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Different approaches to braided river research

Thomas Wöhling (left), Antoine Di Ciacca, Alice Sai Louie, and Scott Wilson (right) at Technische Universität Dresden

Researchers on two different sides of the world are working to understand the dynamics of braided rivers and their interactions with aquifers, using two different approaches.

Lincoln Agritech’s Scott Wilson and Antoine Di Ciacca, together with Dresden-based colleague Thomas Wöhling and University of Canterbury PhD student Alice Sai Louie, set out to understand how braided rivers recharge regional aquifers, to improve water resource management.

Their work is part of a five-year project funded by the Ministry of Business, Innovation & Employment.

Meanwhile, in Lyon, France, researchers saw that in braided rivers a significant part of the water flows through the subsurface, which has high ecological importance. They wanted to understand the dynamics of that flow.

The different starting points have led to different research strengths.

“The French team has a lot of experience making thermal images of the river from remote sensing,” says Antoine. “This seems to be very valuable for looking at groundwater/surface water interactions over areas of a few kilometres. They’re also expert at studying the structure of the braided rivers from aerial images, such as the number of braids and how they are connected from a surface water point of view.

“On the other hand, we have done a lot of direct observations of the groundwater, such as drilling piezometers to monitor water level and temperature, measuring radon activity to trace water flow, and fibre optic installations in the subsurface,” says Antoine. “All this gives us information of the flows from the rivers to the groundwater.”

The two groups of researchers recently met to compare and contrast their research, and explore opportunities for collaboration, during a three-week European study and presentation tour by Scott, Antoine, and Alice. They met Hervé Piégay, a research director at the National Centre for Scientific Research, and postdoctoral researchers Barbara Belletti and Baptiste Marteau.

“We were impressed by the amount and quality of the work they have been carrying out in France,” says Antoine. “They have studied many different river sections and have been able to connect their river observations to geomorphology, hydrogeology and ecology.

“However, they are still lacking measurements and understanding of the subsurface processes, and this is where we think we can collaborate.”

Earlier, Scott and Antoine had presented at EGU2023, one of the world’s largest science meetings, with around 19,000 participants.

In his presentation, Conceptualisation of Groundwater Recharge from Braided Rivers, Scott showed that braided rivers indirectly recharge regional aquifers through what is called the “braidplain aquifer”, the gravels surrounding the river. “Water exchange between the river and regional aquifer is mediated by the braidplain aquifer (there is no direct exchange of water between the river and regional aquifer).”

In his presentation, Model simplification to simulate groundwater recharge from perched gravel-bed braided rivers, Antoine presented a modelling framework for groundwater recharge from braided rivers.

They also visited Thomas and Moritz Kraft at Technische Universität Dresden, Germany, to plan and coordinate their joint work on modelling the Selwyn and Wairau rivers.

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