Waikawa Estuary Salt Marsh Restoration

Name of case study

Waikawa Estuary Salt Marsh Restoration

Location

Marlborough, New Zealand

Year

2021

Scale

Urban/ landscape scale

Area / size

1400 m2

NbS employed

Constructed salt marsh/ mud flats

Type of NbS

Ecosystem restoration

Initiator

Council

Funder

Marlborough District Council

Budget

$301,000

Design group

Te Ātiawa o Waka-a-Māui Iwi, Marlborough District Council

Salt Ecology, (2021), Schematic outline of the main restoration area showing the general layout of reshaping and planting. Annotated photograph. Located in ‘A summary of salt marsh restoration, Waikawa Estuary, Marlborough report no. 081.
Climate change benefits
  •  Biomass cover loss
  • coastal erosion/ wave attenuation
  • sea level rise
  • storm surge
Societal / socio-cultural benefits
  • Biodiversity health and conservation
  • climate change adaptation
  • disaster risk reduction
  • pressures of urbanisation
Ecological benefits
  • Aesthetic value
  • cultural diversity and history
  • disturbance prevention
  • habitat provision
  • soil building

Summary of case study

The Waikawa Estuary Salt Marsh Restoration project began by increasing the cover of cobble and substrate over 800 m² in the upper tidal portion to reshape the estuary shoreline, which had been eroded by wave energy. Following this restoration, planting efforts were undertaken to expand the existing salt marsh. The salt marsh area increased by 350%, initially covering 200 m² and now spanning 900 m² (Salt Ecology 2021). This expansion has improved biodiversity by introducing various historically displaced estuarine plant species and provided shoreline protection from erosion. The erosion of the shoreline, especially near residential areas backing onto the estuary, was a significant factor driving the restoration efforts.

The planted vegetation buffer has facilitated adaptation to climate change, as the salt marsh is suited to changing tidal conditions. With sea level rise, lower vegetation is specifically planted to withstand submersion in water, with some plants capable of absorbing salt water. Salt marshes can keep pace with sea level rise through accretion. As the salt marsh establishes, plant material is deposited, and sediment is captured, allowing the marsh to move uphill and further inland as the sea rises over time (University of Massachusetts Amherst 2017).

In terms of mitigation, the salt marsh restoration project has reduced the increased wave attenuation within the estuary (Salt Ecology 2021). This improvement has resulted in better flood control, ensuring greater safety for local residents as storms become more frequent.

The Marlborough District Council collaborated with Te Ātawa iwi to identify site enhancement opportunities, integrating indigenous knowledge to address historical damage to the estuary and achieve better biodiversity conservation and health outcomes. This collaboration facilitated the reintroduction of multiple historically displaced estuarine plants into the area.

A summary of the project indicated that the restoration costs were offset by locally depositing the degraded material as part of reshaping the shoreline. This approach provided future-proofing cost benefits for long-term impacts, as the restoration work has minimized the potential for coastal erosion (Salt Ecology 2021).

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References
  • Salt ecology. (2021) A summary of salt marsh restoration, Waikawa Estuary, Marlborough (Report No. 081) prepared for Marlborough District Council, August 2021.
  • University of Massachusetts Amherst. (2017). Ecology and vulnerability, coastal: salt marsh. https://climateactiontool.org/ecogroup/coastal-salt-marsh#:~:text=Salt%20marshes%20are%20vulnerable%20to,migration%20inland%20and%20uphill%2011.

Further resources:

<< Constructed salt marsh/mudflats