How to measure the coastal currents of Dwarka?

1. Where is Dwarka?

Dwarka is a city situated on the western coast of India in the state of Gujarat. It is a place of great religious and historical significance, being one of the seven most ancient cities in the country and a major pilgrimage site for Hindus.

The city is situated on the shores of the Arabian Sea. Its coastal setting endows it with a unique charm. The surrounding landscape is a beautiful blend of sandy beaches and clear blue waters. Culturally, Dwarka is rich with a heritage that dates back centuries. The local population is deeply involved in religious and fishing activities.

The Arabian Sea, which is adjacent, is immense and dynamic. Marine life in the coastal waters off Dwarka is abundant, with a wide range of fish species and other sea creatures. The sea is also an important trade and transportation route, with small fishing boats and occasional larger vessels plying its waters.

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

Various factors affect the coastal currents near Dwarka. The seasonal winds are one of the main causes. During the monsoon season, the strong winds blowing from the southwest during June to September can definitely influence the direction and speed of the coastal currents. These winds push the surface waters, leading to changes in the current patterns.

The tidal forces, too, play a major role. The tides, due to the gravitational pull of both the moon and the sun, bring about the rise and fall of water along the coast. The strength and direction of tidal currents change with the phase of the tide. The topography of the seabed off Dwarka influences the currents, too. Submarine ridges and valleys channel and deflect the flow of water.

Besides, the large-scale oceanic circulation patterns in the Arabian Sea can interact with the local coastal currents. The inflow of different water masses from the open sea can change the temperature, salinity, and velocity of the coastal currents.

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

Surface Drift Buoy Method: In this method, buoys are left on the surface of the water to drift with the currents. With the help of satellite-based tracking systems or other positioning methods, one can trace the path of these buoys over a certain period of time, thus providing data on the direction and speed of the surface currents. This technique provides information only for the surface layer and may not be representative of the currents at deeper levels.

Anchor Boat Method: In this, a boat is anchored in the coastal waters, and by using instruments, the water flow around the boat is measured at different depths. Though it has a very critical approach, enabling the detailed study of more data in the surrounding area of the boat, the disadvantages of the method include a very small area covered, while the work is pretty labor- and time-consuming.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP method is an advanced and quite efficient mode of measurement. The technique involves the use of sound waves to measure water velocity at multiple depths all at once. It can give a very detailed profile of the current from the surface down to a certain depth, giving a more comprehensive and accurate picture of coastal currents than the previous methods.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the basis of the Doppler effect. They send out sound pulses into the water. As these sound waves engage with particles in the water-like sediment particles or even small organisms-the frequency of the reflected sound waves changes by means of the Doppler effect. If the particles are moving towards the ADCP, the frequency of the reflected waves is higher than the emitted waves; if the particles are moving away, the frequency is lower.

The ADCP measures the frequency shifts of reflected sound waves at different angles and depths to calculate water velocity in various directions. Multiple transducers within an ADCP send and receive these sound signals, each enabling it to create a detailed profile of the water velocity throughout the water column, from the surface down to specific depth depending on the capabilities of the instrument.

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

The equipment to be employed for high-quality measurement of the coastal currents around Dwarka should have dependable materials that can bear the heavy marine environmental conditions like the corrosion by saltwater, high and low temperature variations, and impacts from floating debris.

The size of the equipment should be small enough that it will be easily deployed and installed, whether in boats, buoys, or at the seabed. A small size also makes it easier in handling during transportation and maintenance.

The weight of the equipment shall be light. For floating or moored devices, their weight is expected to be as light as possible for perfect buoyancy and stability. It must also consume very low power for the potential ability to operate continuously over extended periods without the need to replace batteries or large-scale power supply.

Another important factor is the cost-effectiveness. Measuring in large-scale, along the coast, should be economically feasible. For an ADCP, a casing made from Titanium alloy would be a perfect choice. As known, Titanium alloy features excellent corrosion resistance, an essential quality in the salt-filled marine environment. On the other hand, this alloy is also strong but lightweight, just what was needed for high-quality current-measuring equipment.

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

While selecting the equipment for current measurement at Dwarka, the first consideration is the purpose of use.

Ship - borne ADCP: This is suitable for measurements from a moving vessel. It can record the coastal currents continuously as the ship moves along the coast, providing a series of data points over a relatively wide area covered by the ship's route.

Bottom - mounted ADCP: especially used for fixed-point measurements on the seabed, the instrument would give a record of water flow near the bottom. The importance will be very vital as that will record the stable, long-term record necessary in understanding how the bottom topography interacts with the coastal currents.

Buoy-mounted ADCP: Used when the purpose is to measure the currents in a certain area over 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 - A 600kHz ADCP is often a good choice for water depths within 70m, a 300kHz ADCP is more appropriate for up to 110m and a 75kHz ADCP is recommended for deeper waters up to 1000m.

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.