Types of Nature-Based SuDS

INTRODUCTION

When landscape architecture and civil engineering skills are combined, suitable NbSuDS designs can be produced for every site that can deliver cost effective drainage solutions which provide resilience to the changing climate and offer value for nature and people.

The number of NbSuDS options presents an opportunity for creativity and fun for both the designer and the end user. Designs can and should be integrated into the wider design to increase the value that can be achieved. Opportunities for multifunctionality that can enhance a site while providing multiple benefits include, but are not limited to:

• Provision of usable play and recreational space

• Playful use of contours and landform

• A reduction in hard surfaces to mitigate the urban heat island effect

• Integration of attractive vegetation that will tolerate the changing climate

• Integration of habitat for biodiversity value and BNG requirements

• Provision of shady spaces for respite from heat

• Integration of educational opportunities through signage and visible design features

• Integration of active travel

The types of NbSuDS interventions outlined in this section are not an exhaustive list of all possible features but are intended to be an indication of those commonly used in drainage design. Many of these intervention types have blurred lines between one another, and even the most experienced SuDS practitioners may disagree over the terminology used to define a feature. Developers and designers should not feel limited to only using features listed in this document. Note that whilst an indicative illustration is shown for each intervention type listed, this is intended to be illustrative only and the exact details of each intervention will differ depending on the nature of the site, and the project drivers.

WHICH TYPE OF NBSUDS SHOULD I USE?

Not all NbSuDS features will be suitable for all sites, but due to the flexibility of the intervention types, there are very few sites where NbSuDS of some variety will not be feasible.

The type of NbSuDS intervention used will depend largely on specific site and project conditions such as:

• The amount of space available;

• The budget available;

• The amount of surface water runoff and where it originates from;

• The character of the site and whether it is urban, suburban, peri-urban or rural.

Influencing this decision might also be the specific project drivers or requirements, which may stem from the funding origins or the requirements of any additional funding which has been obtained. These will generally be site-specific and relate to any existing issues or deficiencies. Possible project drivers or requirements might include:

• Flood risk management (water quantity) which may relate specifically to fluvial flooding, surface water flooding, sewer flooding or a combination of the above;

• Water quality, requirements for minimum quality that can be released to a river or requirements to improve the quality coming from a site;

• Local biodiversity and BNG requirements;

• Local amenity and recreation, such as provision of open space or playspace;

• Climate adaptation;

• Economic and social regeneration;

• Health and wellbeing;

• Educational opportunities.

There are opportunities to maximise the biodiversity potential of these different NbSuDS by creating a variety of habitat niches for flora and fauna. Planting of native flora and the presence of permanent or semi-permanent water, will help to achieve maximum biodiversity benefits and contribute to local and national biodiversity objectives. All of the intervention types listed can be lined and can be designed to be suitable for contaminated sites or sites with vulnerable groundwater.

Types of interventions and their potential to cover multiple benefits

The exact benefits achieved by an intervention, or combination of interventions, will vary depending on its specific design. The table on the next page is intended to illustrate which of the multiple benefits may be easier to achieve with each type of intervention and guide developers and designers towards the type of intervention that is suitable for their site.

Water Quantity The potential to mitigate flooding through water storage, responding to the increased likelihood of flood events because of the changing climate.

Water Quality The potential ability for an intervention to remove or treat pollutants.

Amenity Value The potential for an intervention to provide amenity value for people.

Biodiversity/BNG Potential The potential for an intervention to provide for biodiversity, and in turn achieve project BNG requirements.

Climate Adaptation The potential to build resilience against the impacts of climate change by mitigating the urban heat island effect and introducing drought-tolerant landscapes.

Installation Cost The relative cost to install an intervention compared to its benefit.

Maintenance Cost The relative cost to maintain an intervention once installed.

Newbuild or Retrofit

The beauty of NbSuDS interventions is that they can be incorporated into most developments be they:

• New build schemes, such as new housing developments, new building developments (commercial, educational etc.) or even new infrastructure from electricity substations to transport interchanges etc.

• Retrofitted into the existing built environment such as modifications to the highway or public realm to help manage stormwater where currently it is not, all whilst bringing multiple benefits at the same time.

