Scientists study water movement in Pelorus/Te Hoiere
A new study by Council’s environmental scientists is looking at groundwater quality and how water moves through parts of Te Hoiere/Pelorus catchment, where hydrology is little understood.
Hydrology is the study of water flow on and below the surface, and how this impacts water quality and quantity alongside land uses.
The one-year study will see several samples taken each season from more than a dozen groundwater wells, as well as surface water locations that flow into the Rai River. Council’s Pete Davidson will study the groundwater and Charlotte Tomlinson will lead the science on surface water.
“Rivers and streams are where most of the water quality monitoring takes place but are the nutrients found in groundwater and wells more interconnected to our rivers and streams than we’ve previously thought? This study will provide some insight,” Pete said.
Pete will drill four new wells over summer, with landowners granting access to 11 existing wells, to measure the water table and water quality. Meanwhile, Charlotte is looking at the levels and flow of surface water into the Rai River. Where the two will overlap is looking at the level of the surface water and how it flows to groundwater (in bores or wells) to better understand how the whole system is working.
Understanding the interaction between groundwater and surface water is not well understood in Te Hoiere/Pelorus, and the flow of nutrient runoff throughout the catchment is even less understood, Pete said.
“Currently, we know that nitrogen is elevated in the groundwater of just one well because that’s the one we regularly monitor for our reporting. But we don’t know if that’s indicative of the whole catchment,” he said.
In terms of surface water, Council only has one permanent gauge at Rai Falls to measure levels. The historic data on the catchment’s waterways have been ad hoc throughout the years. In November, Council began to take measurements at 15 surface water sites around Rai. This information will be coupled with water level measurements in new and existing wells.
“We’ll begin to understand how water moves through gravels in the catchment, both above and below ground,” Charlotte said. “For example, landowners have seen the river go dry in the Opouri River in some reaches, but then water resurfaces downstream. We are trying to understand why.”
Help from the local community has been key, with some landowners granting access to their wells and others sharing their rainfall data and local knowledge with Council.
This study is expected to improve how water quality is measured in the catchment. Currently, water quality measurements only take flow into account where this data is available—and there isn’t consistent data in Te Hoiere/Pelorus compared to other areas in Marlborough.
This work by Council has been accelerated, but is not part of, Te Hoiere Project. With the Project so far supporting more than 50km of fencing and 100,000 native plants to improve freshwater, Council is seeking to better understand the flow of nutrients and any potential leaching of nutrients into the ground away from waterways.