ADCP's application in flood management of Luvua River

1. Where is the Luvua River?

The Luvua River is in the Democratic Republic of the Congo. It is a main tributary of the Lualaba River, itself a major contributory of the Congo River system.

The river has its source in the highlands of the Katanga Province. As it flows, it passes through a landscape that includes savannas, forests, and wetlands. Along its course, it provides water for various local activities such as fishing, agriculture, and domestic water supply.

In terms of climate and rainfall, the region has a tropical climate. It faces heavy rainfall throughout the whole year, and continuous water supply from precipitation is a main factor in maintaining its water flow. Such heavy rainfall often causes fluctuations in water levels, creating a potential for flooding if the rain is heavy or persists over a long period of time.

2. What are the reasons for floods in the Luvua River?

Heavy Rainfall and Tributary Input: The key issues that generally bring about floods include heavy rainfall in the catchment area, combined with the inflow from its tributaries. There is substantial rainfall around the catchment area of the Luvua River, and the water from several smaller streams and tributaries that feed into it can raise its volume in very short order. The rain-fed runoff from the surrounding highlands adds to the rising levels of water.

Relief: The low-lying areas and floodplains along the course of the river can easily allow the water to spread out and accumulate. Relatively flat regions slow down the flow of water, which increases its chances of causing floods. When the capacity of the river is exceeded by the influx of water, it overflows into these flood-prone areas.

Human - Induced Changes: Some human activities in the region can affect the flood patterns. For example, deforestation in the catchment area reduces the forest's ability to intercept and retain rainwater. This leads to more surface runoff and a faster influx of water into the river, increasing the flood risk.

Acoustic Doppler Current Profiler (ADCP) is an effective tool for understanding and managing the flow of the Luvua River during its flood stage.

3. How do ADCPs using the Doppler principle work?

ADCPs operate based on the Doppler principle. The device emits an acoustic signal into the water. As the water is flowing, the signal interacts with the moving water particles. When the acoustic signal is reflected back to the ADCP current meter, the frequency of the reflected signal changes due to the Doppler effect.

The frequency of the signal emitted is measured by the ADCP current profiler, against the frequency of the signal received. From this frequency shift, it can calculate the velocity of the water at each depth. These devices normally have multiple transducers that send and receive acoustic signals in various directions. This will enable it to obtain a profile of the velocity of water across a section of the river.

For example, if the water is flowing towards the ADCP flow meter, then the reflected signal will have a higher frequency compared to the one emitted. If it is flowing away from the ADCP profiler, the signal reflected will fall on a lower frequency. By precisely measuring these changes in frequency and with the appropriate mathematical algorithms, it is possible for the ADCP meter to correctly determine the velocity of the water at several points within its measurement range.

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

Velocity Measurement

During flood events in the Luvua River, Acoustic Doppler Current Profiler (ADCP) 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

Another thing that this ADCP current profiler can do is measure the flow rate of the Luvua River. It estimates the total volume of water that would run through the cut per unit time-that is, the flow rate-just by estimating water velocities measured at different points across the section and the known cross-sectional area of the river. The information provided is crucial in deducing the general volume of water in case of a flood and for decision-making on flood control and water resource management.

Application in Sediment Transport Research

Other than flow and velocity measurements, ADCP flow meter finds application in sediment transport research along the Luvua River during floods. When water flows, it carries sediments. The ADCP flow meter can detect the changes in the backscattered acoustic signal caused by the presence of sediments. By analyzing these changes, researchers can estimate the quantity and motion of sediments, a very important factor in understanding the long-term evolution of the riverbed and the action of floods on the river's sedimentary environment.

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

Flood Warning

Velocity and Flow Data Monitoring: In this regard, the real-time velocity and flow data from ADCP current profiler are continuously monitored. If the measured water velocity exceeds the threshold value, or there is a significant rise in the flow rate, then it might indicate that the peak flood is approaching or there is going to be a flood. It can be an early warning for relevant authorities to take certain necessary precautions like evacuating people residing in low-lying areas or taking extra measures to save the flood protective structures.

Water Level Prediction and Warning: Measured flow data correlated with historical data of water level and appropriate hydrological models can be used to predict future water levels from ADCP data. If the predicted water level is above the flood warning level, timely warnings can be issued to the public to get ready for the flood.

Risk Management

Water Conservancy Project Scheduling Decision Support: The proper flow and velocity data from ADCP flow meter  will support decision-making for the operating plan of water conservancy projects like dams and sluices. The regulation of the release of the dam's waters, according to the measured water flow, controls the water level in the Luvua River and lessens the impact of flood disasters.

Flood Disaster Assessment and Emergency Response: The data collected by ADCP current meter during the flood event can be used afterward to assess the severity of the flood. Inundation extent, velocity of flood flow, and deposition amount of sediment can be included. This information is vital in formulating emergency response plans and the carrying out of post-flood reconstruction and rehabilitation work.

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

The measurement of the Luvua River currents can be carried out with regard to several factors for its high-quality performance. First of all, the equipment used in the measurement should contain reliable materials. More specifically, this refers to the casing of the ADCP current meter. The casing is recommended to be made of titanium alloy. Titanium alloy has high strength, enabling the equipment to bear the pressure and impact of the water flow in the river, besides being highly corrosion-resistant-which is quite important, taking into consideration the water environment of Luvua River, which may contain various corrosive substances.

Other than material reliability, the size and weight of the equipment should be as small and light as possible. This makes it easier to install and operate the ADCP flow meter in various locations along the river, especially in areas difficult to access. Low power consumption is also very important, as longer continuous operation will be possible without frequent battery replacement or connection to a power source. Besides, equipment cost should be comparatively low to enable large-scale measurement. A lower cost means that more ADCPs can be deployed along the Luvua River, providing more comprehensive and detailed data for flood management.

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

The following aspects should be considered to choose the right equipment for current measurement in the Luvua River. First, based on the type of measurement it will be used for, if it is for horizontal cross - section measurement, then it should be a Horizontal ADCP. In the case of vertical cross - section measurement, it should be a Vertical ADCP.

Secondly, for different water depths, different frequencies are appropriate. For instance, a 600 kHz ADCP shall be suitable for water depths within 70 m. If the water depth in the Luvua River is within this range and the measurement requirements match, a 600 kHz ADCP can also be considered. In deeper waters, such as those over 70 m up to 110 m, a 300 kHz is more appropriate since it will provide an accurate measurement in such depth.

There are quite a few famous brands of ADCP current meter in the market, such as Teledyne RDI, Nortek, and Sontek. However, for those looking for a cost-effective option, PandaADCP by China Sonar is a great choice. Made from all-titanium alloy material, it ensures its non-fading durability and reliability in water. Besides, it can offer an incredible cost-performance ratio. You can learn more about it on its official website: (https://china-sonar.com/).

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