The Manawatu aquifers, North Island, New Zealand: Clarification of hydrogeology using a multidisciplinary environmental tracer approach

Abstract

Abstract:A recently developed approach to carbon isotope methodology (process recognition via isotope diagrams) is applied in a multidisciplinary study of precipitation-recharged aquifers of the lowlands-plains area of the Manawatu (south-west North Island). Urban and rural areas rely on groundwater from the upper levels of a deep basin sequence comprising marine and terrestrial sediments of Pleistocene age. Hydrochemical and isotopic ( 18 O, 3 H, 13 C and 14 C) data are merged with known details of geology and hydrogeology to reveal two separate confined aquifers within the depth range to 200 m. The shallower of these, below unconfined, locally recharged groundwater, is recharged on the foothills of the Ruahine Range to the north-east of the study area; flow direction is NE-SW. The deeper confined aquifer is recharged on the Tararua Range to the immediate east; flow direction essentially is transverse (SE-NW) to that in the shallower aquifer. Two processes are identified as dominant contributors to concentration and isotopic composition of dissolved inorganic carbon (DIC), namely addition of CO 2 from decay of organic materials and carbonate dissolution. Limitations of carbon isotope methods in determining residence times are illustrated by the data. Although the confined groundwater is essentially tritium-free, only a few samples showed conclusive evidence of significant ageing on the time-scale of 14 C.

Paleogroundwater in the Moutere Gravel Aquifers Near Nelson, New Zealand

“…Taylor and Evans (1999) reported a 14 C age of 31,000 yr for groundwater at a depth of 238.4-241.4 m in the Whenuakura Formation near Hawera. Another deep groundwater at Shannon was reported as having a 14 C age of 40,000 yr (CB Taylor, personal communication; see also Taylor et al 2001). Both bores are in sedimentary formations.…”

Sketch-based interface and modelling of stratigraphy and structure in three dimensions

“…Reservoirs deposited in shallow-marine environments are important groundwater resources in many areas of the world (e.g. Taylor et al 2001;Mayo et al 2003;Huysmans et al 2008;Fahad Al-Ajmi et al 2015) as well as oil and gas reservoirs and targets for geological CO 2 storage (e.g. Jackson et al 2009;Sech et al 2009;Ashraf et al 2013).…”