Water-table geometry and related groundwater recharge near Halkett, Waimakariri River, New Zealand

Abstract

Observations on groundwater levels south of Halkett on the Waimakariri River in the South Island of New Zealand have revealed the existence of a superficial, unconfined aquifer and an apparently confined aquifer lower down, instrumental in massive recharge of groundwater below the coastal Canterbury Plain. At a Hydraulic Gradient of 1 a velocity of up to 15000 m/day has been measured to occur through clean-washed gravels. A small inflow from the north bank to the riverbed has been measured. Close to the riverbed a layer of lower permeability connects the river channel to the unconfined aquifer. Presumably this is due to small-particle influx from the river channels. Water seeps from the river channels to underflow from where it seeps away to recharge underground aquifers. The indications are that the rate of recharge can exceed the rate of feeding to underflow from the river channels at low stages.