Geological challenges and geohazard monitoring of a mega engineering hydropower project in Iceland

Abstract

Geohazards must be considered, assessed and mitigated for all life-cycle phases of most mega infrastructure projects. This paper presents a unique mega engineering project, the 600 MW Kárahnjúkar Hydropower Project in Iceland. The construction site presented several interesting and complex geological and geophysical conditions, such as an unexpected discovery of an active fault in the foundation of the main dam (mega dam) and earthquake activity in a nearby volcanic zone caused by a subsurface volcanic intrusion during the first impoundment. The related apprehensions included predictions of: Persistent movements and opening of faults in the dam foundation causing excessive leakage, large reservoir induced crustal deformation that could trigger volcanic eruption or near field earthquake action such as reservoir triggered earthquakes that might affect the safety of the dam structures. The approach taken to resolve these apprehensions was to undertake specific investigations, assessments and monitoring, through a novel multidisciplinary organization. The focus of the paper is on describing the development and implementation of a holistic multi-source geohazard monitoring program for the main reservoir, Hálslón Reservoir and its dams. The discussion starts with a definition of what constitutes monitoring of geohazards within the framework of the project. This is followed by an outline of the monitoring networks implemented comprising instruments monitoring seismicity (micro-seismic stations and strong-motion instrumentation), crustal movements (continuous global positioning systems and benchmarks), fault movement (extensometers, joint and crack meters), groundwater elevation and leakage. Finally, a summary of key results from the geohazard monitoring is given. The geological challenges and related apprehensions are linked to the relevant research and investigations carried out, the monitoring networks installed, and the results produced, which demonstrate that during and after the first impoundment the key monitored processes were all within the pre-set limits. The case presented is relevant for current and future mega engineering projects as it demonstrates that a monitoring program set up to guard operational safety in the spirit of potential failure mode analysis, will provide important information on geo-environmental impact of a mega engineering project, not only for scientific interest but also for public information.