How to Measure the Water Current of the Kagera River?

1. Where is the Kagera River?

In East Africa, the Kagera River is a significant source of water. In fact, it was known to be one of the sources of the Nile River. This river rises in the highlands of Burundi and Rwanda and flows across Tanzania to Uganda.

The Kagera River passes through various landscapes, including mountains, hills, and plains. Along its course, it is an important source for the communities it serves. It provides water for drinking, irrigation, and livestock. The fertile plains near the river are used for agriculture, with crops such as bananas, maize, and coffee being grown.

Cultural impacts bind the Kagera River with the lives of local people. It is included in their traditions, stories, and even religious beliefs. Most festivals and ceremonies are associated with this river and its flooding-low-flow periods.

2. What is the Nature of Flow Rate in the Kagera River?

The flow rate of the Kagera River is highly variable. It is influenced by the seasonal rainfall in the region. During the wet season, which usually occurs between March and May and October and December, the river has a considerable increase in flow. Heavy rainfall in the highlands of Burundi and Rwanda raises the level of water and makes the current strong.

It diminishes its flow rate during the dry season. The river normally has a flow but does so at a very meager rate. The average rate is basically depended upon: the rainfall amount over upstream areas, topography responsible for the collection and runoff into the river basin, water utilization by local people as well as for agricultural purpose.

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

There are many ways of measuring the water current of Kagera River:

Velocity Meter Method: Conventional methods involve mechanical and electronic velocity meters. It involves placing these meters within the water at strategic points to determine how fast the water is moving over them. However, these measurements must be taken multiple times at different locations and sometimes at different depths to get an effective understanding of the current, as this can be very tedious and may not result in a continuous profile across all water columns.

ADCP Method: ADCP current meter is a more advanced and efficient way of measuring water current. It uses sound waves to measure the velocity of water at different depths simultaneously. 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 a more complete and accurate measurement of the water current across different sections of the river.

Buoy Method: In this method, buoys are located in the river and their movements are followed over time. The displacement of the buoys due to the water current gives an indication of the speed and direction of flow. However, this method has limitations: it may not provide very accurate velocity measurements at different depths and can be affected by external factors such as wind and waves, which can influence the movement of the buoys.

Among these, the Acoustic Doppler Current Profiler (ADCP) method is a more advanced and convenient option of measuring the water current of the Kagera River.

4. How Do ADCPs Using the Doppler Principle Work?

The operating principle of ADCPs is based on the Doppler effect. When an acoustic signal from the ADCP current meter transducer is emitted into the water, sound waves start an interaction with the moving particles of water. In cases when the water is in flow, the frequency of reflected sound waves back to the transducer changes-a thing that is generally called a Doppler shift.

If the water is moving towards the transducer, the frequency of the reflected waves will be higher than the emitted frequency. If the water is moving away from the transducer, the frequency will be lower. By precisely measuring this frequency shift at multiple angles and depths, the ADCP flow 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 Kagera River Currents?

The equipment for measurement of the Kagera River currents should have the following features for high-quality measurement: The materials used in its construction need to be reliable for accurate and consistent measurement. A small size is beneficial for easier deployment and retrieval in the river, especially in areas that are difficult to access. The equipment should also be lightweight to simplify the installation process and reduce the effort required for handling.

Low power consumption is essential to ensure that the equipment can operate for extended periods without the need for frequent battery replacements or a complex power supply setup. Cost - effectiveness is another important factor as it enables more widespread use and larger - scale measurement campaigns.

When it comes to the casing of the ADCP meter, titanium alloy is an excellent choice. Titanium alloy has many advantages. It is highly resistant to corrosion, which is essential since the equipment is always in contact with water that may contain various minerals, sediments, and pollutants. It also has a good strength-to-weight ratio, allowing for strength with light weight in the casing. Additionally, it resists mechanical stresses during deployment and operation in the flowing water of Kagera River.

6. How to Choose the Right Equipment for Current Measurement?

The selection of the appropriate equipment for the measurement of the current of the Kagera River would be based on two basic considerations:

Depending on the purpose of usage, for a horizontal cross-section measurement, the HADCP is the suitable one. This model aims to correctly quantify flow velocities over a horizontal plane of the river. The intention is also for lateral analysis that determines current distribution. On the other hand, in case one desires the measurement on the vertical cross-section, then he needs Vertical ADCP as the more fitting model that targets profiling on the surface from top to bottom through the line profile in the column of water.

Different frequencies of ADCPs correspond to different water depths. For example, an ADCP profiler frequency of 600 kHz can work for water depths up to 70 m. It would be efficient in giving the correct measurements of current in relatively shallow areas of the Kagera River. On the other hand, the 300 kHz will be more suitable for greater water depths up to a depth of 110 m, useful in those areas of the river where it possesses 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.