How can we estimate the coastal currents of Aqaba?

1. Where is Aqaba?

Aqaba is a coastal city in Jordan marking the tip of the Gulf of Aqaba in the South. It is an energetic port city that has a privileged topography.

The city is bordered by the Red Sea, with its shoreline being one long stretch of magnificent sandy beaches and crystal-clear waters. The Red Sea, surrounding this area, is literally a haven for marine life: it has extensive coral reefs considered to be part of a world-important ecosystem. These are home to huge varieties of colorful fish, mollusks, and other sea creatures, therefore making it a hot destination for diving and snorkeling enthusiasts.

On the human level, Aqaba is a hub of trade and tourism activities. It serves as a major entry point into Jordan for most of its imported and exported goods. Tourism also plays a very significant role, with tourists coming to see historical sites, such as old forts, and natural beauties. The local culture represents a mix of Jordanian traditions and the influence of sea-faring and trading communities that have been part of Aqaba's history.

The Gulf of Aqaba is a relatively narrow body of water, part of the Red Sea. The shape of the gulf and the topography around it have a great impact on the water circulation and the coastal currents. The mountains near the coast can affect the wind, which consequently influences the sea currents.

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

Various factors are involved in the establishment of coastal currents near Aqaba. The general circulation of the Red Sea is a basic determinant. The conjunction of the Red Sea with the Indian Ocean through the Bab el-Mandeb Strait determines the general pattern of water movement. Thermohaline circulation, caused by temperature and salinity gradients, plays its role in molding the currents.

The wind patterns play the decisive role. The winds crossing the Gulf of Aqaba can push the surface currents in a particular direction. For instance, the northerly winds during summer can push the surface water to move in a certain direction, affecting the movement of coastal currents. Another important factor is the seafloor topography near Aqaba. It is possible to observe that the water, while in flow, changes direction and speed due to the ridges, canyons, and shoals underneath the sea.

The tides have their share, too. The gravitational pull of the moon and the sun causes the sea level to rise and fall, creating tidal currents. In the narrow confines of the Gulf of Aqaba, tidal currents can combine with other factors in a complex pattern of water movement.

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

Surface Drifting Buoy Method

It is based on the deployment of buoys at the water surface, which are left free to drift due to currents. By using satellite-based tracking systems or other positioning ways to monitor their movements over time, information about the direction and speed of the surface currents can be acquired. However, this method gives more data for the surface layer; it may not provide detailed information about the currents for different depths.

Moored Ship Method

In this method, a ship is anchored at a particular place in the coastal area. Instruments on the ship measure the characteristics of the water flow in the vicinity. While this can provide quite accurate data for the area around the ship, it has its drawbacks. The presence of the ship itself might alter the local flow, and the spatial coverage is restricted to the area around the anchored ship.

Acoustic Doppler Current Profiler (ADCP) Method

Acoustic Doppler Current Profiler (ADCP) is a better and more efficient way to carry out the measurement of current in coasts. They make use of acoustic waves for measuring the range of water at various levels. Along with sending acoustic pulses, it depicts the detailed profile from top to a particular depth of currents through analyzing the reflected signal - shifted by Doppler. This provides a better understanding of the vertical structure of the coastal currents near Aqaba and is less susceptible to interference from external factors, such as the influence of the ship.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They send acoustics into the water. The frequency of the reflected signal changes once it interfaces with moving particles in the flow; this could be sediment, plankton, or even small organisms. The frequency change is proportional to the speed with which these particles move.

The ADCP current meter has several transducers, each emitting and receiving acoustic signals in different directions. Determination of the Doppler shift in multiple directions will yield the velocity components of water in three-dimensional space. These velocity components are then integrated to find the overall water flow velocity and direction at different depths.

5. What is needed for high-quality measurement of Aqaba coastal currents?

In any case, reliable materials must be used, high-quality measurement intended for Aqaba's coastal currents. It needs to be tough enough to support the strong marine environment outside: seawater with its corrosive effects, which depends partly on the pressure experienced at depth. A small, light sensor is preferred since this is an advantage for practical deployment methods it might be fixed to a buoy, taken by a light boat, or even launched from a fixed platform.

The power consumption by the equipment should be very low, especially in cases of long-term monitoring. Equipment should be able to function on limited power sources such as batteries or solar panels. Cost-effectiveness is another critical factor. To carry out large-scale measurements along the coast of Aqaba, the equipment used in the measurement process should be inexpensive.

For the casing of ADCPs, titanium alloy is one of the most suitable materials. First, it has very good corrosion resistance; thus, it can afford to resist corrosive seawater. Another important property is that this material has a very high strength-to-weight ratio that can be useful for durable but lightweight designs. It is more resistant to the high pressure in greater depths and therefore able to ensure the reliability of the equipment in deep water measurements.

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

Based on Usage Purpose

• Shipborne ADCP: Should the interest be in measuring currents while the ship is in motion or during a specific voyage along the coast of Aqaba, then the shipborne ADCP will be suitable. It can be fixed on the hull of the ship and measures data while the ship is sailing.
• Bottom-mounted ADCP: For long-term, fixed-location monitoring of the currents near the seabed, a bottom-mounted ADCP is the way to go. It can be firmly placed on the seafloor to provide accurate information about the water flow close to the bottom.
• Buoy-mounted ADCP: When the purpose is to measure currents at different depths in a more flexible manner and over an area wider, a buoy-mounted ADCP is preferred. It can drift to a certain extent with the currents and collect data during the movement.

According to Different Frequencies

• The 600kHz ADCP will suffice for waters of up to 70m in depth. This should yield high-resolution measurements suitable for the usually relatively shallow coastal waters found around Aqaba.
• Between 70 and 110 meters of water, the 300 kHz ADCP would be appropriate. In this case, it offers a good balance between the range and accuracy of the medium-depth water.
• For deeper waters, up to 1000m, a 75kHz ADCP is recommended. It can penetrate to greater depths and provide reliable current data in the deeper parts of the coastal area around Aqaba.

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.