ADCP in the Lomami River Flood Management

1. Where does the Lomami River occur?

The Lomami River is of great importance in the Democratic Republic of the Congo and is a major tributary to the Congo River.

Geographically, it runs right through the heart of the Congo Basin rainforest, which is sharply etched on the very fertile and biodiversity-rich landscape teeming with a wide array of plant and animal species. Most of the reaches of the Lomami River lie in isolated reaches of the country with very little human infrastructure and form an integral part of the intricate web of water bodies that supports the entire ecosystem of the Congo Basin.

The area has a tropical climate for precipitation. The precipitation occurs throughout the year with no definite dry season. Precipitation is heavy and frequent to allow sustaining the volume and flow of the river. Rain accounts for the general humid environment and flooded surrounding rainforest.

2. What are the causes of flooding in Lomami River?

Intense and Prolonged Rainfall: With the continuous high and frequent rainfall in the area, just an increase in intensity or duration of rain may cause the river to flood. The additional volume of water can rapidly exceed the river's capacity. Due to the absence of a virtual insignificance of any dry season in which natural draining would have occurred and reduced the level of water, the river remains constantly at or near high-water mark.

Topography and Drainage: The basin of the rainforest in which the Lomami River falls is topographically flat. As a result, water spreads out easily. Along its course, it has huge floodplains and wetlands. These areas would fill up rapidly during heavy rains, causing the water to spill over and flood the surrounding areas.

Human and Natural Obstructions: Sometimes, the trees that fall and block the natural flow of the current, together with debris from the rainforest, intervene in and disrupt the natural flow of water. Further, in areas with some human activity involving small-scale logging or fishing camps, poor waste management and improper construction near the river disrupt the normal water flow and create probabilities for flooding.

It can therefore help in understanding the flow of a river during a flood event and its management.

3. How do ADCPs Using the Doppler Principle Work?

The Acoustic Doppler Current Profiler(ADCP) work by the so-called Doppler principle. The device sends an acoustic signal into the water. In case of water flow, this signal scatters on the moving particles of water. In this situation, because of the Doppler effect, the frequency of the signal reflected back to the ADCP changes.

The ADCP measures the Doppler shift between the frequency of the emitted signal and the one received. The analysis of such a frequency shift enables it to measure the velocity of water at different depths. Normally, the device contains several transducers that may send and receive acoustic signals in different directions. In this way, they can profile the velocity of water within a section of the river.

For example, if the water is flowing towards the ADCP profiler, then the reflected signal will have a higher frequency compared to the emitted one. On the contrary, in case water flows away from the ADCP meter, then the reflected signal will have a lower frequency. With precise frequency changes and appropriate mathematical algorithms, the ADCP flow meter will calculate precisely the velocity of water at a number of points of its measurement range.

4. Applications of ADCP to the Lomami River Floods

4.1 Velocity Measurement

ADCP current profiler plays an important role in the measurement of water flow velocity during flooding events of the Lomami River. It continuously monitors water velocity across depth and location for real-time data about the speed of the water. These records are important in providing insight into the dynamics of the flood by determining the direction and strength with which floodwaters might move.

4.2 Flow Measurement Application

Another capability of ADCP current meter is the measurement of flow rate in the Lomami River. These can be combined into the total volume of water flowing through a section per unit time-the flow rate-since measured water velocities at various points across the area will be used to attain this together with the previously secured cross-sectional area of the river. This information becomes vital when calculating the accumulated amount of floodwater and is also instrumental in making decisions regarding measures for flood control and management of water resources.

4.3 Application in Sediment Transport Research

Besides flow and velocity measurement, acoustic doppler flow meter has also found an application in sediment transport research of the Lomami River during flood conditions. As the water moves, it carries the sediments along with it. First, the ADCP can detect changes in the backscattered acoustic signal reflected by sediments. By analyzing these changes, an estimation of the amount and movement of sediments can be calculated, thereby contributing to the understanding of the long-term evolution of the riverbed and floods on the sedimentary environment.

5. How can the data measured by ADCP be used with respect to flood warning and risk management for the Lomami River?

5.1 Flood Warning

• Velocity and Flow Data Monitoring: Real-time flow data obtained is continuously monitored along with the velocity data by the acoustic doppler velocity meter. If the water velocity measured should happen to be above a certain threshold, or if the flow rate initially shows any sudden, significant increase, this can be an indication of an impending flood peak or flood situation. This will allow the necessary authorities involved-local conservation groups or a community within close proximity-to take proper measures in advance, such as moving to higher ground or securing the equipment and supplies needed to continue sustaining them.
• Water Level Prediction and Warning: Measured flow data correlated with the historical data of water level and appropriate hydrological models can help in predicting the future water level using ADCP data. If the predicted water level is expected to exceed a certain critical level, warnings can be issued to the local population, thus enabling them to prepare for the flood.

5.2 Risk Management

• Decision Support for Scheduling Water Conservancy Projects: The accurate flow and velocity information provided by ADCP will support decisions about any water conservancy projects that may be contemplated in the area. For instance, the pattern of flow would help in planning the construction of small-scale dams or diversion channels which could hold the water level and decrease the impact of floods.
• Flood Disaster Assessment and Emergency Response: Based on the flood event data provided by acoustic current meter, one can determine the intensity of a flood that involves the inundation area, velocity of flood waters, and the quantum of sediment deposition. This information is highly useful in formulating emergency response plans and also in conducting post-flood reconstruction and rehabilitation work.

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

A few things can be considered necessary for high-quality measurement of Lomami River currents. First, the equipment to be used should be of reliable materials. This casing is very important for the ADCP. Since the river water could be corrosive, given a large amount of organic matter and minerals in it, the casing should be manufactured from corrosion-resistant material like a titanium alloy. The high strength of the titanium alloy will help the equipment to resist the water pressure and impact in the river.

Besides material reliability, the size and weight of the equipment should be as small and light as possible. This will make it more feasible to install and operate the ADCP in different locations along the river, especially in remote and difficult-to-access areas in the rainforest. Another important one is the low power consumption that can maintain it running all the time, rather than changing the batteries or linking to a power supply frequently. The cost of this equipment should also be relatively lower to enable large-scale measurement. A lower cost means more ADCPs can be deployed along the Lomami River for more comprehensive and detailed data about flood management.

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

Given that appropriate equipment needs to be chosen for current measurement in the Lomami River, a number of aspects are to be considered. If the kind of measurement that is needed happens to be for horizontal cross-section measurement, it needs to be a Horizontal ADCP. Also, when the measurement is for the vertical cross-section, a Vertical ADCP will be appropriate.

Different frequencies suit different water depths. For instance, a 600 kHz ADCP would go for water depths within 70 m; if the water depth in the Lomami River is within this range and in the event that the measurement requirements match, a 600 kHz ADCP should work. While it will suffice for waters up to 70 m, for deeper waters ranging up to 110 m, a 300 kHz ADCP is more appropriate and can take more realizable data measurement in such depth areas.

There are several known ADCP brands in the market; among them are Teledyne RDI, Nortek, and Sontek. However, for a cost-effective option, China Sonar ​PandaADCP provides an inexpensive alternative. It is made of all - titanium alloy material, which ensures its durability and reliability in the water environment. Moreover, it offers an incredible 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.