Lake Brunner, named after Thomas Brunner, has the Maori name Moana Kotuku, meaning “lake of the white heron”. It lies in a glacial basin, 280 ft above sea level, 17 miles west of Greymouth. Elongated north-north-east, with a maximum length of 5.6 miles and a maximum width of 4.4 miles, the lake has an area of nearly 15 square miles. For the most part the depth of the lake is more than 100 ft. the maximum being 357 ft. The basin was formed during the Last Glaciation by glaciers that spread northwards from Taramakau Valley on either side of Mt. Te Kinga, between Hohonu Range and the Southern Alps. Crooked River, draining from the Alps, has a large, growing delta that fills much of the eastern side of the basin, and the small Orangipuka River is building a delta out from the glacial valley between Hohonu Range and Te Kinga. East Hohonu River, draining from the granitic Hohonu Range, has a much smaller delta. The mountains and high morainic country to the west of the lake are covered with native bush; tussock and grass cover the morainic country to the north and east, and the extensive deltas are mainly swamp. Arnold River drains the lake into Grey River, hydro-electric power generated at Kaimata being based on a normal flow of 1,200 to 1,500 cusecs. The minimum discharge is 700 cusecs and the maximum measured discharge is 5,500 cusecs, but in extreme flood the discharge is likely to be about 8,000 cusecs.
by Frederick Ernest Bowen, B.SC.(DURHAM), New Zealand Geological Survey, Otahuhu.