The Wairoa River has a catchment area of 1,415 sq. miles, almost all of it soft Tertiary rocks, and much of it rugged and forested. Lake Waikaremoana is formed in the rockfall-dammed headwaters of a tributary, the Waikaretaheke, which has a confluence with the Waiau River 14 miles from the coast. The combined catchment of these two is 545 sq. miles. Two large tributaries drain from the north, the Ruakituri River, from Maungapohatu (4,482 ft) and the Hangaroa River with its headwaters only 15 miles west of Gisborne. The shape of the catchment is that of a nearly regular triangle with its apex on the coast of Hawke Bay. Much of the catchment of the Wairoa is very little known and is probably the most difficult country in the North Island.
Although the minimum flow of the Wairoa River is less than 500 cu. ft. per second, the largest flood on this river, 404,100 cusecs in 1948, submerged the Wairoa traffic bridge and flooded parts of the town to a depth of 3 ft. This flood flow is one of the largest recorded for any river in New Zealand, being exceeded only by floods on the Buller River.
The usual meaning assigned to this name is the literal one – “long river”.
by Thomas Ludovic Grant-Taylor, M.SC., New Zealand Geological Survey, Lower Hutt.