How will we quantify these Murdeshwar coastal currents?

1. Introduction of Murdeshwar

Murdeshwar, a coastal town in Bhatkal Taluk, is situated in Uttara Kannada district, Karnataka State in India. It lies along the coast of the Arabian Sea and is known especially for its magnificent Shiva statue and the ancient Murdeshwar Temple.

Geographically, the coastline of Murdeshwar presents a catchment area of undulating sandy beaches and rocky sprays; a wide, strong body of water called the Arabian Sea forms a part of it. It contains a variety of colored fish, crabs, and other sea animals in its waters. In fact, tides coming out of this sea affect its shoreline and change the apparent shape of the land by their high and low tide variation.

The town is culturally an important pilgrim destination. Devotees throng to the Murdeshwar Temple in large numbers throughout the year. Most of the customs and festivals of the people here are related to either the temple or the sea. In fact, the people of Murdeshwar are bound to the sea because fishing and other sea-related activities are a significant part of their livelihood.

The waters around Murdeshwar belong to the dynamic environment of the Arabian Sea. The area witnesses the effect of the monsoon winds. The southwest monsoon brings heavy rainfall and strong winds that can cause rough seas and powerful waves from June to September. During the rest of the year, the sea breeze gives very pleasant climatic conditions as a characteristic feature of this town.

2. What is the status of the coastal currents off Murdeshwar?

Variability in coastal currents off Murdeshwar results from several factors. One major determinant is the wind conditions. During the southwest monsoon, strong winds displace surface waters and give rise to significant wind-driven currents. These may be carrying sediments and nutrients with them, impacting coastal ecology. The northeast monsoon has a different character, although it too is very influential.

Tidal currents are another important component of the current regime. The semi-diurnal tidal pattern is predominant in the Arabian Sea off Murdeshwar. The tidal rise and fall result in tidal currents that interact with the wind-driven currents. The topography of the seabed, with underwater features like sandbars and channels, can deflect and modify the currents near Murdeshwar.

The inflow of fresh water from nearby rivers and streams can also influence the density of the coastal waters. Density differences may lead to complex circulation patterns. The larger - scale oceanic circulation in the Arabian Sea, such as the Somali Current, has an indirect influence on the local coastal currents, too.

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

Surface Drifting Buoy Method: A surface-drifting buoy can be deployed into the water. The buoy's movement is tracked using GPS or other tracking devices. By observing the displacement of the buoy over time, the speed and direction of the surface current can be estimated. However, this method is limited to the surface layer and the buoy's movement can be affected by winds and waves.

Anchor-Boat Method: A boat is anchored in a certain position along the coast. Current meters are then deployed from the boat to measure the current at different depths. This gives a more detailed view of the current profile at a particular point but is restricted to the area around the anchored boat and may not capture the full spatial variability of the currents.

ADCP Method: The Acoustic Doppler Current Profiler (ADCP) is a more advanced and efficient way of measuring the flow of water in the coastal area. It can measure simultaneously the velocity of water at different depths. By emitting sound waves and analyzing the Doppler shift of the reflected waves, ADCPs can provide a comprehensive understanding of the current profile from the surface to the seabed.

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

ADCPs are based on the principle of the Doppler effect. They send out acoustic pulses into the water. These pulses interact with the moving particles in the water, such as sediment, plankton, and other small organisms. When the particles are moving towards the ADCP meter, the frequency of the reflected wave is higher than the emitted one. On the other hand, when the particles are moving away from the ADCP profiler, the frequency of the reflected wave is lower.

The velocity of water at these different depths is able to be calculated with this very precise frequency shift measured. This is enabled by a very large number of ADCPs featuring multiple transducer elements capable of transmitting beams in multiple orientations. They can thereby take the measurement of three - dimensional current structure-a lot more close to representing flow patterns in water properly, for instance.

5. What is required to do accurate measurement of Murdeshwar coastal currents?

The equipment for high-quality measurement in the coastal currents in Murdeshwar should have reliable materials. Since seawater is corrosive, it has to be able to stand the forces of long-term exposure. The device must be compact with a lightweight facility to provide easy deployment and retrieval of the equipment, especially for areas where access or the conditions are not so well.

Long-term operation, especially for continuous monitoring, requires low power consumption. Cost-effectiveness is also a very important factor to be able to make widespread and frequent measurements.

The casing of the ADCP flow meter is preferably made from titanium alloy. Titanium alloy provides excellent corrosion resistance, an essential property in the corrosive seawater environment. It is strong and able to resist the pressures exerted by the water column and the forces of waves and currents. Its relatively low density helps keep the weight of the equipment low, making it more manageable during installation and maintenance.

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

Choice of equipment for current measurement will depend upon the application.

For Ship-based Measurements: Ship-mounted ADCP is suited for it since the vessel can make measurements while underway to give wide area mapping of currents.

For Near-Bottom Currents: A bottom-mounted ADCP can be used. This is best suited for studying the near-bottom currents, which become very important in understanding the sediment transport and benthic ecosystems.

For Surface and Upper Water Column Measurements: A buoy-mounted ADCP is quite suitable. It provides continuous measurements over the surface and upper-layer currents.

For the different frequency of ADCP, its appropriateness is on behalf of different water depth; that is, a 600 kHz ADCP is adequate in water depths up to around 70m and the 300 kHz ADCP fits best in water depths up to about 110m or a 75 kHz could allow water depths up to approximately 1000 m.

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 offers 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.