This guide is predominantly intended for new build situations, however the principles can be applied to retrofit. Retrofit NbSuDS offers an opportunity to make places more resilient to future climate scenarios by replacing existing impermeable surfaces with planted areas that increase drainage capacity, habitat and cooling, amongst other benefits. Different constraints and considerations come into play with retrofit installation but professionals experienced in designing retrofit schemes are available and their advice should be sought.

Other Water Improvement Schemes

Other interventions which may not traditionally be considered ‘NbSuDS’ may also be capable of achieving the same or similar social, economic and environmental benefits. Opportunities for river restoration, daylighting and offline flood storage should be considered in addition to NbSuDS opportunities where they may arise.

LONGBRIDGE RIVER RESTORATION

Birmingham, West Midlands On the site of the former MG Rover factory in Birmingham, residential development at Longbridge sought to restore a section of the River Rea and Callow Brook to the south of Birmingham. The scheme reintroduced planting, naturalising and re-meandering the riverbanks to slow the flow of the river and improve capacity to reduce flood risk. The scheme demonstrates how water, people and wildlife can all be benefited through well considered design.

INFILTRATION AND DETENTION BASINS

Infiltration and detention basins are landscaped depressions for temporary runoff storage that can also serve to improve the quality by capturing waterborne pollutants.

Infiltration basins can reduce the volume of water passed downstream and aid ground water recharge by allowing infiltration. Detention basins are similar, providing storage to reduce runoff rates and provide water quality improvements but they do not infiltrate so have limited volume reduction. Both basins can be designed into a site with varied planting or hard paving for habitat and recreational space. They are a large intervention type used to collect large areas being drained. As a result they are located towards the downstream end of a site’s drainage network. Basins are normally dry but will typically have low points as wet zones where frequent day-to-day storms first fill. This range of conditions is ideal for creating habitat niches which attract a wide variety of wildlife, increasing biodiversity value.

Where might be suitable: Basins are mostly associated with larger sites in suburban, peri-urban and rural areas. Poorly designed basins are often fenced off in the corner of a development or by a roadside, with over-engineered inlet and outlet structures, often driven by the design using steep side slopes (steeper than 1 in 4 or 1 in 3). Good basin design can avoid the need for these elements and provide something that is both beautiful and functional. In many situations it is appropriate to allow recreational access into the dry part of the basin and it can be more centrally positioned within a development to maximise the social and environmental benefits of the feature.

ADVANTAGES AND DISADVANTAGES

Most of the potential disadvantages of basins can be mitigated through the design process, particularly on new development sites where there is greater control over the depth of the incoming drainage network.

Advantages:

• Can aid climate adaptation through significant flood reduction and large scale planting of resilient diverse species

• Simple to design and construct

• Simple to maintain

• Can double-up as recreational land; seating and play opportunities can be safely integrated into the design of the basin

• High potential for BNG due to large footprint and capacity for diverse habitat types with wetter and drier areas

• Likely to be favourable under Schedule 3 where green at-surface interventions are expected to be favoured

Disadvantages:

• The incoming flows/pipework drives the depth. Helping to keep upstream pipework shallow can help keep basins shallow

• Deep basins require a larger footprint when using people friendly slopes of 1 in 4 or shallower

• Headwalls and associated maintenance infrastructure can be unattractive and overengineered when designed with little thought; softer solutions are available

• Benefits to water quality can be lower compared to other solutions, where infiltration is not possible and/or where this has not been considered appropriately

CAMBRIAN NORTH BASIN STUDY

Llanelli, Wales

Cambrian North Basin in Llanelli, Wales, was completed in 2017 and demonstrates how water management can be combined with recreational and biodiversity opportunities. Amenity value was added by promoting sustainable travel and health and wellbeing through the design. A new footpath provides important connections for the existing desire lines between Llanelli Town Centre and the Wales Coast Path, previously linked by highway. Furthermore, the project has created three seating areas encouraging socialising, and managing water on the surface has increased awareness of sustainable water management within the community, who were engaged during the design process to address any specific concerns within the design and ensure that it was positively received. The basin attenuates 1ha of surface water flows and reduces CSO events at the Cambrian Sewage Pumping Station by five per year.

Client/Lead: Welsh Water
Retrofit/New Build: Retrofit
Key Project Drivers: Combined Sewer Overflow (CSO) Reduction
Cost: £800,000 (Alternative storage tank design costed at £1.3m)

PONDS AND WETLANDS

Ponds are landscaped depressions similar to basins but designed with a permanent pool of water. Wetlands are ponds with a larger proportion of shallow zones.

