GWRP supports efforts to evaluate the use of groundwater age data to improve our overall understanding of recharge and thereby improve groundwater availability studies through the following activities: Groundwater samples will be collected and analyzed to fill important data gaps in existing groundwater availability studies and to demonstrate age-dating techniques that could be used in future studies to understand recharge conditions.
Shallow ground-water systems are commonly used for drinking water sources and they make up a large part of the baseflow in rivers and lakes.
H measurements (in the 1970s) showed non-zero concentrations in the deep groundwaters, but these were discounted at the time as due to “at most a few percent of very young water”.
However, reinterpretation in light of the C ages in this work has revealed much younger ages for the deep waters than was previously believed, with average ages of 38 years in 1971, 71 years in 1976, 98 years in 1985, greater than 120 years in 1986, and greater than 150 years in 1993–1994.
Mean ages measured since have gradually increased showing increasing upflow of much older water from depth – this water has 10–15% rainfall recharge and is sourced from the inland plains region.
There is now (in 2006) a steep gradient in age from west to east across Christchurch (from 300 years to 1400 years) showing that a large body of much older, deeper water is stored on the seaward side of the system where the deep aquifers are blind.