How to measure the coastal currents of Bharuch?

1. Where is Bharuch?

Bharuch is a city in the state of Gujarat, India. It is situated on the banks of the Narmada River and near the Gulf of Khambhat. It is a city with a rich historical and cultural background.

It is strategically placed and has been a vital trading and transportation center for many hundreds of years. The cultural identity of the place is characterized by the amalgamation of different traditions. The mainstay of the local inhabitants is provided by industries relating to petrochemicals and agriculture.

Regarding the aspect of the coastline, proximity to the Gulf of Khambhat is quite relevant. The gulf is a semi-enclosed shallow water body with peculiar hydrodynamic conditions. Bharuch forms a part of the region dominated by both estuarine and coastal features. Fresh water and sediments from the Narmada River flowing into the gulf at Bharuch create diverse gradients in this area-from the brackish waters in the vicinity of discharge of freshwater to the saline regions of the coast. Many types of marine fauna inhabit the coastal waters: fish, crustaceans, and mollusks. The presence of a port in the area also shows that maritime activities are important in the area.

2. What is the state of the coastal currents in the Bharuch area?

In this part of the coastal area of Bharuch, the currents take part in many factors. Most important of all, it is the tides that have the most crucial part in these currents. Semi - enclosed nature of the Gulf of Khambhat brings out extreme tides. Gravitational attraction of moon and sun shows a complicated pattern of fall and rise. Tidal current might be very powerful and alters the water movement direction at frequent intervals, especially at spring tide.

The river discharge from the Narmada also has an effect on the coastal currents. Inflow of freshwater can cause density-driven currents in its mixing with the more saline seawater. The amount of river discharge varies seasonally, which in turn can modify the current patterns. During the monsoon season, the river flow increases significantly, causing changes in the coastal current regime.

The wind patterns, especially during the monsoon months (June - September), also have an impact. The southwest monsoon winds can drive the surface waters and influence the direction and speed of the coastal currents. The shape of the gulf and the local topography, including the presence of shoals and channels, can redirect and modify the flow of the currents.

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

Surface Drift Buoy Method: It is a method that deploys buoys onto the water surface. These buoys drift due to currents. Employing satellite-based tracking systems or other positioning techniques can monitor the buoy movements at different times. This shows the direction and speed of surface currents. However, this method primarily deals with the surface layer and may not provide a full understanding of the currents at different depths.

Anchor Boat Method: This involves anchoring a boat in the coastal waters. Instruments are then deployed to measure the flow of water around the boat at different depths. While this can provide more detailed data for the area around the boat, this is a relatively labor and time-consuming method. Besides, the area that can be covered is limited only to the vicinity of the anchored boat.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP current profiler method is an advanced and efficient way to measure coastal currents. It can measure the velocity of water at more than one depth simultaneously by using sound waves. By emitting sound pulses and analyzing the Doppler-shifted reflections from particles in the water, it can create a detailed profile of the current from the surface down to a certain depth. This gives a more accurate and full representation of the coastal currents than some of the other methods.

4. How do ADCPs using the principle of the Doppler work?

The operation of ADCPs is based on the Doppler effect. They emit sound pulses into the water. When these sound waves interact with particles in the water, such as sediment particles, plankton, or other small organisms, the frequency of the reflected sound waves is different from that of the emitted waves because of the Doppler effect. Particles moving towards the ADCP current meter reflect waves at a higher frequency than those emitted, while particles moving away reflect waves at a lower frequency.

By measuring the frequency shift of the reflected sound waves at different angles and depths, the ADCP flow meter can calculate the water velocity in different directions. Several transducers on an ADCP meter send and receive these sound signals, thus providing a detailed profile of water velocity throughout the water column from the surface to a certain depth, depending on the instrument's capability.

5. What do the measurements of Bharuch coastal currents require?

The equipment for measurement of the coastal currents near Bharuch has to be made from reliable materials. Since there is a harsh marine environment-which includes salt-water corrosion, temperature fluctuations, and even the possibility of impacts against floating debris-the equipment must be durable.

Small equipment is essential to make deployment and installation easier. Whether installed on boats, buoys, or at the seabed floor, small size makes handling and installation more feasible. In addition, it facilitates the transportation and maintenance processes.

The weight of the equipment should be light, particularly for floating or moored devices. A light weight means proper buoyancy and stability. Another important aspect is low power consumption, since continuous operation over long periods is highly desirable without requiring frequent changes of batteries or a large power supply.

Another critical factor is cost-effectiveness. The equipment should not be too expensive to conduct large-scale measurements along the coast. For ADCPs, a casing made from titanium alloy is an excellent choice. First, titanium alloy resists corrosion very well, which is essential in the salty marine environment. It is also strong and lightweight, satisfying the requirements for high-quality current-measurement equipment.

6. How to select appropriate equipment for current measurement?

While selecting equipment for the measurement of current near Bharuch, the usage purpose should be considered as the first factor.

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

Bottom-mounted ADCP: It is ideal for fixed-point measurements at the seabed. It provides a stable long-term record of the flow near the bottom, something of great importance to capture the interaction between the bottom topography and the coastal currents.

Buoy-mounted ADCP: Employed when the purpose is to measure the currents in 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.

Considering frequency, within 70m water depths, the 600kHz ADCP should be a good option; within 110m depth, a 300kHz ADCP should be used, while within 1000m deep waters, the 75kHz is a better choice.

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.