Ponds and wetlands attenuate and treat surface water runoff with potential for significant biodiversity and amenity value. For maximum quality benefit they should be made up of a series of smaller connected components (ponds). They are normally located at the end of a site’s drainage network.

Ponds & wetlands offer exceptional potential for both BNG and amenity value as well as water quality treatment, due to the diversity found within a single wetland.

Where might be suitable: Wetlands are typically more appropriate for peri-urban and rural locations although some suburban sites may be appropriate. Ponds may be appropriate for all locations although their character might change drastically depending on the context.

ADVANTAGES AND DISADVANTAGES

Advantages:

• Excellent capacity for removing water pollutants

• High potential for amenity value, and can incorporate boardwalks and platforms to enhance this further

• High potential for BNG due to large footprint and capacity for diverse vegetation types between wetter and drier areas

• Can aid climate adaptation through significant flood reduction and planting of resilient diverse species

• Can provide linkages and green corridors connecting areas of semi-natural habitats

• Likely to be favourable under Schedule 3 where green at-surface interventions are expected to be favoured

• Likely to encourage community participation during installation and through maintenance, generating a sense of ownership due to biodiversity potential and perception of ‘naturalness’

• Permanent water provides wildlife benefits and increases urban cooling

Disadvantages:

• Only the volume above normal water level (NWL) is available for surface water storage. Ponds need to be designed to have the permanent water typically at least 1m deep in places (but with shallow shelves around edge for safety) to help maintain stable water conditions, reducing stagnation and allowing provision of water for wildlife throughout a variety of seasons

• The incoming flows/pipework drives the depth to NWL. Helping to keep upstream pipework shallow can help keep the NWL shallow

• Deep ponds can require a large footprint

• Headwalls and associated maintenance infrastructure can be unattractive and overengineered when designed with little thought; softer solutions are available

• Design and construction need to consider lining details, if ground conditions require

• Poorly designed or constructed ponds can present greater health and safety risks leading to excessive fencing, signage and safety equipment. A pond that is well planned and designed can avoid these and become a valuable community asset

• Can be vulnerable to colonisation by invasive or dominant species which would increase maintenance requirements. A risk likely to increase as the climate warms. Ecologist involvement in the design can help reduce this

BEAM PARKLANDS

Dagenham, East London

Client/Lead: Environment Agency
Retrofit/New Build: Retrofit
Key Project Drivers: Biodiversity enhancement and amenity value

Beam Parklands is an exemplary habitat creation project within a flood storage area, which also connected the 53ha park to the wider community.

Community engagement was central to the approach for the design of the park, and the sense of community ownership generated from those events was key to ensuring that what was once an area vulnerable to vandalism is now a valued site within the community.

The project created over 12ha of new diverse habitats, improved access to and through the park, created natural play areas, protected the existing valuable habitats and protected species and re-used all materials sustainably on-site through the construction process.

BIOSWALES

Bioswales are shallow vegetated channels which provide treatment, attenuation and can infiltrate. Bioswales can be used for source control and/or conveyance.

They are generally used to drain roads and car parks but can be used to convey flows close to ground level from source to the next SuDS feature. They can be very similar to raingardens or other bioretention systems, the key difference being that they typically have a dished profile on the surface, where the majority of water is stored during large storm events. They can also be designed as shallower features to convey water from different areas to a central deeper area.

Whilst bioswales are typically linear features, they often function and appear better when they adopt a more naturalistic form, and can include expansions (mini-basins), contractions and variations in gradient to give both a more naturalistic aesthetic and to slow and control the conveyance of water through the bioswale, maximising the potential for infiltration and quality treatment.

Bioswales can be grassed or can be planted with a variety of vegetation types to improve their biodiversity provision.

Where might be suitable: Bioswales can be appropriate for almost all sites, although their specific character might be different depending on the context. Where bioswales are used in city centres, they are more likely to resemble raingardens and may be used where advantageous to mimic the appearance of a raingarden in places where underground storage layers are not necessary. In more suburban and rural areas they could have a more naturalistic character.

ADVANTAGES AND DISADVANTAGES

Advantages:

• Linear features that can provide habitat corridors and can themselves have large footprints that contribute to BNG

• Can aid climate adaption through significant flood reduction, planting of resilient diverse species and solar shading through incorporated tree planting

• High potential for water quality treatment, especially when vegetated

• Can have high amenity value when designed well and planted attractively

• Can be used to convey water from one NbSuDS feature to another, or from multiple sources to a smaller number of NbSuDS features

• Can be very cost effective • Simple to design and construct • Simple to maintain

• Likely to be favourable under Schedule 3 where green at-surface interventions are expected to be favoured

Disadvantages:

• Storage capacity is low for their footprint when compared to other intervention types. Therefore they may not be suitable for highly constrained sites draining large areas

• Poorly designed bioswales which are straight and have consistent, steep gradients can appear over-engineered and do not offer significant amenity value

• Steep slopes require check dams to hold water back, increasing the cost

MANOR FIELDS PARK

Sheffield, South Yorkshire

Manor Fields Park in Sheffield, South Yorkshire, is a prime example of how NbSuDS can aid development and regeneration, and how economic, social, and environmental benefits can be realized through holistic and well-considered design.

Constructed on former wasteland, where antisocial behaviour was rife and burnt-out cars would be dumped, the scheme was a catalyst for the successful regeneration of the Manor Estate which was once labelled the worst estate in Britain by a national newspaper.

The site is on the side of a hill, and so the design incorporates a ‘treatment train’ of basins and ponds connected by vegetated conveyance swales, with the gradient managed through various check dams.

Originally completed in the early 2000s, the site has continued to take surface water from several local housing estates, the ongoing development of which contributes to funding the management of the park. In 2023, an additional wetland area was designed to increase capacity, provide more habitat diversity and allow for another 148 homes to be constructed in the local area.

Manor Fields is now a haven for wildlife, with almost 90 species of birds recorded on the site, as well as numerous wildflower meadows, woodland pockets, and a more naturalistic aesthetic which promotes biodiversity. In addition, the park is used by local residents for both active and passive recreation.

Client/Lead: Sheffield City Council
Retrofit/New Build: Retrofit
Key Project Drivers: Water quantity and amenity value

RAINGARDENS

Raingardens are shallow vegetated channels which provide treatment, attenuation, and can be used for source control.

They can make use of traditionally hard-paved space, grass verges, or unused public realm areas, for example, traffic calming islands. They consist of vegetation in an engineered soil mix overlying a storage layer (e.g. coarse graded aggregate or high void geocellular storage).

Raingardens are suitable for a wide variety of settings but are more typically associated with urban and suburban areas. They often, although not always, replace previously impermeable surfaces such as in highways and streets or urban squares and plazas. Throughout the urban realm, they can double up as traffic calming measures providing segregation for pedestrians and cyclists from traffic, enhancing the accessibility to and safety of active travel networks, and separating cyclists from air pollution sources.

Raingardens are typically planted with herbaceous plants and grasses which thrive in low-fertility engineered soils, and can be supplemented with shrub and tree planting.

Where might be suitable: They can be positioned adjacent to roads, built out into roads, on the edge of open spaces, and within car parks. Minimum width and length of 1.5m are recommended but length is only limited by other constraints.

ADVANTAGES AND DISADVANTAGES

Advantages:

Flexible in shape and can be sized for large and small areas
Can have high amenity value when designed well and planted attractively
Good potential for retrofit as they can accommodate buried services
Simple to design and construct
Simple to maintain
Likely to be favourable under Schedule 3 where green at-surface interventions are expected to be favoured

Disadvantages:

If vertical walls below ground are needed, for vehicle loading reasons, this can drive up the costs. However, designing to have stepped or battered excavation can keep the costs much lower
Small footprint raingardens are not recommended as it reduces their ability for the raingarden to remain healthy
Inlet design and placement need to be considered carefully during design to ensure water is captured effectively

CHARTER SQUARE AND HEART OF THE CITY

Sheffield, South Yorkshire

In the centre of Sheffield, this redeveloped part of the city centre uses NbSuDS raingardens to drain the roads and public realm. Their use has changed the feel of the square, creating a green, healthy corridor, an attractive space to spend time with improved biodiversity, whilst promoting economic investment.

