ADCP's Application in Flood Management of the Murrumbidgee River

1. Where is the Murrumbidgee River?

The Murrumbidgee River lies in southeastern Australia. This river is a major part of the Murray - Darling Basin. The source of this river is in the Australian Capital Territory, and then it flows through New South Wales.

It passes through cities like Wagga Wagga. The climate in the Murrumbidgee River basin is generally semi-arid to temperate. Rainfall is variable, but most of it usually falls within the wet season from October to March. The snowmelt from the mountains in the upper reaches also contributes to its water volume. The river is important in agricultural irrigation, supplying water for the extensive farming activities in the region. It also supports a great variety of aquatic life and forms part of the area used for recreational reasons.

2. Why does flooding occur in Murrumbidgee River?

Flooding in the Murrumbidgee River is caused by the following reasons. The rainfall during the wet season sometimes becomes heavy and continuous; this is one of the immediate causes. When the raining surpasses the usual limit the river can carry, the water level increases overnight.

The topography of the river basin also intervenes: there are sections of relatively flat floodplains that can allow water to spread during a flood event easily, and then there is a change in land use, such as agriculture and urbanization, that can reduce the natural capacity of the land to retain water. For instance, huge clearing of vegetation for farming results in increased surface runoff. Given the importance of flood management, Acoustic Doppler Current Profiler (ADCP)  provides a more accurate and efficient way to measure and manage the river's flow during flood events.

3. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of the Doppler effect. The instrument sends acoustic signals into the water. The moving particles of water scatter these signals. When the acoustic waves are reflected back after interaction with the moving particles, due to the Doppler effect, the frequency of the reflected waves is changed.

The ADCP current meter has multiple transducers that can transmit and receive acoustic signals in various directions. Precise measurement of the frequency shift of the reflected signals provides the velocity of the water flow at various depths and across different sections of the river cross-section. For example, in the Murrumbidgee River, it measures the flow velocity from the riverbed to the water surface and across different widths of the river.

4. What are the applications of ADCP in floods of the Murrumbidgee River?

Flow Velocity Measurement: One can accurately measure the flow velocity of the Murrumbidgee River during floods by using an ADCP profiler. This will be important in determining the speed at which water is moving through different parts of the river. By monitoring the flow velocity, we can identify where the water is flowing rapidly, which might be a potential flood surge or change in the flood behavior. For example, flow velocity changes near the riverbanks or in the main channel can be closely monitored.

Flow-rate Measurement Application: By combining the measured flow velocity with the cross-sectional area of the river, the flow rate can be calculated. This is particularly useful in cases like the Murrumbidgee River floods, where an estimate of the total volume of water passing through a given section per unit time is required. This aids in flood forecasting and understanding the overall magnitude of the flood.

Sediment-Transport Research: Sediment is moved in large quantities in the Murrumbidgee River during flooding. ADCP current profiler can detect the movement of sediment particles through the analysis of backscattered acoustic signals. This enables the researcher to study the sediment - transport patterns during floods, which is important to understand the long - term evolution of the riverbed and the impact on the hydrological characteristics of the river.

5. How can the data measured by ADCP be utilized for flood warning and risk management of the Murrumbidgee River?

Flood Warning Aspect

Monitoring Flow-Velocity and Flow-Rate Data: In cases where real abnormalities occur within the variation, it permits continuous flow and changes in ADCP meter. Given this approach, for each point threshold of velocity along the watercourse where these exceed flow velocity thresholds, a sharp increase of a flow may trigger early flooding. Thus, a more updated system on the real variation could immediately be transferred to the proper authorities as an early warning to concerned groups along rivers.

Water-level Prediction and Warning: The flow data obtained from ADCP can be used in conjunction with other hydrological models to predict water - level changes. By analyzing the relationship between flow - rate and water - level, more accurate flood warnings can be issued, especially in the flood - prone areas of the Murrumbidgee River.

Risk Management Aspect

Water-Conservancy Project-Dispatching Decision Support: Accurate flow data from ADCP provides valuable input in the operation of water-conservancy projects such as dams and canals along the Murrumbidgee River. Decisions related to the release or storage of water can be taken more effectively to mitigate flood risks downstream.

Flood - disaster Assessment and Emergency Response: After a flood event, the ADCP-measured data can be used to assess the extent and impact of the flood. This helps in formulating appropriate emergency-response strategies, including rescue operations and damage-assessment surveys.

6. What's needed for high-quality measurement of Murrumbidgee River currents?

The equipment should include reliable materials for high-quality measurement of current in the Murrumbidgee River. It shall be able to resist the tough aquatic environment, including resistance against the corrosive waters and possible impacts from the floating debris and sediment flow. Small size and low weight are advantageous for quick and easy installation and placement of the equipment at various sampling sites along the river.

The power consumption also needs to be low for continuous operation in remote areas where the power supply may be limited. It has to be cost-effective, too, because large-scale deployment may be required to monitor river currents comprehensively.

The casing of an ADCP is preferably made from a titanium alloy. The corrosion resistance of titanium alloy is excellent, which will be very important in withstanding the corrosive effects of the Murrumbidgee River water over time. It also provides a good strength-to-weight ratio, making the equipment more durable and easier to handle.

7. How to Choose the right equipment for current measurement?

For current measurement equipment selection in the Murrumbidgee River, the purpose of the measurement should be put into consideration. For horizontal cross-section measurement, a Horizontal ADCP, HADCP, can be considered for its detailed flow-velocity information across the width of the river. In the case of vertical cross-section measurement, a Vertical ADCP is more appropriate for flow-velocity distribution from the bed to the water surface.

Regarding the frequency of ADCP, for relatively shallower parts of the Murrumbidgee River (e.g., water depth less than 70m), a 600kHz ADCP can provide accurate measurements. For deeper areas (around 110m), a 300kHz ADCP is more suitable. There are various ADCP brands available, including well - known ones like Teledyne RDI, Nortek, and Sontek. Additionally, there is a recommended Chinese ADCP brand-China Sonar PandaADCP. It is made of all-titanium alloy material and offers excellent performance and cost-effectiveness. You can visit its website (https://china-sonar.com/) for more information.

Here is a table with some well known ADCP instrument brands and models.