How to Measure Water Current of Benue River?

1. Where is Benue River?

The Benue River is a major watercourse in West Africa. It is the largest tributary of the Niger River. It rises in the Adamawa Plateau in Cameroon and flows in a westerly direction through Nigeria.

It passes through grasslands, savannas, and floodplains. Down the course of its length, it also is an important lifeline to many communities. Scores of cities and towns, such as Makurdi in Nigeria, draw water from the Benue for water supply, fishing, and transportation. Its fertile floodplains are extensively used for agriculture and grow crops such as yam, cassava, and maize.

It culturally holds a place in the Benue River. This has deeply interlinked the tradition and belief of the ethnic locals. The river was told as part of folklore, religious and social ceremonies associated with it. A source of inspiration for local art, music, and dance.

2. What is the flow rate of the Benue river?

The flow rate of the Benue River is pretty variable and depends on seasonal rainfall events. During the wet season between April and October, the stream increases considerably. This is contributed by heavy rain in most parts of its catchment area, which includes most of the highlands of Cameroon. The water rapidly rises hugely, and the current becomes considerably strong, carrying an enormous sediment and debris load.

In the dry season, it decreases from November to March. The river still has a flow, but it is much slower. There are also man-made structures like dams and weirs that can regulate the flow to some extent. The average flow rate depends on a number of factors, including the amount of rainfall in the upstream regions, the efficiency of water management systems, and the topography of the river basin, which determines the rate of water runoff.

3. How to measure water current of Benue River?

There are various ways of measuring the water current of the Benue River.

Velocity Meter Method: It is the conventional method, where mechanical or electronic velocity meters are used. These meters are set up at discrete points in water and record the speed of the water passing by a meter. This method requires multiple placements at different locations and depths to arrive at an overall picture of the current. It may be a rather time-consuming process and is not able to give a continuous profile of the current through the water column.

ADCP Method: The ADCP current meter is a more advanced, efficient way of measurement of water current. It uses sound waves to measure simultaneously the velocity of water at different depths. By emitting acoustic signals and analyzing the Doppler shift of the reflected signals, it can create a detailed profile of the current from the surface to the riverbed. This allows for the actual and more precise measurement of the water current across different sections of the river.

Buoy Method: This is the method in which buoys are laid in the river and then followed for some time. The displacement of the buoys, depending upon the water current, reflects the speed and direction of the flow. This, however, is a method that can be employed to a limited extent only. It does not provide any accurate account of velocity at different depths. Further, this system can easily fall prey to outside interferences such as wind and ripples, which will eventually mark the buoy's travel pattern.

Of all these methods, the ADCP current profiler method is more advanced and convenient for the measurement of the water current of the Benue River.

4. How do ADCPs using the principle of Doppler work?

The operating principle of ADCPs is based on the Doppler effect. When an acoustic signal is emitted from the ADCP meter transducer into the water, the sound waves interact with the moving water particles. Because the water is in flow, the frequency of the reflected sound waves back to the transducer changes-a phenomenon known as the Doppler shift.

If the water is moving towards the transducer, then the frequency of the reflected waves will be higher than the emitted one. If the water moves away from the transducer, the frequency will be lower. By precisely measuring this frequency shift at multiple angles and depths, the ADCP meter can calculate the velocity of the water in different directions and at different levels within the water column. This enables it to create a detailed profile of the water current, providing valuable information about the speed and direction of the flow from the surface to the riverbed.

5. What’s needed for high - quality measurement of Benue river currents?

The equipment for high-quality measurement of the currents of the Benue River should possess some qualities. The materials used in its construction should be reliable to ensure that accurate and consistent measurements are obtained. A small size is an added advantage since it enhances deployment and retrieval in the river, especially in those areas that are difficult to access. The equipment should also be lightweight to simplify the installation process and reduce the effort required for handling.

The low power consumption allows operating the equipment for a long period, without the need to frequently change batteries or prepare complex supplies, while cost-effectiveness will facilitate more extensive usage and be able to handle large-scale measurement campaigns.

In terms of the ADCP flow meter casing, a titanium alloy is a perfect choice, "Titanium alloy boasts several positive features. It is highly resistant to corrosion, which is very important as the equipment is constantly in contact with water that may have various minerals, sediments, and pollutants. This material has a good strength-to-weight ratio, allowing for a casing that is durable but lightweight. This will be able to withstand all mechanical stresses occurring during deployment and in operation in the flowing water of the Benue River.

6. Selection of Appropriate Equipment to Measure Current

While choosing the right equipment for measuring current in the Benue River, two factors should be taken into consideration.

Accordingly, depending on the usage purpose, if the purpose is horizontal cross-section measurement, then the Horizontal ADCP current profiler (HADCP) is the suitable option. It is designed to precisely measure the flow velocities over a horizontal plane in the river, which helps in knowing the lateral distribution of the current. For a vertical cross-section measurement, the Vertical ADCP is more appropriate, since it focuses on profiling the current from surface to bottom along a vertical line in the water column.

Different frequencies of ADCPs suit different water depths. For instance, an ADCP with a frequency of 600 kHz is suitable for water depths within 70 m. It can provide current measurements in the relatively shallower parts of the Benue River with good accuracy. An ADCP current meter with a frequency of 300 kHz is more appropriate for deeper waters up to 110 m, which can be useful in areas where the river has greater depth.

There are well - known brands of ADCPs such as Teledyne RDI, Nortek, and Sontek. However, for those looking for a cost - effective option with good quality, the China Sonar PandaADCP is highly recommended. It is made of all - titanium alloy material and offers an incredible price - performance ratio. You can find out more about it on its website: https://china-sonar.com/.

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