ADCP's application in flood management of Chambeshi River

1. Location of the Chambeshi River

The Chambeshi River is located in Zambia and forms one of the major tributaries within the catchment area of the Congo River. It originates from the highlands of Northern Province, Zambia.

As it flows, it passes through a range of landscapes including grasslands, woodlands, and wetlands. The river is a vital water source for local communities, providing water for domestic use, fishing, and some agricultural activities.

It falls under the tropics, given the climatic condition, and the rainfall pattern ranges from wet to dry; most times, it starts in November and moves into April. With this seasonal rainfall, inflow of tributaries, and runoff from the highlands, the river is adequately fed. This clearly shows a fluctuation in water levels and brings a case of flooding, especially during heavy and consistent rainfall.

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

Heavy Rainfall and Tributary Input: The heavy rainfall of the wet season is the basic cause of flood events. Because of the big catchment area of the Chambeshi River and various tributaries, a lot of water might enter the main channel in quite a short period of time. The water from the tributaries may combine with direct rainfall on the river itself, causing a rapid rise in water levels.

Topography: The floodplains and low-lying areas present along the course of the river let the water spread out and accumulate. The generally flat terrain in most parts of the river's path contributes to slowing the rate of water flow, thus easily causing flooding. The meeting of tributaries offers different waters at times of high flow and thus aggravates the flood situation.

Soil and Vegetation Changes: The changes brought about in the soil and vegetation cover by human activities or nature alter flood patterns. For instance, the reduction ofland absorbency and water retention capacity due to deforestation in the catchment area increases surface runoff and hastens the rate at which water feeds into the river, consequently increasing flood risk.

Acoustic Doppler Current Profiler (ADCP) is considered an effective equipment in managing the flow of the Chambeshi River during flood events.

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 ADCP measures the differential frequency between the emitted signal and the received signal. By analyzing this frequency shift, the velocity of the water at different depths can be calculated. These devices usually have multiple transducers that can send and receive acoustic signals in different directions. This enables them to profile the water velocity over a section of the river.

For instance, in the case where water is coming towards the ADCP current profiler, the reflected signal would have a much higher frequency compared to the emitted one. In contrast, if the water flow is away from the ADCP profiler, then the reflected signal will have a lower frequency than that emitted. With precise measurements of such frequency changes and appropriate mathematical algorithms, the ADCP can quite accurately determine the velocity of the water at various points within its measurement range.

4. The applications of ADCP to the Chambeshi River floods.

Velocity Measurement

Acoustic Doppler Current Profiler (ADCP) plays a vital part in determining the actual velocity of water flow during flood events of the Chambeshi River. It ensures real-time data on the rate of movement of water by continuously monitoring water velocity at varied depths and locations. This information is very critical in understanding the dynamics of floods, such as the direction and intensity of the movement of floodwaters.

Application of Flow Measurement

The ADCP current profiler is also capable of measuring flow rates in the Chambeshi River. By summing measured water velocities at multiple points across a cross-section area of known size, it can determine the volume of water flowing through that section per unit time, which is the flow rate. This information is crucial in estimating the general volume of the water during a flood, as well as for indications on flood control and management of the water resource.

Application in Sediment Transport Research

Apart from flow and velocity measurement, ADCP flow meter finds its application in the study of sediment transport mechanism in the Chambeshi River during flooding. While the water moves, it transports sediments. All effects due to the presence of sediments can be detected by the ADCP profiler, which acts on changes in the backscattered acoustic signal. Such changes, after being analyzed, give an estimation of the amount and movement of sediments, a factor very vital for understanding the long-term evolution of the riverbed and floods on the river's sedimentary environment.

5. How is the data measured by an ADCP useful in flood warning and risk management of Chambeshi River?

Flood Warning

Velocity and Flow Data Monitoring: In this regard, real-time velocity and flow data obtained from ADCP meter are continuously monitored. If the measured water velocity is greater than the threshold or if the flow rate is rising significantly, it may indicate the arrival of a flood peak or possible flooding. This, in turn, allows for early warning to relevant authorities for taking necessary mitigation measures such as evacuation of people in low-lying areas or reinforcing flood defenses.

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

Risk Management

Support in Scheduling Water Conservancy Projects: Precise flow and velocity data from ADCP flow meter will support decision-making on the operation of water conservancy projects relating to dam and sluice operations. For instance, using the measured flow rate of the water, the release of water from a dam can be controlled to manage the water level in the Chambeshi River in mitigation against flooding disasters.

Flood Disaster Assessment and Emergency Response: The ADCP data collected after the occurrence of a flood can be used to determine the extent of severity. This will involve details like the extent of inundation, velocity of the flood waters, and the amount of sediment deposition. Such information is useful in formulating emergency response plans and for carrying out post-flood reconstruction and rehabilitation work.

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

Many factors are needed to provide high-quality measurement for the Chambeshi River currents. First is the use of high-quality equipment made of reliable materials. Of particular importance is the casing of the ADCP current profiler, and it is recommended to be of titanium alloy. The strength of the titanium alloy is high enough to bear the pressure and impact of the flowing water in the river, while it is very highly resistant to corrosion-which is very important given the water environment in the Chambeshi River that may have a huge variety of corrosive substances inside.

Aside from material reliability, the size and weight of the equipment should be small and light. This makes the installation and operation of ADCP flow meter in various locations along the river relatively easier to manage, especially in areas that are inaccessible. Low power consumption is also important for longer continuous operation without necessarily needing to change the batteries or connect the device to a power source frequently. Finally, the equipment cost should be as low as possible to be able to measure on a large scale. With the lower cost, more ADCPs can be deployed along the Chambeshi River for more comprehensive and detailed data regarding flood management.

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

When choosing the right equipment for current measurement in the Chambeshi 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. As an example, a 600 kHz ADCP would be appropriate for water depths within 70 m. In this case, if the water depth in the Chambeshi River falls within this and the measurement requirements are appropriate, then a 600 kHz ADCP is workable. For deeper waters, those exceeding 70 m up to 110 m, a 300 kHz ADCP is more appropriate because it can give more accurate measurements in such depths.

Within the market, there are several famous brands: Teledyne RDI, Nortek, and Sontek. However, these are costly options; if the client is looking for a more economically reasonable solution, then the China Sonar PandaADCP will do. All-titanium alloy material ensures its durability and reliability in the water environment. Moreover, it offers an incredible cost-to-performance ratio. You can get 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.