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Groundwork

01.1 / Public Realm / Civic

Tidal Commons

Reclaimed edge. Shared ground.

Location
Wellington Harbourside
Year
2024
Scope
4.2 HA Estuary Daylight
Area
4.2 ha
Procedural site model — 38° / seed 12.7

Daylighted tidal estuary and permeable public boardwalk reconnecting stormwater marsh to coastal pedestrian flow.

The brief

A decommissioned stormwater outfall was writing 90 litres per second of raw overflow into a tidal basin that had silted to half its depth. The council needed the capacity back; the neighbours needed the fence to come down. We were asked whether both could be true.

  1. Restored saltmarsh channel at low tide with a timber boardwalk crossing
    01The daylighted channel at low tide — 40% of the original marsh footprint reconnected.
  2. Infiltration basin planting reading as a broad soft basin across the site
    02Infiltration terraces step down 1:12 toward the harbour edge.
  3. Rooftop meadow matrix of native grasses over a transit concourse
    03Seed mix trialed on the neighbouring roof before being broadcast here.

[ Approach ]

Four phases on the ground

  1. 01

    Read the land

    Eighteen months of tide gauges, sediment cores and dawn wading. The old channel was still legible under the silt — so the new estuary follows the historic alignment rather than a straight line, and the outfall was moved rather than enlarged.

  2. 02

    Sketch the possibilities

    Eleven options tested against three hard constraints: flood storage, uninterrupted cycle access, and a saltmarsh species palette that could survive being submerged twice a day. Six were discarded on the third constraint.

  3. 03

    Grow the proposal

    A 1:200 physical model in the studio let us watch the tide come in. Terraced reed beds double as flood storage; the boardwalk rides the crest of each terrace so it never closes.

  4. 04

    Steward the delivery

    Two planting seasons of supervision on site. 41,000 oioi and 9,000 pingao went in by hand across the first winter, and the sedum trays on the boardwalk are now self-seeding.

Outcome

Peak storm storage improved by 34% and the foreshore has not been closed to the public since opening, including through two king tides. The saltmarsh has recorded eleven nesting pairs of oystercatcher in the second season.

Flood storage gain
+34%
Marsh reconnected
40% of baseline extent
Native plants
50,000
Public access
2.1 km continuous

Materials

  • Reclaimed greywacke fill
  • Cedar boardwalk on stainless pin piles
  • Oioi / pingao / saltgrass marsh matrix
  • Geotextile-weeded basalt gabion steps

Credits

  • Lead designer — Isla Vance
  • Project architect — Callum Reid
  • Planting design — Maya Chen
  • Marine structure — Tomas Lindqvist
Client
Wellington City Council — Te Atiawa o Te Awa
Collaborators
Tonkin & Taylor, Māpua Environmental Ltd

Site model / plan

The model above is generated from this drawing's height field, which is shared between the shader and the CPU so planting lands exactly on the surface.

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