How can we quantify the coastal currents of Xaafuun?

1. Where is Xaafuun?

Xaafuun is a coastal town in the East African state of Somalia. It lies on the Indian Ocean coast. This gives it a beautiful, dynamic coastal environment.

The coastline along this town is characterized by a meandering shore of sandy beaches meeting the usually warm and mostly clear waters of the Indian Ocean. Marine life in the area is very rich. Many species of fish exist, and the presence of coral reefs makes a very essential habitat for various marine organisms. The local people have been related to the sea since ancient times. Fishing is a significant part of economic activity and is part of local culture and heritage. It also takes part in the local and regional trade that moves such goods as fish, agricultural products, and other commodities. As such, the Xaafuun port contributes to the local economy of this village.

2. What is the situation of the coastal currents near Xaafuun?

The coastal currents around Xaafuun are controlled by a variety of variables. The large - scale ocean circulation patterns of the Indian Ocean are a huge influence. Among all the monsoon-influenced currents, the Somali Current is the strongest, where the Southwest Monsoon enhances the Somali Current and probably causes strong north-eastward-flowing currents along the coast. While, on the other hand, in the Northeast Monsoon, the current pattern may change with the flow being reversed or significantly modified.

The tidal forces also play a significant role. The regular rise and fall of the tides have effects on the speed and direction of the water movement. High tides can bring in stronger currents and may cover more of the shore area, while at low tides, parts of the seabed may be exposed and the pattern of the nearshore current changed.

Moreover, topography in the bottom topography at Xaafuun modifies the currents. Submerged ridges and canyons, as well as banks underwater, may either deflect or break up the flow in a current. These features give rise to intricate, localized flow features whereby the water swirls or abruptly changes direction near the coast.

Another critical factor is the wind, particularly due to seasonal monsoons. During the monsoon seasons, powerful winds can push the surface waters and, therefore, cause changes in the flow direction and flow velocities at different depths.

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

• Surface Drift Buoy Method: This involves the deployment of buoys onto the water surface, which just drift according to currents. By tracing the buoy movements, usually by satellite-based or other positioning systems, one can get information on the direction and speed of the surface currents. This method mainly provides data for the surface layer and may not give comprehensive understanding for the currents at different depths.
• Anchor Boat Method: This involves mooring the boat in coastal waters and, with the use of instruments, measuring the flow of water at different depths around the boat. While this can give more detailed information about the currents in the immediate vicinity of the boat, it suffers from limitations regarding area coverage and can be affected by the movements of the boat itself due to waves and other factors.
• Acoustic Doppler Current Profiler (ADCP) Method: ADCP current meter is an advanced and efficient way of measuring 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. Thus, ADCP current profiler has the added advantage of providing current profile information from the surface to quite considerable depths continuously, making it an ideal tool for observing coastal currents near Xaafuun.

4. Principles of operation: The working principle of ADCPs using the Doppler principle.

The principle behind ADCPs is the Doppler effect. They emit sound pulses of a known frequency into the water. Due to the presence of suspended sediment or other small organisms, the sound waves reflected from them will experience a frequency shift due to the Doppler effect, proportional to the velocity of the water carrying them.

The ADCP flow meter determines the frequency shift of the reflected sound waves from different directions and at different depths, enabling it to calculate the multiple dimension velocity components of the water flow-usually horizontal and vertical. An ADCP meter uses several acoustic beams to get a better view of the current structure. This allows for the construction of detailed current profiles that show precisely how the water is moving at different depths along the Xaafuun coast.

5. What's needed for high-quality measurement of Xaafuun coastal currents?

The equipment to be used for high-quality measurement of the coastal currents at Xaafuun should have the following characteristics: The materials from which the equipment was made of should be reliable in order to resist such tough conditions of the marine environment. It has to be resistant to saltwater corrosion, mechanical tension due to waves, and temperature fluctuations.

Its size should be as small as possible to allow deployment and to install on-site in various locations, such as on boats or on the bottom, or on buoys with ease. Besides, a light design will mean an excellent case of easy manipulation and transportation. Low power consumption is necessary in order to secure long-term activity independent from frequent battery change-over and wide-range power feeding. Economic profitability of the measurement sensors is also requested for large-scale deployment.

In the development of ADCP profiler casings, titanium alloy also proves to be a very commendable material. With high strength, it provides the possibility for it to sustain mechanical forces within the marine medium. It is highly resistant to corrosion by seawater, thus guaranteeing the service life of the machinery. Its relative low density in comparison with other metals makes it suitable in applications where there is a need to keep the weight in check, making it quite suitable and appropriate for marine current measurement machines.

6. How to choose proper equipment based on the actual measurement?

By the Utilization Purpose

• Ship-Borne ADCP: This is suitable when measurements needed while the ship is in motion. It gives one the continuous data regarding currents while sailing along the coasts. It would be helpful during research vessels and naval ships for surveys.
• Bottom-mounted ADCP: Very well-suited for long-term measurements with much stability at a fixed location at the seabed. The provided information on the current patterns over a longer period of time in a specific area is very detailed. It is useful for understanding the local hydrodynamic conditions.
• Buoy-mounted ADCP: Good for the measurement of surface and near-surface currents when the buoy is deployed in coastal waters. It helps in studying the interaction between the atmosphere and the ocean surface currents.

Based on Different Frequencies

• The 600kHz ADCP would serve relatively shallow coastal waters with a maximum depth of 70m quite well because current measurements are remarkably accurate within this range.
• A 300kHz ADCP will be better suited for water depths from 70 to 110 meters since it should provide enough water column penetration and, therefore, good quality data.
• In much deeper waters of up to 1000m, like in parts of the Indian Ocean near Xaafuun, the most suitable would be the 75kHz ADCP that can measure the currents throughout the water column.
• 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.