ADCP's application in flood management of Murray River

1. Where is Murray River?

Murray River is the longest river in Australia. It runs for about 2,508 kilometers across southeastern Australia. The river begins with its source in the Australian Alps inside New South Wales near a place called Mount Kosciuszko. It flows west through the various parts and forms part of the boundary separating New South Wales and Victoria, further into South Australia.

It passes through many big cities and towns along its course, including Albury-Wodonga, which straddles the New South Wales and Victoria border; Echuca; and Mildura. The various sections of the basin enjoy different rainfalls, although usually, the upper reaches near the mountains are generally wetter. Most of the rain is garnered during winter when cold fronts can bring heavy rain. On the whole, however, the Murray River catchment has a rainfall regime that is rather variable with periods of drought relieved occasionally by heavy rainfall events. Some years may have rainfall below average and thus less water, while other years may bring intense rainstorms that create flood-related problems.

2. What are the causes of floods in Murray River?

There are several reasons for the flooding in the Murray River:

Heavy Rainfall: Heavy and continuous rainfall, especially in the upper catchments of the river, will raise the volume of water coming into the river very fast. For instance, if it rains consecutively for days in the Australian Alps, where it originates, a lot of runoff will be produced and would flow down towards the lower parts, possibly exceeding the normal carrying capacity of the river.

Catchment characteristics: This includes the size and topography of the catchment area. A large catchment implies that water from a vast area drains to the river. If this land happens to have steep gradients in some sections, the rush of water will be quicker. In addition, an area with limited soil infiltration capacity will ensure there is more surface runoff than water going into the ground.

River morphology: The shape and width of the river channel, as well as the presence of any constrictions or meanders, affect how water flows. For instance, if there are narrow sections in the river, water can back up and cause flooding upstream when there is a large volume of water flowing through.

In the context of flood monitoring and management, traditional measurement methods may lack timeliness and precision. As an advanced acoustic technology, Acoustic Doppler Current Profiler (ADCP) has gradually appeared as a more advanced and convenient measuring tool in understanding the flow conditions of the river during flood events.

3. How do ADCPs using the Doppler principle work?

The working of ADCPs is based on the Doppler effect. They emit acoustic pulses into the water. As these pulses interact with moving particles in the water, such as sediment particles or small organisms, the frequency of the reflected sound waves changes due to the Doppler effect. By measuring this frequency shift, the velocity of the water at different depths can be calculated. The instrument commonly has multiple transducers that may send and receive acoustic signals in different directions. For instance, a typical ADCP can measure simultaneously the horizontal and vertical components of velocity. Therefore, a thorough profile of the water velocity from the surface to the riverbed over the entire water column can be developed.

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

Velocity measurement: The ADCP profiler can measure the velocity of the water at various locations and depths during flood events in the Murray River with high accuracy. This is some of the most valuable information needed to explain the dynamic behavior of the floodwaters. For instance, placing ADCP at useful places in the course of the river helps authorities estimate the speed at which the water is running near the bridges or any other important infrastructural installation for a better judgment about their possible effects.

Flow measurement application: ADCP can be used to calculate the flow rate of the river by integrating the measured velocities across the river cross-section. The estimation of the actual flow rate is crucial in predictions of how much water would pass through a given section of a river over some time and for estimates of the overall volume of water involved in the flood, crucial for flood forecasting and management.

Sediment transport research: The sediment movement in case of floods is another important aspect. ADCP flow meter detects the presence and movement of sediment particles in the water through the analysis of backscattered acoustic signals. This will help in understanding how floods may redistribute sediment in the riverbed and along the banks, with implications for river morphology and the long-term health of the river ecosystem.

5. How can the data measured by ADCP be used in the flood warning and risk management of Murray River?

Flood warning

Velocity and flow data monitoring: With the help of acoustic doppler flow meter, continuous monitoring of the water's velocity and flow rate generates real-time data. Wherein, if the velocities and flow rates measured start to exceed beyond certain predefined thresholds, it may indicate that a flood is forming or gaining intensity. For example, if the flow rate at a particular gauging station on the Murray River were all of a sudden much larger than typical, an early warning could be issued to communities downstream.

Water Level Prediction and Warning: Integrating the flow data with information about the geometry of the river and historical relationships between flow and water level can serve to predict changes in water level from ADCP current profiler data. It thus helps the authorities to warn areas that could face the risk of being inundated in due time.

Risk Management

Water Conservancy Project Scheduling Decision Support: Data from ADCP helps in decision-making in the operation of dams, weirs, and other water conservancy projects along the Murray River. For example, if the measured flow during a flood is very high, operators may decide to release some water from the dam in a controlled manner so that there is no excessive pressure on the structure and the flood impact downstream is managed.

Flood disaster assessment and emergency response: The acoustic doppler velocity meter data in the event of a flood could be analyzed to determine the extent of the damage caused by a flood, like riverbed changes and bank erosion. This information is useful for the planning of emergency response activities like stabilization and restoration of the riverbanks.

6. What's required for quality measurement of Murray River currents?

For high-quality measurement of the Murray River currents, several factors are important. Firstly, the equipment should have high material reliability to withstand the harsh aquatic environment, including exposure to water, sediment, and potentially fluctuating water temperatures. Smaller size and weight are preferable because these make the deployment and retrieval of the equipment easy, particularly in a vast river like Murray, whose access to some measurement locations may not be easy. Low power consumption is essential to ensure that the equipment can operate for extended periods without necessarily changing the batteries frequently or needing a complex power supply setup in remote locations. Additionally, a lower cost is beneficial to enable large-scale deployment for comprehensive monitoring of the river. The casing of ADCP is preferably made of titanium alloy.

Titanium alloy has several outstanding advantages. It has excellent corrosion resistance, which is vital when in contact with water for long periods, especially water in the Murray River that may contain various dissolved substances. It also has a high strength-to-weight ratio, enabling structural integrity without adding too much weight to the equipment as a whole. In addition, it is resistant to mechanical impacts and abrasion caused by sediment particles in the water, which enhances the durability of the ADCP device in a river environment. 

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

Several factors should be considered in choosing equipment for current measurement in the Murray River. Based on the purpose of use, if the measurement is to be done on the horizontal cross-section of the river flow, a horizontal ADCP would be suitable, while a vertical ADCP would serve best for vertical cross-section measurement. Since it is also connected with frequency selection, the higher the frequency, the shallower the water depth. For instance, a 600 kHz ADCP will usually suit water depths within 70 meters. That means it has a relatively high-resolution measurement in the more shallow to moderately deep water. Meanwhile, a 300 kHz ADCP is more appropriate for water depth up to 110 meters, since it is capable of deeper penetration into the water column to get the accurate velocity profiles at greater depths.

Some of the better-known ADCP brands in the market include Teledyne RDI, Nortek, and Sontek.

But there is one very good Chinese ADCP brand, called China Sonar PandaADCP. It has an enclosure that is fully made of titanium alloy and, therefore, can guarantee durability and good performance in the aquatic environment. In addition, it provides an incredible cost-performance ratio that would make it one of the most attractive options in the line of reliable and cheap current measurement equipment. You can find more information about it on its official website: (https://china-sonar.com/).

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