How can we measure the coastal currents of Dahab?

1. Where is Dahab

The charming coastal town is lying on the Sinai Peninsula of Egypt, which overlooks the Gulf of Aqaba, itself a continuity of the Red Sea; this makes Dahab almost a haven to many seekers of natural beauty together with laid - back atmosphere.

The geographical setting of this little town is quite captivating. The coastline is a mixture of beaches and rocky shores, lapped by the clear, turquoise waters of the Gulf of Aqaba. The Red Sea region around Dahab is considered one of the world's most lively and diverse marine ecosystems. The area is host to an extensive array of coral reefs that form a complex and colorful underwater landscape. These reefs serve as habitats and a breeding site for thousands of fish species, apart from other marine animals including sea turtles and crustaceans.

As far as human activities are concerned, Dahab is a tourist attraction, particularly for those into water sports and diving. The town has a strong Bedouin heritage, and the local culture reflects both the Bedouin traditions and the influx of international visitors. Fishing is also part of the local economy, whereby the local fishermen rely on the rich waters of the Gulf of Aqaba.

The Gulf of Aqaba, in which the location of interest is nestled, represents a body of water relatively narrow, featuring some particularities in hydrographic characteristics. Surrounding mountains and arid landscapes influence local climate and wind conditions; these, in turn, would have an impact on the conditions of water circulation and coastal currents in the area.

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

A few aspects form the coastal currents of Dahab. First of all, the large-scale Red Sea circulation. Moreover, it is connected to the Indian Ocean through the narrow Bab el-Mandeb Strait, and its connectivity with the open ocean develops the overall movement of the water masses. Thermohaline circulation caused by changes in temperature and salinity influences the current pattern.

It is wind that plays a key factor. The winds that blow across the Gulf of Aqaba can have a mighty impact on the surface currents. For example, at certain times of the year, dominant winds drive the surface water in a specific direction and either enhance or modify the natural flow of the coastal currents. The topography of the seafloor near the coast of Dahab is another important determinant. Any of those underwater features, such as the coral reefs, canyons, and shoals, can make the moving water change direction and/or speed.

The tides also have an extraordinary effect. The gravitational pull of the moon and the sun displaces the sea level upwards and downwards, forming tidal currents. In the relatively narrow Gulf of Aqaba, these tidal currents interact with other factors in such a way as to set up a complex, dynamic pattern of water movement in this area.

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

Surface Drifting Buoy Method

The buoys are set free on the surface of the water and the currents are allowed to take them along. By utilizing satellite-based tracking systems or another positioning method, the motion of such buoys is observed over time to calculate the direction and velocity of the surface currents. Generally speaking, this method delivers the most valuable data about the surface layer and seldom gives the detailed profile of the currents at different levels.

Moored Ship Method

In this technique, a ship is made to moor in some position in the coastal area. The instruments on the ship will measure the characteristics of flow of water in the surroundings. This would give quite accurate data for the area surrounding the ship, but it has limitations. The presence of the ship itself can alter the local flow, and the spatial coverage is limited to the area surrounding the anchored ship.

Acoustic Doppler Current Profiler (ADCP) Method

Acoustic Doppler Current Profiler (ADCP) is a more advanced and efficient means of measuring coastal currents. Acoustic waves are used in ADCP meter to measure the velocity of water at different depths. It does this by first sending out acoustic pulses and then re-analyzes the reflected signals that are Doppler shifted. In this way, ADCP profiler can give highly detailed profiling from the surface into a certain depth. This allows for a more comprehensive understanding of the vertical structure of the coastal currents near Dahab and is less affected by external factors such as the ship's influence.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They emit acoustic signals into the water. Where the signals encounter moving particles in the water, sediment, plankton, or other small organisms, a frequency change occurs in the reflected signal. The change in frequency is proportional to the velocity of the moving particles.

The ADCP current meter has numerous transducers that emit and receive acoustic signals in different directions. By measuring the Doppler shift in multiple directions, it can calculate three-dimensional velocity components of the water. These velocity components are then integrated to arrive at the overall flow velocity and direction of the water at different depths.

5. What is required for high-quality measurement of coastal currents in Dahab?

Therefore, a machine intended to effectively carry out a measurement of coastal currents in Dahab requires the use of reliable materials. It will have to be resistant against the aggressive marine environment-that is, the corrosiveness of seawater and very high pressures at greater depths. Besides, it should also be small in size and lightweight for ease of deployment on a buoy, a small boat, or other available fixed platforms.

Low power consumption is very important, especially in the case of long-term monitoring. The equipment should be such that it can operate with limited power sources, say, batteries or solar plates. Cost-effectiveness will be another important factor. In case large-scale measurements are required to be carried out along the coast of Dahab, the equipment should not be too expensive.

In the case of ADCP flow meter casings, titanium alloy is the best material. It has corrosion resistance, which is essential for survivability in corrosive seawater. It also has an excellent strength-to-weight ratio, which allows a solid design with light weight. At greater depths, such high pressure can be better supported and will ensure the reliability of equipment doing deep-water measurements.

6. Selection of Correct Equipment for Measurement of Current

Based on the Purpose of Use

• Ship-borne ADCP: In cases where the intention would be to make measurements of the currents when the ship is in motion during a given voyage along the coast of Dahab, an ADCP would suit the purpose. It can be mounted on the hull of the ship and gather information while the ship sails.
• Bottom-mounted ADCP: A bottom-mounted ADCP shall be used for long - term fixed - location monitoring of currents near the seabed. It may firmly sit on the seafloor, giving proper information about the water flow close to the bottom.
• Buoy-mounted ADCP: If the aim is to measure the currents at various depths in a more flexible manner and over an area wider, then the buoy-mounted ADCP is favorable. It can drift with the currents to some degree while it collects data during its movement.

According to Different Frequencies

• For water depths up to 70m, a 600kHz ADCP would be effective. It has a higher resolution for the measurement suited to the generally relatively shallow waters along the coastline from Dahab.
• A 300kHz ADCP is better for depths extending between 70 and 110 meters. This has its optimal balance between measurement range and accuracy over medium-depth water.
• For waters deeper, into 1000m, it is recommended to use 75kHz ADCP for greater depths and more valid current data in the deeper parts of the coastal area around Dahab.

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.