It is often taken for granted as a limitless supply of water, but monitoring shows that in the past 30 years the Wairau Aquifer has dropped by about a metre and Council staff are working with scientists in New Zealand and Germany to find out why.
Their investigations are focusing on the relationship with the Wairau River and how it seeps into, and recharges, the aquifer.
There are several factors that might be causing the drop in the aquifer:
- Improved flood control and drainage has reduced the land area for river water to spread and seep into the aquifer
- Gravel quarrying has lowered the channel level relative to groundwater in some areas
- The increase in water taken from the river or pumped from the aquifer for irrigation
- Wairau River flows may have changed
It would be easy to point the finger at grapegrowers and farmers but monitoring shows the aquifer level continues to drop during the winter when the irrigation is turned off.
Researchers are gathering data from wells between the Waihopai River and Tuamarina for a computer model to estimate aquifer recharge rates that will help manage our water resources. This knowledge is important because a long term decline in the aquifer may cause springs to dry up and well levels to drop further.