How do we measure the coastal currents of Trincomalee?

1. Where is Trincomalee?

Trincomalee is a city in the eastern coast of Sri Lanka, where nature and history are mixed. The city is nestled between the Indian Ocean and a series of bays and lagoons.

The coastline of Trincomalee is famous for its deep-water harbors, which have been among the major ports since time immemorial. The beaches here are long and sandy, with clear blue waters that attract both locals and tourists alike. Further, the area is covered with lush greenery, comprising coconut palms and other tropical plants that grow in the warm and humid climate.

The local population is a diverse mix of ethnic groups, each contributing to the rich cultural tapestry of the city. Fishing is a major industry, and the local fishermen have a deep connection to the sea. The city's history is filled with stories of ancient kingdoms and colonial rule. The remnants of forts and other historical structures stand as a testament to its past.

Geographically, Trincomalee is situated adjacent to the Trincomalee Bay, which is a vast body of water that offers shelter to ships. The bay is connected to the open ocean and is influenced by the larger - scale oceanic circulation patterns of the Indian Ocean.

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

Various factors interact in the coastal currents near Trincomalee. The most influential are the monsoon winds. During the southwest monsoon, from May to September, the strong winds blow in a northeasterly direction, pushing the surface waters, while during the northeast monsoon-from December to February-they do so in a southwesterly direction.

Topography of the sea-floor along the coast also has its impact. Underwater ridges, canyons, and sandbars further accelerate or decelerate the currents. The shape of the bay and the inlets also does their job in modification of water flow. Tidal currents- The region receives semi-diurnal tides with two high tides and two low tides each day. The strength of such tidal currents might be fairly big, so their interaction with the wind-driven and other oceanic currents leads to quite complex patterns of flows.

Another important factor is the change of water between the bay and the open ocean itself. The inflow and the outflow of water through the bay entrance may give rise to eddies and other kinds of local current patterns distinctive from the larger - scale ocean currents.

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

Surface Drifter Buoy Method

Surface drifter buoys are one of the simplest and effective means for observing the flow of surface water. The buoys are located on the surface of the water and drift with the currents. Using satellite-based tracking systems or other positioning methods, the movement of the buoys can be tracked over time, giving the direction and speed of the surface currents. Nevertheless, the previous technique provides data only for the surface layer and may not suffice for describing the current structure in the entire water column.

Moored Ship Method

In this technique, the ship is anchored at some particular place near the coast. It carries instruments for measuring water flow at various depths. This facilitates the continuity in measurements at a fixed point. But it has its limitations. The ship's own motion because of waves and wind can impart error into the measurements. Also, it only gives data on the area around the moored ship and might not represent the general situation of the current along the coast.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP method of measurement is more comprehensive in nature and advanced for measuring coastal currents. ADCPs send out acoustic pulses in the water and analyze the returning echoes that are Doppler - shifted. They can thereby measure the water velocity simultaneously at several depths. In such a way, they make a detailed profile of the current from the surface to a depth, depending on the potential of the instrument. It gives a more complete picture of the current behavior of the water column and is an excellent choice for studying the coastal currents near Trincomalee.

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

ADCPs work by employing the Doppler principle. Transducers of an ADCP send out high-frequency acoustic signals into the water. When these signals interact with particles moving in the water-including suspended sediments and/or small organisms-the frequency of the reflected signal changes due to the Doppler effect.

In principle, the frequency of the returned signal will be higher if the particles are moving towards the ADCP profiler, and lower if they are moving away from it. From these phase shifts at multiple angles, over a series of such sets of beams at many successive depth points in the column of water, the water velocities are determined by the instrument. This allows it to create a detailed current profile that shows the speed and direction of the water movement at different depths. The obtained data from ADCPs can be used for analysis of spatial and temporal variability of the coastal currents.

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

The equipment must be made of reliable materials that can give high-quality measurement of the coastal currents near Trincomalee. Because seawater is corrosive and the marine environment is harsh, the equipment needs to be able to withstand these conditions. The size should be compact, the weight lightweight, and the power consumption low.

A small and light device is easier to deploy and retrieve, whether from a boat or from a coastal installation. Low power consumption allows for longer-term monitoring without frequent battery replacements. Cost-effectiveness is also a crucial factor, especially for large-scale measurement projects.

The casing of the ADCP meter is preferably made of titanium alloy. Titanium alloy has excellent properties of corrosion resistance and, thus, is well-suited to use in the marine environment. It also has a good strength-to-weight ratio, which insinuates that it can keep the device relatively light while providing its necessary structural integrity.

6. How to choose the right equipment for measuring current?

Based on Usage

Ship-borne ADCP: When measurements need to be made from a moving vessel, the use of a ship-borne ADCP flow meter will be quite appropriate, with the added advantage of continuative data while the ship cruises down the coast as its travel path and its immediate vicinity, enabling an appreciable coverage of the spatial variability of the currents.

Bottom-mounted ADCP: When long-term fixed-point measurements near the seabed are required, a bottom-mounted ADCP current profiler will be ideal. It can give current profiles with high resolution at a single position that is very useful for research on the behavior of currents locally.

Buoy-mounted ADCP: When flexibility in deployment and measurement of surface and upper-water-column currents is required, a buoy-mounted ADCP current meter is the way to go.

Based on Frequency

The choice of frequency depends on the water depth. For relatively shallow waters of up to 70m, a 600kHz ADCP is usually appropriate. In case of water depths ranging from 70 to 110m, a 300kHz ADCP would be better. For deeper waters-like those that might be found around Trincomalee in places-a 75kHz is suitable for measuring up to about 1000 meters of depth.

There are well-known ADCP 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.