How then do we determine the coastal currents of Bargaal?

1. Where is Bargaal?

Bargaal is a coastal town in Somalia, facing the Indian Ocean. The position by the sea endows it with a unique coastal environment.

The coast of Bargaal is composed of sandy beaches stretching for miles into the clear blue waters of the Indian Ocean lapping on the shores. The sea here is rich in biodiversity, housing a wide range of fish species, from small reef-dwelling fish to larger pelagic species. Besides, there are extensive coral reefs in the vicinity, adding not only to ecological beauty but also serving as a vital habitat for numerous marine organisms.

The local community in Bargaal has a long and intimate relationship with the ocean. Fishing forms part of the basic elements that provide livelihood and character to this locality; it also encompasses the majority of the traditional values. Architecturally, traditions reflect a close contact with the sea. Bargaal's port, despite its smaller size in comparison to the big international ones, contributes immensely in regional and local marine trade and supports the importation of goods like fish, agriculture produce, and other items available locally.

2. What about the coastal currents around Bargaal?

Coastal Currents near Bargaal take an effect from numerous factors. On a broad spatial scale, a well-developed circulation pattern of the whole Indian Ocean is leading. The Somali Current, because of the close linkage with monsoon winds, plays an essential role in local current patterns:. In particular, during the southwest monsoon the Somali Current becomes greatly intensified, and can be responsible for very strong northeastward currents along the coasts, and during the northeast monsoon it switches to a new pattern of the flow.

Tidal forces also considerably affect the current that flows along the coast. Due to regular tides, or the rise and fall of the water level in oceans, the speed and direction of the water movement continuously change. A high tide would bring in heavy currents and, at times, cover more of the shore area, whereas a low tide exposes parts of the seabed which may lead to changes in the current pattern in the nearshore areas.

Topography of the seabed off Bargaal further influences the currents. The underwater topography comprising various features like ridges, canyons, and shoals may further deflect or disturb the current flow. This would lead to a complex and local flow pattern with swirls in water or a sudden change in the direction of flow very near the shoreline.

The wind patterns are another important factor, especially the seasonal monsoons. These strong winds of the monsoon seasons can drive the surface waters and lead to changes in the direction and speed of flow at different levels.

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

• Surface Drift Buoy Method: It is a deployment method whereby buoys are set on the water surface, which drift with the currents. By tracing these buoys, usually through satellite-based or other positioning systems, information about the direction and speed of the surface currents can be obtained. This method, however, principally delivers data on the surface layer and may not give a full understanding of currents at different depths.
• Anchor Boat Method: A boat is kept anchored in the coastal waters. Instruments are deployed to measure water flow at different depths around the anchored boat. It may give fairly detailed information about the currents in close proximity to the boat but has its shortcomings in terms of area coverage, and it will also be subjected to the effects of the boat's movements by waves and other factors.
• Acoustic Doppler Current Profiler (ADCP) Method: ADCP current meter is a more advanced and efficient way to measure currents. It uses sound waves to measure the velocity of water at multiple depths simultaneously. It can be deployed in different ways, such as on boats, on the seabed (bottom - mounted), or attached to buoys. The ADCP's capability to provide detailed and continuous data on current profiles from the surface down to significant depths makes it a preferred choice for observing the coastal currents near Bargaal.

4. How do ADCPs using the Doppler principle work?

ADCPs operate on the principle of the Doppler effect. The instrument sends pulses of sound out into the water at a particular frequency. Where these sound waves encounter particles (suspended sediment or small organisms) that are moving within the water, the frequency of the returned sound waves shifts due to the Doppler effect. This frequency shift is proportional to the velocity of the water that carries these particles.

By measuring the frequency shift of the reflected sound waves from different directions and at different depths, ADCPs can calculate the velocity components of the water flow in various dimensions-usually horizontal and vertical. Multiple acoustic beams are used in an ADCP current profiler to derive a more complete understanding of the current structure. This allows for the detailed current profile that shows just how the water is moving at different depths off the Bargaal coast.

5. What is necessary to obtain quality measurements of Bargaal coastal currents?

Such measurements of the coastal currents around Bargaal would require specific features in the equipment. First, the equipment material should be reliable enough to resist harsh conditions in the sea. It should resist saltwater corrosion, mechanical tension caused by waves, and changes in temperature.

The size of the equipment should be small to allow for easy deployment and installation in various environments, such as on boats, on the seabed, or on buoys. The lightweight design is also good for easy handling and transportation. Low power consumption is desirable to ensure long-term operation without frequent battery replacement or large-scale power supply. Cost-effectiveness is also an important factor to enable large-scale measurements.

In the manufacture of ADCPs, titanium alloy is a very good material for casing. Titanium alloy is of high strength and hence can resist the mechanical forces in the marine environment. It is highly resistant to corrosion by seawater, thus ensuring longevity of the equipment. Its relatively low density compared to other metals makes it suitable for applications where the weight factor is a concern, which goes well with the requirements for coastal current measurement devices.

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

Based on the Use Purpose

• Ship-borne ADCP: This is suitable when measurements are needed while the ship is moving. It can provide continuous data on the currents as the ship sails along the coast. It's useful for research vessels and naval ships during surveys.
• Bottom-mounted ADCP: These will be the most viable solution for measurement over a very long period and at a stable position on the seabed. It yields very detailed information on current patterns in certain areas over an extensive period besides giving insight into local hydrodynamic conditions.
• Buoy-mounted ADCP: Good for the measurement of surface and near-surface currents when the buoy is deployed in the coastal waters. It helps in studying the interaction between the atmosphere and the ocean surface currents.

Based on Different Frequencies

• Generally speaking, for relatively shallow coastal waters, up to a depth of about 70 meters, a 600kHz ADCP is considered appropriate because current measurements in such a depth will be quite accurate.
• On the other hand, for a depth of about 70-110m, a 300kHz ADCP would be most suitable because, in this area, the water column can be properly penetrated to retrieve reliable data.
• For waters as deep as 1000m, as in some areas of the Indian Ocean off Bargaal, the optimum current measurements throughout the water column will be provided by a 75kHz ADCP.
• There are well-known ADCP brands like Teledyne RDI, Nortek, and Sontek. However, for those looking for a cost-effective option, the China Sonar PandaADCP is a good alternative. It's made of all-titanium alloy material and offers an excellent cost-performance ratio. You can visit their website at https://china-sonar.com/ for more information.

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