How to measure the coastal currents of Nagercoil?

1. Where is Nagercoil?

Nagercoil is a city situated in the southernmost part of the Indian state of Tamil Nadu. It is near the tip of the Indian subcontinent and is in close proximity with the Arabian Sea.

The city is famous for its pleasant climatic conditions and rich cultural heritage. Nagercoil is a sea-facing town, and the whole seashore area is an ideal blend of beaches with sand and rocky shores. The beaches here have their fine sand and clear waters, providing all facilities for entertainment both for the local people and for tourists. The place has a tropical charm due to the sprinkling of coconut groves.

Activities like fishing and agriculture form part of the local economy. For most people, fishing is their main livelihood in Nagercoil. The fishermen go into the coastal waters with different traditional and modern boats. The Arabian Sea alongside forms the lifeline of the local ecology and brings in sources of income through fishing and other maritime activities.

While at Nagercoil, there are tops of seabed from very shallow levels near the coastline to quite deep ones seaward. Underwater forms such as reefs and sandbars further affect water movements. Moreover, at Nagercoil, it has geographical location within the realm of the large-scale oceanic circulation system of the Arabian Sea and the Indian Ocean.

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

A few factors are responsible for the variations in the coastal currents near Nagercoil. The monsoon winds are one of the major causes. During the southwest monsoon, from June to September, strong winds blow over the sea and drive the surface currents. These winds push the water in a particular direction, usually parallel to the coast, and have a significant impact on the overall circulation patterns. The northeast monsoon, from December to February, also changes the current dynamics with its own wind patterns.

Equally, larger - scale ocean circulation patterns of the Arabian Sea and the Indian Ocean have their role in the present state. The Somali Current and the North Equatorial Current are influential in determining the water movement in the region. Another significant factor contributing is the tidal forces. The tides in the Arabian Sea rise and fall, creating tidal currents that interact with the other ocean-driven currents. The shape of the coastline and the bathymetry near Nagercoil can either accelerate or decelerate the currents. For instance, headlands and bays can make the currents change direction and speed as the water is deflected or funneled.

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

Surface Drift Buoy Method: Surface drift buoys are a practical means for observing the surface water flow. These buoys are released into the water and are carried along by the surface currents. By 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. This mainly reflects information of the surface layer and might not completely give a picture of currents at different depths.

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

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP profiler is a more advanced and efficient way to measure coastal currents. It makes use of the Doppler effect to measure the velocity of water at multiple depths. By emitting acoustic signals into the water and analyzing the Doppler shift of the reflected signals from particles in the water, ADCP can provide a detailed profile of the current from the surface to a certain depth. This therefore provides a full view of the vertical structure of the coastal currents off Nagercoil.

4. How do ADCPs using the Doppler principle work?

The working principle behind an ADCP meter is the Doppler principle. ADCPs send acoustic pulses into the water column. The pulses scatter on suspended particles in the water, for example, plankton, grains of sand, or any other small debris. In a flow of water, these particles are moving with it. Particles in the water column cause partial reflection of the acoustic pulses back to the ADCP; for moving water, there is a frequency shift in the received signal relative to the emitted signal. The velocity of the water flow is directly related to this Doppler shift.

Since several transducers on the ADCP flow meter send and receive signals at various times in various directions, through the accurate measurements of Doppler shift of the returned signals at different angles and from many layers, the speed and direction of the currents are calculable at points throughout the water column, and even a three-dimensional presentation of the current field with its useful information on both the horizontal and vertical components of coastal currents becomes available.

5. What is required to have high-quality measurement of the currents around Nagercoil coastline?

The equipment to be used for the measurement of coastal currents in Nagercoil should have certain characteristics for high-quality measurement. The material should be reliable and resistant to the corrosive action of seawater and the aggressive marine atmosphere. Small in size and lightweight, the equipment is easy to manipulate and deploy on boats, buoys, or any other platform.

Low power consumption is essential for long - term measurements. The equipment should be able to operate continuously without the need for frequent battery replacements or a large - scale power supply. Cost - effectiveness is also a crucial factor. The equipment should be affordable enough to allow for widespread use and the deployment of multiple units for more comprehensive monitoring.

In the case of ADCPs, a casing made of titanium alloy is an excellent choice. Titanium alloy has a high resistance to corrosion in seawater, ensuring the long-term durability of the equipment. It has a high strength-to-weight ratio, which means it can provide structural integrity while keeping the weight to a minimum. Besides, titanium alloy withstands high pressure, which is suitable for different water depth scenarios in the Nagercoil coastal area.

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

While selecting the right equipment for current measurement in Nagercoil's coastal waters, several factors need to be considered.

Based on the usage purpose, different types of ADCPs are available. If the measurements are to be made from a moving vessel, a ship-borne ADCP current profiler will be suitable. It can measure the currents while the vessel is moving along the coast in a continuous stream of data. If the aim is to monitor the currents at a fixed location near the seabed, a sit-bottom ADCP is a good choice. It can be placed on the ocean floor and record the water flow passing over it. In applications where a floating platform is more convenient, a buoy-mounted ADCP is the way to go.

The frequency of ADCPs, on the other hand, is different depending on the water depth. In water as deep as 70m, an ADCP with a frequency of 600kHz would give high-resolution measurements. Where the water is as deep as 110m, it would be more appropriate to use an ADCP with 300kHz. In much deeper waters, such as those as deep as 1000m, a 75kHz ADCP would be a better choice for current measurements 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.