The Ruataniwha Dam may not be needed because there could be an abundance of groundwater in deep aquifers of the Ruataniwha plains, a former GNS Science team leader says.
The Hawke's Bay Regional Council is developing the Ruataniwha Dam with the aim of improving the health of the Tukituki River and providing certainty of water for farmers through dry summers.
Dr Gil Zemansky said he was surprised the council was pushing ahead with a $600 million water storage project without investigating how much water was in the aquifer.
The regional council confirmed it had not done any research into the deep aquifer and there was little information available, but it believed pumping water from any deep source would still deplete flows in the region's rivers.
Dr Zemansky said the council engaged his team of GNS hydrogeologists in 2012 to gain a greater understanding of the Ruataniwha aquifers, but wanted them to work with a model his team considered not fit for purpose.
"Their groundwater model was not deep enough to cover the aquifer. They left out the deeper aquifers.
"So there are wells that are drilled and they go far deeper that their model went, but they just didn't talk about that at all in their model," he said.
Dr Zemansky said his team put disclaimers on their work with the regional council model saying that GNS Science accepted no responsibility for the accuracy or fitness "for any purpose" of the model.
He said the council reviewed their concerns but did not want to take the time to address them and ultimately terminated their contracts.
"The model did not include the deeper 100 metres or so of aquifer which has been described in the scientific literature as including 'highly porous and permeable' limestone and in which some wells have been installed," he said.
Dr Zemansky said how much water was available from the deep aquifer was poorly defined due to lack of research.
"But the information that there is indicates there are some productive limestone aquifers at depth in the Ruataniwha, and there are also wells that have been drilled, not too many, but there are wells that have been drilled that are tapping into that," he said.
Dr Zemansky said if the aim was to provide water security for farmers through dry summers, properly using the available groundwater resource was a much more economical and efficient way of doing it.
Baylis Brothers has been drilling for water in Hawke's Bay for seventy years and managing director Russell Baylis said there was every indication of an abundance of water in the deep aquifers.
Mr Baylis said deep drilling would determine where the bottom of the aquifer is, which has not been identified.
"We believe that we need to drill at least 300-400 metres to get a good idea geologically what's there," he said.
Mr Baylis said it would take three or four deep well holes to determine how much deep water reserves exist.
Using aquifer water would deplete rivers - council
Hawke's Bay Regional Council principal scientist Mark Trewartha said the council had not conducted any research on the deep aquifers for about a decade and little information existed.
But Mr Trewartha said the council believed the aquifers were connected and pumping deep water out would deplete the amount of water in the entire catchment and reduce the minimum flows of rivers.
He said there could be benefits in drilling deep exploratory wells.
"The benefit is it would provide more information. Whether that would translate into another source of water we don't know," he said.
The council was aware of one well which had been dug to 120 metres and found water, but that had the capability of depleting water flows in rivers.
"Simply put, it had the ability to do that, yes. The capability. It depends on how much they pumped and for how long," he said.
Mr Trewartha said it could cost up to $350,000 to drill a single deep well. so it would be an expensive exercise.
About $15 million of mostly ratepayer and taxpayer money has been spent developing the Ruataniwha Dam so far, with the council's investment company HBRIC having less than half the minimum number of farmers signed up to buy the water to make it viable.