Discover the Harbour
History
The Porirua Harbour and Catchments Community Trust (PHT)
also known as the Porirua Harbour Trust.
Porirua Harbour and Catchment History
Harbour formation
The Porirua Harbour was formed between 16,000 and 10,000 years ago when sea levels rose by 120 meters during the “Great Thaw” after the ice-age, drowning the land and river systems that flowed westward. (Mackintosh, A, 2011). Before that time the coastline was likely to be 20 to 40 kilometers further west. The climate at the end of the ice-age was much colder, with a coastal plain covered in scrub and tussock land extending past the location of mana island.
The Meaning of “Porirua”
The name Porirua comes from the Māori term parirua, meaning “twin flowings of the tide.” This refers to the harbour’s two arms — the Pauatahanui Inlet and the Onepoto Arm — both once thriving ecosystems teeming with life.
Early History
Before settlement, The estuary was largely sandy with clear waters supporting extensive seagrass and shellfish beds, and abundant fish and birdlife, including moa and kiwi (Stevens & Robertson, 2013). At that time, the harbour was surrounded by tall, dense podocarp/broadleaf forest (see Appendix 1) with wetlands in low-lying areas and saltmarsh around the estuary margins, home to native birds, including moa.
First human arrivals
Ngai Tara were the first human arrivals to the Whaitua (Bellingham, 1998). They initially settled near Paremata Point in the Pauatahanui arm of Te Awarua-o-Porirua Harbour around 600 years ago (Blaschke et al., 2010).
The harbour and its surrounds provided abundant food for the first human inhabitants. They dug in the sands for tuangi (cockles) and pipi, trapped birds, hunted moa, netted whitebait, caught marine fish with baited lines, and cultivated kumara crops (Bellingham, 1998). Around 1600, Ngai Tara were displaced by Ngati Ira. Gradually the abundance of food sources began to diminish. Forests were cleared to allow for kumara cultivation, particularly on low east-facing slopes. Around a third of the native vegetation in the Pauatahanui was cleared for these purposes (Blaschke et al., 2010).
Settlement and decline of biodiversity
In the early 19th century Ngati Ira were displaced by Ngāti Toa and large-scale settlement from Britain began in the following decades. Over the course of the next century most of the remaining native forests were burnt, most wetlands were drained, and the land was converted to pasture for farming (PCC, 2015). By the 1940s over 80% of the catchment was grassland. However, since then, the predominance of grassland has reduced. The extent of woody vegetation has increased to over 40% of the catchment, partly due to the planting of pine forests through the 1970s to 1990s, but also due to the retirement of farmland (Blaschke et al., 2010).
However, the loss of forest brought severe ecological consequences. Many native birds that dispersed seeds, along with geckos, skinks, penguins, muttonbirds, and marine mammals, disappeared from the area.
Environmental Impact
Clearance of forests and drainage of wetlands has greatly increased sedimentation rates to the harbour. This has led to a gradual shift from clear waters and clean sands to muddier substrates and more turbid (muddy) waters in the estuaries (Stevens & Robertson, 2013). Reclamation and other harbour edge modifications (eg, for roads, rail, and commercial development) have also resulted in a major loss of habitat for coastal and marine plants and wildlife (PCC, 2015). Many of the remaining shellfish beds have been contaminated by pollutants, and saltmarsh and seagrass beds have been lost. Saltmarsh habitat, for example, has been reduced by around 50% in the Pauatahanui Inlet and over 95% in the Onepoto Arm (Blaschke et al., 2010).
Sedimentation
Urbanisation brought further changes and reduced the harbour’s tidal prism — the volume of water flowing in and out with the tide.
By the mid-1970s, sedimentation rates had surged to 6–9 mm per year, and in parts of the Pauatahanui Inlet up to 10–15 mm per year. At those rates, scientists estimated that the inlet could become completely infilled within 145–195 years, and the Onepoto Arm within 290–390 years (Gibb, 2009; 2011).
A Legacy of Restoration and Action
While the legacy of degradation is significant, the future is more hopeful.
Today, the community, councils, and organisations such as PHT (Porirua Harbour and Catchment Community Trust) are working together to restore the health of the harbour and its ecosystems through education, collaboration, and on-the-ground action.
Learn More
Discover more about Porirua’s rich natural and cultural heritage through the links below: