How to measure coastal currents of Thoothukudi?

1. Where is Thoothukudi?

Thoothukudi is a port city and one of the major cities in southeastern Tamil Nadu, India. The Gulf of Mannar and the Palk Strait are the strategic locations where it is located.

The long coastline comprises sandy beaches interspersed with rocky shores. With clear, blue waters, the sea enhances the natural beauty of this place. The port is one of the busiest in Thoothukudi, offering a wide variety of goods such as minerals, chemicals, and agri-ware. The port offers a vital trade link to the local economy and an important link for the broader international market.

The sea has a very close linkage with the local community. Fishing, being one of the vital economic activities, finds one of the most important fishing harbors as the hub of activities continuously. The fishing community herein is well adapted to coastal conditions and possesses sound and enriching traditional knowledge concerning the sea. Marine bio-diversity is not uncommon in areas around Thoothukudi. The Gulf of Mannar is renowned for its coral reefs, which support a diverse range of fish and other marine organisms.

The seabed near Thoothukudi has a variable topography. There are shallow areas close to the shore that are suitable for near - shore fishing and other activities. Further out, the depth increases, and the presence of underwater ridges and channels can influence the flow of coastal currents.

2. What is the condition of the coastal currents around Thoothukudi?

Various factors interact in causing the coastal currents off Thoothukudi. First, there are the monsoon winds. The southwest monsoon brings strong winds from June to September and drives the surface currents. These winds push the water in a particular direction, usually parallel to the coast, and have a great influence on the overall circulation patterns. The northeast monsoon, from December to February, also changes the dynamics of the current with its wind patterns.

The larger-scale ocean circulation features of the Indian Ocean are equally critical. The North Equatorial Current and the Bay of Bengal's circulation feature have impacts on the water movements in this area. The tidal forces are another significant factor in this context. 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. The shape of the coastline and the bathymetry near Thoothukudi can either accelerate or decelerate the currents. For example, the presence of headlands and bays can cause the currents to change direction and speed as the water is deflected or funneled.

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

Surface Drift Buoy Method: Surface drift buoys are one of the useful methods to observe the surface water flow. These buoys are released into the water and are carried along by the surface currents. Using GPS or other tracking systems to monitor the position of the buoys over time, the direction and speed of the surface currents can be determined. However, this method mainly provides information about the surface layer and may not give a complete picture of the currents at different depths.

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

ADCP Method: It is a more advanced and efficient way of measuring coastal currents. It applies the Doppler effect for measuring the velocity of water at different depths. In ADCP profiler, detailed profiling of the current is done from the surface to a certain depth by emitting acoustic signals into the water and analyzing the Doppler shift of the reflected signals from particles in the water. This will provide full information on the vertical structure of the coastal currents off Thoothukudi.

4. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of the Doppler. They send acoustic pulses into the water column. These pulses interact with the suspended particles in the water, such as plankton, sand grains, or other small debris. As the water is in motion, the particles move along with it. These particles reflect the acoustic pulses back to the ADCP meter. When these pulses are reflected back, there is a frequency shift in the received signal with respect to the emitted signal. This frequency shift, termed the Doppler shift, is directly related to the velocity of the water flow.

Several transducers have been fitted onto the ADCP flow meter that can send and receive signals in multiple directions. The determination of the exact Doppler shift of the signals received at different angles and depths makes it possible to compute both the speed and direction of the water current at every single point in the water column. This will also permit the development of a three-dimensional view of the current field and yield meaningful data for the horizontal as well as the vertical component of coastal currents.

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

For high-quality measurements of the currents at Thoothukudi coastal, the equipment must be so constituted as to exhibit definite characteristics. The materials being used for equipment need to be reliable, taking on the corrosive impact both from seawater and marine atmospheric conditions. The unit size and weight should preferably be small, since these aspects favor an easy manipulation of the device in general and particularly its deployment on a boat or floating buoy, among other platform types.

The measurement equipment has to be of low power consumption for long-term measurements; it needs to operate continuously without frequent changes of batteries or a large-scale power supply. Furthermore, cost-effectiveness has to be ensured, It has to be inexpensive to enable the deployment of several of these units to perform full monitoring.

In the case of ADCPs, a casing made of titanium alloy is quite appropriate. The reason is that titanium alloy has very good resistance to corrosion in seawater, which will make the equipment last for a long time. It has a high strength-to-weight ratio, which means it can provide structural integrity while keeping the weight to a minimum. Also, the titanium alloy has the ability to resist high pressures, hence it can be used in various water depth conditions of the Thoothukudi coastal area.

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

While selecting the proper equipment for current measurement in Thoothukudi's coastal waters, several factors are to be considered.

Based on the usage purpose, different types of ADCPs are available. The measurement can be taken from a vessel if it is moving with the help of a shipborne ADCP current profiler. In this manner, while the vessel cruises along the coast, currents are measured. If it has to continuously monitor currents at a particular location and near the bottom, the sit - bottom ADCP can be used. It can be set 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 should be used, as high-resolution measurements are obtained at this frequency. For a depth up to 110m, a 300kHz ADCP is most suitable. And for still deeper waters up to 1000m, a 75kHz ADCP provides a better choice for measuring currents accurately and reliably.

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.