THE science of aquifers and groundwater is a complicated matter.
Revelations earlier this year that Chinese company Nongfu Spring Natural Mineral Water wants to buy the Otakiri Springs water bottling plant and increase its take from 700,000 litres of water a day to five million litres provoked concerns.
The company said it would create jobs and bring economic development to the district, but members of the community opposed the sale and the Chinese company’s desire to increase the bottling plant water allocation because of the impact it would have on New Zealand freshwater.
The Tarawera aquifer needed protecting, they said.
To inform the debate, the Beacon asked Bay of Plenty Regional Council environmental scientist Raoul Fernandes to explain the science behind aquifers and how they work.
In response to the request, Mr Fernandes sent a 1000-word email accompanied by four diagrams and links to several websites. It is obvious aquifers and their associated science is not a simple matter.
Firstly, there is no such thing as the Tarawera aquifer and, secondly, a basic understanding of hydrogeology is required to understand how they work.
Hydrogeology is the branch of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth’s crust. Or, in scientific language, the study of the interrelationships of geologic materials and processes with water, especially groundwater.
Mr Fernandes said hydrogeology was a “bit perplexing at times but easy to understand once you have the basics”.
“For example, the term Tarawera aquifer is not the best description of what I assume you mean the groundwater beneath the Tarawera region.”
Mr Fernandes said in the hydrogeological cycle, groundwater wasn’t all of the water stored in the ground but that which was held in the saturated part of the rocks.
He said an aquifer could be generalised as either being unconfined or confined and was a geological unit that could store and transmit water.
“Water that recharges into the aquifers comes from the rain. Recharge for the sedimentary units in the plains is from rainfall in the plains, while the recharge for the volcanic units is in the hills south of the plains. There may also be some exchange of water between the units and thus the sedimentary layers could receive additional recharge from below. We are currently running a work programme to understand this.
“A portion of the rain that falls will soak through the ground and will eventually reach the saturated zone. This saturated zone has a different potential energy at different points. In an attempt to equalise, water will flow from a point of high potential energy to a point of low potential energy; we thus get groundwater flow.
“This is the fundamental principle on how groundwater flows and thus keeps moving along the hydrological cycle. For our aquifers, this recharge forms the hills (higher potential energy) towards the coast (lower potential energy).
“In general, for confined systems the flow of groundwater is on a large scale toward the coast. For unconfined systems, water may flow into a stream, river or lake and then to the coast, as well as towards the coast directly.”