How to measure the coastal currents of Daman?

1. Where is Daman?

Daman is one of the union territories of India and is located on the western coast of the Arabian Sea; it is a place famous for its unique amalgamation of Portuguese and Indian cultures since it was once a colony of Portugal.

The city is famous for its beautiful beaches, historic forts like the Fort of Moti Daman and Nani Daman, and laid-back coastal life. Local people are involved in fishing, tourism, and small-scale trading. The coastline of Daman is a stretch of scenic beauty, with sandy shores and clear blue waters that attract tourists.

The adjacent Arabian Sea is immense and dynamic. It forms home to a variety of marine life, including colorful fish, sea turtles, and types of shellfish. It also provides a major transportation route with fishing boats and fewer cargo ships upon its waters. The tidal action is prominent, the ebb and flow of the tides influencing both the coastal environment and the behaviors of the local marine life.

2. What is the condition of the coastal currents near Daman?

The coastal currents near Daman depend on many factors. First of all, there are the monsoon winds. The southwest monsoon brings strong winds from June to September, which may drastically affect the direction and speed of the coastal currents. The winds push the surface waters to form different current patterns.

Other important factors will be tidal forces. The gravitational pull of the moon and sun creates tides, and the associated tidal currents can be quite strong. The ebb and flow of the tides can change the movement of water near the coast. The shape of the coastline and the topography of the seabed count too. For instance, ridges and valleys in the bottom topography may be able to deflect currents, while coastline curvature may decide whether currents flow along or perpendicular to the shoreline.

Besides all that, the coastal currents also interact with the larger-scale ocean circulation patterns in the Arabian Sea. Inflow of different water masses from the open sea may change the temperature, salinity, and thereby the general characteristics of the coastal currents.

3. How to observe the Daman coastal water flow?

Surface Drift Buoy Method: It involves the deployment of buoys onto the surface of the water. These buoys would always be traveling in tune with the currents. Based on the movement of buoys over time using systems from satellite positioning tracking or other positioning systems, information about the direction and speed of the surface current may be derived. However, this method yields data mostly on the surface layer and may not give a complete insight into the currents at different levels.

The anchor boat method: This technique involves the anchoring of a boat in general coastal waters. Instruments are then used to determine the amount of water flow around that boat at different varied depths. While this can make for much more detailed information in an area surrounding that boat, it is a rather labor-intensive and time-consuming method. Also, it allows only partial coverage of the area, which restricts its application very much.

Acoustic Doppler Current Profiler Method: ADCP current meter is another modern and efficient method for the measurement of coastal currents. It relies on the use of sound waves to measure the velocity of water at several depths simultaneously. It can provide a very detailed profile of the current right from the surface down to a certain depth, giving a more accurate and comprehensive picture of the coastal currents compared to the other methods.

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

ADCPs work by the Doppler effect. They send pulses of sound into the water, and when these sound waves reflect back from particles in the water-such as sediment particles or other small organisms-the frequency of the reflected sound waves shifts due to the Doppler effect. If the particles are moving towards the ADCP profiler, then the reflected waves have a higher frequency than emitted waves; if the particles are moving away, the reflected waves have a lower frequency.

The ADCP flow meter calculates the velocity of the water in different directions with the frequency shift of the reflected sound waves impinging at variable angles and depth. It allows for a very fine profile, with several transducers emitting and receiving the sound signals regarding the velocity of the water along the entire depth from the surface down to a depth dependent on the capability of the instrument.

5. What is needed for high-quality measurement of the Daman coastal currents?

The equipment to measure the coastal currents near Daman must be made from reliable material. It has to resist the harsh marine environment, which includes salt-water corrosion, temperature fluctuation, and even possible impacts from floating debris.

Small in size; this is because the equipment is to be allowed for deployment and installation easily on both boats and buoys, or even on the seabed itself. A small-sized gadget will also be easier in transport ways and maintenance.

The weight of the equipment shall be light. In floating or moored devices, a light weight is necessary for good buoyancy and stability. Low power consumption is also important to ensure long continuous operation with infrequent battery replacement or small power supply.

It should also be cost-effective. The apparatus must be reasonably affordable to carry out large-scale measurements along the coastline. In the case of the ADCPs, the casing is best made of titanium alloy. The reason is that the titanium alloy resists corrosion very well, which is the most critical factor in salty marine water. It is also solid and relatively light, thus fitting all requirements of high-quality current-measuring machinery.

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

The purpose of usage is the first factor in choosing the equipment for current measurement over Daman.

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

Bottom-mounted ADCP: For fixed-point measurement at the seabed, yielding a stable, long-term record of water flow near the bottom and relevant for studies on the interaction of the bottom topography and the coastal currents.

ADCP on Buoy: In a situation where one has to measure currents of a particular area over a longer period by floating on the water surface, it is used. This is done in areas of interest where the instrument can be deployed to continuously collect data while there is no requirement to always keep the vessel present at that location.

These should suffice with a frequency of 600kHz for water depths within 70m, a 300kHz ADCP for maximum depths up to 110m, and a 75kHz ADCP in deeper waters of at most 1000m.

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.