How can we measure the coastal currents of Kinniya?

1. Where is Kinniya?

Kinniya is a town in the Trincomalee District of Sri Lanka and is situated on the east coast of the island, facing the Indian Ocean. The area is a blend of natural beauty and cultural significance.

It has long stretches of sandy beaches and clear blue waters. The seashore scenery is dotted with palm trees and other tropical vegetation, which grow well in the warm and humid climate. The local ecosystem is quite rich, with a number of marine species living in the waters near the shoreline. The local community has been known for fishing traditions, as the sea has been a vital source of livelihood.

Geographically, Kinniya is proximal to the Bay of Trincomalee and reflects the influence that water circulation patterns of that larger body of water have imposed. The bay acts as a buffer between the coastline in this town and the open Indian Ocean, moderating further the impact of oceanic forces. The area also features several small inlets and lagoons that add to the complexity of the coastal environment.

2. What is the condition of the coastal currents close to Kinniya?

Various factors act upon the coastal currents near Kinniya. The monsoon winds play a significant role. During the southwest monsoon (May to September), the winds blow from the southwest to the northeast. This causes the general direction of the surface currents to be northeasterly. In contrast, during the northeast monsoon, which occurs from December to February, the reverse in wind direction pushes the water in a southwesterly direction.

In these beaches, topography of the bottom underwater close to the coast is involved in the process. Possible sandbars, ridges and channels submerged underwater may shift along those features not only speed but also direction of currents: if there is a certain position of a sandbar the current can split around or change course. There is also an important element involving tidal currents. Local semidiurnal tides means having two high tides and two low tides during each day. Ebbing and flowing of tides may cause changes in the current velocity and direction, while the interaction with the wind-driven and other oceanic currents results in a complex flow regime.

Another influential parameter concerning the coastal currents is the water exchange between the bay and the open ocean. The inflow and outflow of water through the entrances of the bay and the inlets induce the formations of eddies and local current patterns contrasting to the larger - scale ocean currents.

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

Surface Drifter Buoy Method

Surface drifter buoys are a useful way to observe the surface water flow. These buoys are deployed on the water surface and are carried along by the currents. They can be tracked using satellite-based tracking systems or other positioning methods. By monitoring their movement over time, one can obtain information about the direction and speed of the surface currents. However, this method provides data only on the surface layer and may not give a comprehensive understanding of the current structure of the whole water column.

Moored Ship Method

In the moored ship method, a ship is anchored at a location near the coast. Instruments on the ship measure the flow of water at different depths. This allows for continuous measurements at a fixed point. But it has limitations. Movement of the ship itself, by waves and wind, may also lead to errors in measurement. Again, it only provides information for the area around the moored ship and may not represent the general condition of the coastal current.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP method is a more sophisticated and extensive measurement technique of the coastal current. ADCPs emit acoustic pulses into the water and analyze the Doppler-shifted echoes that return. By doing so, they can measure the velocity of water at multiple depths simultaneously. This provides a detailed profile of the current from the surface down to a certain depth, depending on the instrument's capabilities. It provides a better view of the contemporary behavior of the water column and will be very useful in further studies of the coastal currents around Kinniya.

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

ADCPs work on the principle of the Doppler effect. They emit high-frequency acoustic signals into the water. When these interact with moving particles in the water, such as suspended sediments or small organisms, the frequency of the reflected signal shifts by the Doppler effect.

If the particles are moving towards the ADCP profiler, 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 shifts at different angles and depths, the ADCP can calculate the velocity of the water at various points in the water column. This allows it to create a current profile that is quite detailed, showing the speed and direction of the water movement at different depths. Data obtained from ADCPs can be used to analyze the spatial and temporal variability of the coastal currents.

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

It is desirable that the equipment is made of reliable materials for high-quality measurement of the coastal currents near Kinniya. Because seawater is corrosive and the marine environment is harsh, it must be resistant to those conditions. The size should be compact, lightweight, and with low power consumption.

Small size and low weight make a device easier to be deployed and recovered from or by a boat or any coastal installation. Low power dissipation allows monitoring on longer terms without changing batteries. Among all these issues, cost effectiveness is probably the most decisive, especially when a considerable amount of measurements have to be carried out.

The casing of the ADCP meter is preferably made of titanium alloy. Titanium alloy has excellent corrosion-resistant properties, making it well-suited for use in the marine environment. It also has a good strength-to-weight ratio, which means it can provide the necessary structural integrity while keeping the device relatively light.

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 availed. It provides continuous data as the ship travels along the coast and hence helps in understanding the spatial variability of the currents.

Bottom-mounted ADCP: This is ideal for long-term and fixed-point measurements near the seabed. A bottom-mounted ADCP flow meter will be able to provide detailed current profiles at a specific location, useful in studying the local current behavior.

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 Kinniya 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.