Scientists model risks to Marlborough's main aquifer
Wednesday, 27 December 2017
The best brains in Europe cannot say if recent earthquakes have damaged one of Marlborough's major sources of fresh water.
Although, German scientist Dr Thomas Wohling was able to say one of the region's most valuable natural resources could not be taken for granted as a limitless supply of water.
Wohling said nobody knew what changes might have been forced on the aquifer with recent earthquakes, but the impact on the Wairau River and Wairau Aquifer was now being investigated.
The Wairau Aquifer is the main groundwater system underlying the Wairau Plain and a source of irrigation, drinking and stock water. It powers the shower for homes in Blenheim, Renwick and Woodbourne.
**READ MORE:
* Researching link between Wairau River and aquifer
* Renwick aquifer at 30-year low**
It is the most extensive and important groundwater resource in the region by far, and Wohling was called in to work out why the aquifer was losing volume and whether irrigation restrictions were adequate.
Wohling is an internationally recognised specialist in how aquifers work and why and when they could fail. He leads several research programmes at Dresden University, in Germany, where his computer flow model of the Wairau River and Wairau Aquifer was developed.
His team in Germany could not determine the impact earthquakes had on the Wairau Aquifer. Hydrogeologist Scott Wilson, of Canterbury's Lincoln University, was also involved, along with water experts at the Marlborough District Council.
Wohling's work would help in protecting groundwater quality and that of aquifer springs such as Spring Creek which had declined by about a metre since 1982.
If this continued spring flows would be lower and wells might have to be deepened, especially in western parts of the Wairau Aquifer. This could have implications for seawater intrusion along the east coast of southern Marlborough.
Wohling said there was also a lack of certainty around the role river management and floodway activities, such as gravel extraction or sediment changes, contributed to changes in the Wairau Aquifer recharge mechanism.
'The modelling gives valuable insights into the storage properties of the Wairau Aquifer,' Wohling said.
He said storage could be measured in months rather than years, as previously thought.
'For any recharge, the timing of the low flows matter as it correlates to the low flows in the Wairau River which causes the depletion,' he said.
Wohling said this was exaggerated by irrigation draw off, but if river flows stayed at more than 20 cubic metres per second then depletion in the aquifers would not be seen.
The modelling showed it was not just climate affecting the changes in the aquifers, and its water storage capability was vulnerable to low flow periods.
'This type of modelling has enough information to be able to predict changes. You can ask it questions,' Wohling said.
Crucial information to emerge included confirmation the aquifer was not a long-term storage facility and this decline in storage capability was constant.
Wohling said science for measuring aquifer flow was well advanced and would be ready to test limit setting options in autumn and winter 2018 for inclusion in the Marlborough Environment Plan.