The Watershed Partnership Initiative (WPI): Biofilters Case Study

Figure 1: The community’s finished raingarden/biofilter system. Photo NOAA

Name of case study

The Watershed Partnership Initiative (WPI): Biofilter and raingarden implementation in Tutuila


The Faga’alu watershed in Faga’alu, Tutuila, American Samoa




suburb/neighbourhood scale

Area / size

Faga’alu is a narrow, V-shaped watershed covering approximately 2.48 km2 from Mt. Matafao, to the Pacific Ocean

NbS employed


Type of NbS

Created or constructed living ecosystems


NOAA Coral Reef Conservation Programme and The U.S Coral Reef Task Force

Design group

Partners include: NOAA Coral Reef Conservation Program, National Fish and Wildlife Foundation, Horsley Witten Group, American Samoa Coral Reef Advisory Group, Faga’alu Village, Land Grant, and Samoa Maritime Company.

Figure 2: The community workshop, where the locals learn how to design, build and maintain their rain garden/biofilter system. Photo NOAA
Figure 3: Excavation commences. Photo NOAA
Figure 4: Native planting underway. Photo NOAA
Climate change benefits

The WPI significantly improved the health of the reef and surrounding area. In 2022, the Faga’alu watershed ‘graduated’ after demonstrating ecological improvement and establishing sufficient local capacity to monitor and manage future land-based sources of pollution issues (NOAA, 2022). 

The implementation of biofiltration supports stormwater systems, removes pollutants from the waterways and decreases the presence of water-bourne diseases.

Societal / socio-cultural benefits

The WPI programme was embedded in the community – local participation was a key resource and gave the community a sense of ownership over their resources. In 2022, the village of Faga’alu is now developing a marine protected area in Faga’alu Bay to expand its stewardship of the natural resources found beyond the shoreline (NOAA, 2022).

The fact that this project was able to empower the local community is key to its success. The people of Faga’alu are the people most affected and most invested in the health of the land, the ocean and the reef. Giving them the resources and knowledge to protect that, and the task of maintaining it is truly creating a reciprocal relationship between people and land. 

Ecological benefits

The implementation of biofiltration is a nature-based solution to the pollution that was plaguing the Faga’alu watershed. The filtration removes damaging pollutants that were harming the reef, the ocean and the surrounding land. It improved fishing conditions and the cleanliness of the waterways.

Summary of case study

Faga’alu is a village in central Tutuila Island, American Samoa. The Faga’alu watershed did not meet the American Samoa Water Quality Standards because it had significant levels of land-based pollutants – from agricultural and stormwater runoff, sedimentation, erosion, deforestation and rubbish. The watershed has large areas of steep forested hillsides prone to landslides and residential septic systems were contributing nitrogen, phosphorus and bacteria to the stream and coastal waters (Messina et al, 2016). 

Messina’s (2012) assessment of the watershed identified that sedimentation was severely affecting the health of the coral reef, and increasing rainfall exacerbated the problem.

In 2015, The NOAA Coral Reef Conservation Programme and The U.S Coral Reef Task Force implemented The Watershed Partnership Initiative (WPI), partnering with and training local residents to build raingardens to filter the pollution coming into the area. 

Teams of specialists spent two days with community members, in a workshop that taught locals everything from site selection and design to installation and maintenance. The community did the work themselves, planting native plants on the top. Further plans were made within the initiative, including creating a recycling programme, a tree planting programme and establishing a protected marine area. 

This is a great example of how a local community can be given the tools to create solutions and care for their own natural environment themselves. 

  • Department of Water. (2024). Water sensitive urban design: Biofilters. Government of Western Australia. 
  • Hornsby Shire Council. (2024). Biofilters and Raingardens. Hornsby Shire Council.
  • Messina, A., Rice, S., Vargas-Angel, B., & Biggs, T. (2016). Baseline Assessment of Faga’alu Watershed: A Ridge to Reef Assessment in Support of Sediment Reduction Activities and Future Evaluation of Their Success.
  • National Oceanic and Atmospheric Administration (NOAA). (2015). Protecting American Samoa’s Coral Reefs One Rain Garden at a Time. NOAA Coral Reef Conservation Programme.
  • National Oceanic and Atmospheric Administration (NOAA). (2022). Coral Reef Task Force Graduates First Watershed from Watershed Partnership Initiative. NOAA Coral Reef Conservation Programme.
  • Planning and Urban Management Agency. (2018). Urban Design Standards: Apia Central Business District (CBD) and Waterfront Areas. 
  • Renold, J. (2024). Indigenous Peoples hold Key Knowledge for Sustainable Water Solutions. If Not Us Then Who.
  • UNESCO World Water Assessment Programme. (2018). The United Nations world water development report 2018: nature-based solutions for water.
  • Wiegner, T. (2022). Predicting sea level rise impacts to coastal wastewater infrastructure and water quality for adaptive planning and increased coastal habitat resilience. Pacific Islands Climate Adaptation Science Centre.

Further resources

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