How would the Duba coastal currents be measured?

1. Where is Duba

Duba is a coastal town situated in the region of Tabuk, Saudi Arabia, alongside the Red Sea. It is found between the arid desert landscapes deeper inland and the expanse of the Red Sea.

From the sandy beaches to the clear blue waters along its shores, it is a hallmark of the town. The Red Sea, especially off Duba, is known to host high marine biodiversity. Magnificent coral reefs-which create colorful and intricate underwater worlds-are one of its features. Such reefs are capable of housing a wide range of fish species, from very small colorful reef dwellers to bigger pelagic fish. They also attract various marine mammals and sea turtles, hence making the area a haven for marine life lovers.

Fishing is an important aspect of the local economy, whereby local fishermen depend on the bounty of the sea for their livelihood. Tourist activities are also gradually catching on with Duba being an increasingly popular destination for those seeking beautiful landscapes, tranquil water, water sports, and diving activities.

The waters off Duba are representative of the greater Red Sea ecosystem. The Red Sea is a semi-enclosed sea with its own characteristic circulation patterns; the coastlines around Duba are driven by these larger-scale movements but further influenced by local factors, including coastline geometry and the presence of significant underwater topography.

2. What are the coastal currents near Duba?

Coastal currents around Duba depend on a host of factors. On a large scale, the Red Sea circulation plays a major role. The inflow of water from the Indian Ocean via the Bab el-Mandeb Strait lays the general base on which the whole water movement within the Red Sea depends. Combined with the thermohaline circulation driven by differences in temperature and salinity, these determine the general flow patterns affecting the coastal currents around Duba.

Wind patterns also play an important role. Seasonal winds across the Red Sea can act to drive the surface currents. During some months, for example, northerly or southerly winds can push the water along the coast, strengthening or altering existing current patterns. The topography of the seafloor off Duba's coast is another important determinant. In such an area, underwater ridges, canyons, and shoals will make the water change direction and speed in its flow.

The tides, in their influence of gravitational pulls by the moon and the sun, are also present. The tidal currents are quite high in the coastal areas of Duba, especially within the bays and inlets. They interact with other factors to form a complex and dynamic pattern of water movement.

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

Surface Drifting Buoy Method

It consists of buoys deployed, free to drift according to currents. By following their movements by means of satellite-based tracking systems or other positioning methods, the direction and speed of the surface currents can be found after some time has elapsed. Still, this approach mainly yields data for the surface layer and may not give detailed information about currents at different depths.

Moored Ship Method

In this method, a ship is positioned at some place in the coastal area and instruments onboard the ship measure the characteristics of water flow in its surroundings. While this may give quite good data for the area surrounding the ship, it is not without limitations. The presence of the ship can affect the local flow, and the spatial coverage is restricted to the area surrounding the anchored ship.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP current meter is a more sophisticated and effective means of measuring littoral currents, using acoustic waves for the measurement of water velocity at various depth levels. The technique of ADCP profiler works by transmitting acoustic pulses and processing the Doppler-shifted reflected signals to yield rather high resolution of the current profile from surface to a certain depth. This can enable a better understanding of the vertical structure of the coastal currents near Duba and is less affected by external factors such as the ship's influence.

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

ADCPs are based on the principle of the Doppler effect. They send acoustic signals through the water. As soon as these signals strike moving particles in the water-sediment, plankton, or any small organisms-the frequency of the reflected signal changes. The change in frequency depends upon the velocity of the moving particles.

The ADCP current profiler has several transducers that emit and receive acoustic signals in different directions. It calculates the velocity components of the water in three-dimensional space by measuring the Doppler shift in multiple directions. These velocity components are then integrated to determine the overall water flow velocity and direction at different depths.

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

The equipment has to be made from good and reliable material for high-quality measurement of the coastal currents at Duba. This has to be resistant to that harsh marine environment: first, the corrosive action of seawater and then the high pressure at greater depth. It should not have a big size and weight to make its deployment on a buoy or small boat or fixed platforms easy.

Low power consumption is necessary, especially for long-term monitoring. The equipment should be able to operate on limited power sources, such as batteries or solar panels. Cost-effectiveness is another important factor in the equipment. In order to carry out large-scale measurements along the coast of Duba, the equipment has to be affordable.

For the casing of an ADCP meter, titanium alloy is a very good choice. The corrosion resistance is high in this alloy, so it can bear the salty seawater. The ratio of strength to weight is also high, so this material can be used in a strong but light case. This material can endure the high-pressure environment at a greater depth and guarantee the reliability of the equipment during deep-water measurements.

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

According to the Usage Purpose

• Shipborne ADCP: If the intention is to measure the currents while the ship is in motion or during a specific voyage along the coast of Duba, a shipborne ADCP is suitable. It can be installed on the hull of the ship and collect data as the ship sails.
• Bottom-mounted ADCP: The bottom-mounted ADCP could be considered for the monitoring of near-bottom currents over long periods at fixed locations. An upward-looking bottom-mounted ADCP would rest upright on the ocean floor and deliver flow information near the bottom.
• Buoy-mounted ADCP: When the objective is to measure the currents at different depths in a more flexible manner and over a wider area, then a buoy-mounted ADCP is preferable. It can drift to some extent with the currents and collect data during its movement.

Based on Different Frequencies

• Water depths of up to 70m would merit the use of a 600kHz ADCP, whereby high-resolution measurements could be carried out suitable for the relatively shallow coastal waters near Duba.
• Within the 70- to 110-m water depth, a 300kHz ADCP would be appropriate; it offers a good balance between measurement range and accuracy in such medium-depth waters.
• For deeper waters, say 1000m, it would recommend a 75kHz ADCP since it gives depth penetration and better current information where the area around Duba is relatively deep.

There are well-known ADCP 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, which provides excellent durability. It also offers an impressive cost-performance ratio. You can find more information on its website: https://china-sonar.com/.

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