How to measure the coastal currents of Rajkot?

1. Where is Rajkot?

Rajkot City is located in the state of Gujarat, India. It is not a sea-facing city itself but is relatively near to the Arabian Sea coastline. It falls in one of the most historically and culturally rich regions.

The city is traditionally known for its handicrafts, local markets, and education centers. The people of Rajkot carry a blend of urban and traditional Gujarati values. For its connection to the coast, it has the benefit of economic activities and resources that the surrounding coastal areas provide.

The diverse range of ecosystems has further stretched the adjacent coastal areas around the Arabian Sea. The various ecosystems found in the coastal waters offer different species of fish, mollusks, and a number of species of seaweed. The sea is also responsible for maintaining the local climate: for temperature and humidity variations. A number of fishing villages and ports exist along the coastline, through which much maritime trade and fishing is carried out.

2. What is the condition of the coastal currents off Rajkot?

Various factors are involved in causing the coastal currents off Rajkot. The monsoon winds have a considerable effect. During the southwest monsoon season from June to September, the resultant strong winds push the surface waters of the Arabian Sea. These winds can cause the coastal currents to change their direction and speed, leading to a dynamic flow pattern.

Tidal forces are another crucial determinant. The gravitational pulls of the moon and the sun determine tides, and related tidal currents can be both strong and weak, while at the same time variable in direction. The shape of the coastline and the general topography of the seafloor in the surrounding regions also influence the currents. Local submarine features like sandbar formations, ridges, and any canyons will, meanwhile, deflect the water flow either to reinforce or disrupt typical current patterns.

Besides, the large-scale oceanic circulation in the Arabian Sea can interact with the local coastal currents. The inflow of different water masses from other regions can bring changes in temperature, salinity, and density, which in turn can modify the characteristics of the coastal currents near Rajkot.

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

Surface Drift Buoy Method: This is a method whereby buoys are deployed on the water surface, which are allowed to drift with the currents. Through satellite-based tracking systems or other positioning methods, their movement over time can be monitored to get information on the direction and speed of the surface currents. This method, however, provides data basically for the surface layer and may not represent the currents at deeper levels.

Anchor Boat Method: This method involves anchoring a boat in the coastal waters. Instruments are then used to measure the water flow around the boat at different depths. While it can provide more detailed data for the area around the boat, it is relatively labor- and time-intensive. Besides, it has limitations as regards the area it can cover.

Acoustic Doppler Current Profiler (ADCP) Method: ADCP is a more advanced and efficient way to measure coastal currents. It uses sound waves to measure the velocity of water at multiple depths simultaneously. It can provide a detailed profile of the current from the surface down to a certain depth, giving a more accurate and comprehensive picture of the coastal currents than the other methods.

4. How do ADCPs using the Doppler principle work?

The principle of operation of ADCPs is based on the Doppler effect. They emit sound pulses into the water. As a result of the interaction of these sound waves with particles in the water, such as sediment particles or small organisms, due to the Doppler effect, the frequency of the reflected sound waves has changed. If the particles are moving towards the ADCP, the frequency of the reflected waves is higher than the emitted waves, and if they are moving away, the frequency is lower.

It works out the speed of the water in various directions by finding the frequency shift of the reflected sound waves, at different angles and different depths. With multiple transducers transmitting and receiving such sound signals, it thus becomes possible for the ADCP to obtain a high-resolution profile of the whole water column's velocity from surface to as far down as the instrument capability can achieve.

5. What is required to obtain good quality measurement of the currents at Rajkot coast?

Good quality measurement of coastal currents at Rajkot requires that all equipment be made from good-quality materials. It has to endure hostile marine conditions such as corrosion of salt water, variations in temperature, and potential jolts from floating debris.

The size should be compact for easy deployment and installation, whether on boats, buoys, or at the seabed; this same compactness offers convenience during transport and for maintenance services.

It needs to have light weight. Light in weight, for floating or moored devices, will be the basic characteristics for buoyancy and stability. Low power consumption also remains very important for allowing the possibility of continuous operation during very long periods without frequent battery replacements or large power supply.

Another very important aspect is the cost-effectiveness. For the measurement of a long stretch of coast, the equipment needs to be fairly cheap. For ADCPs, a casing made from titanium alloy is one of the best choices. This is because of its excellent resistance to corrosion, which is a key characteristic needed in salty marine water. Besides, it is tough yet lightweight, just what high-class current-measuring equipment deserves.

6. How to Select appropriate equipment for current measurement?

While selecting equipment for the measurement of current near Rajkot, the very first factor which needs consideration is the usage purpose.

Ship - borne ADCP: Suitable for the measurement from a moving vessel. It continuously records the coastal currents while the ship is moving along the coast; hence, giving a series of data points over a comparatively wide area falling under the route covered by the ship.

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

Buoy-mounted ADCP: It is used when the purpose is to measure the currents of a particular area over a longer 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.

For water depths within 70m, a 600kHz ADCP is a good choice, considering frequency. In depths up to 110m, it would be more appropriate to use a 300kHz ADCP, while for deeper waters, such as up to 1000m, the most recommended is a 75kHz 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.