How to Measure Water Current of Volta River?

1. Where is Volta River?

It is the key river of western Africa. It began in Burkina Faso and goes its way through the majority of that country, from the arid and semi-arid regions to the north of Burkina Faso down to where the river, as a small stream, goes winding through savannas and farming lands.

Further downstream, the Volta River forms part of Ghana, where it becomes more fundamental, passing through bustling cities and towns like Akosombo. The Akosombo Dam, built on the Volta River, is one of the most marvelous feats of engineering; it was impounded to form Lake Volta, one of the largest artificial lakes in the world. Lake Volta stretches out for an area the size of a considerable portion of the country, supplying water for irrigation, fishing, and hydroelectric generation.

Traditionally, this river and the lake have enriched the life of the local communities. People living along its banks hinge much activity on the Volta River. Fishing is the most important economic activity, with a wide variety of fish species caught and sold in local markets. Boats and canoes ply their trade across the river, carrying people and goods across.

The Volta River basin has very good biodiversity. Major parts of its riverbanks are consumed by several plant species, including high-grown grass and trees shading and being the habitat for various animal species. Hippos, crocodiles, and a variety of bird species populate the river and the lake and their surroundings. This situation has influenced the cultural and economic life of the regions through which the Volta River passes since local festivals and traditions often take place around the river and the natural resources within it.

2. What is the flow rate in the Volta river?

The flow rate of the Volta River is very important in the regions it serves. The nature of the flow of the river varies with the seasons and rainfall around its catchment area. During the wet season, normally experienced between May and October in the region, the river markedly overflows. Its tributaries contribute volumes of water to the river as a result of which the main river channel swells.

Akosombo Dam can greatly regulate the flow rate by storing water in its reservoir during wet seasons and releasing it during dry seasons to keep the flow downstream as steady as possible. The consequences of the flow rate of the Volta River include that at Akosombo Dam, a consistent and adequate flow of water is called for if efficient power production is to be realized.

The flow of the river affects the fishing industries. Adequate flow is required to maintain fish health and its migratory pattern. Again, it is the flow rate that controls the sediment transportation. During high flow, sediments are transported downstream and deposited. This may impact the riverbed and quality of the water. In all, the flow rate of the Volta River is a factor that gives ecological, economic, and social well-being to regions wherein the river flows.

3. How to measure water current of the Volta River?

Measuring the water current of the Volta River can be achieved in several ways. Conventionally, one of the ways of measuring this is through the use of a current meter. These are mechanical devices put into the water at particular points along the river. They measure the speed at which the water is passing by, often through the rotation of a propeller or similar mechanism.

Another method involves the use of floats. These floats are deployed along the river and the time taken to cover over a known distance is measured; hence, the speed can be calculated using the formula for calculating speed: speed = distance / time. In this way, an approximation of the water current speed can be reached.

On the other hand, the measurement of water currents has been better and more efficiently done by the Acoustic Doppler Current Profiler(ADCP).

3.1 How do the ADCPs using the Doppler principle work?

The ADCP current meter work according to the Doppler effect. They emit acoustic pulses into the water column. These pulses interact with particles and other substances in the water. Since the water is in motion, this reflects changes in the frequency of the acoustic pulses.

If the water is moving towards the ADCP current profiler, the returning signal frequency is higher than the initially emitted. In the case when the water is moving away from the ADCP doppler, then its frequency is lower. Processing this Doppler shift, the ADCP flow meter can determine the velocity and direction at different depths.

This allows for profiling of the water current with information on how the current varies from surface to riverbed. In fact, this is quite crucial in the delivery of critical data that can be applied in deducing the various flow aspects of the Volta River due to different locations and further regulation by topographic structures such as the Akosombo Dam.

3.2 What is needed to have quality measurement of currents in the Volta river?

For high - quality measurement of the Volta River currents using ADCP meter, several requirements related to equipment should be achieved.

The device should be made of reliable materials. Since, in conditions of the Volta River environment, the temperature is very high, with high humidity and sediment presence, the ADCP profiler must be able to withstand all those factors.

It should be of a small size and compact. This is because the Volta River has a big expanse with several various points through which one may access it. A small device would therefore be much convenient in terms of transportation and deployment across various locations down and along the river.

A light ADCP would also be preferable. This enhances handling ease during installation and retrieval procedures, considering that some of the areas may be inaccessible.

Low power consumption: it will also be required to use low power so as to allow long term monitoring of the current of the Volta River, especially in those remote areas where sources of power may be very limited.

Cost-effectiveness: Large-scale measurements along the Volta River cannot afford costly equipment; therefore, whatever equipment is obtained must be cost-effective and not at the expense of quality.

For the ADCP casing, titanium alloy is the perfect material. With titanium alloy, the corrosion resistance is great, which is very important since the ADCP will be continuously submerged in the water of the Volta River; it may contain minerals and other substances that might cause corrosion over a period of time. However, this can be handled very well by the titanium alloy.

It is also robust and rugged and can withstand the physical forces that may arise at installation and in use. Such would include pressure fluctuations as the different levels of the water change and impacts from debris floating down the river.

3.3 How to Choose the right equipment for current measurement?

In the selection of proper equipment for the Volta River for measurement purposes, the intended use has to be a primary consideration.

HADCP is used where the objectives are to measure the horizontal cross-section of the river's current. The design of Horizontal ADCPs is essentially to deliver data that represents the current, across a horizontal plane within the river.

If emphasis has to be laid on acquiring a current vertical cross-section, then a vertical ADCP shall be highly suitable. The vertical ADCPs can provide variable details of the current from the surface to the riverbed in the vertical direction.

Taking depth into consideration, a 600kHz ADCP would be good for waters not exceeding 70m. At a higher frequency of 600kHz, you get the resolution you need for the accurate measurement of the current in shallower waters.

An ADCP with 300kHz frequency is most applicable for deeper waters up to a depth of 110 meters. The lower frequency of 300kHz allows deeper penetration through the water column in this much deeper area, hence is reliable in measuring current.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese ADCP brand, China Sonar PandaADCP, is also a great option. It is made of all - titanium alloy material, providing excellent durability and corrosion resistance.

Moreover, China Sonar PandaADCP offers an incredible cost - performance ratio. You can find more information about this brand on their website: https://china-sonar.com/.

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