How to Measure the Water Current of the Zambezi?

1. Where is the Zambezi?

The Zambezi River is one of the massive waterways in southern Africa. It is among the most extensive rivers across the continent, flowing over a couple of countries such as Zambia, Angola, Namibia, Botswana, Zimbabwe, and Mozambique.

Its source is in the highlands of north-western Zambia, not far from the border with Angola. Further on, it meanders across different types of landscapes: high plateaus, savannah, and upper reaches. It progressively cuts deep gorges and valleys, with the most famous one being the Batoka Gorge.

It forms part of the core African ecosystem. From hippos and crocodiles in the water to elephants, lions, and literally tens of thousands of other animals on its banks drinking, all kinds of animals will be found in or around its waters and tributaries. The river supports large floodplains important to migratory birds and other wetland-dependent species.

The Zambezi River has been culturally at the heart of its people's life for a very long time. It provides the means for transportation, water for drinking and irrigation, and fishing areas. Additionally, it is surrounded by numerous good local traditions and stories. There are myths and magic around this particular river.

2. What does the Flow Rate of the Zambezi look like?

The flow rate of the Zambezi is highly variable and depends on many factors. There is a pronounced wet and dry season in the river. During the wet season, normally from November to April throughout most of its basin, heavy rainfall swells the river.

Because of this, the tributaries add to the flow, and the Zambezi can be a torrent of considerable power. One of the world's most spectacular waterfalls is located on the Zambezi-the Victoria Falls. During the wet season, from November through April, the volume of water going over the falls is enormous, and the flow rate in the river below the falls is very high.

During the dry season-which is from May to October-flow is considerably reduced. Downstream, this river narrows to width and sometimes breaks into smaller channels. The average flow also changes along the length of the river. Since the local patterns of rainfall and gradient of the land may be applicable for the upper reaches, while evaporation and extraction for irrigation may lower the flow downstream.

3. How to measure the water current of the Zambezi?

There is a number of ways in which the water current of the Zambezi is measured. Traditionally, one of the ways involves the use of floats. A buoyant object is let into the river and its time to travel a known distance is determined. This forms a general estimate of the surface current speed. This method has its limitations since it gets affected by wind and other surface disturbances.

The more traditional approach is with current meters. These are mechanical or electronic units placed in the water that measure the speed of water passing through them. These can be more accurate than floats but are limited to a single point in the water column.

One of the most advanced and most highly accurate ways of measuring the current of the water is by means of an ADCP current profiler.

3.1 How Do Acoustic Doppler Current Profiler(ADCP) Based on the Doppler Principle Work?

The principle of the Doppler effect has been utilized in the ADCP flow meter for their working. The instrument sends acoustic pulses into the water. These pulses scatter off suspended particles and other materials present in the water. Because of the movement of the water, the frequency of the reflected acoustic signals is changed.

This frequency shift is measured by the acoustic doppler flow meter, which utilizes the Doppler equation for calculating water velocity at various depths. Pulses can be emitted in different directions and at various frequencies to create a very complex profile of the current throughout the water column. This gives a more holistic view of the current structure of the river than traditional methods.

3.2 What is needed for high-quality measurement of the Zambezi currents?

The measuring devices need to be reliable, taking into account how harsh the conditions of the river are, whether it is during strong currents in the wet season, high sediment load, or the possible direct exposition of the elements.

The equipment should be compact and lightweight. This is an important consideration for ease of deployment, especially in remote areas along the river or from boats. The consumption of power is preferable to be low to enable long-time operation with a single set of batteries or limited external power sources. Cost-effectiveness, as relevant to large-scale measurements, is another factor.

Making the casing of acoustic doppler velocity meter with titanium alloy has certain merits. Its resistance to corrosion is very high, and that is a major requirement in this water-rich environment of Zambezi. It is also strong and durable to bear the physical forces exerted on to it from the river current and other possible impacts. It will be lighter and more convenient for installation and transportation.

3.3 How to Choose the right equipment for current measurement?

The equipment to measure the current of Zambezi will be selected with regard to the specifics that such measurement would entail. In horizontal measurements across a section, a horizontal ADCP, HADCP, can be utilized. This would provide a wide view of the current flow on a horizontal plane that would be useful in ascertaining general flow patterns of the river.

The vertical ADCP would be more proper for vertical profile measurements of the current. It would give more information about the velocity of the water at different depths, which is very important in the study of stratification and mixing of the water column.

With regard to frequency selection, a 600 kHz ADCP is quite suitable for the relatively shallow reaches of the Zambezi, say up to about 70 meters in depth. For deeper reaches reaching to about 110 meters in depth, one may have to use the 300 kHz ADCP.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option with good quality, the China Sonar PandaADCP is a great choice. It is made of all - titanium alloy, providing durability and resistance to the Zambezi's environment. It also offers an excellent price - performance ratio. You can visit https://china-sonar.com/ for more information.

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