National study seeks to arrest Wairau aquifer decline

Recent rain has replenished river flows and soil moisture and eased water restrictions across Marlborough but the long-term decline in Wairau aquifer levels continues.

Senior Environmental Scientist, Groundwater, Peter Davidson and Environmental Scientist, Hydrology, Charlotte Tomlinson are working with Lincoln University to look at Wairau

River management solutions that could be introduced to arrest the decline in aquifer levels.

A better understanding of how braided rivers such as the Wairau interact with groundwater is the focus of the Gravel Bed Rivers (GBR) National Research Project, now in its fourth year.

The study is due for completion in October.

Mr Davidson said there was a willingness at Council to apply the lessons learnt from the study to “arrest and restore” the aquifer.

“I think people understand the need to maintain the aquifer and flood protection cannot be compromised, so whatever we do, the various needs will have to co-exist. Any changes in the way we manage the mighty Wairau requires a coordinated approach,” he said.

The groundbreaking hydrological research is being done with Council’s rivers, science and policy teams. In the longer term, it could result in changes to the river’s gravel management plan and some adjustment to the width of the river, which has over time become constrained to one channel.

Mr Davidson said groundwater tended to be “out of sight and out of mind” but the aquifer was an extension of the river itself, while springs were the surface expression of the aquifer.

Studies have now shown that an unintended consequence of providing the Wairau Plains with flood protection has been a reduction in the natural aquifer recharge rates from the Wairau River in the Rapaura area. This has likely been compounded by gravel extraction and a depleted natural gravel supply from nearby catchments since the 1960s, Mr Davidson said.

While the Wairau is the only

Marlborough aquifer that is affected, it’s likely that other South Island braided rivers with constructed flood works have a similar issue.

In September, the findings of the

GBR research project will be presented to Council and the public at a series of workshops.

Natural recharge rates into the Wairau aquifer have gradually declined since the 1960s