How can we measure the coastal currents of Bahrain?

1. Where is Bahrain?

Bahrain is a small island country in the Persian Gulf. It comprises one main island and several smaller islands. Geographically, it lies between Saudi Arabia and Qatar.

The topography of Bahrain is a unique combination of arid plains and a beautiful coastline. The capital is Manama, a very modern city with high-rise buildings combined with a rich history. So the land of the islands is surrounded by shallow waters of warm water of the Persian Gulf. These waters host marine life of all kinds such as brightly colored fish, different varieties of shellfish, and coral reefs. The coasts of Bahrain are of sandy beaches, rocky shores, and natural harbors.

The Persian Gulf, in which Bahrain is situated, is a strategic waterway for shipping and trade. It is also part of an important area for the oil and gas industry, as Bahrain has its own reserves and a very extended offshore infrastructure. Being an island state in this gulf turns it into a kind of crossroads for the intensive sea going and exchange of cultures.

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

A variety of different factors combine to give rise to the coastal currents in the area near Bahrain. One of these is the tidal currents. In the Persian Gulf, tidal action under the pulling action of the moon and sun works on the water and produces almost regular cycles of rise and fall. Tidal ranges sometimes go through variations and may show heavy fluctuations within the coastal areas because of tidal currents.

Equally important are the wind-driven currents. The prevailing winds around the region can push the surface waters to develop surface currents. During certain seasons, winds, for example, Shamal blows from the northwest, hence influencing the direction and speed at which this current moves. In short, the interaction of this wind-driven and tidal currents produces complex circulation.

The underwater topography around Bahrain is another important factor. Underwater ridges, channels, and shoals may act to deflect and alter the flow of water. Shallow areas can slow down the currents while deeper channels can accelerate them; thus, a dynamic and variable current regime may exist.

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

Surface Drift Buoy Method: This method involves the deployment of buoys on the water surface, which are allowed to drift with the currents. These buoys are normally fitted with GPS or other tracking devices. By observing the buoy movements over time, the direction and speed of the surface currents can be determined. This method mainly provides information on the surface layer and may not give a detailed understanding of the vertical structure of the currents.

Anchor Ship Method: The method involves anchoring a ship at a particular place near the Bahrain coast. Equipment like current meters is attached to the ship for measuring the flow of water around the ship. The method would give very good results only in the close vicinity of the ship, without much capability to scan large areas with varying depths.

ADCP Method: The advanced and more efficient way of measuring the currents along the coast is the ADCP current meter method. This uses the Doppler effect to measure the velocity of water at different depths in the water column. The ADCP current profiler emits acoustic pulses into the water and measures the frequency shift of the reflected signals from moving water particles. It provides information about the current flow vertically, starting from the surface to the bottom of the sea.

4. How do ADCPs based on the Doppler Principle Operate?

Doppler principle-based ADCPs make use of transducers which are pulsed into the water with acoustic pulses. Moving water particles reflect these pulses; the frequency of reflected waves changes due to a well-known phenomenon called the Doppler effect. Such frequency shift is proportional to the velocity of the particles about an instrument that does some specific calculation.

They usually have multiple transducers that measure the water velocity in multiple different directions. With such pulses in multiple directions, ADCPs can detect a frequency shift of the reflected signal and compute the three-dimensional velocity of the water - namely, east-west, north-south, and vertical directions. The time taken for the sound waves to travel from the transducer to the water particles and back is also measured. This, combined with the frequency shift, is utilized for the precise determination of speed and direction in water flow at different depths.

5. What is required to make high-quality measurements of the currents in Bahrain coastal waters?

The equipment for high-quality measurement of coastal currents near Bahrain should possess certain features in their build. The material used for the equipment should be reliable and withstand the harsh marine environment. The device should be of small size and lightweight for easy deployment and handling. Low power consumption is also vital for its operation, especially for continuous and long-term monitoring.

The casing of the ADCP flow meter is preferably made of titanium alloy. Its properties of resistance to corrosion, highly important in a saline environment like that of the Persian Gulf, are excellent. It has a high strength-to-weight ratio; hence, it provides good durability while keeping the equipment relatively light. This material can withstand the pressure changes associated with different water depths.

6. How to Choose Proper Equipment for Current Measurement?

Selection of Equipment for current measurement in Bahrain will consider the following aspects:

According to the purpose of use, one may choose the appropriate type of ADCPs. For example, it is possible to install a ship-borne ADCP on board a ship that measures the currents while the ship is moving; it helps cover the major areas of the coastal waters. A bottom-mounted ADCP is fixed on the seabed and gives stable measurements of the currents passing above. It is ideal for long-term monitoring at a specific location. A buoy-mounted ADCP combines the advantages of mobility and ease of deployment, thus enabling measurements in different areas.

Regarding the frequency of ADCP profiler, it is related to the water depth. For water depths up to 70m, a 600kHz ADCP is a good choice since it provides high - resolution data in shallow waters. In deeper waters, say near 1000m, a 75kHz ADCP is recommended to ensure accuracy of measurement over a large vertical range. For depths up to 110m, a 300kHz ADCP will be more appropriate.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost-effective option with good quality, the China Sonar PandaADCP is worth considering. It is made of all-titanium alloy material and offers an excellent 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 moels.