ADCP Application in Araguaia River Flood Management Introduction

1. Location of the Araguaia River

The Araguaia River is one of the most important rivers in Brazil. It lies in the central region. The river originates from the Brazilian Highlands and then flows northwards for approximately 2,627 kilometers until it merges with the Tocantins River.

It passes through various regions, greatly affecting the ecosystems and the human component present. Cities and towns along its course benefit from its water resources for activities like agriculture, transportation, and even domestic use. Some of the notable areas it crosses involve regions that are important for cattle ranching and farming.

In general, the Araguaia River basin has a tropical climate, with quite well-defined wet and dry seasons. Its wet period normally occurs from December to May of every year. During this period, heavy rains pour into the river, raising its water level considerably. Where the rainy season, between December and May, the water level rises with high rainfall; however, during the dry season, from June to November, rainfall decreases and so does the water level of the river. The topography of the river regulates the hydrological properties along with yearly rainfall distributions. Thus, floods may occur.

2. Why does flooding happen in Araguaia river?

There are many factors causing flooding in the Araguaia River. This is mainly due to heavy rainfall during the wet season. When the rain falls heavily and continuously over a wide area of the basin of the river, the amount of water flowing into the river increases rapidly. The tributaries join in and contribute to this inflow, so that if the total volume of water becomes more than the natural carrying and sumping capacity of the river, the level of water starts rising, thus resulting in floods.

The topography of the river basin itself usually plays its part. Parts of a river basin might be rather flat, where water does not flow rapidly, sometimes causing it to collect. On the side of human activities, deforestation in the watershed is another factor. The possibility of the land to absorb water decreases with the cutting of trees. Instead of the water infiltrating into the ground, more water runs off the surface to enter the river, hence aggravating the flood situation.

Given the urgency for efficient flood management, Acoustic Doppler Current Profiler (ADCP) has become one of the highly valued tools in its regard. It provides advanced and convenient methods of measurement of the flow characteristics of the river compared to the traditional methods of measurement. This will provide enhanced monitoring and response towards the flooding.

3. How are the Doppler Principle ADCPs working?

The operation of ADCPs is based on the principle of Doppler. They send out acoustic signals into the water. These acoustic waves meet and interact with moving entities in the water, like suspended sediment particles or even water molecules that are flowing with the current. When the emitted waves are reflected back by these moving entities, a change in frequency occurs. This change in frequency, commonly referred to as the Doppler shift, has a direct relationship with the velocity of the moving objects.

ADCPs are fitted with several transducers that emit acoustic pulses in various directions. For example, a downward-looking ADCP current profiler  would beam pulses at the riverbed. It can calculate the velocity of the water flow at a given depth within the water column by analyzing the Doppler shifts of the reflected signals from different depths. From this velocity information, and considering the geometry of the river 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 the Araguaia river?

Velocity Measurement: ADCP flow meter will be able to measure the velocity of the water flow in multiple points, at different depths with high precision during flood events in the Araguaia River. This becomes crucial for understanding the rate at which the floodwaters are moving. For instance, this could contribute to predicting when the flood will reach susceptible areas along the riverbanks or cause an impact on bridges and infrastructures. Continuously monitoring the velocities will allow authorities to take timely measures toward safeguarding lives and properties.

ADCP current meter calculates the flow rate of the river by integrating the velocity across the cross-sectional area of the river. During a flood, knowing the volume of the flow accurately determines the scale of the flood and whether the extent of the floodwater could overwhelm flood control structures or even overflow banks. Such data will help make informed decisions on the best ways to mitigate flooding.

The flood waters flow with a quantity of sediment particles. Acoustic Doppler Current Profiler (ADCP) is able to detect such sediment particles through the analysis of backscattered acoustic signals. Sediment transport research during flooding helps in understanding how the riverbed may change regarding deposition or erosion and how this impacts future flood risks along the Araguaia River.

