Hancox, G.T. 1973 Tokaanu Penstock Slope geology and groundwater seepages. Lower Hutt: DSIR, New Zealand Geological Survey. New Zealand Geological Survey report EG 174 9 p.
Abstract: Following the commissioning of the Tokaanu Tunnel in July 1973, springs and seepage areas developed on the penstock slope between anchor blocks 4 and 5. Total water flow from this area averages about 250 gals/min. At the same time there is also a marked increase in water-flow from the access adit for the Tokaanu Tunnel. During the frist three months after flooding of the tunnel flows from the adit have arranged about 300 gals/min. In this report the geology of the Tokaanu penstock slope is outlined and the relationship between the geology and the springs is also discussed. Remedial measures (drainage and observation drill holes) undertaken to date aer referred to briefly. Four plans accompany this report. (auth)
