How can we measure Shalateen's coastal currents?

1. Where is Shalateen?

A small coastal town at the southern parts of Egypt bordered by the Red Sea in an arid desert landscape where the deserts reach the sea.

It also has sandy beaches with rocky areas. The waters of the Red Sea around Shalateen are considered one of the richest areas in biodiversity. Shalateen has a strong coral reef area full of life, sheltering a range of fish from the tiniest and brightest reef dwellers to larger pelagic fish. Also, it is a place where sea turtles and other marine mammals exist.

Meanwhile, fishing constitutes an important human activity in the area, as it contributes highly to the local economy. Its tourism potentials have slowly transformed the place into a destination for tourists interested in visiting natural wonders or participating in various water sports such as diving and snorkeling.

The Red Sea, in which Shalateen is situated, is a semi-enclosed sea. Regarding the larger-scale patterns of the Red Sea, for instance, the inflow of water from the Indian Ocean through the Bab-el-Mandeb Strait, each has an impact on the circulations of water out there. Local topography-for instance, the shape of the coastline and features underwater, such as reefs and shoals-makes its impact known by shaping the water movement.

2. What is the situation of coastal currents around Shalateen?

Various elements interact in determining the coastal currents around Shalateen. First, there is the large-scale circulation of the Red Sea. The inflow of water from the Indian Ocean through the Bab-el-Mandeb Strait, with thermohaline circulation caused by differences in temperature and salinity, sets the general flow patterns affecting the coastal currents.

The wind patterns, in turn, are of much significance. Wind over the Red Sea is able to drive the surface currents. For example, different seasons might alter the course and speed of winds and therefore the direction and speed of the surface water. Another very crucial factor would be the seafloor topography of the seafloor adjacent to Shalateen's coastline. Any ridges, canyons, or shoals in the water make it change its course and speed when flowing.

Changes in the tides, related to gravitational pull from the moon and sun, also act. In the bays and inlets off Shalateen coasts, tidal currents can be very strong. These tidal currents interact with other factors in such a way as to form a complex, dynamic pattern of water movement.

3. How to Observe the Shalateen Coast Water Flow?

Surface Drifting Buoy Method

This technique utilizes buoys, which are positioned on the surface of the water and allowed to drift with the currents. By using a satellite-based tracking system or other positioning techniques to monitor the movement of a buoy over time, it would provide an indication of the direction and speed of the surface current. However, this technique mainly provides information for the surface layer itself and fails to give comprehensive information for currents at various other depths.

Moored Ship Method

Here, the ship is anchored at a specific location in the coastal area and used to measure the characteristics of the water flow with instruments on board. Although this indeed allows for quite precise results for the surroundings of the ship, it has some drawbacks: the presence of the ship influences the local flow, and only a small region can be measured in the vicinity of the anchored ship.

Acoustic Doppler Current Profiler (ADCP) Method

The measurement of coastal currents is rather more sophisticated and effective in the ADCP method than in the earlier-mentioned approaches. By propagating ultrasonic waves within a medium of water, ADCP gauges water's velocity across diverse depth profiles. Emitted pulses send back shifted echoes through the action of Doppler and analyze detailed information regarding currents at or from surface waters down to an attainable depth. This will provide a better understanding of the vertical structure of the coastal currents around Shalateen and be less affected by external factors, such as the influence of the ship itself.

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

The ADCPs work by the principle of the Doppler effect. They send acoustic signals through the water. These signals have a frequency change when they run into moving particles in the water-sediment, plankton, and small organisms in the flow-and reflect back to the instrument. This change in frequency is proportional to the velocity of the moving particles.

It consists of a series of transducers in an ADCP, where each transmitter emits and receives acoustic signals in multiple directions. Since it measures the Doppler shift in multiple directions, the three-dimensional components of water velocity are calculated. These further get integrated and calculate the mean flow velocity as well as direction at the different depth variations.

5. What is required by the high-resolution measurement of coastal currents of Shalateen?

High-quality measurement of the coastal currents in Shalateen requires the equipment to be made from reliable materials. The equipment must be able to withstand the harsh marine environment that includes high pressure at greater depths, along with the corrosive effect of seawater. It should be small in size and light in weight for easy deployment on buoys, small boats, or fixed platforms.

The power consumption is to be minimum, particularly for long-term monitoring. Equipment designed on limited power sources such as batteries or solar panels would be favorable. It should be cost-effective as well. For large-scale measurements to be made along the coast of Shalateen, the equipment must not be very expensive.

In the manufacture of ADCP casing, very good material will be titanium alloy. It provides a very high resistance to corrosion, which is necessary against the corrosive action of seawater. It will also provide the required high strength with light weight. In this way, this material will better resist such a high-pressure environment at greater depth and ensure reliability for deep water measurements.

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

By Purpose of use

• Ship-borne ADCP: In case the intention is to measure the currents while the ship is in motion or during a specific voyage along the coast of Shalateen, a ship-borne ADCP would be appropriate. It can be installed on the hull of the ship and collect data as the ship sails.
• Bottom-mounted ADCP: If it is for long-term fixed-location monitoring of the currents near the seabed, then a bottom-mounted ADCP will be perfect. It can be firmly installed on the ocean floor and is essentially employed for giving correct information about the water flow 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, a buoy-mounted ADCP is preferred. It can drift to some extent with the currents and collect data during its movement.

Based on Various Frequencies

• For water up to 70m deep, a 600kHz ADCP shall be sufficient; the resultant high-resolution measurements will be adequate for the reasonably shallow coastal waters off Shalateen.
• Between 70 and 110m water depth, a 300kHz ADCP would be more suitable. It gives an adequate balance between the measurement range in medium-depth waters. For waters as deep as 1000m, a 75kHz ADCP is highly recommended, since it can penetrate to greater depths and provide reliable current data in deeper parts of the coastal area around Shalateen.

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.