Scientist to research Rangitata
A close eye will be kept on the Rangitata River as major studies on its history and water quality get underway.
Freshwater scientist Dr James Brasington, formerly of Waikato University, has recently taken the reins as director of Waterways Centre for Freshwater Management, a joint-research centre between the universities of Canterbury and Lincoln.
Brasington said he was looking forward to progressing the study of sediment buildup in the Rangitata, and in particular how it relates to water extraction and flood harvesting.
A proof of concept study he ran last year showed it was possible to map the accumulation of fine sediment across the riverbed using laser scans obtained from helicopter surveys.
‘‘It’s the first study of its kind, and we are working closely with Environment Canterbury on it,’’ Brasington said.
"We really need robust, scientific evidence to support the decisions we propose to manage our rivers. Our proof of concept study demonstrated how new technologies can help by better characterising the complex character of the river and monitor the change in its condition over time."
Brasington said it hoped to survey the lower 60 kilometres of the Rangitata to determine the level of sedimentation this autumn.
The river has had a Water Conservation Order over it since 2006, and in recent times it has come under the microscope as Rangitata Diversion Race Management (RDR) has applied to take an extra 10 cumecs from the river during high flows.
An ECan independent panel granted RDR the consent, but it is in the appeals process with Ngai Tahu.
Following major flooding in the Rangitata in December there has been concern from local authorities about the state of the river.
ECan will soon begin the second stage of its river protection work, which could take up to two years and cost more than $1 million.
Meanwhile, Timaru District Council is applying for NZ Transport Agency funding to help repair some of its strategic routes damaged in the flooding.
‘‘Braided rivers like the Rangitata are prone to such breakouts. They are often caused by the build of the riverbed, reducing the capacity of the river to carry flood flows. The effects can be catastrophic,’’
Brasington said.
"With increases in the frequency and intensity of rainfall over the coming decades due to climate change, such events are likely to pose significant hazards’’.
The Department of Conservation has also appointed a ranger dedicated to the restoration of the Rangitata River, and Brasington hoped he would be able to work with DOC on some projects.
He said he was also hoping to join up with the New Zealand Salmon Anglers Association to study the longer-term history of the
Rangitata River. This will involve creating an oral history of the river and an archival study based on the analysis of historical satellite and aerial imagery.
This research will involve analysing early aerial photography and satellite imagery, back as far as the 1960s, providing an objective basis to compare how the Rangitata, Waimakariri and Rakaia rivers have changed over the past 50 years.
"We want to really tell the stories of these rivers and better understand how they’ve been impacted, information which is critical for managing their futures.’’
Brasington has specialised in researching braided rivers for more than 20 years.
"They’re a fascinatingly complex
‘‘We have some of the best examples of braided rivers globally and have a duty to care for not just the natural, but also the social and cultural processes and practices of these unique environments.’’
James Brasington
system, with networks of channels that are always in flux. They are a little bit like the hydrological equivalent of watching the flames of a fire’’ he said.
"This constant shifting creates diverse habitats and a rich ecology, but also mobile boundaries formed by erosion and sedimentation and a contested space of land ownership.
‘‘We have some of the best examples of braided rivers globally and have a duty to care for not just the natural, but also the social and cultural processes and practices of these unique environments.’’