ADCP's Application in Flood Management of Tapajós River

1. Where is Tapajós River?

The Tapajós River is located in the Amazon Basin of Brazil. It is a major tributary of the Amazon River. It rises in the Brazilian Highlands and flows northward through a vast expanse of the Amazon rainforest.

Geographically, it passes through a landscape full of dense tropical vegetation, including a wide variety of trees, vines, and other plants. The river hosts diverse wildlife, such as various species of fish, river dolphins, and countless bird species. Along its banks are indigenous communities that have a long-standing relationship with the river. The Tapajós also serves as an important transportation route for local people and is a vital part of the regional economy, facilitating trade and travel.

In a broad rainfall view, the Tapajós River Basin falls into a typical tropical rainforest climate: high throughout the year and not characteristically seasonal in pattern. Indeed, this large volume of rain and fairly steady precipitation through the year allows a considerable volume of water to run in the bed, though making the surrounding territories rather susceptible to floods if its water lifts as a consequence of meteorological extremities or for some other reasons.

2. What are the Reasons for Floods in Tapajós River?

Heavy Rainfall: The Tapajós River receives heavy rainfall throughout the year because it is situated in the Amazon rainforest. Severe and continuous rain may raise the water level of the river very quickly. Its catchment area is very extensive, implying that water coming from a wide area gathers in it, overwhelming its carrying capacity and resulting in flooding.

Tributary Overflows: There are a lot of tributaries within the Tapajós River. These can easily rise when heavy rainfall pours and, if at all, simultaneously, into the primary channel of the main course, which might worsen the flood situation with much higher levels of water.

Relief and Drainage: The topography along the banks is essentially flat in many places. This, therefore, allows the waters to spill over their banks and quickly flood the areas surrounding a river. Moreover, with the intricate design of the waterways coupled with the presence of natural barriers or constrictions in the course, the usual flow of water could be resisted and back up to flood.

Deforestation and Land Use Changes: While the Amazon rainforest is vast, deforestation in the Tapajós River Basin does have effects. When forests are removed, the land's capability to absorb and retain water decreases. This results in increased surface runoff, which then flows into the river, raising the volume of water and the chance of flooding. The use of ADCP flow meter thus ensures a more sophisticated and accessible means of measurement and management for flood-related situations than has existed heretofore.

3. How do ADCPs Using the Doppler Principle Work?

The working of ADCPs is based on the Doppler principle. ADCPs emit acoustic signals into the water. The acoustic waves interact with moving particles in the water, like sediment, debris, and different velocity water parcels. Due to the Doppler effect, the frequency of the reflected waves changes after the emitted waves bounce back from these moving objects.

The ADCP measures this frequency shift. By knowing the speed of sound in water and the angles of the emitted and received signals, it can calculate the velocity of the water at different depths. Multiple transducers in the ADCP current meter are used to measure the velocity in different directions. By integrating these velocity measurements over different depths and cross - sectional areas of the river, the flow rate and other important hydrological parameters can be determined.

4. What are the Applications of ADCP in Floods of Tapajós River?

Velocity Measurement: The ADCP current profiler will be able to measure the velocity of water flow at different locations and depths of the Tapajós River with high accuracy. During flood events, this information is crucial in understanding the dynamics of the flood. It helps in identifying the areas where the flow is rapid and could endanger riverbanks, bridges, and other infrastructure. It also allows for monitoring how the flow velocity changes over time as the flood progresses.

Flow Rate Measurement Application: ADCP flow meter calculates flow rate by using the measured velocity data in combination with the cross-sectional area of the river. This is essential for the forecast of the amount of water that would be passing through different sections during a flood. It enables anticipation of the flood peak and its impact downstream, important for flood management strategies.

Sediment Transport Research: Flooding in the Tapajós River can transport a high amount of sediment. ADCP profiler can analyze the sediment movements by detecting echoes of acoustic signals affected by sediment particles. This provides valuable insights into how floods affect the riverbed's evolution, sediment deposition, and erosion processes, which is important for maintaining the stability of the river channel and the surrounding ecosystem.

5. How can the Data Measured by ADCP be Utilized in Flood Warning and Risk Management of Tapajós River?

Flood Warning

Velocity and Flow Rate Data Monitoring: Continuous monitoring of the velocity and flow rate data through ADCP flow meter allows for the timely identification of abnormal increases in these parameters. The flow rate approaching or exceeding such critical values is indicative of an imminent flood peak. This enables timely warnings to be issued to the indigenous communities and other settlements along the river, besides the relevant authorities.

Water Level Prediction and Warning: Correlating the measured flow rate and velocity data with historical water level records will help in developing models to predict future changes in water levels. This helps in providing advance warnings about the areas that may get inundated and the height of floodwaters, enabling people to take preventive measures.

Risk Management

Water Conservancy Project Scheduling Decision Support: With the help of ADCP meter, decisions regarding the operation-such as small dams or reservoirs in the basin of the Tapajós River-can be supported in determining when and how much water should be released so as to reduce the impact in case of floods downstream.

Flood Disaster Assessment and Emergency Response: In the event of a flood, ADCP profiler can be used to collect data that can be applied post-flood to assess the severity of the flood: for example, the extent of inundated areas and the flow characteristics during the flood. This information guides emergency response efforts, including the allocation of relief resources and the planning of post-flood recovery work.

6. What is Necessary for High-Quality Measurement of the Currents of the Tapajós River?

It is necessary that the measurement equipment is manufactured with material that is reliable for high-quality measurement of the Tapajós River currents. Its casing should be able to stand harsh conditions in the river, such as impacts due to floating debris, corrosion by the chemical composition of the water-which can be influenced by the rainforest environment-and the warm, humid climate of the region. The size of the equipment should be small enough to be easily installed and deployed at different locations in the river, especially locations that are deep in the rainforest with limited accessibility.

The design should be lightweight for ease of transport and installation. Low power consumption is also a major factor in being able to operate continuously for long periods of time without requiring changes in batteries or high-energy sources. Cost - effectiveness is another important factor to enable large - scale deployment for comprehensive monitoring. The casing of ADCP current meter is preferably made of titanium alloy. Titanium alloy has several outstanding advantages: it has excellent corrosion resistance, crucial for long-term exposure to river water; it has a high strength-to-weight ratio, providing sufficient strength while keeping the weight of the equipment at a reasonable level. This material is durable enough to guarantee stable performance under the diverse environmental conditions of the Tapajós River Basin.

6. Selection of Proper Equipment for Measurement of Current

While selecting appropriate equipment for the measurement of currents at the Tapajós River, there are many points to be considered: the first one, due to the purpose of its usage, if the goal of measurement is horizontal cross - section measurement, then Horizontal ADCP, or HADCP, will fit in this case because it can measure with much precision the flow velocity along with other parameters of horizontal direction across the river section. It would be more appropriate to make vertical cross-section measurements using a Vertical ADCP, as it can obtain detailed velocity profiles along the vertical axis of the river. Different frequencies should be chosen according to the actual water depth.

For water depths within 70 meters, an ADCP flow meter with a frequency of 600 kHz is usually good enough to provide relatively accurate measurement results in this depth range. When working in deeper water areas up to 110 meters, the ADCP profiler frequency should be 300 kHz because it can penetrate more effectively to larger depths and provide valid data. There are various ADCP brands available in the market, such as Teledyne RDI, Nortek, and Sontek. However, it is worth highlighting a high-quality and cost-effective Chinese ADCP brand-China Sonar PandaADCP. It is made of all-titanium alloy material, ensuring excellent performance and durability. You can find more information on its website: (https://china-sonar.com/)

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