Wairoa River

The river is formed by the confluence of the Hangaroa and the Ruakituri rivers which meet at Te Reinga Falls, and it flows 65 km to drain into the sea near Wairoa township. Mean annual flow is 65.545 cumecs (at Maramaru NIWA site). The upper boundaries of this large catchment lie in the indigenous forest of Te Urewera National Park. The main tributaries of the Wairoa in the west and north-west are the Waiau River, the Waikaretaheke River draining Lake Waikaremoana, the Mangaaruhe River, and the Ruakituri River. The main tributaries on the eastern side of the catchment are the Hangaroa and Mangapoike rivers.

The Wairoa catchment is dominated by fine, soft sedimentary geology – sandstone and siltstone. The exception is the Waiau River in the farthest north-western part of the region, which has its sources in hard sedimentary greywacke and argillite. Only some small tributaries in the area of the Wairoa River mouth have alluvial deposits of gravels, sand and mud. The high amount of rainfall and comparably low infiltration rate in this catchment result in relatively low base flows, and an increased incidence of floods.

The climate in the upper Wairoa catchment is characterised by extremely high rainfall and cool temperatures while the lower catchment has a warmer, drier climate.

The land-use in the catchment is mostly farming, predominantly hill country sheep and beef farming. Forestry is the second largest land-use. The township of Wairoa is on the lower reaches of the river. Discharges from the meat processing plant and municipal sewage treatment enter the river below the township and are subject to consents, with stricter conditions being imposed on the freezing works consent. The river flats in the lower reaches are used for cropping, horticulture and pasture.

A wide range of fish is present in the catchment, including native species valued for fishing and as traditional Māori kai (food). The critically threatened longfin eel and the koaro (which is rare in Hawke’s Bay) can be found in the Wairoa catchment; also the inanga, bluegill bully, yelloweye mullet, shortfin eel, torrentfish, lamprey, Cran’s bully, common bully, giant bully, redfin bully, mullet, chinook salmon, common smelt, and black flounder. There are large populations of both brown and rainbow trout. The Ruakituri River has large trout populations in the middle and upper region, the Hangaroa River has trout in the upper reaches, and the Waiau River has populations of both trout species throughout its length, with high numbers of large sized trout in the remote upper reaches.