How to measure the coastal currents of Virar?

1. Where is Virar?

Virar is a suburb in the Palghar district of Maharashtra, India. It is very close to the Arabian Sea. The place comes under the Mumbai Metropolitan Region and is developing day by day in terms of population and infrastructure.

The local landscape is a judicious blend of the growth of urban development with local natural beauty. People of Virar are engaged in a number of vocations that range from small business enterprises to services, and even agriculture concerning the surrounding areas. There is much vibrant local flavor, and festivals and community events are quite an integral feature of life here.

The Arabian Sea nearby has a great influence on the region. Marine life, including fish, crabs, and different mollusks, is common in the sea waters off Virar. The sea itself has a moderating influence on the climate of the area through the cooling action of sea breezes. The coastline comprises beaches with sand and some tidal regions. Tidal movements are of importance in determining the coastal environment and controlling the distribution of sediments.

2. What is the present status of Virar coastal currents?

The coastal currents near Virar are determined by various factors. The major determinants among them include tidal forces. Tides are caused by the gravitational pull of the moon and the sun, while the associated tidal currents can be strong in one direction or another. The shape of the coastline and the topography of the seabed further affect the currents. Sandbars, channels, and other submerged features can redirect and modify the water flow.

The monsoon winds, more so the southwest monsoon winds, impinge very strongly upon entrance. These winds may displace the surface waters and have a seasonal trend in coastal currents with respect to direction and speed. Such density-driven currents may be modified by freshwater advection from rivers passing nearby and mixing with seawater in the area. The intersection of different water masses can result in complex current patterns.

Besides, the large-scale ocean circulation in the Arabian Sea might be interacting with the regional coastal currents. The advection of water masses from other regions may impose changes in temperature, salinity, and other characteristics of the coastal currents.

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

Surface Drift Buoy Method: This involves setting buoys onto the water surface and letting them drift with currents. Using satellite-based tracking systems or any other positioning methods, the movement of these buoys over time can be traced and information on the direction and speed of surface currents is obtained. However, this mainly provides data for the surface layer and may not be representative of currents at different depths.

The anchor boat method: The anchor boat method involves the anchoring of a boat in coastal waters. Water flow at various depths is measured by using instruments. Although it can give more detailed data in the surroundings of the area close to the boat, this might be somewhat labor and time intensive. It has limitations as to the area it is supposed to cover.

Acoustic Doppler Current Profiler Method: The ADCP current meter method is a more sophisticated and proficient method of measuring coastal currents. It utilizes sound waves for the measurement of the velocity of water simultaneously at depths more than one. It can give a profile of the current in detail from the surface to a depth that it is able to cover, more precisely and comprehensively compared to the other methods.

4. How do ADCPs using the principle of the Doppler effect work?

ADCPs work on the principle of the Doppler effect. They send sound pulses into the water. When those sound waves run into particles in the water, due to the Doppler effect, the frequency of the reflected sound waves changes. If the particles are moving towards the ADCP meter, then the frequency of the reflected waves is higher than that emitted; if they are moving away, the frequency is lower.

The ADCP current profiler calculates the velocity of water at various directions and depths through frequency shifts of reflected sound waves coming back to it at different angles and, in turn, depths. An ADCP profiler with several transducers can send and receive sound signals that allow this instrument to produce a highly resolved profile of the velocity across the water column from the surface all the way to a depth below it that is within the specific instrument capability.

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

The measuring equipment for the coastal currents around Virar should be made from a durable material. It should be able to withstand the harsh marine environment, including salt-water corrosion, temperature fluctuations, and probable physical impacts from floating debris.

The size of the equipment should be as small as possible to allow for easy deployment and installation. On either a boat, buoy, or seabed, the small size makes it easier to handle and install. Transportation and maintenance are also not a problem.

The weight of equipment should be as light as possible, especially floating or moored devices, for good buoyancy and stability. Other major factors could be the use of low power consumption to allow for the realization of a continuous operation over a long period without changing the power supply frequently or using a huge amount.

The cost is another important aspect. It shall not be too expensive to be capable of doing large-scale measurement along the coast. For an ADCP flow meter, a casing from Titanium alloy is a very good choice. This is because the metal owns an extremely good corrosion resistance highly required in salty marine environments besides its good strength and low density, which satisfies its requirements as a high-class current measurement device.

6. How to Select appropriate equipment for current measurement?

Selection of equipment for current measurement at Virar shall depend primarily on the purpose of usage.

Ship-borne ADCP: This can be installed on a moving vessel for data recording. It will thus continuously record the coastal currents when the ship moves along the coast and give a succession of data points over the fairly wide area covered by the track of the ship's path.

Bottom-mounted ADCP: Fixed-point measurements at the seabed. It provides a stable and long-term record of the water flow near the bottom, which is important to understand the interaction between the bottom topography and the coastal currents.

Buoy-mounted ADCP: This is used when the purpose is to measure the currents in a particular area for a long period while floating on the water surface. It can be deployed in areas of interest and provide continuous data without the need for a vessel to be present all the time.

Frequency

For water to a depth of about 70m, an ADCP with a 600kHz should suffice, and for up to 110m, an ADCP at 300kHz will suffice, while water to the extreme of 1000m needs a 75kHz frequency ADCP.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth mentioning. It has a casing made entirely of titanium alloy and offers an excellent cost-performance ratio. You can find more information about it at https://china-sonar.com/.

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