How can we measure the Coastal Currents of Panaji?

1. Where is Panaji?

Panaji is the capital city of the Indian state of Goa. It is located on the west coast of India, along the Arabian Sea. This coastal city is a beautiful blend of Portuguese - influenced architecture and laid - back beach culture.

Geographically, Panaji is nestled between the sea and the lush Western Ghats. The coastline is a major attraction, with sandy beaches that stretch for miles. The Arabian Sea here is vibrant and dynamic, a body of water that is home to a diverse range of marine life, with fishing being an important activity in the waters adjacent to it. The estuaries and tidal creeks around Panaji add to the complexity of the coastal environment.

The city, culturally, reflects its Portuguese colonial past. Churches, old forts, and colored houses dot the city. Its local cuisine is a delicious combination of Goan and Portuguese tastes, with a heavy seafood influence. The people of Panaji have a close association with the sea, and fishing, going to beaches, and water sports are very much part of their way of life.

The climate of Panaji is influenced by the sea. The sea breezes bring a pleasant coolness, and the monsoons play a crucial role in shaping the coastal environment. The southwest monsoon, in particular, brings heavy rains and affects the water levels and currents of the Arabian Sea.

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

The various factors influence the nature of coastal currents near Panaji. The monsoon winds create a significant impact. Strong winds during the southwest monsoon, which usually lasts from June to September, drive the surface currents. Such wind-driven currents may transport sediments and nutrients, impacting the coastal ecology in certain ways. The northeast monsoon influences the currents but with variation in patterns.

Tidal currents form one of the most important features of the current system. The Arabian Sea off Panaji receives semi-diurnal tides. Tidal action produces strong tidal currents in which the wind-driven currents superimpose. The topography of the seabed around Panaji, with its sand bars, reefs, and channels, deflects and modifies the currents.

The inflow of freshwater from rivers and streams from the area can also contribute to the setting of coastal currents. Because of the difference in the density of fresh water and salty water, this can evolve into intricate circulation patterns. The greater-scale oceanic circulation within the Arabian Sea, involving the Somali Current and the Arabian Sea Gyre, can influence the local current indirectly as well.

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

Surface Drifting Buoy Method: A surface-drifting buoy is released into the water and its movement tracked by GPS or any other tracking devices. From observed displacements of the buoy, after a time interval, estimates of speed and direction in the surface current can be obtained. However, it is only applicable for the surface layer and wind and waves may also influence the movement of the buoy.

Anchor-Boat Method: A boat is anchored at a certain location near the coastline, and current meters from the boat measure the current at higher and lower levels. This permits a more detailed view about the current profile at any given point, but, again, it is limited to an area surrounding the anchored boat and may not capture all the spatial variability of currents.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP current meter is an advanced and more efficient method for the measurement of flow in coastal water. It is able to measure simultaneously the water velocity at several depths. In the case of an ADCP, by sending out sound waves and then analyzing the Doppler shift of the reflected waves, it provides a complete understanding of the profile of the current from the surface to the seabed.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They send out acoustic pulses into the water. These pulses scatter off the moving particles in the water, including sediment, plankton, and other small organisms. When the particles are moving towards the ADCP meter, the reflected wave frequency is higher than the frequency emitted; when the particles are moving away from the ADCP current meter, the frequency of the reflected wave is lower.

From this frequency shift, the exact velocity of the water can be pre-calculated at discrete depths. Most ADCPs have multiple transducer elements that transmit beams in various directions. Such an approach helps in deriving the three-dimensional structure of the current and, as a result, an accurate representation of the pattern of water circulation.

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

This requires that the equipment for such high-quality measurement of coastal currents be of reliable materials. Given seawater's corrosive action, resistance against long-term exposure also ought not to be compromised. Considering that the device needs to have light weight and small size regarding the deployment and retrieval features due to certain areas with very minimum accesses in which deployment and retrieval condition gets critical.

Low power consumption is of the essence for long - term operation, especially when it comes to continuous monitoring. Cost-effectiveness will also be an important factor, enabling widespread and frequent measurements.

The housing of the ADCP profiler shall be of titanium alloy. This ensures excellent corrosion resistance in a corrosive seawater environment, is strong, and can withstand pressures imposed by the water column and the forces of waves and currents. Its relatively low density also serves to keep the equipment weight low, making it easier to handle during installation and maintenance.

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

The choice of equipment depends on the specific application.

For Ship-based Measurements: A ship-mounted ADCP is suitable. It allows for measurements while the ship is in motion, enabling the mapping of currents over a larger area.

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.

Not many aspects are taken into consideration, but as far as frequency is concerned, an ADCP has different frequencies suited for different water depths: A 600kHz ADCP applies to water depths up to 70m, a 300kHz for water with depths up to about 110m, and finally, a 75kHz in water with depths up to 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.