"The Buller is the major river of the west coast of the South Island and is named after Charles Buller who did much to further the colonisation of New Zealand. Its Maori name, Kawatiri, is believed to mean “deep and swift”, an appropriate description of the river with the greatest flood discharge in New Zealand. ... From its source at Lake Rotoiti (1,997 ft), it flows in a changing but predominantly westerly direction for 105 miles to reach the sea at Westport, crossing the north-trending geologic and topographic grain of the country."
by Frederick Ernest Bowen, B.SC.(DURHAM), New Zealand Geological Survey, Otahuhu. www.teara.govt.nz/en/1966/buller-river/1