The Whakatane River rises in the heavily forested Urewera Country some 3 ½ miles west-north-west from Lake Waikaremoana. Adjacent watersheds are Rangitaiki to the west, the Mohaka to the south, and the Wairoa to the south-east. Ruatahuna lies beside the Whakatane River only 6 miles north of its southern watershed, and here the river is crossed by the Rotorua-Waikaremoana main highway in a more or less extensive clearing in the dense forest. The main part of the river lies in the angle of a major fault which is a northern extension of the Wellington fault. The rocks of the catchment are mainly Triassic and Jurassic greywackes, sparsely fossiliferous, with some Tertiary sandstones at Ruatahuna.
The Bay of Plenty coastal plain extends as a broad valley some distance up the Whakatane River, but above this the river flows through gorge-like topography. It floods more or less seriously once or twice a year, inundating about 1,000 acres of land. The catchment area is 601 sq. miles, with minimum flows of about 200 cusecs, and flood flows of about 30,000 cusecs.
by Thomas Ludovic Grant-Taylor, M.SC., New Zealand Geological Survey, Lower Hutt.