Ōpāwaho / Heathcote River

The Ōpāwaho / Heathcote River here in Christchurch, New Zealand, gets most of its water from springs near Templeton Road. Its catchment area can stretch all the way west to Yaldhurst and Pound Road during wet weather, draining about 100 square kilometers. The river itself winds around the base of the Port Hills, flowing from west to southeast, eventually reaching the Avon Heathcote Estuary / Ihutai before it empties into Pegasus Bay.

The largest tributary is the Cashmere Stream, and you've also got Curletts Stream flowing through an industrial area before it joins the Ōpāwaho. The river passes through a lot of suburbs, including Wigram, Hillmorton, where those main springs are, and then Hoon Hay, Spreydon, Cracroft, Cashmere, Beckenham, St. Martins, Opawa, Woolston, and Ferrymead.

The original Māori name, Ō-pā-waho, means 'The Place of the Outward Pā' or 'The Outpost'. That refers to a fortified settlement that was an outpost to Kaiapoi Pā, built on higher ground just downstream from where the Opawa Road Bridge is now. It was a crucial resting spot for Ngāi Tahu people traveling between Kaiapoi Pā and Te Pātaka o Rākaihautū, which is Banks Peninsula. This area was also a rich source of food, especially tuere, or blind eel, and kanakana, which are lamprey. Before urbanization, the river used to meander through extensive wetlands. Mid-19th century survey maps, called the 'Black Maps,' show that the river corridor was low-lying and very wet, with lots of flax, toetoe, raupō, tutu, ferns, and tī kōuka, or cabbage trees. The iwi of Waitaha, Kāti Māmoe, and Ngāi Tahu had a close relationship with the river over centuries, using it for food and transport. They gathered waterfowl and forest birds from the swamp forest and set traps for inanga (whitebait), pātiki (flounder), and tuna (eel). The European name, Heathcote, is named after Sir William Heathcote, who was the secretary of the Canterbury Association.

The river provided a lot of water for industries in Woolston, like wool scouring, but it became increasingly polluted until the Woolston industrial sewer was built in 1966. Flooding was also a big problem until 1986, when the Woolston Cut was created. This 510-meter cut allows floodwaters to bypass a long loop of the river, which is now called the Woolston Loop. That project cost NZ$2 million, but it caused trees on the riverbank to die as far upstream as the Opawa bridge, and the banks collapsed. They found out the trees died from saltwater moving further upstream with each tide, which killed them. The soil structure also changed, with a sodium and calcium exchange in the clay molecules weakening the soil, and tunnelling mud crabs extended their range up the river, further weakening the banks. To fix this, the Woolston Tidal Barrage was built at the upstream end of the cut, and it only opens during floods. Under normal conditions, the Heathcote still flows through the Woolston Loop. Even with the cut, parts of the Ōpāwaho / Heathcote River have flooded during heavy rainfall.

In 2008, the Christchurch City Council consulted on a management plan for the section of river between Colombo Street and Opawa Road, which was adopted in 2009. The water quality in the Ōpāwaho / Heathcote River was rated poorly by the council in 2020, with eight of the thirteen worst monitored sites in Christchurch rivers or streams being in this catchment.