The growing medium uses locally sourced crushed quarry waste along with locally composted green waste and a natural silty loam reclaimed from sugar beet washings. This innovative approach to manufactured soils heavily reduces the maintenance requirements when compared to traditional soils, whilst still allowing for beautiful and biodiverse planting.

Client/Lead: Sheffield City Council
Retrofit/New Build: Retrofit
Key Project Drivers: Amenity value

GREY TO GREEN

Sheffield, South Yorkshire

The bioswales and raingardens that are integral to Grey to Green form a key strategic component in the regeneration of Sheffield’s City Centre. In an area once dominated by an unattractive dual carriageway and complex junctions, this 1.3km scheme reclaimed a large proportion of that highway and returned it to pedestrians and cyclists.

Active travel routes are bounded by the lush vegetation of raingardens and bioswales, providing air pollution mitigation, amenity value, biodiversity value, and dealing with surface water from a large expanse of hardstanding. Phase One of the scheme was completed in 2016, so it has a long period of operation.

Client/Lead: Sheffield City Council
Retrofit/New Build: Retrofit
Key Project Drivers: Water quantity, water quality, and amenity value

BIORETENTION TREE PITS

Bioretention tree pits utilise underground storage to maximise available space in urban areas.

Bioretention tree pits are specialist interventions where the growing medium for trees is engineered to store surface water, whilst providing suitable growing conditions for a tree. This can be as part of a raingarden or as street trees (without lower level planting).

Tree species selection is critical to the success of a bioretention tree pit. Design factors such as pit size, physical constraints, tolerance of urban conditions, shading, and type of urban environment must all be factored in.

Bioretention tree pits are typically more associated with areas of hard landscape, where there is insufficient space in the landscape to include other NbSuDS interventions. They can be particularly useful for constrained car parks where there is insufficient space for bioswales or raingardens, and can be incorporated or retrofitted with minimal or no loss of parking spaces.

Where might be suitable: Areas of hardstanding where trees can be accommodated but other NbSuDS cannot fit.

ADVANTAGES AND DISADVANTAGES

Advantages:

Flexible in shape and can be shaped to avoid underground services
As the primary storage area is below surface, they can have a small amount of land-take at surface level and can accommodate some vehicular and pedestrian overrun
Potential to add substantial amenity value to a project
Likely to be favourable under Schedule 3 where green at-surface interventions are expected to be favoured
Very low maintenance requirement after establishment period
Good for reducing the urban heat island effect by providing shade and through evapotranspiration (releasing moisture into the atmosphere)
Can be effective for air pollution mitigation, subject to species selection
Canopy interception and transpiration aid with reducing flood risk and water returned to the sewer network

Disadvantages:

Can be more expensive to construct than other NbSuDS interventions
Limited BNG value due to lack of diversity
No at-surface storage means water volume stored is typically inefficient compared to other intervention types
Poor selection of tree species and inadequacy to consider future climates can lead to failure, but good species selection can allow trees to thrive

WOOD STREET

Cardiff, Wales

In the centre of Cardiff, one of Wales’ most constrained streets was redeveloped to support the regeneration of the area for economic growth whilst allowing easier movement by both pedestrians and cyclists, separating them from vehicles. The use of NbSuDS is central to the drainage and incorporates 15 bioretention tree pits (plus 10 within raingardens) to help with surface water attenuation, removing water from the sewers via tree pits and raingardens, but also to help reduce urban heat island effects through shade and evapotranspiration.

Client/Lead: Cardiff City Council
Retrofit/New Build: Retrofit
Key Project Drivers: Water quantity and climate adaptation

MANSFIELD SUSTAINABLE FLOOD RESILIENCE TOWN CENTRE PILOTS

Mansfield, Nottinghamshire

Severn Trent is undertaking the largest retrofit SuDS programme in the UK, and an early part of the works focused on placemaking in Mansfield town centre. The innovative design at Memorial Gardens (shown) captures water from the bus station roof, taking it down into a series of cascading raingardens and bioretention tree pits, all within a space that has been transformed from a surface car park into a green and beautiful public space.

"These gardens bring endless benefits to our communities, alleviate the growing risk of flooding, and make Mansfield cleaner and greener.”
— Councillor Andy Burgin, 2023

Client/Lead: Severn Trent and Mansfield District Council
Retrofit/New Build: Retrofit
Key Project Drivers: Water quantity and amenity value

GREEN AND BROWN ROOFS

Green roofs are roofs with a substrate and vegetation layer. Brown roofs feature aggregates and soil providing habitat for different soil-dwelling species.

