How to Measure Water Current of Luapula River?

1. Where is Luapula River?

The Luapula River is a major river in southern Africa. It lies between Zambia and the Democratic Republic of the Congo. The headwaters of the river are situated in the highlands of Zambia, and it flows through a landscape that combines savannas, wetlands, and areas of thick vegetation.

This river is a vital part of the local ecosystem. It provides a habitat for a diverse range of wildlife: hippos and crocodiles can be seen languishing in its waters, while there are many species of fish that occur in the river. Wetlands along its edges support typical waterbirds like herons and storks. Besides, small fishing communities line the banks, along with villages. The local inhabitants derive their livelihood from fishing and small-scale agriculture carried out along the Luapula River. The river also plays its other role in the sense of transportation, whereby canoes are familiar sights on the waters.

Culturally speaking, the Luapula River enjoys particular importance in the traditions of local tribes. It is said that quite a number of stories and mythologies have always related themselves to this place for the generations that lived around them. The river, important for religious and social rituals of the tribes, contains in fact spiritual water.

2. What is the nature of flow in the Luapula river?

The Luapula River is important to the regions through which it runs. Its flow rate undergoes seasonal fluctuations. It is usually higher during the wet season, generally from November to April in the region. The river's flow increases significantly at this time of the year due to heavy rainfall in the upstream sections and the resultant overflow of surrounding wetlands. As a result, the current becomes stronger and can carry more sediment and nutrients downstream. These will enrich the floodplains and be good for the local agriculture and the overall health of the ecosystem.

During the dry season, which lasts from May to October, the flow rate decreases. The river still flows, however, maintained by groundwater seepage and the storage of water in its tributaries. The average flow rate depends on the level of precipitation in the catchment areas, the topography of the river basin that determines how water is collected and drained, and the water-use patterns of the local communities, including fishing and small-scale irrigation.

3. How to measure water current of Luapula River?

There are many ways of measuring the Luapula River water current, these include the following: -

Velocity Meter Method

Traditional techniques apply mechanical or electronic velocity meters. The meters are placed in the water at chosen locations and measure the velocity of the water passing. However, in order to achieve a good understanding of the current, multiple placements at different locations and depths must be done. This is quite time-consuming and cannot give a continuous profile of the current throughout the water column.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP is more efficient and of higher quality than any other current measuring technique. It relies on sound waves for simultaneous water-velocity measurement at various water-depth intervals. This it can achieve by transmitting acoustic signals, and with the reception of the signals after reflection from particles in water, coupled with analysis for Doppler shift, can create an efficient profile of the current all the way from the surface to the bed of the river. Therefore, accurate measurement of the current across the cross-section becomes easy and well documented.

Buoy Method

This is done by installing buoys in the river and observing the displacement of these buoys over time. The displacements of the buoys by the water current indicate the speed and direction of flow. This method, however, suffers from some drawbacks. It may not provide correct velocity measurements at different depths, and can be affected by extraneous factors such as wind and waves that can influence the movement of the buoys.

Of the available methods, the ADCP method is more advanced and convenient in the measurement of the water current of the Luapula River.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. When a water mass is in motion, an acoustic signal emitted from the ADCP transducer into the water reflects off the moving water particles and returns to the transducer at a different frequency; this change in frequency due to the movement is termed the Doppler shift.

If the water is flowing toward the transducer, the frequency of the returned waves will be higher than that of the emitted frequency; if it's flowing away, the frequency is going to be smaller. Measuring this very shift with precision at numerous angles and depth, ADCP will determine the actual speed in different directions along a number of levels across the column of water. This enables it to create a detailed profile of the water current, while at the same time giving very important information on the speed and direction of the flow from the surface to the riverbed.

5. What's needed for high-quality measurement of Luapula River currents?

For high - quality measurement of the Luapula River currents, the measuring equipment should have certain characteristics. The materials used in its construction need to be reliable to ensure accurate and consistent measurements. A small size is beneficial as it allows for easier deployment and retrieval in the river, especially in areas with difficult access. The equipment should also be lightweight to simplify the installation process and reduce the effort required for handling.

The low power consumption is necessary to enable the equipment to work for a long period without changing the batteries frequently or using a complicated power supply system. Cost-effectiveness is another important factor since it allows wider usage and larger-scale measurement campaigns.

For the casing of the ADCP, titanium alloy is an excellent choice. Titanium alloy has many advantages. It is highly resistant to corrosion, which is very important because the equipment is in contact with water that may contain different minerals, sediments, and pollutants. It has a good strength-to-weight ratio, which will enable a strong yet light casing. In addition, it will be able to resist mechanical stresses during deployment and operation in the flowing water of the Luapula River.

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

Two main factors must be considered when choosing the right equipment to measure the Luapula River current.

Depending on the usage purpose, for horizontal cross - section measurement, the Horizontal ADCP (HADCP) is the suitable option. This unit will calculate flow velocities over a horizontal plane of the river in such detail and accurately; it provides helpful insight into the current's lateral distribution. For the purposes of measurement with a vertical cross-section, the Vertical ADCP should be considered since its concept covers profiling current from the surface to the bottom along a vertical line in the water column.

The ADCPs of different frequencies suit different water depths: for instance, the ADCP frequency of 600 kHz suits a water depth within 70 m. This can, therefore, be used for current measurements in relatively shallow parts of the Luapula River. An appropriate frequency of an ADCP is 300 kHz to be applied for deeper waters up to 110 m, and that could be helpful in these places of the river.

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.