or at the end of the pipe.
- If a separate system exists but connects downstream to the combined network then there may be a possibility of discharging to a retrofitted SuDS.
- Use of source control techniques to attenuate rate of runoff and entry to the drainage system.
- Manage flows from downpipe connections.
The use of SuDS can provide the following benefits when disconnecting surface water:
- Reduce flood risk by reducing sewer flows arising from surface run-off.
- Reduce pumping costs.
- Reduce pollution from CSOs and storm tanks.
- Improve the operation of Wastewater Treatment Works (WwTW).
What are the design principles for sustainable drainage systems?
The CIRIA SuDS Manual (C753) 2015 sets out specific design principles to ensure that the benefits of flood control, water quality improvements and amenity benefits are realised.
There are also other options for design storm events:
- Sewers for Adoption also gives recommendations for flood return periods for SUDS design.
The selected flood return period should allow for both pluvial and fluvial flooding and should be selected on a risk based approach to take into account the consequences of flooding. The effects of climate change rainfall and flood predictions should also be taken into consideration.
The CIRIA SUDS Manual (C753) gives hydraulic design guidance on:
- Conveyance design
- Storage design
- Infiltration design
- Hydraulic modelling
The principles of managing drainage exceedance are outlined in Section 2.6 of this Manual. Information on designing for exceedance events is contained in the following CIRIA publication, ‘Designing for Exceedance in Urban Drainage-Good Practice’ (C635) Balmforth et al 2006.
How to retrofit SUDS in existing developments?
UKWIR have published the following report on retrofitting SUDS. Exploring the Cost Benefit of SUDS can be retrofitted to remove surface water from the combined sewerage network.
Below is a brief step by step guide on identifying potential SUDS retrofit opportunities.
- Review sewer network to identify CSO flooding and pumping station locations.
- Review historic flooding locations and identify location of pollution spills.
- Identify separately sewered and combined sewered areas.
- Identify areas where existing surface water sewers discharge back into the combined sewer.
- Assess whether removal of surface water upstream will improve the performance of the sewer network.
- Identify sites where it may be feasible to retrofit SUDS.
- Select appropriate SUDS technique of management train.