ADCP's application in flood management of Lualaba River

1. Location of the Lualaba River

The Lualaba River is a major river in Central Africa. It flows through the Democratic Republic of the Congo. It constitutes an important part of the Congo River system, as it forms the upper stretch of the Congo River before it assumes the name Congo.

It rises in the highlands of the Katanga Province, and later meanders mostly in a southwest direction through savannas, forests, and wetlands. It ensures water not only for agriculture and fishing but also for the supply of water to the homes of the communities along its banks.

In terms of climate and rainfall, the region has a tropical climate. There is a significant amount of rainfall throughout the year, which contributes to the river's water volume. The wet climate means that the river is generally well - supplied with water, but heavy and persistent rainfall can lead to fluctuations in water levels and a risk of flooding.

2. Why Does the Lualaba River Flood?

Heavy Rainfall: One of the major causes of floods in the Lualaba River is indeed the plenty of rainfall in the area. Continuous heavy rain is able to raise the volume of water in the river very fast. Because of its large catchment area, a number of different tributaries and runoff areas come together into the Lualaba River.

Topography: The low-lying areas and the floodplains along the course of the river have provided space for water to spread out and collect. The water comes to a near standstill on account of the relatively flat areas and the heavy flow raises the chances of flooding. Where the confluence of tributaries can add more water during high-flow periods, this will further aggravate the flooding condition.

Human-Induced Changes: Human activities related to deforestation and improper use of land in the catchment area may alter the flooding profile of the river. Deforestation decreases the interception and detention functions of the forest, thus allowing more surface runoff and more water reaches the river faster.

First, Acoustic Doppler Current Profiler (ADCP) can be a useful tool in understanding and managing the flow of the Lualaba River during flood events.

3. How do ADCPs using the principle of Doppler work?

ADCPs work on the principle of Doppler. A device emits an acoustic signal into the water. Since the water is in flow, the signal interacts with the flowing particles of water. The frequency of the reflected signal to the ADCP current meter because of the Doppler effect changes when the acoustic signal is reflected back.

The ADCP measures the difference between the frequency of the emitted signal and the received signal. It calculates the velocity of the water at a variety of depths by analyzing this frequency shift. These devices usually possess multiple transducers that have the ability to send and receive acoustic signals in different directions. This enables them to create a profile of the water velocity across a section of the river.

For instance, if the water is moving towards the ADCP current profiler, the return signal will be of a higher frequency compared to the one emitted. If the water is moving away from the ADCP, the return signal will be of a lower frequency. Precise measurement of these changes in frequency, using the appropriate mathematical algorithms, allows the ADCP flow meter to correctly calculate the velocity of the water at multiple points along its measurement range.

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

Velocity Measurement

During flood events in the Lualaba River, ADCP current profiler  is crucial for accurately measuring the velocity of the water flow. By continuously monitoring the water velocity at different depths and locations, it provides real - time data on how fast the water is moving. This information is essential for understanding the dynamics of the flood, such as predicting the direction and intensity of the floodwaters' movement.

Flow Measurement Application

It can also measure the flow rate of the Lualaba River. By combining the measured water velocities at several points across a section of the river with the known cross-sectional area of the river, it can calculate the total volume of water flowing through that section per unit time (the flow rate). This information is essential in analyzing the general volume of water during a flood and for decision-making purposes on flood control and water resource management.

Use in Sediment Transport Study

Besides measuring flow and velocity, ADCP current meter helps in studying the sediment transport of the Lualaba River during flooding. The moving water carries sediments. The ADCP profiler can detect the changes in the backscattered acoustic signal due to the presence of sediments. From the analysis of these changes, it is possible to estimate the quantity and motion of sediments, which is relevant for the understanding of the long-term evolution of the riverbed and also the impact of floods on the river sedimentary environment.

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

Flood Warning

Velocity and Flow Data Monitoring: In this regard, real-time velocity and flow data from ADCPs are monitored continuously. If the measured water velocity is greater than a threshold value or the flow rate increases significantly, that may indicate an upcoming flood peak or possible flood occurrence. This allows the relevant authorities to take precautionary measures such as evacuating people from low-lying areas or strengthening the flood defenses.

Water Level Prediction and Warning: Measured flow data can be correlated with historical water level data by using appropriate hydrological models to predict future water levels based on ADCP data. If the predicted water level is likely to exceed the flood warning level, warnings can be issued to the public well in time so that they may prepare themselves against the flood.

Risk Management

Support to Water Conservancy Project Scheduling Decision: The correct data about flow and velocity by ADCP current profiler will help in operating water conservancy projects like the dam and sluice. It may thus, according to the measurement of water flow, adjust the release of water from a certain dam to control the water level in the Lualaba River and reduce the impact caused by floods.

Flood Disaster Assessment and Emergency Response: The ADCP data after the flood event would be helpful in assessing the magnitude of flood. It may comprise information like inundation extent, floodwater velocity, and quantity of sediment deposition. This kind of information is needed for formulating emergency response plans and carrying out post-flood reconstruction and rehabilitation works.

6. What is required for high-quality measurement of the currents in the Lualaba River?

High-quality measurement of currents in Lualaba River requires consideration of a number of things: equipment used must be made of reliable materials; casing of ADCP flow meter holds particular importance. Casings are recommended to be made from titanium alloy. It has a high strength that permits the equipment to bear the pressure and impact of the water flowing in the river. It is also highly corrosion-resistant due to the water environment in Lualaba River, which may contain various corrosive substances.

Besides material reliability, the size and weight of equipment should be small and light. This makes the installation and operation of the ADCP meter in various places along the river easier, especially in areas that are difficult to access. Low power consumption is also quite important, allowing it to operate continuously for longer without needing frequent battery replacement or attachment to a power source. The cost of the equipment should also be relatively low to enable large-scale measurement. A lower cost will mean that more ADCPs can be deployed down the Lualaba River for more comprehensive and detailed data in flood management.

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

When choosing the right equipment for current measurement in the Lualaba River, several aspects need to be taken into account. Firstly, depending on the type of measurement required, if it is for horizontal cross - section measurement, a Horizontal ADCP (HADCP) should be selected. If it is for vertical cross - section measurement, a Vertical ADCP is the appropriate choice.

Secondly, different frequencies are suitable for different water depths. For example, a 600 kHz ADCP can only be applied in water depths within 70 m. Therefore, if the depth in the Lualaba River lies within this range and the purpose of measurement fits, then the 600 kHz ADCP can be considered. In cases where the water is quite deep, even over 70 m up to 110 m, for example, a 300 kHz ADCP is desirable since it will yield better results at such a depth.

There are a number of well-known ADCP current profiler brands in the market, including Teledyne RDI, Nortek, and Sontek. However, for buyers looking to save money, an excellent option is the China Sonar ​PandaADCP. It is made of all-titanium alloy material that has been assured to be strong enough for use in a water environment. Besides, it can realize an incredible price-performance ratio. You can find more about it on their official website: (​https://china-​sonar.com/).

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