How to measure the coastal currents of Rameswaram?

1. Where is Rameswaram?

Rameswaram is a famous pilgrim town and is situated in the Pamban Island of the Gulf of Mannar, Tamil Nadu, India. It is an island separated from the mainland by the Pamban Channel and is one of the holiest places for the Hindus.

The blue waters of the Indian Ocean and the Gulf of Mannar almost surround the town on all sides. The Rameswaram coastal areas are a combination of sandy beaches and rocky outcrops. The beaches are not only a place of worship and spiritual connection but also a haven for various marine life. The Gulf of Mannar is a rich and diverse marine ecosystem, known for its coral reefs, seagrass beds, and a wide variety of fish and other sea creatures.

Fishing and tourism shape the local economy. The fishermen of the region ply their boats in these coastal waters, with catches made by traditional boats or modern fishing. The tourist influx to Rameswaram comes for the ancient temples as well as to see the beauty of nature along its shores. Pamban Bridge, an engineering marvel, is in this island, which provides connectivity to the mainland as part of transportation.

The topography of the seabed around Rameswaram is peculiar, with the presence of reefs and other submerged features intercepting the flow of water. Shallow areas close to the coast extend into deeper ones further offshore, and these gradient changes have an important bearing on the behavior of the coastal currents.

2. What is the state of the coastal currents around Rameswaram?

The coastal currents off Rameswaram are influenced by a multitude of factors. The wind due to the monsoon blows with much strength. During the southwest monsoon, ranging from June to September, strong winds blow over the sea surface, impelling the surface currents. These winds push the water in a particular direction and are responsible for influencing the overall patterns of circulation. During the northeast monsoon, ranging over December to February, other changes in current dynamics take place with its winds.

Another factor is the larger-scale oceanic circulation of the Indian Ocean. The North Equatorial Current and the influence of the Bay of Bengal's circulation patterns play a part in the water movement near Rameswaram. The tidal forces are important, too. The tides in the Gulf of Mannar cause the water to rise and fall, creating tidal currents that interact with the other ocean-driven currents. There could also be acceleration or deceleration of currents due to the presence of the Pamban Channel and other surrounding coral reefs. Deflected by the reefs, funneled through the channel, the water changes in its speed and direction.

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

Surface Drift Buoy Method: The surface drift buoy is one of the practical ways to observe the surface water flow. These buoys are released into the water and are carried along by the surface currents. The position of the buoys, as determined by GPS or other tracking systems over time, can be used to determine the direction and speed of the surface currents. This method provides information only about the surface layer and may not give a complete understanding of the currents at different depths.

Anchor Boat Method: Water flow can be measured using an anchor boat. The boat is kept anchored at a location, and from it, current-measuring instruments are deployed at different depths. This allows measurement of the speed and direction of currents at different vertical levels. But this method is somewhat stationary and may not cover a large area efficiently.

The Acoustic Doppler Current Profiler is a more advanced and more efficient method of measurement in the realm of coastal current measurement. It relies on the Doppler effect, measuring the velocity of the water at different levels. Working on the principle of producing acoustic signals in water and observing the Doppler shift that occurs when these signals get reflected by particles moving through the water, an accurate profile of the current, ranging from the surface down to a certain depth, is acquired with ADCP meter. It clearly shows a detailed representation of the vertical structure of coastal currents in the surroundings of Rameswaram.

4. The workings behind the principle of the ADCPs applying the Doppler effect?

An ADCP utilizes the working principle known as the Doppler principle: an acoustic pulse sent down towards the water column through which the suspended particles within - for instance, planktons and sand grains and minute flotsam and jetsam - oscillate as part of the flowing water. When these particles reflect the acoustic pulses back to the ADCP flow meter, the received signal has a different frequency compared to the one emitted. This frequency shift of the received signal with respect to the emitted signal is normally referred to as the Doppler shift and is directly related to the velocity of the flow.

ADYC boasts many transducers, which will be able to send and receive signals in different directions. By accurately measuring the Doppler shift of received signals from various angles and at several depths, it can measure the speed and direction of the water currents at various points in the water column and enables a three-dimensional representation of the current field to be done; that is, it acquires valuable data on horizontal as well as vertical components of the coastal currents.

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

To attain a high-quality measurement of coastal currents in Rameswaram, certain characteristics will be required by the equipment. The equipment material is recommended to be reliable and resist the corrosive action of sea water and harsh marine conditions. A small size and light weight are advantageous for easy manipulation and deployment either on boats, buoys, or other platforms.

The possibility of low power consumption is necessary for long-term measurements; the equipment must be able to operate without frequent battery replacement or large-scale power supplies. Another important aspect is cost-effectiveness: the equipment should not be so expensive that it limits the number of pieces that can be deployed for wide coverage.

In the case of ADCPs, a casing made of titanium alloy is quite ideal. It is highly resistant to corrosion in seawater and thus can ensure long-term durability of the equipment. It has a high strength-to-weight ratio, meaning it can provide structural integrity while keeping the weight to a minimum. Moreover, titanium alloy can resist high pressure, so it's suitable for different water depth scenarios in the Rameswaram coastal area.

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

For choosing the right equipment for current measurement in Rameswaram's coastal waters, several factors are to be considered.

Depending on the usage purpose, there are different types of ADCPs available. For measurements from a moving vessel, a ship-borne ADCP current profiler is suitable. The currents can be measured while the vessel is moving along the coast, and continuous data streams can be obtained. If the goal is to monitor the currents at a fixed location near the seabed, a sit-bottom ADCP is a good option. It can be placed on the ocean floor and record the water flow passing over it. For applications where a floating platform is more convenient, a buoy-mounted ADCP is the way to go.

Regarding the frequency of ADCPs, it depends on the water depth. For water depths up to 70m, an ADCP with a frequency of 600kHz is recommended as it provides high - resolution measurements. For depths up to 110m, a 300kHz ADCP is more appropriate. And for deeper waters up to 1000m, a 75kHz ADCP is a better choice to ensure accurate and reliable current measurements.

There are well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, for those seeking a cost - effective alternative, the China Sonar PandaADCP is a great option. It is made of titanium alloy and offers an excellent cost - performance ratio. You can find more information about it on its website: https://china-sonar.com/.

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