This Canterbury river lies between the Rakaia and Hurunui Rivers, with its catchment on the main divide and its mouth 8 miles north of Christchurch. The larger tributaries to the Waimakariri all flow from the north and are, from west to east, the Bealey, Poulter, and Esk. The only tributaries from the south of any consequence are Broken River and Kowai, both of which are considerably smaller than any of those from the north. On rare occasions, usually in mid-winter, short stretches of the Waimakariri River up-stream of the Esk have been dry for brief periods. The catchment is about 1,000 sq. miles in area and runs for 30 miles along the main divide from the Foy Pass in the north (leading into the Taramakau) to the Harman Pass at 4,316 ft in the south (leading into the Taipo). Like the other large Canterbury rivers, such as the Rakaia and Rangitata, the Waimakariri is snow fed and generally unaffected, or but little affected, by south-west rain. It is in fresh during north-west wind conditions which are more common between October and March. The average flow at the main road bridge is 2,000 – 2,500 cusecs; the highest recorded flood was in excess of 120,000 cusecs and the lowest flow recorded is 1,400 cusecs.
For the last 30 miles of its course the Waimakariri leaves its gorge in the hills to flow across the Canterbury Plains and enter the coast near Kaiapoi. Small coastal ships are able to cross its bar with some difficulty and use the port of Kaiapoi.
The only railway line to Westland for the most part follows the Waimakariri as far as its junction with the Bealey River where it turns up that river to pass beneath Arthur's Pass at 3,020 ft via a 5½-mile tunnel. The main road to the West Coast follows the same route westward from Cass, but east of Cass it swings several miles to the south to follow the Broken River basin and Porters Pass.
It is generally accepted that the Maori name for the river means “cold water”.
by Henry Stephen Gair, M.SC., New Zealand Geological Survey, Christchurch.