Effects of Geothermal Induced Subsidence

Abstract

Subsidence is a consequence of large scale geothermal development, although the magnitude varies greatly between fields. Subsidence is not unique to geothermal fields: it is covon where fluids (oil or water) are drawn fiom aquifers. The greatest subsidence (measured by both area affected and cost of mitigation) arises fiom withdrawal of groundwater for irrigation or municipal use. Geothermal subsidence can be substantial - many metres - but generally has little practical consequence. Wairakei maximum subsidence is about 15 m, but the effects are relatively slight, whereas much less subsidence at Ohaaki means that the Waikato River may inundate adjacent land and structures. Although the subsidence may be relatively large (tens or hundreds of millimetres per year) because it occurs over distances of kilometres, specialised survey techniques are required to measure it accurately.