Nature-based stormwater management 

A filter strip on the side of a road. Photo: Susdrain

Nature-based stormwater management systems can work on small and large scales to support existing urban stormwater infrastructure. 

Trenches, bump-outs, soakaways, soak wells, filter strips, filter drains and infiltration trenches (gravel trenches) are all methods of small-scale Sustainable Drainage Systems (SuDS), and examples of nature-based stormwater management. 

Soakaways and soakwells:

Underground tanks or pits filled with rocks, or lined with brick, concrete or rubble that can be used on small or large scales. They store surface water and run off, supporting stormwater systems and preventing erosion. They can also manage overflow from other rainwater collection systems and because of their simplicity can be any shape or size, depending on where they are needed (NWRM, 2014).

Filter strips:

Filter strips are vegetated sections of land designed to accept runoff as overland sheet flow. They are most effective when the strip is wide and densely planted. They remove excess solids and pollutants before discharge to an infiltration system (SuDS Wales, 2024). They can be used along roads or other impervious surfaces, increasing permeability, preserving riparian zones and preventing erosion. Filter strips can also form biodiversity corridors. 

Filter drains and infiltration trenches:

Shallow excavations filled with rubble or stone that create temporary subsurface storage of stormwater runoff. They are useful on roadsides, but are limited to relatively small catchments. Infiltration trenches allow water to exfiltrate into the surrounding soils from the bottom and sides of the trench. (susDrain, 2024). 

Sustainable drainage systems (SuDS):

Sustainable drainage systems (SuDS) are interventions and supports designed to temporarily store water during storm events, reduce peak flows and reduce surface water runoff, by mimicking the natural cycle of water management by retaining water where it lands (The Flood Hub, 2021).

SuDS strategies vary, but their key feature is that they intercept water at the source, reducing the volume of runoff and supporting stormwater systems. Drainage methods involve infiltration (where collected water is filtered into the subsoil), retention (where water is stored in a storage area) and conveyance (where water is transferred away from the source to be discharged) (The Flood Hub, 2021).

Name of NbS

Nature-based stormwater management

Type of NbS

Hybrid living/engineered interventions

Location

Nature-based stormwater management can work on small and large scales, in urban, rural and periurban areas. Strategies like soakwells can work on large scales, but also on smaller, single house scales. Filter strips can be implemented in urban planning, or along roadsides in infrastructure projects. All can be adjusted and designed depending on scale and requirements. 

A filter strip on a roadside. Photo: WaterTech

Relationship to Indigenous knowledge

These SuDS systems are not specifically linked to indigenous knowledge systems, however management of water through nature-based systems does support traditional belief systems of reciprocity, interconnectedness and stewardship.

Climate change benefits
  • soil erosion and landslides
  • desertification
  • drought
  • flooding
  • increased incidence / distribution of disease
  • increased temperatures
  • soil erosion and landslides
  • urban heat island effect
  • reduced fresh water availability / quality
  • Wind / storm damage

Nature-based stormwater management systems like trenches, bump-outs, soakaways, soak wells, filter strips, filter drains and infiltration trenches are simple but effective ways to support drainage capacities. In many recent cases of extreme weather events across the Pacific, existing drainage and stormwater infrastructure has been proven to be incapable of keeping up. 

Supporting infrastructure with nature-based stormwater systems has been proven to be effective in creating additional aid, in ways that are gentle on the natural environment.

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Societal / socio-cultural benefits
  • disaster risk reduction and resilience
  • waste management and hygiene
  • fresh water security and quality

Nature-based stormwater management systems can be employed on small or large scales. Methods like soakwells and soakaways can be implemented in residential homes, where flooding is becoming an increasing concern. This is a cost effective solution, easily installed by anyone, and purchased from a local hardware store or created. For residents of cities in New Zealand, Fiji, Vanuatu, for example, where a 2023 Cyclone saw widespread damage to homes from flooding, a soakwell can provide additional storm resilience. 

On wider, urban scales, filter strips and infiltration trenches can be implemented in cities where flooding and increased rainfall is creating widespread damage. All of these strategies are specifically designed to support stormwater systems during disaster events, and to increase the resilience of communities. 

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Ecological and biodiversity benefits
  • disturbance prevention
  • habitat provision

As well as their clear case for disturbance prevention, by supporting existing stormwater infrastructure, nature-based stormwater management systems like filter strips can provide habitat provision to urban areas. Strips of vegetation in impervious urban environments like roadsides creates biodiversity corridors for birds and insects. Biodiversity corridors allow birds and insects to move through urban areas within natural environments, and maintain ecological connectivity. Wildlife is always on the move – migration, shifting habitats, patterns of pollination and food gathering, to name but a few. Supporting these natural movements and patterns by creating natural spaces for creatures to move through supports healthy ecosystems and maintains our biodiversity. 

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Technical requirements

The technical requirements for these nature-based stormwater strategies depend on their size and requirements. On small scales, they can be implemented with a few simple tools. On larger, urban and public scales, they will require more technical considerations around how they connect to public drainage infrastructure and stormwater systems, as well as potential engineering, large-scale excavation that may trigger geotechnical requirements, consideration of vegetation, and materials.

A filter strip explained. Image: SuDS Wales

Issues and Barriers

There are no real barriers to these SuDS being implemented on small, private scales, aside from a lack of knowledge about their use and efficacy. On larger scales, local governing bodies need to accept that nature-based SuDS can genuinely make a difference to disaster resilience and flooding by supporting existing stormwater systems.

Opportunities

Across the Pacific, cities and communities are increasingly vulnerable because of increases in rainfall and flooding, and stormwater infrastructure that cannot keep up. These methods are cost-effective, low maintenance, easily and quickly implemented and genuinely go a long way towards helping to ease pressure on stormwater systems during extreme weather events.

Financial case

There is no denying that managing stormwater will need to be a focus of government plans for infrastructure funding across the Pacific. Already, Pacific Island nations are committing millions to upgrading water infrastructure. But typical modern methods take time to build and implement. Implementation of SuDS like these immediately will protect and support both current and future water infrastructure projects, in a cost-effective, sustainable way.

A typical soakaway system. Image: Office International de l’Eau
A soakwell system in use. Image: Houspect
References