How to measure the Coastal Currents of Udupi?

1. Where is Udupi?

Udupi is a coastal town in the state of Karnataka, India. It is situated along the Arabian Sea and is quite famous for its beautiful beaches, temples, and rich cultural heritage.

Geographically, the coastline of Udupi is something to marvel at. The sandy beaches, like Malpe Beach, are not only a tourist attraction but also an important part of the local ecosystem. The Arabian Sea, which fronts Udupi, is expansive and has a turbulent body of water. It forms the habitat for much marine life like various kinds of fish, crabs, and other invertebrates. It influences climatic conditions too: in the evenings, sea breezes make it pleasant and thus moderating.

Udupi is culturally famous for its age-old temples. The Sri Krishna Temple is one of the most famous pilgrimage spots in this city, which attracts devotees from far and wide. The local cuisine here is a mouth-watering combination of coastal and traditional South Indian flavors, and seafood is abundant due to the proximity to the sea. People of Udupi share an attachment with the sea, and fishing and other sea-related activities are very significant for the local economy.

The waters off Udupi form a part of the Arabian Sea and are influenced by a variety of factors. Most important among these are the monsoon winds, especially the southwest monsoon from June to September, which brings heavy rainfall and may result in variations in sea levels and wave patterns. The tides also play an important role in shaping the coastal environment.

2. What is the situation of the coastal currents near Udupi?

The coastal currents off Udupi have been influenced by several factors, of which the influence of monsoon winds is dominant. During the southwest monsoon, there is a flow of strong winds that mobilizes surface currents. The wind-driven currents may also carry sediments and nutrients with far-reaching implications to coastal ecology. The northeast monsoon has different patterns affecting the currents.

One of the important components is tidal currents. The semi - diurnal tides are well pronounced in the Arabian Sea off Udupi. Tidal flow of seawater, due to ebb and flow, causes tidal currents that will interact with wind - driven currents. Seabed topography in the vicinity of Udupi has sandbars, reefs, and channels, all capable of deflecting or otherwise modifying the currents.

Besides this, the fresh water inflow from the nearby rivers and streams is an important factor affecting the density of coastal waters. Density difference would, in turn, facilitate a complex circulation pattern. Somewhat larger - scale oceanic circulation within the Arabian Sea, for example Somali Current and Arabian Sea Gyre, can affect the local coastal currents indirectly.

3. How to Observe the Flow of Water in Udupi Coast?

Surface Drifting Buoy Method: In this method, a surface-floating buoy is floated into the water. The drifting pattern is then monitored via GPS and other tracking modules attached to it. Since buoy motion is dependent upon water surface displacement, measuring its drift over a particular interval of time will give out a good estimation of the rate of movement and direction. But here, the analysis remains in the surface layer. Furthermore, it gets affected by every air wave, wind, etc.

Anchor-Boat Method: A boat is anchored in a given position, offshore from the coast. The current meters are launched from the boat at different depths to measure the current. This gives an even finer resolution of the current profile at a certain point; however, this method is limited to the vicinity of the anchored boat and may not capture the full spatial variability of the currents.

Acoustic Doppler Current Profiler (ADCP) Method: This is an advanced and effective means of measuring the flow of water in the coast. The ADCP current meter can measure simultaneously at various water depth levels. It can estimate the current profile from the surface to the seabed with comprehensive knowledge by emitting sound waves and analyzing the Doppler shift of the reflected waves.

4. How do ADCPs based on the Doppler Principle Work?

The operation of ADCPs is based on the Doppler effect. They transmit acoustic pulses into the water. These pulses interact with moving particles in the water, which include sediment, plankton, and other small organisms. Particles moving towards an ADCP current profiler reflect a wave of higher frequency compared to the frequency of emission. On the other hand, if the particles are moving away from an ADCP, the reflected wave will be at a lower frequency.

This frequency shift is precisely measured by the ADCP flow meter to compute the velocity of the water at various depths. Most ADCPs have multiple transducer elements that send out beams in different directions. This allows them to measure the three-dimensional structure of the current, providing a more accurate representation of the water flow patterns.

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

The equipment for measurement of coastal currents in Udupi should be made of reliable materials for high-quality measurement. Since seawater is corrosive, the equipment should be able to bear long-term exposure. The device should be compact in size and lightweight for easy deployment and retrieval, especially in areas with limited access or difficult conditions.

It needs low power consumption for long-term operation, especially for continuous monitoring. Cost-effectiveness is another vital enabling factor to consider for widespread and frequent measurements.

The housing of the ADCP meter is preferably made of a titanium alloy. The use of titanium alloy ensures excellent resistance to corrosion, which is cardinal in seawater with a high degree of corrosiveness. Besides, it is strong and able to bear the pressures exerted by the water column and the forces of waves and currents. Its relatively low density helps to keep the weight of the equipment low, making it easy to manipulate during installation and maintenance.

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

The choice depends on the specific application for which it is being utilised.

For Ship-based Measurements: A ship-mounted ADCP will suffice for the same. This system offers the added advantage of being able to take measurements while the vessel is in motion and allows the charting of currents over a much greater region.

For Near-Seabed Currents: A bottom-mounted ADCP can be used. This is ideal for studying the currents close to the seabed, which is important for understanding sediment transport and benthic ecosystems.

For Surface and Upper-Water-Column Measurements: A buoy-mounted ADCP is a good option. It provides continuous measurements of the surface and upper-layer currents.

The depth of the water, on the other hand, determines the ADCP frequency of operation. In general, a 600 kHz ADCP is suitable for water depths up to about 70m, while a 300 kHz ADCP is appropriate for water depths up to about 110m, and a 75 kHz ADCP can support water depths up to about 1000m.

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.