How to measure the coastal currents of Chavakachcheri?

1. Where is Chavakachcheri?

Chavakachcheri is a town in the Jaffna Peninsula of Sri Lanka. This is a place of great historical and cultural importance. The town is surrounded by a landscape that is a blend of agricultural fields and small water bodies.

There, in Chavakachcheri, rich cultural heritage blends into the day-to-day activities of its inhabitants, with the distinctive language, art, and religious behavior of the Tamil speaking. It includes traditional handicrafts and colorfully vibrant local markets. Geographically, concerning this area's positioning relating to a body of water, lies the Palk Strait, which is an extension of sea that separates the India land mass from the land mass of Sri Lanka. The semi-enclosed nature of the strait influences the coastal waters off Chavakachcheri. Relatively calm waters compared to the open ocean, the tides and other oceanic processes have their effects. A number of fishing villages dot the coasts, with local fishermen depending on the bounty offered by the strait for their livelihood. The shorelines are a mix of sandy beaches and areas with mangrove forests, which play an important role in the coastal ecosystem.

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

This includes several reasons for the development of coastal currents around Chavakachcheri. Due to proximity to the Palk Strait, the tidal current is considerable. Because of the rise and fall of sea level occurring every six hours, the water does the to-and-fro oscillations, sometimes with violent energy in certain areas.

Another important reason for coastal current variability is the monsoon winds. The southwest monsoon and the northeast monsoon bring winds from different directions. While the southwest monsoon winds may drive the surface waters in one direction, the northeast monsoon can reverse or alter this flow. In addition, inflows and outflows through the Palk Strait, with its several channels to the Bay of Bengal and the Arabian Sea, can give rise to very complicated current patterns. Topography of the sea floor in the area, such as shoals and channels, can also be a factor in the speed and direction of the currents.

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

Surface Drifter Buoy Method

Surface drifter buoys are those that go into the water surface for tracking the movements of the uppermost layer of water. They are simple, economically viable tools. By the use of satellite-based tracking systems, one can monitor the position of the buoys as time progresses. This will provide information on the surface currents and may not give a complete understanding of the currents throughout the water column.

Moored Ship Method

The ship is moored in one location off the coast, in which instruments are installed to carry out water flow measurements. Its advantages are that it allows making continuous measurements in one fixed point. It also has a number of shortcomings-the ship itself moves depending on the waves and winds, bringing errors into measurements. Moreover, data could be given only to this place of the moored ship.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP profiler is an advanced and efficient means of measurement for the currents in the coast. It measures the water's velocity at different depths using acoustic pulses. By emitting the sound waves and analyzing the frequency shift of the reflected waves due to the Doppler effect, it provides the profile of the current right from the surface to a certain depth with good resolution. It is also a more holistic method compared to the first two techniques, since it can record the current's variability along the water column.

4. How does the ADCP, with its operation principle based on the Doppler principle, work?

Their mode of operation is based on the Doppler effect. ADCPs emit acoustic signals in the water column. When these signals fall upon moving particles in the water, like sediment grains or small organisms, the frequency of the reflected signals changes. If the particles are moving towards the ADCP, then the frequency of the reflected signal is higher than the emitted frequency, and if they are moving away, it is lower. By measuring these frequency differences at multiple angles and depths, the ADCP meter can calculate the velocity of the water at different points in the water column. This allows for the creation of a detailed current profile, showing the speed and direction of the water movement at various depths.

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

The equipment must be made of reliable materials that would ensure high-quality measurement of the coastal currents around Chavakachcheri. It should be able to resist the corrosive action of seawater and the harsh marine environment. The desirable features include compact size, light weight, and low power consumption. A small and light device is easier to handle during deployment and retrieval operations. Low power consumption allows for longer-term monitoring without frequent battery replacements.

Another important factor, especially for large-scale measurement projects, is the cost-effectiveness. The casing of an ADCP flow meter is preferably made of titanium alloy. The use of titanium alloy is suitable for ocean seawater because it has excellent resistance to corrosion. It also has an excellent strength-to-weight ratio, ensuring durability but relative lightness of the equipment.

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

Based on Usage

• Ship - borne ADCP: If the measurements are to be taken from a moving vessel, a ship - borne ADCP is suitable. It can provide continuous data as the ship travels along the coast.
• Bottom - mounted ADCP: For long - term and fixed - point measurements near the seabed, a bottom - mounted ADCP is a good choice. It can provide detailed information about the current profiles at a specific location.
• Buoy - mounted ADCP: In situations where deployment and measurement flexibility of surface and upper - water - column currents are required, a buoy - mounted ADCP current profiler is the way to go.

Based on Frequency

The choice of frequency depends on the water depth. For water depths up to 70m, a 600kHz ADCP is usually appropriate. For depths between 70m and 110m, a 300kHz ADCP is a better fit. And for deeper waters, such as those that may be found near Chavakachcheri in some areas, a 75kHz ADCP is suitable for measuring up to around 1000m depth.

There are well - known ADCP current meter brands like Teledyne RDI, Nortek, and Sontek. For a cost - effective option with excellent quality, the China Sonar PandaADCP is a good alternative. It is made of titanium alloy and offers a great price - performance ratio. You can find more information at https://china-sonar.com/.

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