Drone assisted Streamflow Gauging

Streamflow gauging's during high flow conditions or flood events is crucial for a wide range of operations within surface water engineering.? The most common requirement primarily from hydrometry field is the development and or further enhancement of stage-discharge relationship at a flow monitoring site.? Hydrometry is not the only field in surface water engineering that are dependent on high flow measurements and specialists in surface water modelling, water infrastructure management, water infrastructure design, flood forecasting, emergency services and land use planning to name a few.

Streamflow gauging’s during flood events are notoriously challenging due to high water velocities, presence of vegetation, floating debris, increased channel width especially when flood water spill over onto the flood plains and health and safety.?

“There exists an unwritten code in almost every single organization of which hydrographer performed the highest streamflow gauging”

During my junior years as Hydrographer, flood measurements were predominately performed from either a bridge, overhead cableways or manned boat cableways using a horizontal axis current meter with either a 50kg or 100kg sounding weight depending on the water velocity.? This was a physical and time-consuming process and the extent of the measurement exercise normally span over several days to perform a series of streamflow gauging’s at one flow monitoring site.

With the introduction of acoustic Doppler current profilers (ADCP) in Hydrometry operations the possibilities in improving data quality and operations have expanded exponentially.? The first application of ADCP, more than three decades ago was with a manned flood boat (USGS).? Since then, there was significant development on ADCP instruments, processing software as well as different measurement platforms.? Organizations have used a range of platforms since then from existing infrastructure designed for current meters to remote control boats, manned boats, kayaks, jet-skis and even helicopters (NZ).

Over the last decade or so, organizations started to focus their attention on improving data quality, measurement efficiency and health and safety requirements. ?The renewed focus streamlined the type of platforms used during ADCP streamflow gauging’s.

WaterNSW identified the need of combining the latest technology available on the market to perform streamflow gauging’s during the November 2022 floods in the Murrumbidgee River, Australia.

• acoustic Doppler current meter - RiverSurveyor M9
• remote piloted aircraft system (RPAS) - DJI
• unmanned surface vehicle (boat) - Q-Boat hull, retrofitted with Surfbee electronic hardware and motors.

This is not the first time WaterNSW is pushing boundaries in the application of acoustic Doppler instruments and remote-control boats.? WaterNSW was the first organization that performed autonomous stationary measurement using RiverSurveyor M9, Hemisphere S631 RTK and Surfbee Flowseeker remote control boat.

?The Background

The decision to look for alternative approaches to improve the overall data accuracy and measurement efficiency during the November 2022 streamflow gauging’s were based on the following events,

• The broader region experiencing the third consecutive rainfall event, with river systems across the state flowing at high levels for many months,
• Major contributing dams are now above capacity and spilling,
• After a recent gauging of 96 000ml/d, it was identified that a different approach is required to perform streamflow gauging’s at higher flows.

The Plan

Perform flood gauging at 410004, Murrumbidgee River at Gundagai

• It was previously identified that the hydrometric team could measure the flow along the transect where the old road bridge had been demolished,
• There were minimal fences obstructing the path, with power lines situated up stream and old bridge piers downstream,
• A remote piloted aircraft system (RPAS) was used as a scout for the unmanned surface vehicle (boat).? The transect width of over 500m is beyond operator ability to clearly distinguish the unmanned surface vehicle or identify any objects in the water.

The Outcome

• The RPAS provided clear and real-time footage of the boat, which was vital during the entire measurement process.
• The streamflow gauging was completed without any issues encountered during the moving boat measurements.
• Operators were not required to enter the water during the streamflow gauging, apart from launching the boat at the water edge.? This greatly enhanced health and safety, especially during major flood event
• The RPAS contractor collected photogrammetry of the Gundagai flood plain.

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