How to measure the Coastal Currents of Kochi?

1. Where is Kochi

Kochi belongs to the south-western Indian state of Kerala. A fascinating, coastal city in southernmost India is richly bounded with its maritime history on geographical sketches. The natural beauty is such that it happens to be on the west Arabian Sea and forms part of a natural harbor in geography. Geographically, blessed with long and beautiful coasts, a haven for different ranges of coastal and marine ecosystems is available here.

It is an important centre of trade and commerce. The port in Kochi has been a lifeline of shipping and fishing activities since time immemorial. A variety of fish species in the adjacent waters facilitate the fishing industry to a greater extent. Sandy beaches and backwaters form the coastline of the city. The backwaters consist of a complex network of lagoons, canals, and estuaries that run into one another, being not only a tourist attraction but an essential component in the local ecology and transportation.

Culturally, Kochi is a melting pot. Because of its history as a trading port, it has been influenced by various cultures. The colonial architecture that dominates the Fort Kochi area is a standing example of the Portuguese, Dutch, and British influence. The local art forms, festivals, and cuisine also bear this cultural stamp. The climate in the city is essentially moderated by the sea, with the Arabian Sea breezes bringing a pleasant touch to the tropical climate.

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

Multiple factors influence the nature of the coastal currents near Kochi. For one, the winds of a monsoon character are paramount in such a setting. During June-September, the southwest monsoon contributes to strong winds that eventually drive the surface currents, while the wind-driven current itself may transport sediments and nutrients important to coastal ecology. Equally interesting is the northeast monsoon, albeit with different patterns.

Tidal currents also play an important role. The semi - diurnal tides are predominant in the Arabian Sea around Kochi. These tidal fluctuations produce strong tidal currents which, in turn, interact with the wind -driven currents. Seaward of Kochi, the bottom topography is very complex and influences the pathways of the currents. Localized underwater sandbars, reefs, and channels could deflect and accelerate the currents.

The fresh water inflow from the numerous rivers and backwaters in this region can alter the density of the coastal waters. This density gradient can induce estuarine circulation patterns, which, in turn, affect the coastal currents. The larger-scale oceanic circulation in the Arabian Sea, such as the Somali Current and the Arabian Sea Gyre, indirectly influences the local coastal currents.

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

• Surface Drifting Buoy Method: It is a conventional method whereby a buoy is sent into the water. Thereafter, the movement of the buoy will be followed by GPS or other tracking systems. The speed and direction of the surface current can be found by observing the buoy's displacement after a certain period of time. However, this is limited to the surface and the buoy's movements will be influenced by the winds and waves, which tend to result in less accurate measurement from the actual water current.
• Anchor - Boat Method: A boat is anchored at a particular place nearshore, and current meters are lowered from the boat to measure currents at different depths. That gives a better resolution for the current profile at the point in question. This method, however, applies only to the area in the vicinity of the anchored boat and may not adequately capture the full spatial variability of the currents.
• ADCP Method: The ADCP profiler is an advanced, efficient technique that can measure simultaneously the velocity of water at several depths. The ADCP can give the current profile from surface to seabed by emitting sound waves and analyzing the Doppler shift of the reflected waves.

4. How do ADCPs using the Doppler principle work?

The principle of operation of ADCPs is based on the Doppler effect. ADCPs emit acoustic pulses into the water. These pulses interact with moving particles in the water, such as sediment, plankton, and other small organisms. When the particles are moving towards the ADCP, the frequency of the reflected wave is higher than the emitted frequency. Conversely, when the particles are moving away from the ADCP, the frequency of the reflected wave is lower.

With this frequency shift measured precisely, the ADCP meter will be able to determine the velocity of the water at every different depth. Most ADCPs have a number of transducer elements, each sending a beam in a different direction. This allows them to measure the three-dimensional structure of the current and therefore gives a much more accurate representation of the patterns of water flow.

5. What's needed for high-quality measurement of Kochi coastal currents?

The equipment for measurement of the coastal currents in Kochi should have the following qualities: It should be made with materials that are reliable enough to bear the corrosive effects of seawater and the harsh marine environment. The device should be compact, with a small size and light weight, to enable its easy deployment and retrieval, especially in areas with limited access or challenging conditions.

Low power consumption is one of the key features needed for long-term operation, especially in continuous monitoring. It has to be cost-effective in order to enable wide and frequent measurements.

The casing of the ADCP flow meter is preferably made of a titanium alloy. Titanium alloy offers excellent corrosion resistance, which is very important in the corrosive seawater environment. It is strong and able to resist pressures exerted by the water column and forces of waves and currents. Its relatively low density helps keep the weight of the equipment low, making it easier to maneuver during installation and maintenance.

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

The choice of equipment depends on the application.

• For Ship - based Measurements: A ship-mounted ADCP can be used. It allows measurement while the ship is in motion, thus enabling mappings over a larger area of currents.
• For Near - Seabed Currents: A bottom - mounted ADCP can be used. This is ideal for studying the currents close to the seabed, which is important for understanding sediment transport and benthic ecosystems.
• For Surface and Upper - Water - Column Measurements: A buoy - mounted ADCP current profiler is a good option. It provides continuous measurements of the surface and upper - layer currents.

These values of frequency correspond to suitable applicability in different water depths; in particular, a 600 kHz ADCP is acceptable when working in water as deep as 70m, a 300 kHz ADCP is appropriate at depths up to about 110m, and frequencies of 75 kHz provide the ability to work at water depths up to about 1000m.

There are several well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand - China Sonar PandaADCP is also a great option. It is made of all - titanium alloy material and offers an excellent cost - performance ratio. You can visit their website at https://china-sonar.com/ for more details.

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