ADCP's Application in the Flood Management of Madeira River

1. Where is Madeira River?

Madeira River is one of the most important water bodies of South America. It lies basically in Brazil. It forms part of the largest tributaries of the Amazon River. Starting from the highlands of Bolivia, it flows for about 3,250 km through Brazil before meeting the Amazon River.

The river cuts through several sub-regions of Brazil that have high biodiversity levels and are also host to many indigenous groups. The river courses through various towns and cities depending on it for transport, fishing, and a source of water supply for both domestic and agricultural uses. The climate conditions in the Madeira River basin are tropical with heavy rainfall throughout the year. Yet, there still exist a well-marked rainy and dry season. The rainy season, which is usual between November and April, is characterized by heavy rain that falls frequently; therefore, the water level is remarkably higher. The dry season, which ranges from May to October, makes the water level move backward, but the river remains part of the most important aspects of the ecosystem and economy in this area.

2. What are the causes of flooding in the Madeira River?

The floods in the Madeira River are due to a number of factors. One major reason may be attributed to heavy rainfall during the wet season. During this period, the precipitation is high over the catchment area of this river, and the different tributaries funnel this water into the main channel. This usually occurs when the volume of water that reaches the Madeira exceeds the river's carrying and draining capacity down to its mouth. The water level then rises to flood the areas around it.

The second factor relates to topography. There are a lot of flat areas or simply regions with poor drainage systems along the course of the river. Water is indeed accumulated rather than flowing away, hence aggravating the flood situation. Deforestation in the watershed also plays a part. As trees are cut down, less water is absorbed by the land and more becomes surface runoff. This further contributes to the volume of water entering the river through increased runoff, thus increasing the chances of flooding and its intensity.

With the emergence in the need for effective flood management, Acoustic Doppler Current Profiler (ADCP) has become more advanced and convenient in measurement aspects compared to the traditionally used measurement tools. It can provide vital data on the flow characteristics of the river to aid higher functionalities in understanding and managing flood events better.

3. How do Doppler principle-based ADCPs work?

Basically, ADCPs operate on the principle of Doppler. They transmit acoustic signals into the water. These signals start an interaction with moving particles in the water, such as sediment particles or water molecules that are flowing with the current. The acoustic waves reflected back from these moving entities undergo a shift in frequency. This shift in frequency, commonly referred to as the Doppler shift, is directly proportional to the velocity of the moving entities.

Normally, ADCPs are multiple-transducer instruments with a typical transmission of acoustic pulses in various different directions. For example, the downward-looking ADCP meter would be able to measure the velocity profile of the water column from the water surface down to the riverbed. By analyzing the Doppler shifts of the reflected signals from different depths within the water column, the ADCP flow meter is able to calculate the velocity of the water flow at each depth. From this velocity information, by considering the geometry of the river's cross-section, it is then possible to calculate other important parameters, such as the flow rate of the river.

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

Velocity Measurement: In the case of flood events on the Madeira River, ADCP current profiler will be able to make precise velocity measurements of the water flow at several locations and depths. This information is fundamental because it shows the speed at which floodwaters are moving. For instance, it could determine how soon floodwaters will reach certain vulnerable areas along the riverbanks or reach and affect infrastructure such as bridges and ports. Continuous monitoring of this velocity allows authorities to take appropriate preventive measures in order to save lives and property.

Flow Measurement Application: ADCP current meter determines the flow rate of the river by integrating the velocity over the cross-sectional area of the river. From a flood perspective, accurate knowledge of flow volume is critical to determining flood magnitude, whether the flood will overwhelm control structures, or result in significant inundation in local communities. This data guides decisions regarding flood mitigation strategies.

Sediment Transport Research Application: The floodwaters of the Madeira River carry a high amount of sediment as they flow. ADCP flow meter can analyze the backscattered acoustic signals to study these moving sediment particles. Sediment transport during flooding is important in assessing the evolution that the riverbed will go through, deposition and erosion sites, and how this impacts future flood risks and general health of the river ecosystem.

