How to measure the coastal currents in Kilinochchi?

1. Where is Kilinochchi?

Kilinochchi is a town in Sri Lanka, in the Northern Province, situated in a region with quite a complex history and recently awakened to new life.

The landscape of Kilinochchi is a combination of flat plains and scattered water bodies. The area is rich in natural beauty, with lush vegetation that thrives in the tropical climate. The local culture is deeply influenced by the Tamil traditions. The people here have a strong sense of community and are known for their tenacity and unique art forms such as traditional dance and handicrafts.

It is relatively close to the sea, the Palk Bay. The Palk Bay is a shallow sheet of water that forms part of the greater body of water separating Sri Lanka from India. The coastal areas around Kilinochchi have a varied ecosystem. There are sandy beaches as well as areas with extensive mangrove forests. These mangroves act like a natural barrier to coastal erosion and are a home to a wide variety of marine and terrestrial species. The waters of Palk Bay are influenced by the inflow of rivers and estuaries, creating a unique environment that is both productive and vulnerable. Local fishing is an important aspect of the economy, with local fishermen dependent upon the bay for a catch.

2. What is the condition of the coastal currents in the vicinity of Kilinochchi?

The coastal currents in the vicinity of Kilinochchi are determined by several variables. The tidal forces, which come with the semi-diurnal tides in the Palk Bay, establish a regular pattern of water movements. Depending on the tide, it might be possible to notice major shifts in the speed and direction of the current.

The monsoon winds have a determining role. Large wind fields of the southwest monsoon can push surface waters in one direction, probably toward the northeast, whereas such a trend may be reversed by the northeast monsoon. The topography bottom of the sea off a coastline, including shoals, channels, and submerged sand bars influence this flow of currents. A general convergence of currents, divergence, and rate of flow are caused accordingly. Further, the possibility of exchange of water between the relatively small Palk Bay with the open ocean through narrow channels may lead to complex variable current patterns.

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

Surface Drifter Buoy Method

The surface drifter buoy is a straightforward tool in observing the water flow within the coastal region. These kinds of buoys would be put onto the water surface and conveyed by currents. By utilizing satellite-based tracking systems or any other ways of positioning, the displacement of the buoys is able to be monitored as time progresses. However, this method gives the main result about the surface current, and such information may not provide adequate details about the current structure throughout the vertical profile in the water column.

Moored Ship Method

This is the method whereby a ship is moored near the coast. Instruments on the ship are used to measure the flow of water at different depths. This allows for continuous measurements at a fixed location. It also has its disadvantages. Movement of the ship due to waves and wind can introduce errors in the measurements. It also provides data for the area around the moored ship and may not represent the overall coastal current situation.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP flow meter technique is a sophisticated and complex means of measuring coastal current. ADCPs measure water velocity at multiple depths, by emitting acoustic pulses. In addition, they can paint a very detailed profile of the current right from the surface to a certain depth using sound waves and analyzing the Doppler-shifted echoes. This enables a more realistic representation of the current behavior of the whole water column, which is particularly useful in studies of coastal currents off Kilinochchi.

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

Principle of ADCP meter ADCPs work based on the Doppler principle. A high-frequency acoustic signal is transmitted into the water from the instrument. Wherever this signal intercepts the moving particles of the water, because of the Doppler effect, the reflected signals backshow a different frequency than that which is emitted. If the targets are coming, the frequency of the reflected signal will be higher; if the targets are going away from the ADCP, lower.

Measuring these frequency shifts at varying angles and depths, the ADCP profiler calculates the velocity of the water at discrete points in the water column. This enables it to create a detailed current profile of the speed and direction of the water movement at various depths. The data so acquired can then be used in order to analyze the characteristics of the coastal currents concerning their variability in time and space.

5. What is required for high - quality measurement of the Kilinochchi coastal currents?

The equipment to be used for the high - quality measurement of the coastal currents near Kilinochchi should be made of reliable materials. The device has to be designed to operate in corrosive seawater and a harsh marine environment. The compact size, light weight, and low power consumption are some other desired features.

It also means that a small and lightweight device is easier to deploy and recover, from either a boat or from a coastal installation. Low power consumption allows for longer-term monitoring without frequent replacement of batteries. Cost-effectiveness is another important factor in large-scale measurement projects.

The casing of the ADCP is preferably made of titanium alloy. The reason for this is that the corrosion-resistant properties of this alloy are excellent, hence very suitable for marine applications. Besides, it also has a good strength-to-weight ratio, which will mean structural integrity with relatively light equipment.

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

Based on Usage

• Ship - borne ADCP: When the measurements are to be taken from a moving vessel, a ship - borne ADCP would be appropriate. It can provide continuous data as the ship travels along the coast and thus enables better understanding of the spatial variability of the currents.
• Bottom - mounted ADCP: The bottom-mounted type is adequate for long- and fixed-point measurements near the seabed. It is able to give detailed current profiles in one location and is applicable in studying local current behavior in detail.
• Buoy - mounted ADCP: When flexibility in deployment and measurement of surface and upper - water - column currents is 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 relatively shallow waters up to 70m, a 600kHz ADCP is usually appropriate. For water depths between 70m and 110m, a 300kHz ADCP is a better fit. And for deeper waters, such as those that might be found near Kilinochchi 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. However, 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.