How to measure the coastal currents of Kollam?

1. Where is Kollam?

Kollam is a coastal city in the state of Kerala, India. It is situated along the coast of the Arabian Sea and is a major port city. The city is famous for its natural beauty and rich cultural heritage.

Scattered with a series of beautiful beaches, like the Thirumullavaram Beach, the coast of Kollam attracts visitors in large numbers. These are lines of fringes with coconut palms, very often presenting a tropical paradisiacal environment to any viewer. The city has canals and backwaters in almost all directions, which make it part of the local ecology and transportation system. The backwaters join the Arabian Sea and house various kinds of flora and fauna.

The local economy is different, with fishing playing a great role. Fishermen in Kollam ply the waters along the coast with whatever boats are available, from small wooden canoes to even more modern mechanized boats. Kollam boasts a busy port, which transacts all types of goods, including spices, which have a significant place in the commercial history of the region.

The seabed topography near Kollam has changing contours from shallow sections nearer the shores to somewhat deeper sections as one goes further. The sandbars and channels beneath the water at depth also control the movement of the water. Its position at the Arabian Sea, it must therefore be subjected to monsoon winds and to general circulation of the Indian Ocean.

2. What is the condition of the coastal currents near Kollam?

The coastal currents off Kollam are influenced by many factors. The winds of the monsoon exert a strong influence. The southwest monsoon from June to September brings strong winds which drive the surface currents. The winds push the water in one direction, often parallel to the coast, and may dramatically change the circulation patterns. Similarly, the northeast monsoon from December to February modifies the dynamics of the current with its wind.

The larger-scale ocean circulation patterns of the Arabian Sea and the Indian Ocean are one. The Somali Current and the North Equatorial Current, which border the area to the southwest and northeast respectively, have their effects. And then there are tidal forces, another critical factor, tides in the Arabian Sea raise and lower the level of the water, thus forcing tidal currents that interact with the other currents driven by the ocean. The shape of the coastline and bathymetry around Kollam would accelerate or decelerate the currents. For example, headlands and bays cause the currents to deflect, changing direction and speed when the water is funneled or deflected by the headlands and bays.

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

Surface Drift Buoy Method: The observation of surface water flow is conveniently done by using surface drift buoys. These buoys are set free in the water and are carried by the surface currents. The direction and speed of the surface currents can be determined using GPS or other tracking systems to monitor the position of the buoys over time. 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: The water flow can be measured by using an anchor boat. An anchor boat is anchored at a specific location, and the current-measuring instruments are deployed at different depths from the boat. 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.

Acoustic Doppler Current Profiler (ADCP) Method: ADCP profiler represents an advanced, more efficient method of measuring coastal currents. It is based on the Doppler effect for water velocity measurements at different levels. By emitting acoustic signals into the water and analyzing the Doppler shift of the reflected signals from particles in the water, ADCP can give a detailed profile of the current from the surface down to a certain depth. This provides a better idea of the vertical structure of the coastal currents off Kollam.

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

ADCPs use the principle of Doppler. They send acoustic pulses into the water column. The pulses interact with the in-water suspended particles like plankton or sand grains or other minute debris. Since the water is in motion, so are the particles. When these particles reflect the acoustic pulses back to the ADCP meter, there is a frequency shift in the signal received compared to the signal emitted. This frequency shift is directly related to the velocity of the water flow.

The ADCP flow meter has several transducers that send and receive signals in various directions. By precisely measuring the Doppler shift of the received signals from different angles and depths, it calculates the speed and direction of the water currents at various points in the water column. This allows the three-dimensional representation of the current field to be built, providing valuable data about both the horizontal and vertical components of the coastal currents.

5. What’s needed for high - quality measurement of Kollam coastal currents?

For high-quality measurement of the coastal currents in Kollam, there are specific characteristics that the equipment should have. The equipment material used should be good and durable enough to sustain the corroding effects of sea water and the harsh marine atmosphere. Smaller size and lighter weight are advantageous since these features make handling and deploying the equipment easier on a boat, a buoy, or other platforms.

Other issues are that the power consumption needs to be low for the long-term measurements. Such devices must operate continuously without replacements of batteries or a great power supply. Cost is another issue, the device's cost must be low, within the limits to enable as many devices as possible, with many units deployed everywhere in order to have better monitoring.

For ADCPs, a casing of the titanium alloy is an excellent choice. The resistance to seawater corrosion is very good for 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 has the capability to withstand high pressure; hence, it can be used at different water depth scenarios of the Kollam coastal area.

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

For the selection of proper equipment in the measurement of currents at Kollam coastal waters, several aspects are to be considered.

With regard to usage purpose, different types of ADCPs are available. For measurements from a moving vessel, an ADCP can be shipborne. It can record the currents while the vessel is running along the coast, with a continuous stream of data being provided. A sit-on-bottom ADCP is available if the objective is to monitor the currents at a certain fixed location near the seabed. It can be laid on the ocean floor and record the flow of water passing over it. For applications where a floating platform is more convenient, a buoy-mounted ADCP current profiler is the way to go.

Regarding the frequency of the ADCPs, it has relation to the water depth, since for the 70m water depth, it uses an ADCP frequency such as 600 kHz ; and finally, for depths up to a maximum of 110 meters, a 300 kHz frequency has to be used; however, for greater profundities reaching 1000 m, a 75 kHz frequency is more fitting since this will ensure the continuity, precision, and reliability in this kind of measurement of ocean currents.

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.