How to measure coastal currents of Chennai?

1. Where is Chennai?

Chennai, formerly known as Madras, is a major metropolis situated on the Coromandel Coast of the Bay of Bengal in southern India. This city is the capital city of the state of Tamil Nadu and is a vigorous center of culture, commerce, and industry.

Geographically, the city has been bestowed with a very long coastline, seemingly going into eternity. The sandy beaches, like Marina Beach, form part of the identity of Chennai and attract locals and tourists alike. The Bay of Bengal next to it is one huge body of water which plays an important role in defining the city. The sea stands as a livelihood provider for a substantial population engaging in fishing and other related activities.

Chennai is also a major port city. The Chennai Port, one of the largest in India, handles a large volume of cargo traffic comprising containers, petroleum products, and other goods. The city's economy is diverse, with large-scale representation from the automobile, IT, and textile industries.

The waters around Chennai are known for their variety of marine life. The mangrove forests, which exist along parts of the coastline, protect the shoreline from erosion and provide a habitat for many species. The climate of Chennai is tropical, with the sea breeze often providing a bit of relief from the heat.

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

The coastal currents near Chennai are influenced by a multitude of factors. The most influential factor is the monsoon winds. The northeast monsoon during the months of October to December brings rain and strong winds that could raise the surface currents drastically. These winds may also cause the movement of water masses and influence the mixing of different water layers.

In the Bay of Bengal near Chennai, tides are semidiurnal, having two highs and two lows in every day. In such an aspect, tidal currents will also be stronger at the times of spring tide conditions. The current is essentially modulated by topography and bathymetry-geomorphology along a coast consisting of bays, headlands, etc., where shallow water may give further acceleration or diversion of such a flow of currents.

The inflow of fresh water from the nearby rivers and estuaries affects the current at the coast. In addition, the mixing of freshwater and seawater changes the density and salinity of the water, which could modify the current patterns. These rivers carry sediments and nutrients that might greatly affect the coastal ecosystem and the movement of the currents.

3. How to Observe the Coastal Water Flow of Chennai?

Well, surface drifting buoy methods represent one of the traditional ways of monitoring ocean surface currents. The buoy is set on the surface and allowed to take courses of currents. Usually, such buoys have already been equipped with either GPS or any other device to track the positions that buoys may cover after some time. These means provide information on current velocities only in the surface layer and do not give the general view of vertical structure.

Moored Ship Method: A ship is moored in a position at a given location near the coast and current-measuring instruments are deployed from it. This can allow currents to be measured at various depths. However, there are a few disadvantages of this method. The ship itself interferes with the local pattern of currents, and it may be an expensive and logistically cumbersome operation to obtain long-term measurements.

Acoustic Doppler Current Profiler Method: This is a more modern and efficient method of measurement of the flow of water in the coast. ADCPs can measure simultaneously the velocity of water at several depths. They work by emitting sound waves into the water and detecting the Doppler shift of the reflected waves. The Doppler shift is dependent on the velocity of the water, and through an analysis of this, a precise profile of the current is obtained from the surface to the seabed.

4. How do ADCPs applying the Doppler principle operate?

The operating principle of ADCPs is based on the Doppler effect. An ADCP that sends a sound pulse into the water interacts with the in-water particles, such as sediment, plankton, or any other small object. If the water is in motion, the frequency of the reflected sound waves will be different from the transmitted frequency.

This shift in frequency, or the so-called Doppler shift, is linearly proportional to the velocity of the water. An ADCP measures this shift in frequency and then interprets the shift as a measurement of the speed and direction of the water current. Usually, an ADCP transmits sound pulses in all directions, often in a conical or fan-shaped pattern. By doing so, it can measure the current velocity in a three-dimensional space and build a comprehensive profile of the current throughout the water column.

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

The equipment to measure coastal currents near Chennai should have many desirable characteristics for high - quality measurement. The constituent materials used in the fabrication of the device should be dependable. For instance, the housing of the ADCP profiler must be resistant to seawater corrosion and mechanical action caused by waves and currents.

First of all, the device should have small size and light weight, since this will make its deployment on different platforms or even in situ on the seabed much easier. Another decisive factor is low power consumption, especially in long - term and remote measurements that will enable the device to work for an extended time without frequent battery replacements or recharging of the power sources.

Cost-effectiveness is another important factor. In order to have large-scale measurements, the equipment cost should not be very high. Use of titanium alloy for the casing of ADCPs is good. It is highly resistant to corrosion, which is very much essential in a marine environment. It is strong and durable to bear such pressure and impacts the device will get during operation.

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

The choice of the right equipment for current measurement near Chennai depends on the specific use case. For measurements from a moving boat, a ship - borne ADCP meter is suitable. It can provide real - time data about the water currents as the boat moves through the water.

For fixed - point measurements near the seabed, a bottom - mounted ADCP flow meter is a better choice. This type of ADCP can provide stable and continuous measurements of the currents at the bottom of the water column.

For measurements at a floating position, such as on a buoy, a buoy - mounted ADCP current profiler is the appropriate option.

In the case of ADCPs, different frequencies suit different water depths. For water up to 70m in depth, a 600kHz ADCP is suitable. For depths up to 110m, a 300kHz ADCP would be more appropriate, and for very deep waters of up to 1000m, a 75kHz ADCP is best.

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 worth considering. It is made of all - titanium alloy material, which provides excellent durability and corrosion resistance. It also offers an incredible cost - performance ratio. You can find more information about it on the website: ​https://china-​sonar.com/.

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