Mansergh, G.D.; Findlay, R.H. 1977 The geology of State Highway 73, upper Otira Valley. NZMS 260 K33. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 276 15 p.
Abstract: Between mileages 95 and 96 State highway 73 is routed to pass over an ancient rock slide on the eastern bank of the Otira River. The rock slide, which probably dammed the Otira River, covers an area of some 56 hectares and is itself covered over much of its surface by colluvium. The Otira River is actively undermining the colluvium exposing the rock slide to erosion and presenting stability problems within both the colluvium and the rock slide material on which the road is sited. The geometry of the rock slide has not been established and methods are suggested for investigating this. Without this additional detail no practical solution can be proposed for stabilizing the rock slide or scree. The 'inferred' geometry of the slide is such that no practical solution can be proposed, and it is suggested that a new alignment be chosen for the roadway. A geologically more suitable route would be along the floor of the Otira valley on the western bank. (auth)
