Source: Environment Canterbury Regional Council
Our new Rakaia water balance model can calculate the average daily river flow at the Rakaia River mouth for the first time.
The Rakaia is one of Waitaha’s most iconic landscapes – a braided river that flows across central Canterbury from the mountains to the sea.
Its stunning natural landscape was recognised when the river was made subject to a Water Conservation Order (WCO) in 1988, protecting the river, its habitat and recreational values.
The river is fed by rain and snowmelt on the Southern Alps, so flow varies considerably, and the WCO sets minimum flow levels, below which water cannot be taken for use.
Accounting for water movement on the Rakaia
Despite the WCO, the Rakaia is still used as a water source for hydroelectric power generation and irrigation.
As the regulator, we are responsible for ensuring water users are compliant with their resource consent conditions. These include not taking water when on restriction, and adhering to daily and annual volume limits.
Water takes have flow meters installed. These devices send us information on water taken each day.
The Rakaia water balance model combines these data with that from a flow recorder operated by NIWA near Fighting Hill in the Rakaia Gorge, and accounts for natural loss to groundwater and water discharged from Highbank Power Station into the river, to calculate the daily average flow at the river mouth.
View the
Rakaia water balance model on our Rakaia River webpage.
Preserving the river mouth environment
As the Rakaia emerges from the gorge, it spreads out over a wide gravel bed in several ever-changing braids. This makes measuring flow volumes almost impossible.
Water and Land Science Manager Elaine Moriarty says creating this model was the best way to explain river levels at the river mouth.
“Because the Rakaia has so many braids crossing such a wide stretch of the plains, we can’t set up a flow meter.
“We have a passionate community of anglers and recreational river users, and we hope this information will assist them in understanding the variables influencing the flow of the river.”
