City of Launceston Administrative AreasSmoke Free AreasLaunceston LGA Pre1985Central Business DistrictLaunceston LGACentral Activities DistrictSuburbsCouncil Owned LandPublic Land

At the request of the Tasmanian Hydro-Electric Commission a geophysical survey was carried out along a tunnel line at Trevallyn, a suburb of Launceston, North Eastern Tasmania. The excavation of the Trevallyn tunnel is part of the Hydro-Electric Trevallyn Power Development project to utilise the water of the South Esk river for generation of electric power. The construction works are already well advanced. A dam is being built on the river at the Second Basin. Water from the catchment will be diverted through a tunnel two miles long to a power station situated at sea level on the Tamar River. A locality map is given in Plate 1. Three geophysical exploration methods, electrical, seismic and gravitational, were used to locate deeply weathered and fractured zones in the dolerite bedrock, through which the tunnel is being driven.