How can we measure the Coastal Currents of Gokarna?

1. Where is Gokarna?

Gokarna is a small coastal town situated on the west coast of India, in Karnataka state. The town is sandwiched between the Arabian Sea and the Western Ghats. The town boasts its beautiful beaches and ancient temples.

From the geographical perspective, Gokarna coastline holds a great many important sights: Om Beach, Kudle Beach, is not just a haven for tourists; they also form an inseparable part of the ecosystem for locals. The Arabian Sea, lying alongside Gokarna, represents a great volume of water inhabited by numerous species of animals. It serves as a mild modifying agent in the town because sea breezes are so pleasing during the hot months.

Culturally, Gokarna is a place of religious importance. The Mahabaleshwar Temple attracts pilgrims from far and wide. Often, the local traditions and festivals relate to the sea and the religious heritage. People in Gokarna are symbiotic with the sea, and fishing is part of the local economy.

Off Gokarna, the seas represent the continental margins of a greater Arabian Sea. The topography experiences monsoon winds with very heavy rain in the wet season and moderate to calm otherwise. Onshore waves change from swell in good conditions to higher energy surges when storms exist, while both rocky outcrops and sand form a real mixed coastal environment.

2. What are the situations of the coastal currents in the vicinity of Gokarna?

The coastal currents off Gokarna are influenced by various factors. The most prominent among these factors is the influence of monsoon winds. The southwest monsoon, which blows from June to September, creates strong surface currents that run parallel to the coast. These are driven by the force of the winds and can transport sediments and nutrients for a fairly long distance.

The tides also play an important role. The tidal pattern around Gokarna is semi-diurnal in the Arabian Sea. Because of the rise and fall of water level due to tides, tidal currents are generated. These tidal currents, in turn, interact with the wind-driven currents to give a complex pattern of water circulation.

Topography of the seabed off Gokarna determines the paths of the currents. Local underwater sandbars, reefs, and channels could locally deflect and accelerate the currents. Inflow of fresh water from the rivers and streams around would change the density in the coastal waters and thus the current patterns. Larger-scale oceanic circulation off the Arabian Sea, for example, the Somali Current, indirectly influences the local coastal currents.

3. How to observe the Gokarna Coastal Water Flow?

The observation of Gokarna coastal water flow can be viewed by several techniques. Among them, the surface drifting buoy method can be used for observing the same. A buoy is released in the water, and its movements are tracked through GPS or other tracking devices. From the position over time, one can trace the information about the speed and direction of the current on the surface. However, this method is limited to the surface layer and the buoy's movement can be affected by winds and waves.

Another method for measuring currents is the anchor-boat technique. A boat is anchored at a specific location, and current meters are deployed from the boat to measure the current at different depths. This enables a more vertical-oriented measurement, but is restricted to the area around the anchored boat and may not capture the full spatial variability of the currents.

The ADCP current meter method is a more advanced and efficient way of observing the flow of water in the coast. ADCPs can measure simultaneously the velocity of water at several depths. By emitting sound waves and analyzing the Doppler shift of the reflected waves, ADCPs can provide a detailed profile of the current from the surface to the seabed, offering a more comprehensive understanding of the coastal water flow.

4. How do ADCPs using the Doppler principle work?

The ADCPs work on the basis of the Doppler effect. They send acoustic pulses into the water. These pulses interact with the moving particles in the water, such as sediment particles and small organisms. When the particles are moving towards the ADCP meter, the frequency of the reflected wave is higher than the emitted frequency, and when they are moving away, it is lower. This frequency shift is measured by the ADCP, which calculates the velocity of the water at different depths. The ADCP flow meter typically has multiple transducer elements that transmit beams in different directions to measure the three-dimensional structure of the current.

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

This high-quality measurement of coastal currents requires equipment to be made up of materials that give reliable data over a reasonably long period; relatively compact and of low weight so it may allow convenient deployments/retrievals in the hostile coastal environment; low-power consumption allowing long-term operating-for continuous measurements, in fact. Cost-effective to enable regular and more frequent measurements of the key parameters.

The casing of the ADCP current profiler is preferably made of titanium alloy. Titanium alloy offers excellent corrosion resistance, which is crucial in the corrosive seawater environment. It is strong and can withstand the pressures exerted by the water column and the forces of waves and currents. Its relatively low density helps to keep the equipment's weight in check, facilitating easier handling and installation.

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

The choice of equipment for current measurement depends on the specific application. For ship - based measurements, a ship - mounted ADCP is suitable. If the focus is on near - seabed currents, a bottom - mounted ADCP can be considered. For surface and upper - water - column measurements, a buoy-mounted ADCP is a good option.

Regarding the frequency of the ADCP, different frequencies are better for different water depths. A 600 kHz ADCP is usually good for water depths up to around 70m, the 300 kHz ADCP is good for water at about 110m water depth, and a 75 kHz ADCP can also operate in water as deep as approximately 1000 meters.

There are several well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand-China Sonar PandaADCP is also a great option. It is made of all - titanium alloy material and provides an excellent cost-performance ratio. You can visit their website at https://china-sonar.com/ for more details.

Here is a table with some well known ADCP instrument brands and moels.