How do we go about mapping Kwango's coastal currents?

1. Where is Kwango?

Kwango is a province in the Democratic Republic of the Congo. It is found in the south-western part of the country. The Kwango River flows in this region, eventually joining the Kasai River.

The area has a tropical climate; it is well vegetated in most parts. This is evidenced by the local people who are engaged in activities like agriculture, fishing, and trade. The province is rich in natural resources with a diverse ethnic makeup.

Carrying with it sediments and nutrients that would affect the coastal environment, the waters of the Kwango River system finally reach areas where they could impact coastal processes-after passing through several other river systems to possibly reach the sea.

2. What is the condition of the current along the coast near Kwango?

The coastal currents in the vicinity of Kwango-insofar as it is the ultimate connection to the Atlantic Ocean via the Congo River system-are brought about by many factors. Of importance are tidal currents. On the Atlantic Ocean along the Congo-influenced coast, the tides are influenced by the gravitational pull of the moon and the sun. These tidal currents could be strong and may have a great influence on the movement of water in the estuaries and along the coast.

The discharge into the larger river systems and eventually into the sea gives a complex pattern of the Kwango and other related rivers. Freshwater input can cause density differences and influence coastal current patterns. A further major influence arises from wind patterns; trade winds and other seasonal winds drive the surface currents and interact with the river-influenced currents to give a dynamic flow regime.

The local bathymetry, in addition to the shape of the seabed within the estuaries and nearshore area, can redistribute and modify the flow of coastal currents. The bottoms with channels, shoals, and other features will speed up or slow down the currents, or even alter their course.

3. How to observe the coastal water flow of Kwango?

There are a few methods to observe the coastal water flow related to Kwango.

The Surface Drifting Buoy Method

This is a simple, practical method. Buoys are released into the water and are equipped with GPS or other tracking devices. As the buoys are carried by the currents, it can monitor their position and movement over time to determine the direction and speed of the surface currents. The buoys are designed to withstand the water conditions in the locality, with probable debris from the rivers and the influence of salinity as it approaches the sea.

Anchored Ship Method

The ship is anchored at an optimal location near the estuary or in the coastal area where the influence of Kwango waters is maximum. Current - measuring instruments are deployed from the ship to measure the velocity and direction of the water flow at different depths. However, this method has some limitations. The ship can be affected by waves and winds, which may lead to inaccurate measurements. Also, it is not very efficient for covering a large area.

The Acoustic Doppler Current Profiler (ADCP) Method

It is an advanced approach to measuring the flow of water in the coast, so to say, more efficient. An ADCP current meter is able to measure the velocity profile of water currents over a wide range of depths. They work by emitting sound waves into the water and analyzing the Doppler shift of the reflected waves. It gives a fine understanding of the current structure from the surface to the seabed.

4. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of Doppler. They emit acoustic pulses, that is, sound waves, into the water. These sound waves scatter off particles in the water, such as sediment, plankton, and other small particles. When these sound waves are reflected back to the Acoustic Doppler Current Profiler (ADCP), having bounced off the particles, the frequency of the reflected waves changes due to the Doppler effect.

If the particles are moving towards the ADCP flow meter, then the frequency of the reflected wave is higher than the original emitted frequency. If the particles are moving away from the ADCP, then the frequency of the reflected wave is lower. By accurately determining this frequency shift, the ADCP is able to calculate the velocity of the particles. Since the particles are in motion due to water current, the velocity of the particles that is measured will signify the water current velocity.

ADCPs can emit sound pulses in multiple directions, allowing them to measure the current velocity in three - dimensional space and at different depths. For example, in a vertical profile, they can measure the current velocity at different intervals from the surface to the seabed, providing a comprehensive picture of the current structure.

5. What’s needed for high - quality measurement of Kwango coastal currents?

The equipment needs to be made with reliable materials that will allow for high-quality measurements of coastal currents associated with Kwango. A durable casing is required due to the challenging environment with river-borne debris, possible salinity changes, and even wave action, especially closer to the sea.

The size of the equipment should be small to allow easy deployment, at least for locations that are rather difficult to access, as in small boats or shallow coastal waters. Low weight is advantageous for easier handling and installation.

Long-term measurements necessitate low power consumption. Besides this, cost-effectiveness is at issue if large-scale measurements should be allowed. For ADCPs, though, the casing is preferably to be made of titanium alloy. Titanium alloy possesses excellent resistance to corrosion, which is so crucial in the Kwango-associated water environment. In fact, it could easily resist the corrosive action of saltwater and possible impacts from the river water. It is also tough and has a high strength-to-weight ratio, providing a durable yet lightweight structure to protect the internal components of the ADCP profiler.

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

In choosing the right equipment for current measurement related to Kwango, the first consideration shall be its usage.

For Measurements from a Moving Vessel

A ship-borne ADCP meter would be appropriate. It would be able to deliver current data in real time while the ship is moving, therefore allowing a more detailed understanding of how water may flow differently in different places.

For Measurements at a Fixed Location near the Seabed

A bottom-mounted ADCP flow meter serves well. It can continuously monitor the current at a certain place and provide consistent data over time.

Where measurements that have to cover a wide area and do not have a specific depth restriction A buoy - type ADCP current profiler has a larger coverage area and is not restricted to any particular depth.

About the choice of frequency: for a water depth up to 70m, a 600kHz ADCP should be the optimum; for a depth between 70m and 110m, a 300kHz ADCP shall be better; and for very deep water up to 1000m, a 75kHz ADCP is recommended.

There are well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth considering. It is made of all - titanium alloy material and offers a great cost - performance ratio. You can find more information about it on the website: https://china-sonar.com/.

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