Nature Based SuDS Guidance Document

COSTS AND COST SAVINGS OF NATURE-BASED SUDS

Perception of high costs and maintenance costs is a common reason for not incorporating SuDS into a scheme. However, this concern is often unfounded.

At its core, SuDS and NbSuDS should be simple. The simpler a scheme to construct and maintain, the cheaper it will be. Whilst there may be reasons for complexities to be introduced, especially with retrofit, good design should always consider the available budget and light-touch maintenance regimes. The price of NbSuDS can vary enormously depending on site-specific design constraints and project drivers. Because each design is bespoke to a specific site, it can be difficult to predict NbSuDS costings at the start of a project when little design information is available, which can deter its inclusion. However, evidence suggests that savings can be made from the inclusion of NbSuDS. SuDS within managed open spaces can be much cheaper to maintain, and research suggests that maintenance costs for SuDS are, on average, no higher than conventional piped water drainage.

DEFRA indicate that SuDS can be up to 30% cheaper to construct when compared to traditional ‘grey’ drainage infrastructure and only up to around 5% more expensive on more challenging sites. Annual maintenance costs for traditional drainage solutions could be up to 25% greater than the maintenance of SuDS. In addition to cost savings for construction and maintenance, the end user may experience benefits from a reduction in their water bills, subject to water company policy at the time.

Design Factors that Impact on Capital Cost:

Design has a huge role to play in reducing capital cost, which can vary greatly across different types of NbSuDS intervention. See Table 4, which highlights factors that can impact capital costs.

Factors that could increase capital cost	Factors that could decrease capital cost
Retrofitting, as having to work around existing constraints	New-build, as design can be optimised and traffic management is minimised
Interventions on steep slopes that require numerous check dams	Interventions on shallow slopes or flatter sites
Extensive enabling works (pipework etc) to transport water to the intervention	Intervention close to source of catchment
Lined system (where unable to infiltrate or on contaminated land)	Unlined system (infiltrating)
Deep excavations	Shallow excavations
Smaller sites	Larger sites
Complex designs	Simple designs
Vertical excavations (raingardens) next to roads	45-degree battered excavations
Extensive underground pipework	On-surface conveyance

Table 4: Factors that impact capital cost

Design Factors that Impact on Maintenance Costs:

It is important when considering NbSuDS to consider ‘whole life costs’ inclusive of maintenance and even decommissioning/demolition when comparing to traditional drainage infrastructure. Consider what the maintenance cost would have been in a ‘No-SuDS’ alternative scenario, including both the maintenance cost associated with the traditional drainage infrastructure but also the land that the NbSuDS now occupies. For instance, if the area would have been grass, then the cost of mowing this must be considered as a reduction in the consideration.

Advice for Reducing Capital and Maintenance Cost:

• Consider NbSuDS from the start of the design process
• Keep designs simple
• Keep water on-surface as long as possible
• Avoid the need for enabling works by positioning your NbSuDS interventions where water will naturally go
• Infiltrate wherever possible
• Plant species that will thrive in future expected climates can reduce maintenance and replanting costs
• Consider how a light-touch maintenance regime can positively impact biodiversity and provide amenity value, and incorporate this into the design

Factors that could increase maintenance cost	Factors that could decrease maintenance cost
Interventions with bollards, signs, fencing, gates, and other street furniture	Simple interventions
Underground pipework	On-surface conveyance
Fertile soil	Low fertility growing medium that inhibits weed growth
Grass which must be mown	Herbaceous planting that can be cut back once a year, or grass/meadow that can be left to grow long
Formal appearance	An acceptance of a ‘wilder’ aesthetic
Steep earthworks and gradients	Shallow earthworks and gradients
Flow controls that are easy to block and hard to access	Well-designed flow controls that can be accessed from the surface

Table 5: Factors that impact maintenance cost

"Provided that drainage is considered early enough in the outline design of a new development, then there is no reason why SuDS should not become the norm everywhere" - CIRIA (2015) The SuDS Manual

QUEEN MARY’S WALK, Llanelli, Wales

Client/Lead: Welsh Water
Retrofit/New Build: Retrofit
Key Project Drivers: Water quantity

Suburban street located between a residential estate and public playing fields where a retrofit SuDS design looked to convert a traditional tank sewer drainage solution into a green bioswale. The total scheme cost for the tank sewer was estimated at £1.2m in 2013 prices, compared to £787,000 for the SuDS solution. In addition to the cost saving, the SuDS solution allowed for the provision of greater economic, social, and environmental benefits than the tank would have done.

