How to measure the coastal currents of Chabahar?

1. Where is Chabahar?

It is a seaport city situated in the Sistan - Baluchestan province of Iran on the Gulf of Oman, which is strategically and geopolitically very important.

It is a hub of all sorts of activities related to the sea. The city is a cosmopolitan place where various ethnic groups culturally co - exist and the Baloch form one of them. Local inhabitants are involved in fishing, trade, and port-related activities.

The Gulf of Oman, bordering it, is a waterway of primary importance connecting the Arabian Sea and the Indian Ocean. All kinds of fish, turtles, and other sea animals are found in the water. It is a suitable route for major trading; there are ships of various countries which pass through en route to other destinations. This coastline has sandy beaches while the coastline of Chabahar is full of rocks. The port city of Chabahar is an important infrastructure facility that has facilitated trade and economic cooperation between Iran and other regional players, including those from beyond the regional frontier.

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

The coastal currents near Chabahar are controlled by more than one factor. Oceanic circulations in general play an important part. The general circulation in the Indian Ocean and the Gulf of Oman controls the course of flow. Inflows of different water masses from the Arabian Sea and the Indian Ocean can bring alterations in temperature, salinity, and velocity.

Tidal forces are huge, too. The gravitational pull of the moon and sun cause tides, and tidal currents associated can be pretty variable in magnitude and direction. Topography of the coastline and topography of the seabed at Chabahar provides additional influence upon the current. Submarine ridges and valleys will cause changes in the flow of the water, and the shape of the coastline will curve the currents in certain directions.

Monsoon winds, on the other hand, have an impact as well. The southwest monsoon can drive the surface waters during the months of June to September and alter the current patterns. Interaction of wind-driven surface currents with the deeper-lying oceanic currents results in a complex flow regime.

3. How to Observe the Coastal Water Flow of Chabahar?

Surface Drift Buoy Method: This is a method of deploying buoys on the water surface. These buoys are allowed to drift with the currents. By using a satellite-based tracking system or any other method of position monitoring, the movement of such buoys over a certain time will give information on the direction and speed of the surface currents. This, however provides mainly information about the surface layer and not fully interpretable depth currents.

Anchor Boat Method: This is a method where a boat is anchored in the coastal waters. Instruments are used to measure the flow of water at different depths around the boat. Although more detailed data can be derived for the area surrounding the boat, this is generally a labor-intensive and time-consuming method. It also faces limitations in terms of the area it covers.

Acoustic Doppler Current Profiler(ADCP) Method: This is achieved in a more enhanced manner with the use of a device known as the ADCP. Working on the sonar principle, it finally provides the velocity of water at multiple depths all at once. Working on the sonar principle, it gives the detailed profile of current right from the surface down to a certain depth by the emission of sound pulses. This will give a more accurate and full view of the coastal currents than the other two methods.

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

The principle of the Doppler effect is the basis for ADCPs. They send out sound pulses into the water. When these sound waves interact with particles in the water-sediment particles, plankton, or other small organisms-the frequency of the reflected sound waves changes due to the Doppler effect. If the particles are moving towards the ADCP, the frequency of the reflected waves is higher than the emitted waves; if they are moving away, the frequency is lower.

The ADCP calculates water velocity in different directions by calculating the frequency shift of reflected sound waves at different angles and depths. With many transducers sending and receiving these sound signals, the ADCP is able to compile a detailed profile of the flow velocity throughout the water column from the surface down to a given depth, depending upon the specific capabilities of the instrument in question.

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

The equipment to be used for the measurement of coastal currents around Chabahar should be made of reliable materials. The marine environment is harsh, with salt-water corrosion, temperature fluctuations, and possible physical impacts from floating debris; hence, the equipment should be durable.

Equipment size should be small enough for easy deployment and installation whether at the seabed, buoys, or even on boats; small size facilitates handling and installation, and transport becomes easy in cases of maintenance.

Weight-As would be expected-the weight of equipment should especially be light for floating or moored devices. The reason is because a lightweight guarantees proper buoyancy and stability of the devices. Electrical consumption by equipment must be at low levels, permitting the continuous use over periods, without changing batteries often, or taking a heavy power supply along.

It is required to be cost-effective to make the large-scale measurements possible along the coast. The casing of the ADCPs needs to be made from a titanium alloy. Corrosion resistance is high for a titanium alloy, which is pretty much what is needed in this very salty marine environment. Moreover, it is powerful, yet relatively light - exactly what one would require in top-notch current-measuring gear.

6. How to Select appropriate equipment for current measurement?

While selecting the equipment for measurement of current at Chabahar, the purpose for which it is being selected would be the prime consideration.

Ship - borne ADCP: This may be suitable for measurements from a moving vessel. While the ship travels along a coast, it is able to continuously record the coastal currents as a series of data points over a relatively wide area covered by the route of travel of the ship.

Bottom-mounted ADCP: very useful for making fixed-point measurements from the seabed, thus very stable and long-term recordings of the near-bottom flow are achieved. These will be of prime importance regarding the understanding of the interactions between bottom topography and coastal currents.

Buoy-mounted ADCP: Used when one wants to measure the current in a certain area continuously for a longer period from the water surface. Thus, it can be deployed only in areas of interest and get continuous data without physical presence of a vessel throughout the time.

In terms of frequency, the following instruments can be used for water depth: a 600kHz ADCP can be used within 70m; a 300kHz ADCP within 110m; and a 75kHz ADCP for as deep as 1000m.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth mentioning. It has a casing made entirely of titanium alloy and offers an excellent cost - performance ratio. You can find more information about it at https://china-sonar.com/.

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