How to Measure Water Current of Senegal River?

1. Where is Senegal River?

The Senegal River is one of the major waterways in West Africa. Its origin is from Fouta Djallon highlands in Guinea. Then, it flows northwest up to about 1,800 kilometers through Guinea, Mali, Mauritania, and Senegal before it pours itself into the Atlantic Ocean.

It acts as a lifeline to the states it crosses because such areas can be occupied with floodplains, wetlands, and gallery forests. Of all those, floodplains are of particular importance due to the large agricultural activities they observe. Millet, sorghum, and rice are just but some of the produce from these rich soils rejuvenated by the floods every year.

The Senegal River serves as an important transportation route. Local communities use it to transport people and goods. It houses various wild animals, such as different fish species that are important for the local fishing industries, and many bird species whose nesting and feeding spot falls along the river and its wetlands.

2. What does the Senegal River flow like?

Because of the rainfall in its watershed, the Senegal River's flow rate is highly variable. This generally occurs during the rainy season, between June and October, during which the flow becomes much higher. The average value during this time is a few hundred to a few thousand cubic meters per second.

During the dry season, the flow is considerably reduced. Water extraction for agriculture and domestic use, along with the construction of dams on the course of the Senegal River, can affect its discharge. Dams are constructed to store water, control flooding, and generate hydroelectricity. Such structures could possibly manage the downstream flow if not well regulated, leading to shortages in the more downstream areas.

The flow in the Senegal River maintains the ecological balance of the various regions it goes through: by providing irrigation water for farming, maintaining the survival and health of the aquatic life, and by its contribution to the overall hydrological cycle affecting West Africa.

3. How to Measure Water Current of Senegal River?

There is a range of methods used in measuring the water current of the Senegal River.

Traditional Methods

• Float Method: Traditional and easy method to estimate the present speed is by using floats. A float-a marked buoy or any natural object such as a piece of wood-is dropped into the water. By noting the time taken for the float to travel a known distance the surface current speed can be determined. But this is only approximate surface flow and does not give the flow at different depths.
• Current Meters: These are the mechanical or electronic meters that can be submerged at specific points in water. These meters measure the velocity of water passing through them. While they can offer more accurate readings for the point at which they are installed, great care must be taken in their placement and they may not provide a full current profile of the river.

Advanced Method - Acoustic Doppler Current Profiler (ADCP)

This is more advanced and efficient in measuring the water current.

3.1 How do ADCPs Using the Doppler Principle Work?

ADCP current meter work on the principle of the Doppler effect. They send acoustic pulses into the water. As these pulses interact with the moving particles of water, due to the Doppler effect, the frequency of the reflected pulses changes. From that shift in frequency, the ADCP current profiler is able to determine the velocity at each depth.

The ADCP doppler has multiple transducers and sends acoustic signals in several directions. It is capable of measuring horizontal and vertical components of water flow. This enables a three-dimensional mapping of the water current, which is going to be very helpful in understanding the flow of the Senegal River for an apparently complex pattern.

3.2 What's Required to Provide High Quality Senegal River Currents Measurement?

Regarding the high quality of measurement in the Senegal River, ADCP flow meter is very dependent on equipment characteristics. First and most importantly, the casing should be of reliable material; for that matter, Titanium alloy can be a very good selection.

The other advantages of titanium alloy are numerous. It is light in mass, which is good for easy handling and deployment of the ADCP meter in often very remote and difficult places along the Senegal River. Other advantages include good resistance to corrosion. Considering chemical composition in Senegal River water and sometimes harsh environmental conditions in West Africa, corrosion-resistant properties of titanium alloy will ensure long-term accuracy and reliability of the ADCP profiler.

Besides that, it is also preferable that this ADCP will have low power consumption and is low in cost for the extensive measurements along Senegal River. A low-power-consuming ADCP will be allowed to operate longer, thus appropriate for performing continuous monitoring. On the other hand, an inexpensive ADCP can be deployed in wider manners without spending high financial costs.

3.3 How to Choose the Right Equipment for Current Measurement?

Another very important factor in the choice of the right ADCP for measuring Senegal River current is the purposed use. The flow can either be horizontal across a section of the river, in which case a HADCP is appropriate. HADCPs are designed such that they do offer the horizontal velocity components of the water current with rather fair accuracy. 

Vertical Flow Profile Measurement: Vertical flow profile measurement will be better with a VADCP. VADCPs are designed to measure the speed of water along a vertical line in a river at a number of depths.

Frequency: A 600 kHz ADCP will work for the shallower parts of the Senegal River for water depths up to about 70 meters. In deeper sections, it is better to use a 300 kHz ADCP since it provides reliable measurements up to about 110 meters.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option with good quality, China Sonar PandaADCP is worth considering. It is made of all - titanium alloy material and offers an excellent cost - performance ratio. You can find more information on their website: https://china-sonar.com/.

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