5. How is the data measured by ADCP useful in the flood warning and risk management of Madeira River?

Flood Warning

Velocity and Flow Data Monitoring: ADCP profiler provides continuous monitoring of the flow velocity and data, which enables the identification of abnormal changes in the flow early. In the case of velocity rising all of a sudden or a big change in flow rate, it will signal that a flood is imminent or intensification is occurring. These data can be fed into flood warning systems for the timely alerts to be issued to the public and relevant authorities in the areas along the Madeira River. 

Water Level Prediction and Warning: Combining the flow data as measured by ADCP flow meter with other factors, for instance, cross-sectional geometry of the riverbed and historical records of water level, would offer a reasonable prediction for future water levels. If the predicted water level is envisaged to attain or exceed the flood level mark, appropriate warnings can be issued in advance to enable people to evacuate or take protective measures.

Risk Management

Water Conservancy Project Scheduling Decision Support: The measurement through ADCP current meter will, in addition, serve as an important input for decision-making in the operation of water conservancy projects like dams and weirs along the Madeira River. If the measured discharge in case of flooding is above the limit, for instance, then by regulating the gates of these structures, operators can control the flow of water and minimize damages from the flood further downstream.

Flood Disaster Assessment and Emergency Response: In the aftermath of a flood, ADCP data informs one on the extent of the damage caused by the flood. It helps to determine which area was subjected to high-velocity flows, the amount of sediment deposition, and other information. This informs emergency response efforts, including search and rescue and the planning of post-flood recovery and reconstruction work.

6. What does high-quality measurement of Madeira River currents require?

High-quality measurement of the currents of the Madeira River demands attention to many aspects. First, it requires the reliability of materials of the equipment. The ADCP flow meter should withstand the harsh aquatic environment through corrosion from the river water and impacts from floating debris. In addition, smaller size, lighter weight, and lower power consumption are preferred.

A compact and lightweight ADCP current meter would be easier to install and deploy at various locations along the river, especially in places that are somewhat difficult to access. Low power consumption allows longer continuous operations without the need to frequently change batteries or implement complex power supply arrangements, which is advantageous in this long-term monitoring. Besides, a lower cost enables large-scale deployment for comprehensive monitoring of the river. In terms of the casing material, titanium alloy is an excellent option. Titanium alloy has high strength, which allows the ADCP profiler to withstand external forces in the water. It also has excellent corrosion resistance, ensuring that the equipment can maintain good performance even after prolonged exposure to the river water. Additionally, its relatively low density helps in reducing the overall weight of the device while maintaining its structural integrity.

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

Regarding equipment selection for the current measurement in the Madeira River, the first thing to be considered is the intended use. If horizontal cross-sectional flow measurement is the main focus, then it should be a Horizontal Acoustic Doppler Current Profiler (HADCP). It is designed to measure flow velocity and other parameters in the horizontal section, giving, at the same time, important information concerning the lateral distribution of the flow.

On the other hand, for vertical cross-sectional measurements, a vertical ADCP would be more appropriate. It can detect the velocity profile accurately from the water surface to the riverbed along a vertical line, hence useful for understanding the vertical variation of flow.

In addition, various frequencies of ADCPs match different ranges of water depth. For instance, an ADCP flow meter frequency of 600 kHz is usually suitable for water depths within 70 meters. Meanwhile, an ADCP profiler with 300 kHz is highly suitable for water to a depth of 110 meters. The correct choice of frequency according to the actual water depth of the Madeira River would ensure the acquisition of correct and reliable measurement results.

There exist some very famous brands in this ADCP flow meter market, such as Teledyne RDI, Nortek, and Sontek. But there is also an excellent Chinese ADCP brand: China Sonar PandaADCP. It features a casing entirely made of titanium alloy, integrating hardness andexcellence of performance. What's more, it realizes an incredible cost-performance ratio. For more information, please refer to the following website: https://china-sonar.com/.

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