How do we measure the coastal currents of Bosaso?

1. Location of Bosaso

Bosaso is a major port city found along the northeastern coast of Somalia, bordering the Gulf of Aden-a strategic waterway linking the Red Sea to the Arabian Sea.

The coastal area of Bosaso combines both sandy beaches and a bustling port infrastructure. It goes hand in hand with the economy of the city, fishing, and trade by sea, constituting the most prominent activities. From brightly colored fish and different species of crustaceans to an exceptional richness in coral reefs, the Gulf of Aden around Bosaso features warm and salty waters, teeming with life. The sea is connected with local people's centuries-old traditional and cultural upbringing. The port is an important link for both regional and international trade, facilitating the transportation of a wide variety of goods, including livestock, agricultural products, and manufactured goods.

2. What is the condition of the coastal currents near Bosaso?

The coastal currents off Bosaso are of a complex genesis. Large-scale ocean circulation in the Gulf of Aden and the adjoining Indian Ocean plays an important part. The local current regime is influenced by the Somali Current, a major ocean current in the area. This, in turn, is strongly influenced by the monsoon winds that change their direction on a seasonal basis.

The tidal forces are another great factor affecting coastal currents. The periodic rise and fall of the tides in routine ebb and flow sometimes alter the direction and speed of the movement of water. Another critical factor in the analysis is the topography of the seabed off the Bosaso coast. Local underwater ridges, canyons, and shoals may also be causing the redirection or disturbance in the flow of the currents and, therefore, creating a complicated and localized flow pattern close to shore.

The wind patterns, particularly the seasonal monsoons, have the capacity to drive the surface waters to result in changed directions and speeds of coastal currents. For example, during the southwest monsoon, the winds push the water in one direction, and during the northeast monsoon, it could either reverse the flow or modify it.

3. How to Observe the Coastal Water Flow of Bosaso?

• Surface Drift Buoy Method: Buoys are spread on the water surface and are allowed to drift with the currents. The motion of these buoys is usually monitored with the help of positioning systems based on satellites or other techniques, from which the information about the direction and speed of surface currents could be acquired. In this method, one mostly gets data for the surface layer, and comprehensive understanding of currents at different depths may not emerge.
• Anchor Boat Method: A boat is anchored in the coastal waters, and instruments are used to measure the flow of water at different depths around the boat. This, while it may give further detail about the currents in the immediate vicinity of the boat, has obvious limitations as regards area coverage and the movements of the boat itself caused by waves and other influences.
• ADCP Method: An acoustic Doppler Current Profiler is more refined and productive with respect to current measurements. This unit measures water speed with sound waves and simultaneously captures speed at more depths. They could be mounted differently, on a boat, or even from the bottom attached with buoys. The capability of ADCP meter to provide detailed and continuous data on current profiles from the surface to significant depths makes it a preferred choice for studying coastal currents in Bosaso.

4. How do ADCPs using the Doppler principle work?

The basic working principle of ADCPs is the Doppler principle. They send pulses of a particular frequency into the water. When these sound waves encounter moving particles in the water-such as suspended sediment and small organisms-the frequency of the reflected sound wave shifts because of the Doppler effect. This frequency shift is proportional to the velocity of the water carrying those particles.

Consequently, 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 several dimensions-usually horizontal and vertical. Several acoustic beams are usually used in an ADCP profiler to get a comprehensive view of the current structure. This provides detailed current profiles showing how the water moves at different depths along the Bosaso coast.

5. What is necessary for high-quality measurement of the Bosaso coastal currents?

In order to make high-quality measurements of coastal currents in Bosaso, the equipment used will need to possess a few characteristics: it should be manufactured from reliable materials that could withstand harsh conditions found in the sea; resistant to salinity, which corrodes steel and other metals; mechanical forces linked with wave movement; temperature extremes;.

The size of the equipment should be small enough to allow for easy deployment and installation in various environments, such as on boats, on the seabed, or on buoys. A lightweight design is also advantageous for ease of handling and transportation. Low power consumption is preferred to ensure long-term operation without frequent battery replacement or large-scale power supply. Cost-effectiveness is also necessary to realize large-scale measurement.

For the casing of ADCPs, titanium alloy is an excellent material. The mechanical strength of the titanium alloy is high, and therefore it will be able to bear the mechanical forces in the marine environment. It is very resistant to corrosion by seawater, hence ensuring the longevity of the equipment. Its relatively low density compared to other metals makes it suitable in applications where weight is of concern, which is in line with the requirements for coastal current measuring devices.

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

Based on the Use Purpose:

• Ship-borne ADCP: This is suitable when the measurement is required while the ship is in motion. It can provide a continuous record of the currents while the ship is sailing along the coast. It's useful for research vessels and naval ships during surveys.
• Bottom-mounted ADCP: Suitable for long-term measurements at a stable position on the seabed. They give very high-resolution current patterns in a restricted area over longer periods and also serve useful purposes for identifying the local hydrodynamic conditions.
• Buoy-mounted ADCP: It is good for surface and near-surface current measurements when the buoy is deployed in the coastal waters. This can help study the interaction of the atmosphere with the surface currents of the ocean.

Frequency-Based

• A 600kHz ADCP is good to go for fairly shallow coastal waters, with up to a depth of 70m, keeping in view the proper measurement of currents it provides in this range. For waters approximately between 70m and 110m deep, a 300kHz ADCP can be used where the signal can make its way through the water column to get dependable data.
• To deeper waters up to 1000m, as in some regions of the Gulf of Aden around Bosaso, the best measurement option to characterize the currents along the whole water column is represented by the 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.