How to measure the coastal currents of Bushehr?

1. Where is Bushehr?

Bushehr is a major port city found in the southwestern part of the coast of Iran on the Persian Gulf. It's a place where history, combined with the existence of heavy industries and a great harbor, mixes well with its present industrial and maritime essence.

It is set against a backdrop of arid landscapes, with the waters of the Persian Gulf stretching out before it. The local people have had a long dependence on the sea, since fishing and shipping have formed part of the local economy for many centuries. The Persian Gulf near Bushehr is an extremely important waterway for international trade and energy transportation, given the vast oil and gas reserves of the region.

The coastline is made up of a mix of sand beaches, rocky outcrops, and a small number of bays and inlets. The warm climate that characterizes this region, taken together with the tourism sector, attracts locals and tourists alike, while at the same time the waters of the gulf carry an abundance of fish types, turtles, and shellfish. The city further acts as a gateway for other parts of the region, having a well-developed transportation network connecting it with the interior of Iran.

2. What is the condition of the coastal currents off Bushehr?

Various elements, however, modulate the coastal currents off Bushehr. One of the important determinants of these tidal forces is tidal forcing. The tides in the Persian Gulf, which are basically due to the gravitational pull of the moon and the sun, bring about a regular rise and fall of sea level. In places, these tidal currents are quite strong and can also be changed by the lunar cycle and the local bathymetry.

The other factor would be wind-driven currents: these too may contribute, considering that the prevailing winds in a certain region are able to push the surface waters along to create surface currents. Their direction and strength could change with the season and alter coastal circulation accordingly. This might be such that, for instance, different current patterns will be exhibited in winter compared to those during summer, because at one of those seasons wind would be blowing from other directions.

The underwater topography around Bushehr also affects the currents. The presence of underwater ridges, channels, and shoals can redirect and modify the flow of water. Shallow areas may slow down the currents, while deeper channels can accelerate them, creating a complex and dynamic current regime.

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

Surface Drift Buoy Method: This involves setting buoys on the water surface and allowing them to drift with the currents. These buoys are normally fitted with tracking devices such as GPS. By monitoring the movement of the buoys over time, the direction and speed of the surface currents can be determined. However, this method gives essentially information on the surface layer and cannot provide detailed insight into the vertical structure of the currents.

The anchor ship technique involves the anchoring of a ship at a specific point near the shoreline of Bushehr. On the ship, there are fitted current meters in order to measure the water flow around the ship. This method will be quite accurate around the area the ship is placed, although ineffective for the covering of larger areas or simultaneously at various depths.

Acoustic Doppler Current Profiler (ADCP) Technique: The ADCP current meter has more advanced and proficient modes of measuring coastal currents by utilizing the Doppler principle, where the velocities within different parts of the water column are determined. This profiler produces acoustic pulses that project into the water column; from this, the return signals received by the moving particles shift frequency. With this system, it will be very much feasible to obtain comprehensive and practical details concerning the vertical profile that outlines currents from surface level down to the sea bed.

4. How do ADCPs using the Doppler principle work?

These instruments work on the principle of the Doppler. They use transducers that send out acoustic pulses into the water. When these sound waves come across moving water particles, due to the Doppler effect, the frequency of the reflected waves shifts and changes. The frequency shift is proportional to the velocity of the water particles relative to the ADCP meter.

Most ADCPs are multiple transducer types, allowing measurement of water velocities to be determined in three different directions. By inputting pulses in different directions and taking the frequency shift of the reflected signals, the ADCP profiler can precalculate the three-dimensional velocity of the water-that is, the direction of flow toward the east-west, toward the north-south, and upward and downward directions. It also measures the time taken by the sound waves to travel from the transducer to the water particles and back. This information, together with the frequency shift, gives an accurate determination of the speed and direction of water flow at different depths.

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

For high-quality measurement of the coastal currents near Bushehr, the equipment needs to have certain characteristics. The material of the equipment must be reliable and able to withstand the harsh marine environment. The device should have a small size and light weight to facilitate easy deployment and handling. Low power consumption is also essential to ensure continuous operation, especially for long-term monitoring.

The casing of the ADCP current meter would, however, be made of a material, preferably of a titanium alloy. Titanium alloy possesses very excellent corrosion-resistance properties, which would be highly essential in such saline environments as the Persian Gulf. Besides, it can realize high strength with respect to its weight, hence serving to make the equipment much durable yet relatively light in weight. This material has a pressure-resistant capacity related to the different water-depths changes.

6. How to select appropriate equipment for current measurement?

While selecting the equipment for current measurement in Bushehr, consider the following factors.

Depending on the purpose of usage, one can select either type of ADCPs. For instance, a ship-borne ADCP will be installed on a vessel and can measure currents while the ship is in motion. This helps in covering a wide area of the coastal waters. A bottom-mounted ADCP is installed on the seafloor and yields very stable measurements of the currents passing over it. It is ideal for long-term monitoring at one location. The buoy-mounted ADCP is an ADCP which, combined with a buoy, is easy to deploy, mobilize, and take measurements at different places.

The frequency of ADCP depends upon the depth of the water. In as shallow water as 70m, one can use a 600kHz ADCP, which gives high-resolution data in shallow waters. For depths up to 110m, a 300kHz ADCP would be more appropriate. Where the water is deeper, such as near 1000m, a 75kHz ADCP will be able to give the correct measurement over a large vertical range.

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.