The Mohaka River (catchment 910 sq. miles) drains the complex of mountains from the north face of the Kaweka Range northwards for 35 miles. Two of its major tributaries, the Taharua and the Waipunga, rise on the Rangitaiki Plains on either side of the head of the Rangitaiki River. The third large tributary, the Hautapu, rises on the south side of Maungataniwha (4,491 ft). With the exception of the heads of the Taharua and Waipunga, on the Taupo pumice alluvium of the Rangitaiki Plains, which are low-scrub and tussock covered, the whole of the western catchment of the Mohaka is densely forested, precipitous country. After passing out of the axial range, the Mohaka turns abruptly northwards and flows for 25 miles between the axial range and the limestone-covered dip slope of the Te Waka-Maungaharuru Ranges, before turning to flow into Hawke Bay. The river is everywhere deeply entrenched in spectacular gorges, either in hard rock of the main range or in soft Upper Tertiary mudstones. The lower 17 miles is some 250 ft below broad gravel terraces formed during the last glaciation. Because of the river's deep entrenchment, flood damage is small. The minimum measured flow was 600 cu. ft. per second in 1948, and peak flood was 225,000 cusecs in 1938. The 1938 flood inundated and badly damaged the road bridge on the Napier-Wairoa highway.
The river is crossed by two very spectacular bridges. The railway viaduct, 312 ft high and 911 ft long, is one of five railway viaducts in this area that are more than 200 ft high. A recently completed road bridge on the Napier-Taupo road is 165 ft high and 708 ft long.
The literal meaning of the Maori name is “a place for dancing”. This name is believed to have been brought from Hawaiki and its significance is now obscure.
by Thomas Ludovic Grant-Taylor, M.SC., New Zealand Geological Survey, Lower Hutt.