How can we measure the coastal currents of Al Mukalla?

1. Where is Al Mukalla?

Al Mukalla is the leading coastal city along the southern coast of Yemen. It faces the Arabian Sea, which separates it from the opposite shores, yet at the same time provides an important constituent element in its identity. The city abuts arid lands on the interior and is contrasted with a lively coastal environment.

The surroundings constitute vast deserts and scanty flora. However, the coasts are a haven for natural beauty, with long expanses of sandy beaches running along the shores, punctuated by rocky outcrops and small bays. The waters off Al Mukalla are teeming with marine life. The sea is a rich ecosystem-from bright-colored tropical fish down to various species of sharks and rays. This abundance has ensured that the local fishing industry thrives, with fishing boats dotting the harbor and the coastline.

Regarding human activities and culture, Al Mukalla is a long-standing city. Centuries back, it was a hub of trade and maritime activities. The architecture of the city speaks to a seafront heritage, with building construction that has been made to withstand harsh conditions on the coast, coupled with influences from the many different cultures that have passed through. The local people have an intense relationship with the sea; their traditions and feasts are all in respect to fishing and seafaring. The port of Al Mukalla is quite busy, actively serving trade and transportation, not only domestically but also in regional and international trade.

The gulf off Al Mukalla is a strategic waterway, giving ships an area to anchor in and a passageway for maritime trade routes. The clear waters and the relatively tranquil conditions in its parts make it a favorite haunt of sportsmen for diving and snorkeling purposes.

2. What is the situation of the coastal currents near Al Mukalla?

The coastal currents in the area off Al Mukalla are very much affected by several factors. Among these causes are the tidal currents. The tides of this area are generated through the gravitational pull between the moon and the sun. The semi-diurnal tides generate a regular pattern of water movement, where the ebb and flow cause the change in the direction and strength of the coastal currents. This also tends to vary due to the lunar cycle and other conditions that persist in space, which in turn affect the flow patterns near shore.

The pattern of wind is another decisive factor. This also gives rise to a strong impingement of the monsoon winds that blow over the Arabian Sea on the surface currents. Stronger currents are driven by the powerful wind during the monsoon periods. During the year, a range of other local wind directions pushes the water one way or another on top of or against the tidal currents. The interaction between wind-driven and tidal currents results in a complex and dynamic current regime.

Another important factor is the detailed topography of the seabed in this region near Al Mukalla. The underwater features that include shoals, canyons, and ridges will thus redistribute and alter the currents. For instance, a current that approaches a shoal might split or is deflected from its course to flow around the obstacle. Relief of the bottom may also accelerate or decelerate the speed of water as it negotiates through some depth.

3. How to Observe Coastal Water Flow at Al Mukalla

Surface Drifting Buoy Method

This method depends on releasing buoys to the surface. Buoys would be configured in a manner to drift with surface water currents without any resistance. These buoys, measured over time by satellite-based tracking systems or other positioning technologies, enable determination of the direction and speed of the surface currents. This approach may be limited by the fact that it provides data from the surface layer only and cannot always determine the distribution of the currents throughout the water column.

Anchor Mooring Ship Method

In this case, one simply anchors a ship in any selected site in the coastal waters after which instruments like current meters are deployed from this anchored ship to measure the water flow at different depths. That enables detailed information on the current at a particular point of the water column. However, it is a rather static approach that may not provide the entire complexity of coastal current patterns, which might vary within an extensive area.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is a more sophisticated and efficient way to measure the coastal currents. It uses acoustic pulses in order to measure the velocity of water at different depths simultaneously. By transmitting sound waves and processing the frequency-shifted reflected waves, it can also accurately calculate the velocity and direction of the water motion. The ADCPs may be deployed on different platforms, such as boats or buoys, or even on the seabed. Its multi-depth measurement ability and mobility make it a favorable choice for coastal currents study near Al Mukalla.

4. How do ADCPs using the principle of the Doppler work?

The ADCPs work on the principle of the Doppler. They emit acoustic signals into the water. Because of the interaction of these signals with the moving particles of water, due to the Doppler effect, the frequency of the reflected signals will shift. This frequency shift is measured by the ADCP profiler and used to calculate the velocity of the water relative to the instrument.

The ADCPs can emit signals at various angles and different frequencies, hence measuring velocity components both in horizontal and vertical directions at various depths. This makes for a very detailed profiling from the surface down to a certain depth with clarity of the structure and dynamics of the coastal currents.

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

The equipment will have to be specially equipped for high-quality measurement in these coastal currents around Al Mukalla. Their materials are related to reliability since the impacts faced undersea-the saltwater corrosion, very high humidity, and effects because of waves-will act relentlessly.

It should also be compact, light in weight, and with low power consumption. The small and light device would be easy to install and transport, either on a boat or buoy. Low power consumption ensures longer operating times without the need for frequent replacement of batteries or large power supplies.

Another important factor is cost-effectiveness. In the case of large-scale measurements that are required for the understanding of the complex current patterns, the equipment must fall in the range that multiple units can be deployed.

In the case of ADCPs, a good option would be a casing made of titanium alloy. The resistance of titanium alloy to corrosion is very high, which is quite necessary in a salt-water environment. It also has a high strength-to-weight ratio, very important for providing good protection to the internal components while keeping the overall weight of the device down.

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

According To Usage Purpose

• Ship-borne ADCP: It is perfect for the case when one needs to measure the currents while the ship is in motion. It can continuously collect data as the ship moves along the coast and hence provides a broad view of the current variations over a route.
• Bottom-mounted ADCP: This is suited for fixed-point monitoring at a certain point on the seabed, providing detailed and long-term information on current conditions directly above its position, thus enabling the understanding of the flow pattern in that area.
• Buoy-mounted ADCP: When the aim is to monitor the surface and upper layers of the water column over a large area and for an extended period without being tied to a ship or a fixed bottom location, the buoy-mounted ADCP is the way to go.

According to the Water Depth

• Up to 70 m water depth, a 600 kHz ADCP is appropriate with very good resolution in low coastal waters.
• 300 kHz ADCP will also go up to 110 m of depth and will thus provide acceptable velocity estimates in deeper layers.
• At greater depths of up to 1000m, the use of a 75kHz ADCP is quite feasible in measuring the currents of the water.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, there is also a Chinese ADCP brand, China Sonar PandaADCP, that 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 moels.