How to measure the coastal currents in Batticaloa?

1. Where is Batticaloa?

Batticaloa is a major city in Eastern Province, Sri Lanka. This city is situated on the east coast of the island beside the magnificent Batticaloa Lagoon and the Indian Ocean.

The city is famous for its lengthy, sandy beaches and its crystal blue waters. This lagoon, a major geographical feature of the area, is an intricate, productive ecosystem fringed with mangrove forests, which form a natural nursery for many marine species and protect the coast from erosion. Around Batticaloa, there is plenty of coconut and other tropical vegetation to give a lush appeal to the landscape.

The local culture is a dynamic amalgamation of various ethnic groups. Fishing is one of the most important activities in the local economy, and the fishermen are attached to the lagoon and the ocean. The city has a rich history, with ancient forts and other historical structures that stand as witnesses to its past importance as a trading and strategic location.

The waters of Batticaloa become part of the Indian Ocean circulation system. With this opening to the ocean, it allows a continuous change in waters related to tidal and other wind oceanic actions.

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

The coastal currents off Batticaloa are influenced by several factors. The monsoon winds are the most dominant. The southwest monsoon, from May to September, is a strong wind that pushes the surface waters in a northeasterly direction, while during the northeast monsoon from December to February, the winds drive the currents in a southwesterly direction.

The topography of the sea bottom near shore and the form of the lagoon is another element. Underwater ridges, sand bars, and channels all result in speeding up, slowing, and changing the direction of the current. Another essential factor affecting this area is tidal current. The tide in that region is semi - diurnal, that is two highs and two lows are there in one day. The tides may have strong effects on the current velocities and directions, particularly within the lagoon and in the vicinity of inlets that link the lagoon to the ocean.

Water is always exchanged between the lagoon and the ocean, making the present situation even more complex. Gradients in salinity and temperature between the two water bodies may generate density-driven currents, adding further complexity to the coastal current regime.

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

Surface Drifter Buoy Method

Surface drifter buoys are simple and effective ways to observe the surface water flow. These buoys are positioned on the surface of the water and are carried along by the currents. By using satellite-based tracking systems or other positioning methods, the movement of the buoys can be monitored over time, providing information about the direction and speed of the surface currents. This, however, provides data about only the surface layer and cannot help in understanding the structure of the current at the whole water column.

Moored Ship Method

This involves anchoring a ship at a place close to a coast. Instruments on it are used for measuring water flow at various depths. In this method, the continuous measurement at one point is possible. Yet it has its disadvantages. The motion of the ship itself from wave and wind action could impose inaccuracies to the readings; and moreover, this also allows information just in the surrounding waters of the moored vessel, perhaps not a real representative for the overall general current along the coasts.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP profiler is quite advanced and also a holistic methodology to quantify coastal currents. ADCPs send out acoustic pulses into the water and measure the Doppler-shifted echoes that return. In this way, they can simultaneously measure the velocity of water at multiple depths. This gives a detailed profile of the current from the surface down to a certain depth, depending on the instrument's capabilities. 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 Batticaloa.

4. How do ADCPs using the Doppler principle work?

The principle behind the working of ADCPs is the Doppler principle. They transmit high-frequency acoustic signals into the water. These signals are reflected by the moving particles in the water-suspended sediments or small organisms-and in turn change frequency due to the Doppler effect.

If the particles are moving towards the ADCP meter, the frequency of the reflected signal is higher than the emitted frequency; if they are moving away, it is lower. These frequency shifts at different angles and depths enable the ADCP to compute the velocity at various points in the water column.

It thereby can develop a detailed current profile that shows the speed and direction of the water movement at various depths. The 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 Batticaloa coastal currents?

The equipment should be made of reliable materials for high-quality measurement of the coastal currents near Batticaloa. Since seawater is corrosive, it needs to be resistant because of the harsh marine environment. The desirable features are compact size, lightweight, and low power consumption.

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

The casing of the ADCP flow meter is preferably made of titanium alloy. The corrosion-resistant properties of titanium alloy are excellent, making it very suitable for application in the marine environment. It has a good strength-to-weight ratio, which means that the structural integrity it provides is enough while keeping the device relatively light.

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

Based on Usage

Ship-borne ADCP: In case the measurements are to be done from a moving vessel, a ship-borne ADCP is adequate. It will provide continuous data as the ship travels on along the coast, allowing for a better understanding of the spatial variability of the currents.

Bottom-mounted ADCP: These are suitable for long-term, fixed-point measurements near the seabed. A bottom-mounted ADCP can give very detailed current profiles of the area it is set up in and, therefore, can serve for studying local current phenomena 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 will usually suffice. For water depths between 70m and 110m, a 300kHz ADCP will be more suitable. In deeper waters, as may be found in some areas around Batticaloa, a 75kHz ADCP is suitable for measuring up to approximately 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.