2007 – Wave seiching and run-up effects in Lake Aviemore due to seismotectonic displacement of the lakebed

M.G. Webby, C.J. Roberts and J. Walker

The Waitangi Fault passes under Aviemore Dam and Lake Aviemore in the Waitaki Valley in the South Island of New Zealand. Several studies were undertaken in the period 1999-2004 to understand the geology and faulting in the Waitaki Valley and, in particular, to determine the potential for future movement on the Waitangi Fault (Walker et al. 2004). As part of the Aviemore Dam Seismic Safety Evaluation (ADSSE) Project, a numerical hydrodynamic study was undertaken to analyse the pattern of seiche waves generated by fault displacement and to determine the potential wave run-up on the dam face to overtop the dam.

Ground displacement along the Waitangi Fault gives rise to initial wave trains on the lake surface travelling in opposite orthogonal directions away from the fault line and approximately parallel to the axis of Aviemore Dam. These initial wave trains are refracted by the lakebed as they approach the eastern and western lake shorelines and are then reflected off these shorelines. The reflected wave trains interact to create a very disturbed lake surface before a long-period seiching response is set up due to repeated lakeshore reflection. The seiching response is a bimodal one, with a cross-lake component and an along-lake component. The along-lake seiche waves run up on the relatively steep embankment part of the dam and on the vertical face of the concrete gravity part.

Keywords: Seismotectonic, fault, displacement, lake, dam, numerical, hydrodynamic, model, seiche, wave, solitary wave, wave run-up, dam overtopping.