The efforts of geologists who have modelled materials lying underneath the Heretaunga Plains have played a primary and integral role in better understanding water issues in Hawke's Bay, an expert has said.
GNS Science mapping geologist Dr John Begg gave a presentation at the recent water symposium to give thosein attendance a better understanding of the distribution and function of underground gravel layers and fine grained materials.
Having mapped and modelled the Bay for three years as part of an urban geological mapping project, Dr Begg said geologists' role in water quality issues was to provide water experts with information about the materials that ground water resides in.
"We know the materials that stop the surface water mixing with those underground aquifers. So if we can outline the distribution of those materials under the ground then it provides the groundwater people with a fantastic skeleton that they can build their ground water models on," he said.
Dr Begg said a key element in the underground equation was the role of the fine grained materials (aquitards) which sit atop the gravel layers (groundwater aquifers) and essentially seal the gravels to prevent water escaping to the surface and surface water mixing with aquifer water.
"In some places, the seals are modelled as leaky, or incomplete and this has consequences for the groundwater quality. So understanding the three dimensional relationships between these materials is very important and an early step in better quantifying the groundwater resource."
He said while breaches of the aquifer can be natural, drainage from roading, industrial or agricultural areas have the ability to saturate materials sitting above the fine-grained materials and the potential to leak through any breaches and contaminate the water below.
Through studying the distribution of underground materials geologists could identify areas where there may be difficulties and give this information to water experts so they could investigate the problems, Dr Begg said.
"The resource is there for good, sound geological reasons. We understand why it's there and we can map the distribution of the materials, therefore we're in a good position to start better understanding the hydrogeology.
"Really it's the first piece of the puzzle. Once we know the distribution of the materials we can really start to better understand the hydrogeology."
