How can we measure the coastal currents of Bhuj?

1. Where is Bhuj?

Bhuj is a city in the Kutch district of the Indian state of Gujarat. It is located in the western part of India, near the Arabian Sea. Geographically, it lies in a region that is a unique blend of arid landscapes and coastal areas.

It has a rich cultural heritage, a hotbed of handicrafts, pulsating local traditions, and a plethora of historical architecture. People in Bhuj remain attached to their roots and the local way of living.

Next to Bhuj lies the Arabian Sea-the great huge sheet of water that dictates the climate and economy of the land. The coastal waters host a variety of marine life. The sea is also an important transportation route, and fishing is one of the more important economic activities in this area. Along the shores around Bhuj are beaches, tidal flats, and several small islands. Of specific concern here would be the tidal flats because this area is under regular transformation at the hand of tides and the movement of the coastal current.

2. What is the condition of coastal currents in the surroundings of Bhuj?

A variety of factors influences the coastal currents near Bhuj. The most important factors include the monsoon winds. The southwest monsoon blows from June to September, and it carries pretty solid winds that may sometimes cause a drastic change in direction and speed of the coastal currents. Such winds can keep the surface waters moving in the direction they blow and thus bring in different patterns of the currents.

Tidal forces are other important factors. The gravitational pull of the moon and the sun causes tides, with the resulting tidal currents very strong sometimes off Bhuj. On the one hand, a change in tidal levels changes the flow within the coastal area. Coastal morphology and, therefore, underwater topography determine it as well. These irregularities in the bottom topography may divert the currents, while the curvature in the coastline might contribute to the nature of current flow.

Besides, the more regional circulation patterns in the Arabian Sea interact with the local coastal currents. Inflow of different water masses from the open sea alters the temperature, salinity, and overall characteristics of the coastal currents.

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

Surface Drift Buoy Method: The principles of this method involve placing buoys on the water surface. The buoy is allowed to drift due to currents. Similarly, satellite-based tracking systems or other positioning methods can be used to determine their movement over time, in order to find the directions and speeds of the surface currents. However, this method is mainly limited to the surface layer and may not provide a comprehensive understanding of the currents at different depths.

Anchor Boat Method: This method involves anchoring a boat in the coastal waters, then measuring the water flow around it at different deep levels using instruments. However, this method is able to give more detailed information for the area around where the boat was anchored and may be relatively labor-intensive and takes a lot of time; it also has limitations as to its coverage area.

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 compared to the other methods.

4. How do ADCPs based on the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They send sound pulses into the water. The frequency of the reflected sound waves is different from that of the emitted waves when these sound waves interact with particles in the water (like sediment particles or small organisms) 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, and if they are moving away, it is lower.

By measuring the frequency shifts of the reflected sound waves at different angles and depths, the ADCP can calculate the velocity of the water in various directions. The ADCP uses multiple transducers for sending and receiving these sound signals, which enables it to create a detailed profile of the water velocity throughout the water column from the surface down to a specific depth, depending on the capability of the instrument.

5. What’s needed for high - quality measurement of Bhuj coastal currents?

For high - quality measurement of the coastal currents near Bhuj, the equipment should have reliable materials. It needs to withstand the harsh marine environment, including saltwater corrosion, temperature fluctuations, and potential impacts from floating debris.

The size of the equipment should be small in order to facilitate easy deployment and installation, whether on boats, buoys, or at the seabed. Small size also provides more convenience in transportation and maintenance.

The weight of the equipment should be light. In the case of floating or moored devices, a light weight is required for proper buoyancy and stability. Low power consumption is also necessary for long continuous operation without the need for frequent battery replacements or a large power supply.

It has to be cost-effective as well. In order to measure the currents on a large scale along the coast, the equipment must be economically viable. For ADCPs, a casing made from titanium alloy is an excellent choice. The corrosion resistance of the titanium alloy is great, which is essential in a salty marine environment. The alloy is also strong and relatively lightweight, meeting the requirements of top-class current-measuring equipment.

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

While selecting the equipment for current measurement off Bhuj, the first consideration is the purpose of usage.

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: These are the ADCPs which are best used for fixed-point measurements from the seabed. The instrument yields a stable and long record of the water flow near the bottom, crucial for an understanding of the interaction between the bottom topography and the coastal currents.

ADCP - The Buoy - mounted: This is specifically deployed when the intention or goal is to measure over an extended period in certain areas while floating on the water surface. They are usually deployed in an area of interest and may also deliver data continuously without having to make the vessel present always or frequently.

Frequency - A 600kHz ADCP would be a good choice for water depths within 70m, a 300kHz ADCP for depths up to 110m and a 75kHz ADCP 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.