ADCP's application in flood management of Tocantins River

1. Where is the Tocantins River?

The Tocantins River is one of the major rivers in South America. It lies mainly in Brazil. It originates in the central highlands of Brazil and, after running north for a distance of approximately 2,640 kilometers, it falls into the Atlantic Ocean.

It passes through various important cities and regions along its course, like Palmas. The Tocantins River basin is quite varied in terms of rainfall. The upper reaches of the river basin have areas with a more tropical savanna climate. The wet and dry seasons alternate quite regularly. The rainy season would normally fall between November and April and, often enough, thoroughly replenishes this tributary's water volume. Whereas during the dry period between May and October, this level is relatively low. Overall, the hydrological condition of the river and the possibility of a flood entirely depend on annual rainfall patterns.

2. What are the causes of flooding in the Tocantins river?

There is no single factor that causes flood conditions in the Tocantins River. Intense and continuous rainfall in the wet season, for instance, creates a fast rise in the inflow of water in the river. When rainfall supersedes the natural capacity of the river to dispose and take more water, the level of water starts rising. For example, there may be several days with heavy downpours in the upstream regions; therefore, large volumes of water would run to the lower reaches and gradually build up, causing floods.

The second aspect is the topography of the river basin itself. If the catchment area has some relatively flat areas or if the drainage system along the riverbank is weak, this implies that water cannot easily run off, which easily results in water accumulation to form a flood. Likewise, deforestation in the watershed, as a human activity, lessens the ability of the land to absorb water and increases the surface runoff, therefore worsening the flood situation.

For flood monitoring and management, the measurement of parameters in river flow needs to be conducted as accurately as possible. Meanwhile, the Acoustic Doppler Current Profiler (ADCP) appears to be a more advanced and convenient measurement device compared with the traditional ones. It can monitor real-time, detailed data concerning the river's flow conditions, which provides a great deal of help for flood management.

3. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of Doppler. They emit acoustic signals into the water. These acoustic waves change frequency as they encounter moving particles in the water, such as sediment particles or water molecules themselves flowing with the current. This phenomenon of change in frequency due to relative motion is well known as the Doppler shift. By measuring this frequency shift, ADCPs can work out the velocity of the water flow at different depths.

Typically, an ADCP current meter has multiple transducers that send out acoustic pulses in different directions. For example, in a downward-looking ADCP current profiler , it can measure the velocity profile from the water surface down to the riverbed by analyzing the Doppler shifts of the reflected signals from different layers of the water column. It then uses this velocity information with the known geometry of the measurement area to further calculate other parameters such as the flow rate of the river.

4. What are the applications of ADCP in floods of Tocantins river?

Velocity Measurement: ADCP will be able to measure the velocity of the water flow in the Tocantins River accurately at different locations and depths during flood events. This information will be important in understanding how fast the floodwaters are moving, which, in turn, may give ways of predicting the time it takes for the flood to reach certain areas downstream. The continuous monitoring of velocity near the bridges or populated areas keeps the authority prepared with preventive measures in time.

Flow measurement application: ADCP can also calculate the flow rate of the river by integrating the velocity data with the cross-sectional area of the river. Precise flow volume in a flood helps determine its magnitude and whether it would exceed the carrying capacity of the riverbanks or flood control structure.

Sediment transport research application: During floods, the river carries a great quantity of sediment. ADCP detects sediment particles through the analysis of backscattered acoustic signals. This provides useful information to researchers on how floods would have influenced sediment deposition and erosion patterns along the Tocantins River, and thus helps in making predictions about future flood risks and the stability of the riverbed.

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

Flood Warning:

Velocity and Flow Data Monitoring: Under continuous ADCP monitoring, abnormal increases in water flow can be detected well in advance by continuously monitoring the velocity and flow data. For instance, if the measured velocity suddenly increases or in cases when the flow rate exceeds certain threshold values, that would point to the fact that a flood is coming or is intensifying. Such information can then be coupled into flood warning systems to send timely warnings to the public and relevant authorities along this area of the Tocantins River.

Water Level Prediction and Warning: Combining the flow data with other information such as the river's cross-sectional geometry and historical water level records, ADCP data can enable the prediction of future water levels. If the predicted water level is forecasted to reach or exceed the flood level mark, appropriate warnings can be given well in advance for people to evacuate or take protective measures.

Risk management: Water Conservancy Project Scheduling Decision Support: Decision-making in the operation of dams, sluices, and other water conservancy projects on the Tocantins River is supported by data provided by ADCP flow meter. For instance, if the flow measured happens to be too high during a flood, one may decide to open or adjust the gates of the dams to regulate the flow of water and reduce flood impact downstream.

Flood disaster assessment and emergency response: The ADCP data allows assessment of the extent of flood damages after a flood event has occurred, such as the areas affected by high-velocity flows and the amount of sediment deposition. This information guides emergency response efforts, like prioritizing rescue operations and planning for post-flood restoration work.

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

For the highly qualitative measurement of currents in the Tocantins River, several aspects have to be considered: first, the reliability of the equipment's materials. The ADCP profiler should be able to bear the adverse conditions in water, such as corrosion, and impacts if there are floating objects.

Second, it is desired that the size be smaller, the weight lighter, and power consumption lower. A lighter and smaller ADCP will be easier to install and deploy, especially in areas that are inaccessible along the river. Low power consumption allows for longer continuous operations without frequent battery replacements and difficulties in external power supplies, which will be conducive to long-term monitoring. In addition, it should be of a lower cost to enable large-scale deployments for thorough monitoring of the Tocantins River.

In this regard, speaking about casing material, titanium alloy is a great option.

Excellent advantages of titanium alloy include high strength, allowing ADCP to resist any extraneous water-based forces; secondly, the excellent corrosion resistance will ensure the equipment maintains its good functionality even under long-term exposure to river water. Besides, its density is relatively low, which contributes to keeping the device weight relatively low while preserving its structural strength.

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

The intended use of the equipment in current measurement is related to the choice in the Tocantins River. According to the horizontal cross-sectional flow measurement, HADCP-a Horizontal Acoustic Doppler Current Profiler-is a suitable choice. It can obtain the flow velocity and other parameters across a horizontal section of the river and thereby obtain useful information with regard to the lateral distribution of the flow.

Conversely, for vertical cross-sectional measurements, a vertical ADCP is more appropriate as it measures the velocity profile from the water surface to the riverbed along a vertical line with high accuracy, which is needed to understand the vertical variations of the flow.

Besides, the use of different frequencies of ADCPs is applicable to different water depth ranges. Generally speaking, an ADCP with a frequency of 600 kHz will be suitable if the water is within 70 meters deep. On the other hand, an ADCP with a frequency of 300 kHz is more suitable for water depths up to 110 meters. Accordingly, choosing an appropriate frequency according to the actual water depth of the Tocantins River can make sure that measurement results are accurate and reliable.

There are several famous brands in the market, like Teledyne RDI, Nortek, and Sontek. But there is an excellent Chinese ADCP brand - China Sonar PandaADCP. It has a casing made of pure titanium alloy, possessing excellent durability and performance. What is more, it offers an incredible cost-performance ratio. You can learn more about it from its official website: (https://china-sonar.com/).

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