ADCP's application in flood management of Luapula River

1. Location of the Luapula River

The Luapula River is located in Central Africa. It actually forms part of the boundary between the Democratic Republic of the Congo and Zambia on the southwest.

The source of this river is in Bangweulu Swamps in the territory of Zambia. While meandering northwards, the upper reaches of the river run through a number of wetland and floodplain terrain down to where it flows through mixed grasslands and woodlands. It serves as an important watercourse in the region: it provides the local people with water for fishing, household, and limited irrigation uses in agriculture.

Regarding the climate and rainfall, the catchment area of the Luapula River has a tropical climate with a pretty substantial rainfall within the year, with minimal seasonal changes. This high rate of rain falls, and the flat-lying course of the river through the flood areas, can bring sudden changes in the water levels and increase the likelihood of flooding to a greater extent.

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

Heavy Rainfall and Swamp Inflows: These are the principle causes of flooding in the Luapula River. Its catchment area receives substantial amounts of rainfall. The Bangweulu Swamps, which form the source of the river, similarly have the potential to release volumes of water. Whenever heavy rain falls over the swamps and the surrounding catchments, the combined water input into the Luapula River may cause a sudden rise in the levels.

Topography: On many reaches, the course has vast floodplains and low-lying ground. The flattening nature of the terrain slows down the travel speed of the water so that it spreads out and accumulates in big pools. Natural meandering of the river is sometimes joined by many tributaries feeding into it during high-flow conditions, thereby worsening the flooding situation.

Climate Variability: Climate-related factors include changes in rainfall patterns resulting from regional climate oscillations that may lead to changes in flood frequency and magnitude. In this case, the increased intensity or duration of the wet season may result in more serious flooding along the Luapula River.

Basically, Acoustic Doppler Current Profiler (ADCP) is a very useful tool in understanding and managing the flow in case of the Luapula River during flood events.

3. How do Doppler-principle ADCPs work?

The ADCPs use the principle of Doppler. The instrument sends an acoustic signal into the water. In turn, because the water is flowing, the signal clashes with the mobile particles of water. Then, upon return to the ADCP current meter, the frequency of the reflected signal does change due to the so-called Doppler effect.

The Acoustic Doppler Current Profiler (ADCP) counts the frequency of the emitted signal and the frequency received. From these frequency shifts, it calculates the velocity at different depths. These devices typically have multiple transducers that may transmit and receive acoustic signals in several directions. This is how they profile the water velocity across a panel of the river.

For instance, the reflected signal will be at a higher frequency than the emitted signal if water is flowing towards the ADCP current meter. If water is moving away from the ADCP, the reflected signal will come at a lower frequency. Precise measurement of these changes in frequency and application of the appropriate mathematical algorithms allow the ADCP profiler to determine the velocity of the water at various points within its measurement range.

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

Velocity Measurement

The Acoustic Doppler Current Profiler (ADCP) plays a crucial role during flood events in the Luapula River, with precise measurements of the water flow velocities. It provides continuous and real-time data on the rate of water movement at different depths and points. This information is critical for understanding the dynamics of the flood itself, such as predicting the direction and intensity of the floodwaters' movement.

Flow Measurement Application

Another purpose of ADCP current profiler  is measurement of the flow rate of the Luapula River. By integrating the measured water velocities at different points across a section of the river, with the known cross-sectional area of the river, it can calculate the total volume of water passing through the section per unit time-the flow rate. This information is crucial in the determination of the general volume of water in the instance of a flood and for decision-making on flood control and also water resource management.

Application in Sediment Transport Research

Besides the flow and velocity measurements, ADCP flow meter finds application in sediment transport research in the Luapula River during floods. Sediments are carried by flowing water. The ADCP meter is sensitive to changes in the backscattered acoustic signal due to sediments. Researchers can determine the quantity and movement of sediments from the analysis of such changes, important for the long-term evolution of the bed and flood consequences on the river's sedimentary environment.

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

Flood Warning

Velocity and Flow Data Monitoring: In real time, the ADCP current profiler provides continuous monitoring of real-time velocity and flow data. In case the measured water velocity is higher than the threshold value or if there is a marked increase in the flow rate, then that is a signal of flood peak approaching or floodlike situations. The early warning in this respect helps in taking necessary precautions by the authorities concerned, like evacuation of people in low-lying areas or strengthening the flood defenses.

Water Level Prediction and Warning: By correlating the measured flow data with historical water level data and using appropriate hydrological models, ADCP data can be used to predict future water levels. If the predicted water level is expected to exceed the flood warning level, timely warnings can be issued to the public, enabling them to prepare for the flood.

Risk Management

Supporting Water Conservancy Project Scheduling Decisions: The accurate flow and velocity data from ADCP profiler can contribute to the decision-making for the operating mode of water conservancy projects such as dams and sluices. For instance, according to the measured water flow, water can be released from a dam to control the water level in Luapula River to reduce the impact of floods.

Flood Disaster Evaluation and Quick Response: In the case of a flood event, the ADCP-collected data can be used for assessing its severity. This includes details like the inundation extent, the floodwater velocity, and the amount of sediment deposition. Such information is greatly important for formulating emergency response plans and for carrying out post-flood reconstruction and rehabilitation work.

6. What's needed for high - quality measurement of the Luapula River currents?

High-quality measurement of the Luapula River currents will depend on various aspects. First is the type of equipment, which needs to be made of reliable materials. The casing of the ADCP current profiler should be of much priority. It is recommended that the casing be made of a titanium alloy. The high strength of the titanium alloy is beneficial for withstanding the pressure and impact of moving water in the river. The alloy is also highly resistant to corrosion, which is essential considering the Luapula River water environment, which may comprise several corrosive substances.

Besides material reliability, the size and weight of the equipment should be small and light. This makes it easier to install the ADCP flow meter in different locations along the river-especially in some places with poor accessibility-and to operate it easily. Low power consumption is also important because longer continuous operation without frequent battery replacement or connection to a power source is highly desirable. Furthermore, the equipment cost should not be very high to enable large-scale measurement. A lower cost means that more ADCPs can be deployed along the Luapula River, providing more comprehensive and detailed data for flood management.

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

It includes a few aspects that need to be put into consideration while choosing appropriate equipment for current measurement in the Luapula River. First, the purpose of the measurement will determine whether it requires horizontal cross-section measurement or not; then an HADCP should be chosen. This is if it is a case of vertical cross-section measurement, where a Vertical ADCP would do.

Secondly, the frequency usually varies for different water depths. For example, a 600 kHz ADCP is appropriate for water within the depth of 70 m. In the case of the Luapula River, if the water depth falls within this and meets the requirements for measurement, then a 600 kHz ADCP can be considered. If the water is very deep, greater than 70 m up to 110 m, it will be appropriate to consider a 300 kHz ADCP.

There are some famous ADCP current profiler brands in the market, including Teledyne RDI, Nortek, and Sontek. However, if looking to save money, it is worth considering the China Sonar PandaADCP. The material used is all-titanium alloy, ensuring it will be durable enough and reliable in the water environment. Besides, it provides an extreme cost-performance ratio. You can find more information about it on its official website: (https://china-sonar.com/).

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