Assessment of fibre optic network vulnerability to geohazards in the Waitaki valley and Mackenzie Basin.
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The Waitaki Hydro Power Scheme is located in the Mackenzie Basin and Waitaki Valley of the South Island of New Zealand. It is a linked series of lakes, dams, canals, and power stations designed to produce electricity for the New Zealand power grid. Meridian Energy Ltd own and operate the majority of the scheme. A key part of their power generation operation is a fibre optic cable loop, buried approximately 1 metre deep. This cable creates a communication network used to operate the scheme remotely and safely. Loss of the cable would result in severe impact to operation for Meridian Energy. Along its length the cable passes through a variety of terrain which exposes it to a range of potential geohazards. The study considers the hazards that could threaten the integrity of the fibre-optic communications cable.
The study area includes the Mackenzie Basin, Waitaki Valley and Hakataramea Valley. This region was formed by recent tectonic and glacial processes. Tectonic processes are still active across the study area, as are alluvial and slope movement processes. The study area is characterised by highly fractured Torlesse bedrock, overlain by Tertiary basin-fill sediments, which in turn are covered by varying thickness of glacial deposits and post-glacial fluvial and colluvial soils.
The area can be broken into four distinct terrain units using an engineering terrain analysis approach. The differing terrains are defined by a combination of topography, geology, and active surface processes. The terrain units are Formerly Glaciated Terrain, Glacial Outwash Surfaces, Contemporary Alluvial Valley, and Bedrock Hillside. Conceptual ground models for each terrain unit were used to identify potential geohazards. A combination of remote sensing analysis and ground reconnaissance showed the spatial distribution of shallow geohazards. Ground deformation, seismically-induced slope failure, liquefaction, static rockfall, rainfall-triggered debris flows, and flooding were identified as being the primary hazards in the area. Detailed mapping of these hazards highlights the sections of the cable route vulnerable during geohazard events.
Preliminary laboratory testing of the cable strength allowed the determination of strain thresholds for cable integrity. This allows a preliminary understanding of geohazard fragility thresholds.
The information collected and collated in this study can be utilised to perform a comprehensive risk assessment for the cable route.