POTENTIAL FUNDING SOURCES

Funding for SuDS is a dynamic and growing area with opportunities to apply for grants across private and public domains. Funding opportunities for NbSuDS change over time. Table 6 outlines some of the common funding sources, with some examples of previous funding pots, demonstrating the type of funding that may be available. It is recommended to check what funding opportunities are available from the listed sources and investigate other potential options.

Funding sources	Example
Local Government / Local Planning Authorities (LPAs)	LPAs can use planning conditions and Section 106 agreements to deliver SuDS. Some LPAs have established investment programmes to allocate funding for new SuDS. An example is Lambeth Council, who, in partnership with Thames Water (2022), announced a new £6 million programme in 2022 to help reduce flood risk and improve climate resilience across the borough.
Central Government	As part of Defra’s Flood and Coastal Resilience Innovation Programme, 25 projects across England were awarded £150 million to develop innovative solutions to flood and coastal resilience in their communities. The programme will run for 6 years from 2021. The programme fulfils a key government commitment to develop and test new approaches to tackle flooding and coastal change. A number of the selected projects are NbSuDS focused. The Department of Education made grants available for the SuDS in schools project. The programmes' objectives included reducing surface water risk on school sites and increasing biodiversity. The grants funded up to 50% of construction costs for SuDS at schools.
Water Companies	Some water companies in England and Wales have provided funding for SuDS. Thames Water in 2022 announced funding for local authorities and schools to create sustainable urban drainage schemes with a number of rounds of funding. United Utilities is investing a total of £9m in SuDs schemes between 2022 and March 2025. Since 2018, United Utilities have also offered house developers in the North West a revenue opportunity, with a 90% reduction in charges for housing developments that feature sustainable drainage. Outcome payments from water utilities are also possible, subject to negotiation and agreement with the utility company, where reductions in surface water runoff and/or flood risk can be evidenced.
Local Wildlife Trusts, Local River Trusts	Some trusts have access to funds to support the development of SuDs on occasions, whilst also having a network of partners interested in supporting the delivery of SuDs in communities.

Table 6: Funding sources table

Other Not for Profit:
National Lottery Heritage Grants fund projects between £10,000 and £250,000 on the basis that the projects account for protecting the environment, saving heritage, organizational sustainability, and inclusion, access, and participation.

Additionally, from the perspective of local government, local planning authorities could use a combination of planning conditions and Section 106 agreements to deliver SuDS. There is also evidence of local authorities establishing investment programmes to allocate funding to implement new sustainable urban drainage systems.

As set out in HM Government’s Nature Markets Framework (March 2023), there is a commitment to scaling up private investment in nature recovery-based projects. Hence, it can be expected that private investment in SuDS and nature-based solutions will increase in the coming years. Where several ecosystem service outcomes will be delivered, there may be potential to combine funding sources, dependent on stacking and bundling rules across nature markets.

Alongside the previously mentioned funding options, there are also opportunities through local public sector organizations (local councils), environmental organizations (such as the Wildlife Trusts, Woodland Trust, Community Forests, Birmingham Tree People), and private companies (such as Severn Trent, Veolia, housing companies) which may provide funding opportunities for projects.

SALEABLE UNITS

NbSuDS have a unique opportunity for bundling nature markets through considered design, providing greater value-for-money of interventions. Alongside funds, saleable units, a key part of nature markets, provide mechanisms to enable private investments in nature through regulation and incentives. They work by creating credits, or units, which can be bought and sold by suppliers to ensure that net environmental targets are met. Table 7 outlines some of the key nature markets which enable credit trading. More markets are likely to emerge, including the Local Investment in Natural Capital (LINC), which is currently being piloted in the West Midlands region. Other markets exist, such as nutrient credit trading, which are unlikely to be appropriate for typical NbSuDS applications but may be appropriate for larger environmental schemes that include elements of NbSuDS within them.

Nature market	Type of market	Description	Status
Biodiversity Net Gain (BNG)	Compliance nature market	Biodiversity Net Gain is a policy requiring that new developments achieve a 10% net gain. This can be achieved on-site, off-site (if this proxy is owned by the development land owner), or through purchasing credits from an external party.	Launched – applies to small sites from April 2024
UK Voluntary Markets	Voluntary nature market	These voluntary markets provide opportunities for land managers to sell the additional benefits they generate to help meet environmental targets across water quality, flood management, carbon, and biodiversity. An example includes Woodland Carbon Units.	Emerging

Table 7: Nature markets and credit trading