Geological and fracture flow modelling of the Pukekohe aquifer system

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White, P.A.; Reeves, R.R.; Zhan, X. 1996 Geological and fracture flow modelling of the Pukekohe aquifer system . Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 96/08 64 p.

Abstract: A three-dimensional computer model of the volcanic lithologies in the vicinity of the Pukekohe volcanic centre predicts two basalt layers which coalesce underneath Pukekohe Hill. These two basalt layers correspond to the Franklin Basalt and the Bombay Basalt. The model estimates a groundwater resource volume of 0.3 x 109 cubic m within the Auckland Regional Council management area. This volume is equivalent to 43 years' water use within the management area, based on Auckland Regional Council water allocation figures. An estimate of net groundwater recharge is 91.5 mm.yr-1 based on existing environmental data. Rainfall is calculated at an average of 1356 mm.yr-l in the area. Stream discharge is estimated as an annual average equivalent of 524 mm. yr-l. Evapotranspiration is the poorest determined of the three components of the groundwater recharge model. Estimates of evapotranspiration range between 728 mm.yr-l and 847 mm. yr-l. A steady-state heterogeneous groundwater flow model of the Pukekohe area predicts a groundwater head distribution that is similar to a steady-state heterogeneous model including fractures. (auth)