5. How can the data measured by ADCP be used for the flood warning and risk management of Araguaia river?

Flood warning

Velocity and flow data monitoring: ADCP current profiler continuously monitors the velocity-flow data of the Araguaia River. A sudden rise in the velocity or a drastic change in the rate of flow can indicate that a flood is imminent or intensifying. Such real-time data can be fed into early warning systems to provide timely alerts to the local communities, emergency responders, and other relevant authorities so that they may take necessary actions and initiate evacuation plans. Water Level Prediction and Warning: The flow data measured by ADCP current meter can be combined with other factors, such as the cross-sectional shape of the river and the history of water level records, to predict the future water levels. If the predicted water level is projected to reach or exceed the flood threshold, necessary warnings can be issued in advance for people to prepare and relocate to safer areas.

Risk management:Water Conservancy Project Scheduling Decision Support: The ADCP profiler output provides the prerequisite basis for decisions on operating water conservancy projects such as dams and weirs on the Araguaia River. For instance, if during a flood, the measured flow is too high, operators can manipulate the gates of the structures to regulate the flow of water and reduce the impact of the flood downstream.

Flood disaster assessment and emergency response: Based on the ADCP data, after a certain flood event has taken place, it will be possible to conduct an assessment of the flood hazard caused. It can help identify areas that experienced high-velocity flows, quantify sediment deposition, and other factors. This information will provide context to emergency response planning, including search and rescue operations, as well as plan post-flood recovery and reconstruction work.

6. What is necessary for high-quality measurement of the currents of the Araguaia River?

In general, several aspects will be important to obtain high-quality measurement of the Araguaia River currents. First, the reliability of the materials making up the equipment is of essence. The ADCP current meter should be able to withstand the harsh conditions of the aquatic environment: corrosion from the river water and impacts from floating debris.

This should also include small size and low power consumption. A compact and lightweight ADCP current profiler is easier to install and deploy at various locations along the river, especially in hard-to-reach areas. The small power consumption enables operation for longer times without frequent replacement or complex arrangements for power supply, making it operational continuously and for a long time. Cost also matters, and a lower cost allows more extensive deployment for comprehensive monitoring of the river.

In the question of casing material, the most excellent option will be the titanium alloy. The usage of a titanium alloy has a lot of advantages. It has high strength that enables the ADCP flow meter to resist mechanical forces that may befall it from the water. Its excellent corrosion resistance ensures that the equipment remains in good working condition even after prolonged exposure to the river water. Besides, its relatively low density contributes to reducing the weight of the device while retaining important structural integrity.

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

In choosing the equipment for current measurement in the Araguaia River, one should consider the purpose of measurement first. If horizontal cross-sectional flow measurement is needed, it should be a Horizontal Acoustic Doppler Current Profiler. The use of this would help attain accurate measurements of flow velocity and relevant parameters across the horizontal section of the flow in the river, and this can give insight into the lateral distribution of the flow.

In this regard, when there is a need to make vertical cross-sectional measurements, a vertical ADCP meterwould be more appropriate. It can precisely measure the velocity profile from the water surface to the riverbed along a vertical line and can be helpful for understanding vertical variations of flow within the river.

Besides, different frequencies are applied to different water depth ranges. Usually, an ADCP current profiler with a frequency of 600 kHz is ideal for a water depth within 70 meters. In contrast, an ADCP profiler frequency of 300 kHz is best applied to water whose depth reaches 110 meters. Choosing the appropriate frequency based on the actual water depth in the Araguaia River ensures better and more accurate measurement results.

There are a number of very famous ADCP current meter brands in the market, such as Teledyne RDI, Nortek, and Sontek. However, there is also a great Chinese ADCP brand: China Sonar PandaADCP. The casing is all made of titanium alloy, durable, and with very good performance. Moreover, the cost-performance ratio is very impressive. You can learn more about it from the official website: https://china-sonar.com/.

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