What could we use to measure coastal currents in Al Wajh?

1. Where is Al Wajh?

Al Wajh is an elegant port city found on the northwest of Saudi Arabia on the shores of the Red Sea. This city faces lands covered with sand on its backyard, and in its foreground lies the energetic Blue Gulf of the Red Sea. The area surrounding this coastal city of Al Wajh is characterized by incredible natural beauty. It's a haven for lovers of beaches, comprising soft sandy beaches laced with clear turquoise waters. The Red Sea in this region is known for its very special marine ecosystem. A big variety of colorful coral reefs forms a labyrinth-like structure under the water surface. These reefs are a habitat for highly rich and varied marine species that range in size from the small, brightly colored fish to larger predators.

As far as human settlement goes, Al Wajh assumes the form of a small town with an economically viable population: one that pursues different activities. There is much fishing, with fishers going into the sea each day to return with numerous catches. The city also includes a growing tourism industry because of the unspoilt beaches and the opportunity given to tourists to explore the underwater world.

The Red Sea, a semi-enclosed sea of which the adjacent waters of Al Wajh form part, determines a characteristic of the gulfs and bays in its vicinity. Water circulation within them is driven by larger Red Sea patterns, while also influenced by the local topography, including the coastline shape and islands or other submerged features.

2. What is the condition of the coastal currents off Al Wajh?

Various driving elements characterize the coastal currents in the surroundings of Al Wajh. Generally, the overall circulation in the Red Sea plays the major role. In turn, the main driving factor for the Red Sea is the inflow of water from the Indian Ocean through the Bab-el-Mandeb Strait. This water carries different temperature and salinity features, hence affecting density-driven currents in the Red Sea.

The other important factor is wind. The season-sweeping winds that traverse the Red Sea, which have been there since time immemorial, affect the surface circulation of water. For example, during the winter months, the winds push the surface water in one direction, thereby influencing the coastal currents off Al Wajh. The topography of the seafloor also matters. Shoals, canyons, and other features raise the floor, causing the water to bend and alter its speed of flow.

The tides are another important factor. The gravitational pull of both the moon and the sun also forces sea level to rise and drop, at the same time creating tidal currents. Tidal currents can be strong in the bays and inlets around Al Wajh and interact with other factors to produce a complex pattern of water movement.

3. How to observe the coastal water flow of Al Wajh?

Surface Drifting Buoy Method

This is achieved by deploying buoys onto the surface of the water, letting them flow in the currents. Equipped with satellite-based tracking systems or other position-determining technologies, the buoy movements over time yield information on the direction and speed of the surface currents. This method basically provides data for the surface layer, with their main drawback being that they might not give the currents at different depths.

Moored Ship Method

In this method, a ship is moored at some location in the coastal area. The instruments on the ship measure the characteristics of water flow in the surroundings. This may give good data for the area surrounding the ship but has severe 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

ADCP current meter is a more advanced and convenient means of measuring coastal currents. It measures the velocity at different water depths using acoustic waves. By emitting acoustic pulses and analyzing the Doppler-shifted reflected signals, ADCP is able to provide a detailed profile of the current from the surface down to a certain depth. This will give a better understanding of the vertical structure of coastal currents off Al Wajh and are less subject to external influences such as that of the ship.

4. How does the ADCPs with the aid of Doppler principle operate?

ADCPs are based on the Doppler effect. The technique sends acoustic signals in a water body. Because of the movement of moving sediment, plankton, and other small organisms present, the frequency of reflected sound waves changes. In a way, this is parallel to the velocity.

This ADCP current profiler has more than one transducer to emit and receive acoustic signals in various directions. Based on the principle of Doppler shift measured in many directions, it will determine the three-dimensional space components of the velocity. It then integrates the obtained three-dimensional space velocity components in order to derive the mean current water flow velocity magnitude with its direction at each measurement depth.

5. What is required to obtain a good quality Al Wajh coastal currents measurement?

The equipment to measure the coastal currents in Al Wajh must be made from reliable material to give a high quality of measurement. It needs to be able to bear the harsh marine environment, such as the corrosive effect of seawater and the high pressure at greater depth. It should be compact and of low weight for easy deployment on a buoy or a small boat or fixed platform.

It is crucial that power consumption is low, especially for long-term monitoring; the equipment must be able to operate on limited power sources like batteries or solar panels. The low cost of the equipment is another important factor: to carry out large-scale measurements along Al Wajh coast, the equipment needs to be affordable.

Speaking of ADCP flow meter casing, titanium alloy is a perfect material. There is great resistance against corrosion due to the high corrosion resistance in this titanium alloy, which is critical for surviving corrosive seawater. It also has a high strength-to-weight ratio, which will allow the equipment design to be durable and lightweight at the same time. This material can withstand the high-pressure environment at greater depth and ensure that the equipment functions reliably during deep-water measurements.

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

According to the Usage Purpose

• Ship-borne ADCP: In case the aim is to measure the currents while the ship is in motion or on a particular voyage along the coast of Al Wajh, then the ship-borne ADCP can be installed on the hull and the data it collects while the ship sails.
• Bottom-mounted ADCP: Accomplished by a bottom-mounted ADCP is the best means for long-term monitoring at a fixed location near the seabed. It easily can sit on the sea floor to provide information about flow characteristics near the bottom.
• Buoy-mounted ADCP: When the goal 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 gather data along its movement.

Based on Various Frequencies

• To a depth of about 70m, the 600kHz ADCP can be used to advantage. It will give high-resolution measurements suitable for relatively shallow coastal waters near Al Wajh.
• For depths between 70m and 110m, a 300kHz ADCP is most appropriate. It offers the best trade-off between measurement range and accuracy for medium-depth waters.
• In much deeper waters, say up to 1000m, it is recommended to use the 75kHz ADCP, as it can make its way through to greater depth and therefore give reliable current data in deeper parts of Al Wajh's coastal areas.

Some of the leading ADCP brands include Teledyne RDI, Nortek, and Sontek. But, believe it or not, a Chinese brand called China Sonar PandaADCP has entered the market. Its mechanical housing is fabricated with all-titanium alloy for much greater durability. In this case, cost-to-performance can be relatively improved. Please refer to https://china-sonar.com/.

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