Late winter groundwater levels vary widely
August 25, 2006
Late winter groundwater levels vary widely from coast to the mountains in mid-Canterbury (ie between the Waimakariri and Ashburton rivers)
“The good news is that substantial recharge created by rainfall and snowmelt means that groundwater levels in shallow and moderate-depth wells have recovered from the summer season’s record lows,” says ECan hydrogeologist Dr Howard Williams. “The bad news is that groundwater levels in deep wells (100 metres or more) on the Central and Ashburton plains are still showing little sign of recharge as yet and are at historically low levels for this time of year.”
Some aquifers remain at record low levels, Dr Williams says.
Between the Waimakariri and Ashburton rivers, rainfall and snowfall have substantially recharged the groundwater system. According to NIWA records, rainfall has generally been above mean or average values for the time of year, especially near the coast. “These recent wet conditions have provided some welcome recharge but the benefits are, to date, observed only in wells of shallow to moderate depth,” says Dr Williams. “Many years of above average recharge would be required to restore groundwater levels in deeper wells to previous long-term average levels.”
Monthly monitored groundwater levels in the Central Plains illustrate a variety of responses to this rainfall recharge. Shallow wells, such as a 16 metre-deep well south of Dunsandel, indicate a rapid and sustained response to near mean levels from record low levels in May 2006. This well’s groundwater level is higher than it has been for four years, but still below the long-term average.