Both roof types have similar attributes, including attenuating rainwater where it lands, enhancing biodiversity, and improving the amenity value of the space. These roof types also encourage evapotranspiration and help clean water. They can help to reduce building running costs by regulating the internal temperature of the building and can be combined with solar panels, reducing the building's energy consumption.

There are two main green roof types – extensive (shallow substrate and simple planting) and intensive (deeper substrate and wider planting variety as they are more like a landscaped area). Intensive roofs are generally better for surface water control and amenity but have increased roof loads and maintenance requirements.

Where might be suitable: Green roofs can be applied to any building or structure, where structurally appropriate, including bin stores, substations, pumping stations, and bus shelters – both flat or slightly inclined. Brown roofs are similar but generally only favour flat roofs.

ADVANTAGES AND DISADVANTAGES

Advantages:

Good for reducing building energy requirements and can be combined with solar panels
Good at reducing the urban heat island effect in urban areas, by reducing temperatures of the roof surface and surrounding air and releasing moisture through evapotranspiration
Intensive green roofs (roof gardens) can have very high amenity value for building users
Excellent option for achieving BNG on constrained sites
Maintenance complexity can be tailored to the project requirements
No additional land-take requirement
Extensive green roofs can be retrofitted but only where the structure below has been structurally assessed as appropriate

Disadvantages:

Limited amenity value for extensive green roofs and brown roofs
Generally quite costly to design and construct
Limited water storage capacity on extensive green roofs
Limited opportunity for retrofit

THE LIBRARY OF BIRMINGHAM

Birmingham, West Midlands

Birmingham City Council’s library shows how these interventions can be incorporated in a fun way that enhances a new development. It features a brown roof and two elevated garden terraces to provide habitat and green spaces in the heart of the city. The Secret Garden on level 7 is planted with a variety of species to provide colour and interest throughout the year. The level 3 Discovery Terrace includes fruit, vegetables, and herbs to provide a focal point for learning about where food comes from and encouraging ‘grow your own.’ The brown roof is covered in rubble from the construction of the Library and provides a natural city centre habitat for wildlife.

Client/Lead: Birmingham City Council
Retrofit/New Build: New Build
Key Project Drivers: Amenity value

RAINWATER DOWNPIPE PLANTERS

Rainwater downpipe planters are self-contained planters that redirect the downpipe from a roof gutter of a building, taking water into the soil (and sometimes an additional reservoir) with an overflow pipe back into the original downpipe location.

They are simple and attractive features that can be installed without specific design expertise, and can be used as an educational resource in schools and other settings. They are very simple to install and can be purchased off-the-shelf or made bespoke for the purposes of the project. There is the opportunity to include integrated seating to make an attractive feature that serves multiple purposes.

Where might be suitable: Adjacent to a building, where they will not cause an obstruction, and next to an existing or proposed rainwater downpipe.

ADVANTAGES AND DISADVANTAGES

Advantages:

Simple to install and maintain
No excavation required
Good opportunity for education, particularly when used in schools
Easy to retrofit to an existing building where space is limited
When designed and maintained well, they can add an attractive feature to enhance a building
Slows down water entering the sewer system on a local scale

Disadvantages:

Small-scale intervention that has limited value for BNG
Amenity value is limited unless used en masse
Only capable of storing relatively small catchments and volumes individually, but when several are used, this can help to provide greater benefit
Limited ability to improve water quality significantly as only managing roof water which is typically relatively clean

STEBONHEATH SCHOOL

Llanelli, Wales

Stebonheath School is surrounded by a number of residential streets where flooding had been experienced. The school had limited available space and so concentrated on source control measures such as rainwater downpipe planters, a bioretention tree pit, and a playground swale.

The scheme consulted the school children on the proposals and was used as an educational process for the children about sustainable water use. The rainwater downpipe planters are planted on the top with an appropriate palette of plants. Welsh Water included information boards next to the rainwater downpipe planters to aid education, combined with classroom talks.

The scheme demonstrates how NbSuDS can be retrofitted on a small scale and at relatively little cost, and with all of the associated social, economic, and environmental benefits.

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

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Nature Based SuDS Guidance Document