ADCP's application in flood management of Darling River

1. Where is the Darling River?

The Darling River is one of the major rivers in Australia. It is located on the eastern side of the continent, extending through New South Wales. Originating from numerous tributaries in the area of the Great Dividing Range, it stream generally west for a distance of approximately 2,740 kilometers.

This river runs through a number of towns and regions in its course, including Bourke, Walgett, and Menindee. The climate condition varies over the Darling River basin, with much variability in rainfall. The upper reaches may receive higher rainfalls during seasons when favorable weather systems carrying moisture from the east coast prevail, but generally, the region experiences periods of drought as well as times of considerable rainfall. During many years, the rainfall can be sporadic, and when these heavy rainfall events occur in a sporadic nature, it can eventually lead changes in river water level and flow patterns.

2. What causes floods in the Darling River?

Heavy events of rainfall: Heavy and continuous rains over the catchment area can lead to a sudden rush of water in the Darling River. For instance, large-scale storm systems traversing the regions of upper tributaries will develop tremendous volumes of runoff. When these enormous volumes of water meet in the main channel, it will easily exceed normal capacity that the river has to carry water, and this will result in flooding.

Catchment topography: The shape and gradient of the Darling River's catchment play a role. Steep slopes in parts of the catchment can cause the water to flow rapidly toward the river, increasing the rate at which water will accumulate in the channel. Also, areas with extensive flatlands are able to spread out and slow water down, causing potential backwater effects and flooding upstream in sections.

River channel characteristics: The width and depth, as well as any constrictions or blockages in the channel of the Darling, affect its capacity during high-flow events. Narrow sections or places where debris builds up can block easy passage of water and cause backup and flooding in nearby areas.

Given such complex, flood-causing factors, accurate and timely measurement of flow conditions is required. Recently, Acoustic Doppler Current Profiler (ADCP) has been used more conveniently compared to the traditional methods of assessing the river's behavior during flood events.

3. How Do ADCPs Using the Doppler Principle Work?

ADCPs rely on the principle of the Doppler effect. They send acoustic signals or pulses into the water. These pulses interact with the moving particles suspended in the water, like silt, clay, and small aquatic life. Since the particles are moving with the flow of water, the frequency of the acoustic signals reflected back to the ADCP flow meter is changed by the Doppler effect. The precise measurement of this frequency shift gives the velocity of the water at different depths. An ADCP current profiler will typically be fitted with several transducers, each capable of transmitting and receiving signals in various directions. This allows it to measure simultaneously a number of components of the velocity against which a full velocity profile of the entire water column-from the water surface right through to the riverbed-can be generated.

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

Velocity measurement: Accurately under the flood conditions in the Darling River, ADCPs measure water velocity with good resolution in space and depth. This information shall be vital as determination of the travelling speed of flood waters would help in ascertaining the speed at which erosive power can develop in water on riverbanks and infrastructure such as bridges and levees. In the case of high-velocity ADCP-measured velocity near a bridge pier, for instance, the necessary measures can be taken to make the structure more resistant or protect it using adequate construction.

Flow measurement application: ADCP calculates the flow rate of the river by integrating the measured velocities across its cross-sectional area. The measurement of the flow rate is crucial for determining the total volume of water passing through various sections of the river during a flood. This information is applied to flood forecasting and decision-making strategies in flood control and management, such as when and how much water needs to be released from upstream reservoirs.

Sediment Transport Research: Acoustic doppler velocity meter is also useful in the study of the transportation of sediment because the Darling River carries a huge load of sediment. The backscattered acoustic signals from the sediment particles can be analyzed to understand how the floodwaters are redistributing sediment within the river channel and along the banks. The knowledge about long-term changes within the morphology of the river and ecological health is very crucial.

5. How could data measured by the ADCP be used for flood warning and Darling River risk management?

Flood warning

Velocity and flow data monitoring: Velocities and flow rate, as continuously monitored by ADCP, provide real-time data. If these start showing higher values beyond the predefined threshold level, that would indicate the arrival or intensification of a flood. For instance, if the flow rate suddenly surges at a key monitoring point on the Darling River, an early warning can be sent to the communities located further downstream to take preparatory actions.

Water Level Prediction and Warning: Correlating the flow data with historical records and the physical characteristics of the river, ADCP current profiler data is used in the prediction of changes in water level. This helps authorities issue timely warnings to areas that may be at risk of inundation, giving enough time for residents to evacuate or take protective measures.

Risk Management

Water conservancy project scheduling decision support: The data will assist in making an informed decision for the operation of water conservancy projects along the Darling River, including dams and weirs. In the event of a flood, for instance, if the measured flow is very high, operators may decide on releasing appropriate amounts of water from a dam to balance between flood control and storage needs, reducing risks such as flooding further downstream.

Flood disaster assessment and emergency response: In the wake of a flood, ADCP data provides an idea about the effect of such floods on things like riverbed changes, erosion, and infrastructure damage. This information is used to direct emergency responses, therefore guiding the prioritizing of repair and restoration activities.

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

A number of factors need to be taken into consideration to perform the measurement of the Darling River currents with higher quality. The basic equipment should possess reliable materials to withstand the harsh conditions in the river. The casing must be resistant to corrosion from the water, possibly containing various dissolved substances and minerals.

A smaller size and lighter weight are advantageous, as they enable the equipment to be easily transported and deployed in various locations along the river, especially in areas with difficult access. Low power consumption is important to keep it operating continuously without the need for frequent replacement of batteries or a complex power supply arrangement in the remote area. Furthermore, a low cost is desirable for large-scale deployment to monitor the river comprehensively.

For ADCP casing, titanium alloy is thereby highly recommended. Titanium alloy has remarkable properties: excellent resistance to corrosion, that is, it can sustain for a very long time with the Darling River's water without exhibiting traceable deteriorations; its high strength-to-weight ratio allows equipment to stay sturdy while remaining pretty lightweight. It should also be resistant to the mechanical effects and abrasion that sediment particles may cause in the water as well as maintain a reliable measurement device for a long time.

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

The choice of equipment for the measurement of current in the Darling River will depend on the application. Should the interest be the measurement of horizontal flow across the section of a river, then the horizontal ADCP is the one to use. Where the intent of a survey is to derive information on a vertical flow profile, a vertical ADCP will be more suitable.

The choice of frequency is related to water depth: different frequencies are better for different water depths. As a general rule, a 600 kHz ADCP would be perfect for water depths within 70 meters. It can also give good and very accurate measurements at reasonably shallow to moderately deep sections of the Darling River. Whereas the 300 kHz ADCP is more suited to water depths up to 110 meters, as it can go deeper into the water column and yield accurate velocity profiles in these deep waters.

There are several known ADCP brands out there: Teledyne RDI, Nortek, and Sontek. However, a well-noted Chinese brand of ADCP stands out: China Sonar PandaADCP. It has a casing made wholly of titanium alloy, so you can be sure that it is strong enough to stand the aquatic environment. Moreover, it boasts an admirable cost-performance, which turns it into a very good option for those seeking reliable, yet reasonably priced current measurement equipment. More details about this product you can get on its official webpage: https://china-sonar.com/.

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