Abstract

Glencoe Stream is a small watershed draining slopes of the Sealy Range in the Southern Alps, New Zealand. It flows alongside the Hermitage Hotel at Aoraki Mount Cook Village which is a world heritage site with spectacular views towards Mount Cook. The stream is very active and poses a debris flow threat to the hotel as shown by the serious event which occurred in December, 1957. It has developed a debris and alluvial fan in post glacial time which has spread out over the recent glacial deposits in the Hooker valley, to which Glencoe Stream is a tributary. In 1996 the authors studied the geotechnical hazards in the watershed and designed engineering works to protect the hotel complex. An approximate relationship was developed between the magnitude and frequency of flood and debris flow events. The size of events and estimated return periods, together with the assessment of severity or consequences, allowed the level of risk to be addressed. Mitigative measures to protect against the hazards to provide a level of protection comparable to those in other jurisdictions in mountainous terrain were addressed. Design parameters were taken to be a debris flow with a 1:200 return period, a pure water flood of 25 cumecs, and a required debris storage volume of 100 000 m3. Active mitigative measures considered included engineered structures to channel the events into a developed storage area and passive measures included land use zoning and planning restrictions. The engineered measures do not provide protection against extreme events and a residual risk always remains to developments on the fan. The engineered measures were completed in 1999 at a cost of NZ $1.3 M and the zoning to allow controlled development has also been put in place.

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