Monitoring flow in the Murray-Darling Basin

New South Wales, Australia

Australia's Murray-Darling Basin contains extremely precious water resources, but presents hydrographers with a significant challenge because the area is extremely flat. Tens of thousands of square kilometres are braided by slow-flowing rivers and streams with virtually no fall in their channels.  For example, Colombo Creek in New South Wales, has a slope of just 31 meters in 60 kilometers. With such a flat profile, the backwater effect of confluences, fallen trees, slumped banks and even algal blooms can dramatically impact flow and affect the accuracy of rating curves.

"Over the years, we have struggled to manage the hydrographic data for water users," says Danny Hannon, Hydrometric Coordinator for the South West Region for the New South Wales (NSW) Office of Water.  "The challenges of providing accurate, repeatable data have been costly in both manpower and dollars."

Measuring flow in the Murray-Darling Basin is of national importance. Farmers in the basin generate 39 percent of Australia's agricultural income.

For years, flow in Colombo Creek has been gauged eight times per year – lately, with a SonTek RiverSurveyor M9 acoustic Doppler profiler, after which hydrographers plot the data onto a rating curve developed for the station. However, in October 2011, Danny and his team began testing a new SonTek-IQ shallow flow meter.

The objective was to provide a continuous level reading and profile of flow – even in slow-moving water and shallow conditions.

Following a survey of the bed and banks of Colombo Creek at the flow measurement site, the new flow monitor was 'told' where it was located in the cross-section, and the unit's theoretical mode was activated. Danny's team used their RiverSurveyor M9 to gauge flow immediately upstream of the monitor. "We measured 317 Ml/d (1,300 cfs), and by the time we had finished the measurement, the monitor was saying that discharge was 321 Ml/d," recalls Danny.  "This was absolutely brilliant.  In only a short space of time and with no physical input other than the cross-section, we were measuring flows that agreed with our gauging within 1%."

The SonTek-IQ employs five pulsed Doppler beams – one paired with a pressure sensor to provide level data, and four more to create a 3-D measurement of water velocity in the channel.  A specially developed algorithm constantly adapts the acoustic pulse to depth, velocity and turbulence conditions, enhancing the instrument's accuracy in the low-velocity conditions that make the Murray-Darling Basin such a challenge.  The on-board processing yields high-resolution volume and flow data.

The flow meter was anchored onto a small, steel, sliding and angle-adjusting platform on an alloy H-beam and readings are relayed hourly to the Office of Water database via modem. Maintenance requirements are minimal because the flow meter has a long battery life, with a power demand of just 0.5 watts.

Danny and his team have been delighted with the results and expect to deploy more SonTek-IQ flow meters around the Murray-Darling Basin. Continuous monitoring data will improve the accuracy of monitoring, whilst reducing costs and shedding light on water movement in the basin.

 

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Monitoring flow in the Murray-Darling Basin

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Fri, Feb 22nd, 2013 - Ian Thompson

Australia's Murray-Darling Basin contains extremely precious water resources, but presents hydrographers with a significant challenge because the area is extremely flat. Tens of thousands of square kilometres are braided by slow-flowing rivers and streams with virtually no fall in their channels. 

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