ADCP for Kasai River Flood Management

1. Where is Kasai River?

The Kasai River lies in Central Africa. It forms part of the big tributaries of the Congo River. It flows through the Democratic Republic of the Congo and Angola.

It geographically crosses a wide range of different landscapes, which includes extensive plains, areas of savannah, and regions with substantial forest cover. It also flows past many small villages and towns that depend on it for their water supply, fishing, and transportation.

The Kasai River Basin has a tropical climate with well-marked wet and dry seasons. During the wet season, high volumes of rainfall are recorded with heavy downpours of rain. This high volume of rainfall replenishes the river with a lot of water, but it is also a risk since it can easily bring about a rise in water levels and flooding when inflow exceeds the natural drainage capacity of the river.

2. What are the Reasons for Floods in Kasai River?

Heavy Rainfall: Heavy and sustained rainfall in the wet season is a major cause of flooding in the Kasai River Basin. The river has a big catchment area, implying that large volumes of water from various regions converge into it. Where this inflow becomes more than the river can handle in a short period, the water level rises, causing flooding.

Topography: The surrounding terrain also makes the flood formation factor complete. Some stretches of the river have fairly flat regions along its banks. This generally flat topography contributes to slowing the natural flow of water, allowing it to accumulate rather than quickly disperse. There are also portions where the channel itself naturally has constrictive areas or obstacles to hinder the smooth passage of water and thus contribute to backing up and causing floods.

Land Use Changes: Human activities related to deforestation and expansion of agriculture in the river basin implicate the water cycle. Since deforestation reduces the rate of water absorption and retention capability of the land, this scenario increases surface runoff. The excessive runoff flows into the river, adding to the volume of water and heightening the risk of flooding. Against the backdrop of these flood challenges, the Acoustic Doppler Current Profiler (ADCP) offers a more modern and convenient means of measurement against the conventional methods.

3. How Do ADCPs Using the Doppler Principle Work?

The ADCPs rely on the principle of Doppler. They send out acoustic signals into the water. When these acoustic waves encounter the moving particles in water-like sediment grains or parcels of water with different velocities-the frequency of the reflected signals, due to the Doppler effect, is different from the emitted signals.

With ADCPs, these frequency shifts are analyzed in detail to calculate the velocity of the water at different depths. These usually contain several transducers oriented in various directions to measure the components of velocity in various directions, such as horizontal and vertical directions. By integrating these velocity measurements across different depths and sections of the river, important hydrological information can be determined, such as the flow rate of the river.

4. What Are the Applications of ADCP in Floods of Kasai River?

Measurement of Velocity: By using the acoustic doppler velocity meter , there is effective measurement of the flow water velocity of Kasai at different locations and depth which is quite helpful at the occurrence of flood as to how it is moving. It helps in identifying areas where the flow velocity is extremely high and could pose risks to riverbanks, bridges, and local communities along the river. It also allows for monitoring of changes in flow velocity over time as the flood progresses.

Flow Rate Measurement Application: Combining the measured velocity data with the cross-sectional area of the river, ADCP current meter can calculate the flow rate. This is crucial in assessing the overall volume of water passing through different sections of the river during a flood. It allows for the prediction of the flood peak flow and understanding its potential impact downstream, which is crucial for implementing effective flood management and mitigation strategies.

Sediment Transport Research: Flooding at the Kasai River causes a huge movement of sediment. ADCP current profiler can detect the sediment concentration and its movement by analyzing the echoes of acoustic signals affected by sediment particles. This information is important for learning how floods affect riverbed evolution, sediment deposition, and erosion processes in the river for maintaining the stability of the channel and the surrounding environment.

5. How can the Data Measured by ADCP be Utilized for Flood Warning and Risk Management of Kasai River?

Flood Warning

Velocity and Flow Rate Data Monitoring: Continuous monitoring of the velocity and flow rate data by ADCP flow meter allows for the early detection of abnormal increases in these parameters. When the flow rate approaches or exceeds certain critical values, it serves as an indicator of an impending flood peak, enabling timely flood warnings to be issued to communities and relevant authorities along the river.

Water Level Prediction and Warning: The establishment of a correlation between the flow rate and velocity measurements against the historical data on water levels can lead to model development, which will be able to predict the changes in future water levels. This provides an advance warning of the area that might get inundated with the height of floodwater, enabling people to take appropriate precautionary measures.

Risk Management

Decision Support of Water Conservancy Project Scheduling: It will enable ADCP profiler to contribute to the decision in operations related to small dams and reservoirs along the Kasai River, including adjusting the reservoir discharge according to real flow conditions in real time in order to mitigate downstream flood effects.

Flood Disaster Assessment and Emergency Response: Based on the records provided by ADCP, immediately after the occurrence of a flood, an assessment of the degree of the flood disaster could be done, including the area that has been flooded and the flow characteristics during the time of flooding. This guides the emergency response, such as relief resource allocation and post-flood recovery work.

6. What's Required to Obtain High-Quality Measurements of Kasai River Currents?

To obtain high-quality measurements in the Kasai River, a number of features become crucial. First, it should possess reliable material for this equipment since the river's conditions are prone to floating debris, variations in water quality, and possible impacts by the local wildlife.

The size of the measuring equipment should be relatively small, to facilitate installation and deployment at different locations in the river, especially in areas with limited access or in the more remote sections along the banks. A lightweight design is also beneficial as it simplifies the transportation and handling of the equipment during installation and maintenance. The power consumption should be low to allow for prolonged operation without the need to change power sources frequently or to burden the energy supply. Cost should be as low as possible to enable widespread deployment for sufficient coverage of the river.

The casing of ADCP is preferred to be made from Titanium alloy. Titanium alloy has several remarkable advantages. It has excellent corrosion resistance that allows it to stand in service for long periods of time in river water with various chemical compositions. It also possesses a high strength-to-weight ratio, which is sufficient to provide the required structural strength without letting the overall weight of the equipment increase beyond reasonable limits. Furthermore, it is durable enough to provide stable performance under the influence of different environmental factors in the river basin.

7. How to Choose the Right Equipment for Current Measurement?

The choice of the right equipment for current measurement in the Kasai River is based on several considerations. First, depending on the purpose of usage, if the focus is horizontal cross-section measurement, then HADCP can be suitable as it measures the flow velocity and its related parameters in the horizontal direction across the river section with good accuracy. The Vertical ADCP is more appropriate for the measurement of vertical cross-sections, since it can get detailed velocity profiles along the vertical axis of the river.

Different frequencies shall be chosen according to the actual water depth. For the water depth within 70 meters, an ADCP with 600 kHz is generally a good option to provide relatively accurate measurement results in this depth. Where water is deeper, up to 110 meters, the use of an ADCP at 300 kHz is more applicable since it can penetrate to such depth and provide reliable data effectively.

There are several ADCP brands on the market, such as Teledyne RDI, Nortek, and Sontek. However, I want to highlight one high-quality and cost-effective Chinese ADCP brand: China Sonar PandaADCP. The material is all from titanium alloy, ensuring very good performance and a long service life. Besides, the cost-performance ratio is pretty impressive. 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.