ADCP's Application in Flood Management of Purús River

1. Where is Purús River?

Purús River is one of the major watercourses in South America. Geographically, it lies in the Amazon rainforest region, mainly within the Brazilian frontier. It is the major feeding tributary of the Amazon River.

It is a broad tropical rainforest basin hosting an enormous variety of flora and fauna. The climate is generally hot and humid with a high level of rainfall throughout the year. There is relatively little seasonal variation in precipitation, and the consistent rain keeps the Purús River well-supplied with water.

The river runs through sparsely populated parts with some indigenous communities depending on it for their livelihood. These communities depend on the river for fishing, transport, and water supply. Moreover, the Purús River plays a vital role in ecological balance regarding the Amazon rainforest and wetlands around.

2. Why does flooding occur in the Purús River?

Abundant Rainfall: The reason for flooding in the Purús River is continuous and heavy rainfall in the Amazon rainforest. The great catchment area of its basin gathers a large volume of water. Such a large amount of water is continuously added to the river that its water level rises very rapidly, and thus floods occur.

Drainage and Topography: The topography within the basin area and adjacent rainforest contributes. There are areas with flat or low - lying terrain where water may pool easier. Natural drainage patterns can be disrupted by fallen trees, vegetation, and the complex network of tributaries and small waterways. Also, the soil of the rainforest, while generally good at the absorption of water, can get saturated in case of heavy or continuous rainfall; excess water runs off into the river.

Climate Variability and Extreme Events: Climate change may further accentuate extreme weather events and changes in rainfall patterns, sometimes causing heavier-than-normal rainfall. This tends to increase flood frequency and intensity in the Purús River.

In the management of floods, Acoustic Doppler Current Profiler (ADCP) is useful because it offers the depth and detail of the flow of the river not possible by the traditional systems.

3. How does an ADCP using the Doppler Principle Work?

The ADCPs operate based on the Doppler principle. The acoustic signals-a sort of sound waves-emitted by an ADCP current profiler get projected into water. These signals interact with moving particles in the water, such as sediment, organic matter, and water molecules that are flowing with the current. There is a change in frequency when the emitted waves are reflected back by the moving objects.

That change in frequency, commonly called the Doppler shift, has a direct relationship to the velocities of the objects in movement. ADCPs are provided with several transducers that emit acoustic pulses in multiple directions. For instance, a downward-looking ADCP flow meter may calculate the velocity profile of the water column from the water surface to the bed of the river. The ADCP measures the velocity of the water flow at each depth within the water column by analyzing the Doppler shift of the reflected signals.

Once the velocity at various depths is known, and along with knowledge regarding the cross-sectional area of the river (which can be estimated through other means), one could calculate the flow rate of the river and other important parameters concerning the water flow.

4. Application of ADCP in Purús River floods:

Velocity Measurement: ADCP meter  will be able to measure with good accuracy the actual velocity of water flow in each different location and depth during flood events on the Purús River. This is very critical information for understanding how fast the floodwaters are flowing. For instance, it can help predict the arrival time of the floodwater at vulnerable areas, such as indigenous settlements or areas with important ecological habitats. Preventive measures, such as evacuation of people or relocation of wildlife, are taken in time through continuous monitoring of the velocity.

Application to Flow Measurement: ADCP profiler calculates the flow rate of the river by integrating the velocity data over the cross-sectional area of the river. In the case of a flood, this serves to give the magnitude of the flood. It allows a better understanding if the flood waters will exceed the flood-control structures' capacities, if any, and helps in the planning for effective flood-mitigation strategies.

Sediment Transport Research Application: ADCP current meter  can analyze the backscattered acoustic signals to study the movement of sediment that the floodwaters carry. Understanding sediment transport during floods is important for making assessments of changes in the riverbed. These changes can influence the river's navigation, the stability of riverbanks, and the overall health of the river ecosystem.

5. How can the ADCP-measured data of Purús River be used for flood warning and risk management?

Flood Warning

Monitoring of Velocity and Flow Data: By continuous monitoring of velocity and flow data through ADCP flow meter, one can spot the abnormal changes of the river flow quite in advance. A sudden increase in velocity or a radical variation in flow rate might indicate that a flood is imminent or that the flood situation is worsening. Such data can be integrated into flood warning systems for prompt notification of the situation to the local communities, emergency operators, and relevant authorities. Water Level Prediction and Warning: Using ADCP-measured flow data in conjunction with other variables like the cross-sectional geometry of the river and historical records of water levels, future water levels can be predicted. If the predicted water level is forecasted to rise above flood stage, this can be used to issue warnings well in advance so people can evacuate or take protective measures.

Risk Management

Water Conservancy Project Scheduling Decision: Support-Data from ADCP profiler serves as a very valuable input in the decision-making process related to the operation of water-conservancy projects-small dams or diversion channels, if any, on the Purús River. For instance, in times of flooding, the flow data would help determine the amount of release rate from a dam that could possibly reduce the impact of the flood further downstream.

Flood Disaster Assessment and Emergency Response: In cases of emergence of floods, it will be helpful to apply ADCP data to assess the extent of damage caused by the flood. This involves assessment of high-velocity flow areas, quantitative sediment deposition, among other factors. This information can be used in taping proper emergency response and recovery procedures, like search and rescue missions, and post-flood rehabilitation of the affected areas.

6. What is required for high-quality measurements of Purus River currents?

High-quality measurement of Purús River currents requires the following:.

Durable Equipment: The ADCP profiler must be manufactured from materials that can resist the unforgiving environment of the Amazon rainforest. The river water must not easily corrode it, nor must impacts from floating debris (such as branches and logs) easily break it, along with abrasion by sediment.

Portability and Ease of Deployment: The smaller size, lighter weight, and lower power consumption are advantageous. This compact and lightweight ADCP current meter is easy to transport and install in the Purús River basin. The low power consumption offers longer-term operation without the need for frequent battery replacement or a complex power supply arrangement, which is ideal for continuous monitoring.

Cost-Effective Solution: A cost-effective ADCP current profiler is preferred to facilitate large - scale deployment for comprehensive monitoring of the river.

Regarding the casing material, titanium alloy is an excellent choice. Titanium alloy has high strength, allowing the ADCP flow meter to resist external forces in the water. It also has excellent corrosion resistance, ensuring the equipment's long - term performance in the water. Its relatively low density helps reduce the overall weight of the device while maintaining its structural integrity.

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

When choosing equipment for current measurement in the Purús River, consider the following:

Purpose of Measurement: If the horizontal cross-sectional flow measurement is desired, then a Horizontal Acoustic Doppler Current Profiler (HADCP) will suffice. It measures the flow velocity and other parameters at the horizontal section of the river. But if the measurement is for the vertical cross-section, the vertical ADCP is apt since it would measure the velocity profile right from the water surface to the riverbed along a vertical line.

Frequency Consideration: The various frequencies of ADCPs are suited for different water-depth ranges. For instance, a 600-kHz frequency ADCP would generally be suitable for depths up to 70 meters, whereas a 300-kHz ADCP should be more suitable for waters with up to 110 meters of depth. Choosing the correct frequency based on the actual water depth of the Purús River makes sure that proper and effective measurement results are determined.

There are well-known ADCP profiler brands such as Teledyne RDI, Nortek, and Sontek. Additionally, there is a Chinese brand, China Sonar PandaADCP, which features a casing made of titanium alloy and offers a good cost-performance ratio. 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.