How to measure the coastal currents of Jamnagar?

1. Where is Jamnagar?

Jamnagar is a city in Gujarat, India, on the western coast. It is an important city which has gained much importance due to its industrial activities, especially pertaining to oil and gas.

The city has been gifted with a location on the coast of the Arabian Sea. The coastline is a pretty stretch of land, filled with beaches with sand and clear blue waters in some places. The city is culturally very vibrant; it has a lot of traditions and festivals, which show the Gujarati heritage.

The nearby Arabian Sea is quite expansive, dynamic, and large in water body composition. The area provides a big shipping lane whereby there are various vessels traversing because of the existence of ports along its coasts. Various types of fish, crustaceans, and other sea animals can be found within its waters. It even gives rise to modifications within the climate; temperatures remain tempered while moisture from the sea breeze ensures an element of wetness in the region.

2. What are the conditions of the currents off the coast from Jamnagar?

The coastal currents in the vicinity of Jamnagar are influenced by more than one factor. The most powerful influence is that of the monsoon winds. The southwest monsoon, which ordinarily sets in during June and lasts up to September, carries strong winds that drive the surface waters. These winds may alter the direction and speed of the coastal currents, forming different patterns according to the strength and direction of the wind.

Tidal forces are also a significant factor. The gravitational pull of the moon and the sun causes the tides. Tidal currents near Jamnagar can be quite variable, with the ebb and flow of the tides creating a complex pattern of water movement. Topography of the seabed: Submarine ridges and valleys can affect the flow of the currents, either diverting or concentrating the water movement.

The Arabian Sea is surrounded by large-scale ocean circulation patterns, which also interact with the local coastal currents. The movement of water masses from other regions may also bring water of different temperatures, salinities, and velocities into the region that could alter the characteristics of the coastal currents.

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

Surface Drift Buoy Method: This is a technique of deploying buoys that float on the surface. These buoys are left to drift with the currents. Using satellite-based tracking systems or other positioning methods, we can monitor the movement of the buoys over time. This provides information about the direction and speed of the surface currents. However, this method essentially deals with the surface layer contributions and may not represent the currents at various depths.

Anchor Boat Method: In this method, a boat is anchored in the coastal waters. Instruments are then used to measure the water flow around the boat at various depths. While this can give more detailed data for the area around the boat, it is relatively labor-intensive and time-consuming. Additionally, it has limitations regarding the area it can cover.

ADCP is an advanced, more efficient way of measuring the currents in the coast. This method applies sound waves for measuring the water velocity at multiple depths simultaneously. It will give a very detailed profile of the current from the surface down to a certain depth and hence give a more accurate and comprehensive understanding of the coastal currents compared to the other methods.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They send out sound pulses into the water. As these sound waves reflect back from particles in the water-sediment particles or small organisms-the frequency of the reflected sound waves shifts through the Doppler effect. If the particles are moving towards the ADCP, the frequency of the reflected waves is higher than that emitted, and if they are moving away, it is lower.

The ADCP calculates the velocity of the water in various directions by measuring the frequency shifts of the reflected sound waves at different angles and depths. The ADCP sends and receives these sound signals with the help of multiple transducers, thus enabling the creation of a detailed profile of the water velocity throughout the water column from the surface down to a specific depth, depending on the instrument's capabilities.

5. What's required for high - quality measurement of Jamnagar coastal currents?

The equipment to measure the coastal currents near Jamnagar should be made of reliable materials. It needs to be able to operate in the harsh marine environment with salt-water corrosion, temperature fluctuations, and possible impacts from floating debris.

The size of the equipment must be small for easy deployment, installation on boats, buoys, and/or at the seabed; a small size makes transportation more convenient for maintenance purposes as well.

Equipment weight shall be light enough. It is vital as floating or moored devices that need appropriate buoyancy, hence a need to be of sufficiently low weight, along with stability in low power consumption that will help fit the needs for continuous operation sometimes over an extended period with either minimal battery replacement or simply small power supply.

Cost-effectiveness is an important consideration. In order to conduct large-scale measurements along the coast, the equipment should be reasonably affordable. For ADCPs, a casing made of titanium alloy is an excellent choice. The corrosion resistance of the titanium alloy is excellent, which is crucial in the salty marine environment. It is also strong and relatively light, fulfilling the requirements for high-quality current-measurement equipment.

6. Selection of appropriate equipment for the measurement of current

While selecting the equipment for current measurement at Jamnagar, the usage purpose has to be considered first.

Ship - borne ADCP: It is suitable for measurement from a moving vessel. It records the coastal currents continuously as the ship moves along the coast and gives a series of data points over a reasonably wide area covered by the ship's route.

Bottom - mounted ADCP: This is useful for fixed - point measurement at the seabed and gives a steady and long-term record of the water flow near the bottom, something important to understand the interaction between the bottom topography and the coastal currents.

Buoy-mounted ADCP: Used when the aim is to measure the currents in a specific area over an extended 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.

In terms of frequency, for water depths within 70m, a 600kHz ADCP is a good choice. For depths up to 110m, a 300kHz ADCP is more appropriate. And for deeper waters up to 1000m, a 75kHz ADCP is recommended.

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.