How to measure the coastal currents of Palghar?

1. Where is Palghar?

Palghar is a district in the state of Maharashtra, India, having a coastline along the Arabian Sea. It is a region combining natural beauty with rich cultural heritage.

This is a fishing village area, wherein people are attached to the sea. The landscape abounds with coconut groves and fields of paddy, supplementing its rural charm. Culturally, Palghar is a place of various indigenous tribes and other communities co-existent with each other, comprising their own traditions and festivals.

The nearby Arabian Sea composes part of the local ecology. A variety of fish species, prawns, and crabs are found in these waters. Besides seafood, the sea brings in some money through fishing and some small-scale maritime trade. Generally, the coastline is made up of sandy beaches and estuaries, though mangrove forests are found in some areas. Mangroves protect the coast and offer a home for many organisms.

2. How are the coastal currents off the Palghar area?

Various forces prevail over the coastal currents around Palghar. The major one among them is tidal currents. The gravitational attraction of the moon and the sun is the cause of the tides, and the tidal currents associated with them may be pretty strong. The shape of the coastline, with its bays, headlands, and estuaries, can affect the way the tides move and the strength of the tidal currents.

The most prevailing factor is given by the monsoon winds. These winds during the southwest monsoon period-that is, from June to September-push the surface waters of the Arabian Sea. Such winds also alter the direction and velocity of the coastal currents; thus, different current patterns may form during this period. Freshwater inflow from rivers contributes to changes in the density driven currents by mixing with seawater.

Further, large-scale ocean circulation patterns in the Arabian Sea can interact with local coastal currents in the area. This may be in the form of an inflow of different water masses from other regions that carries change in temperature, salinity, and general characteristics of currents.

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

Surface Drift Buoy Method: The principle of this method is to deploy a buoy on the water surface. These buoys are designed to drift with the currents. Through satellite-based tracking systems or any other positioning method to track their motion over time, information related to the direction and speed of surface currents is acquired. This mainly provides data from the surface layer, though it does not provide comprehensive understanding about the currents at different levels.

Anchor Boat Method: The principle herein is that a boat is anchored in coastal waters. Other instruments are thereafter used in the measurement of the flow of water at different depths around the boat. Though this may give more detailed data for the area surrounding the boat, it is relatively labor- and time-consuming. This also has limitations as to the area that it will be able to cover.

ADCP method: More efficiently and effectively, coastal current could be measured using the ADCP current meter technique. It relies on sonar to concurrently determine a series of water velocity ranges with depth. The sound pulses that it puts into the water produce reflections due to shifting of Doppler through the sediment and particles flowing along with the flow of currents at every depth range, while providing the profiling velocity against the depth below the water's surface. That gives a far more realistic and complete picture of the currents along this coast compared to other methods.

4. Principles of Operation of ADCP Applying Doppler Principle

An ADCP current profiler is based upon the Doppler effect. The sonar impulses are emitted into the water by these devices. These sound waves, while interacting with particles in water-sediment particles, plankton, or other small organisms-produce a shift in frequency of the reflected sound waves due to the Doppler effect. If the particles are moving towards the ADCP, the frequency of the reflected waves is higher than the emitted waves; if they are moving away, the frequency is lower.

This, therefore, depends on the Doppler shift of reflected sound waves at various angles and depths, the ADCP flow meter calculates the water velocity in those many directions. The ADCP profiler would transmit and receive these sound signals through a number of transducers and, therefore, is allowed to establish a proper profile of the entire water velocity right from the surface down to a certain depth based on the capability of the instrument.

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

The measuring equipment for the coastal currents around Palghar should be manufactured from reliable materials. Because the marine environment is hostile, with salt-water corrosion, changes in temperature, and even physical impacts due to floating debris, the equipment must be durable.

Small equipment for easier deployment and installation are always advantageous. Whether deployed from a boat, buoy, or from the seabed, smaller devices offer better handling and installations. It also allows transportation and maintenance to be simpler and easier.

Weight - the weight of equipment should be light, especially for floating or moored devices. Light weight will ensure proper buoyancy and stability. Power consumption is very important also because it allows the continuous use for a long period without changing frequently the batteries or having a large power supply.

Cost-effectiveness is important. The equipment should not be prohibitively expensive to take large-scale measurements along the coast. For ADCPs, a casing made from a titanium alloy is an excellent choice. The corrosion resistance of the titanium alloy is excellent and absolutely vital in the salty marine environment; it is also strong yet relatively light in weight and meets the requirements for high-quality current-measurement equipment.

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

While selecting the equipment for current measurement at Palghar, the first consideration is the purpose of usage.

Ship-borne ADCP: It is good for measurements from a vessel in motion. The ship, as it moves along the coast, continuously records the coastal currents to provide a series of data over a wide area covered by the ship's route.

Bottom-mounted ADCP: suited for fixed-point measurement at the seabed. These yield a stable, long record of the water flow in the bottom, which is crucial to understanding how the bottom topography interacts with the coastal currents.

Buoy-mounted ADCP: This system is intended for longer records of currents in a given area while floating at the water surface. They could be deployed in areas where one wants to take data continuously without having the vessel present at all times.

Frequency

In shallow waters of up to 70m, a 600kHz ADCP would suffice, while in waters reaching as much as 110m, the frequency must be 300kHz. Similarly, very deep water-as much as 1000m-shall be adequately served by an ADCP meter with a frequency of 75kHz.

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.