Riddolls, B.W. 1972 Slope stability on North Island main trunk railway north of Waimiha. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 135 13 p.
Abstract: Difficulty has been experienced in maintaining alignment of the railway between Waimiha and the south portal of Poro-r-tarao tunnel. The railway, which follows the valley of the Ohinemoa Stream, is situated on old landslides in several places. Gradual downhill movement is occurring because some of these landslides are at present unstable. The landslides appear to be mostly debris slides composed of mudstone, and probably originated several thousand years ago as a result of oversteepening of slopes due to rapid downcutting by Ohinemoa Stream. While marginal stability is likely to have persisted since that time, many slides may have become more unstable over the last 70 years owing to alterations of natural drainage by the activities of man. Stability should improve if better drainage can be maintained in the affected areas. Two localities south of Te Kuiti at which the railway could be affected by slope instability may also be partly remedied by improving drainage conditions. (auth)
