Groundwater levels update for Central Plains area
July 17, 2006
Groundwater levels update for Central Plains area of Canterbury region
Since Environment Canterbury’s last groundwater and river flow update at the end of May this year, good May rainfall and June/July snow melt has helped change the situation for spring-fed streams in the Central Canterbury/ Ellesmere catchment. In particular, the Irwell River, which has been dry since February 2005, is flowing again.
- ECan records for July show that, in general, there has been a moderate to strong recovery of groundwater levels in shallow and moderate depth aquifers, resulting from the rainfall and snowmelt that occurred in May and June.
- Deep wells in the Central Plains between Te Pirita and Darfield are showing less evidence of recovery and some are still setting new monthly records, indicating the recovery in groundwater levels is still weak.
- The expected strong recovery in shallow and moderately deep wells is also due to the recharge from rivers such as the Selwyn, which began to flow in its middle reaches towards the end of June.
- Spring-fed streams such as Harts Creek are now flowing at about 2000 litres per second, the first time it has risen above its minimum flow of 1000 litres/second since October 28, 2005. (The mean flow for Harts Creek is 1952 litres/second).
- At Coes Ford, the Selwyn River is flowing at about four cubic metres per second.
- The Irwell River is now flowing for the first time since February 2005, going from dry in May to trickles and puddles and now about 100 litres/second flow.
- Rainfall data from National Water and Atmospheric Research for May and June indicate that the Lincoln site received about double the mean rainfall, whereas the rainfall in the period January to April was at about mean levels. In contrast, the rainfall at Hororata has only been at about mean levels since the summer.
- Soil moisture data, also from Lincoln indicate a strong soil moisture surplus since mid-May.
- Groundwater levels in all five of the West Melton groundwater zone monitoring bores are above the measure at which pumping restrictions are required - a turnaround from the end of May.