ADCP in the Chari River Flood Management

1. Where is the Chari River?

The Chari River is an important river in Central Africa. It originates from the Adamawa Plateau in Cameroon and flows right through Chad, finally draining into Lake Chad.

It passes through all manners of landscapes-mountainous and hilly parts of the plateau to the upper reaches, breaking into the plains of Chad downstream. This river is an important water resource for arid and semi-arid regions it traverses by providing water for irrigation and domestic use, supporting ecosystems such as wetlands and floodplains.

From the point of view of climate and rainfall, the catchments around the Chari River are tropical-savanna. A distinct wet season falls in the period between June to September. Within this period, the river receives most of the rain that is supposed to last it for the whole year. Rainfall from the upper catchment area on the Adamawa Plateau is essential for sustaining the volume of water in the river. The flow of the Chari River is entirely at the mercy of the pattern of rainfall, and in years when above-average rain falls during the wet season, there is a very real danger of flooding.

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

Heavy Rainfall during the Wet Season: The most dominant cause of flooding is heavy and continuous rainfall throughout the wet season. The fact that much water falls in a short period can very quickly raise the level of a river and its tributaries. Mountainous upper reaches will easily lead to rapid runoff and send large volumes of water downstream.

Topography: The vast floodplains and low-lying areas along the river provide room where water spreads out and collects. The plains of Chad are so flat that the flow of water is very slow, with a heightened possibility of flooding. The tributaries of the river contribute to the total volume of water during high discharges, which can be disastrous in this type of flood.

Deforestation and Land Use Changes: Deforestation in the upper catchment area reduces the interception and retention of rain by the forest, while increasing soil erosion and depositing the eroded soil in the river, reducing its carrying capacity. Land use changes through human activities of expanding agriculture or urban development disrupt the natural hydrological processes of water flow and drainage that increase flood risk.

It is, therefore, indispensable in understanding and managing the flow of the river during the flood event.

3. How do Doppler Principle-based ADCPs work?

ADCPs work on the principle of the Doppler principle. The instrument sends an acoustic signal into the water, which scatters off moving water particles and reflects the signal back to the ADCP current meter. Due to the Doppler effect, the frequency of the reflected signal changes.

This frequency difference is measured between the signal sent and the received signal by the ADCP current profiler. By analyzing the frequency shift, it calculates the velocity of water at various depths. It normally possesses several transducers responsible for sending and receiving acoustic signals in multiple directions in order to obtain a profile of the water velocity across a section.

For example, if the water is moving toward the ADCP, it produces a signal with a frequency higher than the emitted one and vice versa in the event that it is flowing away. Precise measurement of these changes in frequency, using appropriate mathematical algorithms, gives the ADCP flow meter an accurate estimation of the velocity of the water at several points within its measurement range.

4. Application of ADCP to the Chari River Floods

Velocity Measurement

Acoustic Doppler Current Profiler (ADCP) is important in the proper measurement of the velocity created by the flow of water in the flood events of the Chari River. The technique continuously monitors the water velocity at various depths and locations, hence providing real-time data on the speed at which the water is moving. This could be fundamental to determining the dynamics of the flood, that is, the direction and intensity of movement that the flood water would take.

Flow Measurement Application

ADCP current profiler can also measure the flow rate of the Chari River. By combining the measured water velocities at different points across a section in view with the known cross-sectional area of the river, one will derive the total volume of water passing through that section in every unit time-that is, the flow rate. The data obtained is critical in the general assessment of the water volume during a flood, and hence it is helpful in decision-making on flood control and water resource management.

Application in Sediment Transport Research

Apart from flow and velocity measurements, ADCP current meter is useful in studying sediment transport in the Chari River during floods. As the water moves, it carries sediments. The ADCP meter is able to detect changes in the backscattered acoustic signal due to the presence of sediments. Analyzing such changes, estimates of sediment amount and movements can be made, which is of fundamental importance for understanding the long-term evolution of the riverbed and the action of floods on the fluvial sedimentary environment.

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

Flood Warning

Monitoring of Velocity and Flow Data: The real-time flow velocity and flow data obtained by ADCP will be monitored incessantly. If the measured water velocity is beyond a certain threshold or if the flow rate increases anomalously, it may indicate that a flood peak is imminent or that a flooding event may occur. This gives the relevant authorities an early warning to implement effective measures, such as people moving from low-lying areas, reinforcing flood defenses, among others. Water Level Prediction and Warning: Measured flow data correlated with historical water level data and appropriate hydrological models enable the ADCP data to be used in prediction of future water levels. If the predicted water level is expected to exceed flood warning level, timely warnings can be issued to the public for preparation against the flood.

Risk Management

Water Conservancy Project Scheduling Decisions Support: The flow and velocity information from ADCP profiler can be used to make correct decisions on the operation of water conservancy projects like dams and sluices. For example, according to the measured water flow, water can be released from the dam into the Chari River to control the level of water during flooding. Assessment of Flood Disaster and Emergency Response: The ADCP data after the occurrence of a flood would be useful to quantitatively define the extent of inundation, velocity of floodwater, and deposited sediment amount. All this information is highly essential for drafting emergency response plans and for executing post-flood reconstruction and rehabilitation work.

6. What do high - quality measurements of currents in Chari River require?

In making high - quality measurements of the currents in the Chari River, many factors are to be considered. The equipment used in the measurement must contain reliable materials. The casing of the ADCP current profiler is of essence. It is desirable that the casing is made from titanium alloy. Titanium alloy contains several advantages. Therefore, high strength will let the equipment resist the pressure and impact of running water in the river, and highly resistant to corrosion is very important regarding the water environment of Chari River, which may contain various corrosive substances.

Besides material reliability, its size and weight should be small and light, respectively. This again turns out to be pretty easy to operate and install the ADCP flow meter at various parts of the river, especially for locations that are not easily accessible. The power consumption also should be low, so that it operates uninterruptedly for a longer period without changing the batteries too frequently or connecting to any power source. The cost of the equipment must also be relatively low to enable large-scale measurement. It means less expensive, but all-inclusive, and after that, more ADCPs can be installed across the Chari River to provide higher resolution with detailed information for flood regulation.

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

Selection of proper equipment for the measurement of current in the Chari River considers quite a number of aspects which include whether the type of measurement required is horizontal cross-section measurement; an HADCP should be selected. On the other hand, if it is for vertical cross-section measurement, a Vertical ADCP flow meter will be proper to be chosen.

The second is that different frequencies adapt to different water depth. For instance, a 600 kHz ADCP fits in the water within 70 m depth. If the Chari River water depth falls within this range, with matched measurement requirements, it should work. A 300 kHz ADCP, on the other hand, is more appropriate for deeper waters, say above 70 m up to 110 m; this will give a more precise record in such depth.

There are several known brands on the market, such as Teledyne RDI, Nortek, and Sontek. However, for those seeking an economical option, China Sonar PandaADCP is the best choice. 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.