How to measure coastal currents of Point Pedro?

1. Where is Point Pedro?

Point Pedro is on the northern tip of Sri Lanka. It is also a strategic coastal location that has been marking the entrance to Palk Strait.

The surroundings of Point Pedro are a blend of nature's beauty and the liveliness of human activity. The shoreline consists of sandy beaches and rocky outcrops. The sea adjacent is rich in marine life with a variety of fish species and other sea creatures. The local fishing industry thrives with fishermen setting out in their boats to take advantage of the bountiful waters.

Its geographical location is such that the place lies near the Palk Strait, which separates India from Sri Lanka. The waters in this strait are influenced by the inflow of different rivers from both countries. Climatically, it is a tropical place. The sea is an effective regulator of temperature. In this respect, the breeze coming from the sea would bring a touch of coolness and would affect the climate conditions of the place.

2. What is the situation of the coastal currents near Point Pedro?

Various factors determine the coastal currents around Point Pedro. Of course, the influence of monsoon winds is the dominant one. The northeast monsoon that blows from October to December and the southwest monsoon between June and September drive the surface currents. These winds, together with other atmospheric events, bring about mixing among various water layers and have an influence on the salinity and temperature of the waters in these coasts.

The tides also play an important role. The semi-diurnal tides result in regular ebb and flow. Tidal currents can reach high speeds, especially during the spring tides. The shoreline topography, with headlands and bays, and submarine topography (bathymetry) further affect the current pattern. Where shallow areas or constrictions occur, the speed of the currents may increase or be deflected.

The inflow of freshwater from nearby rivers and estuaries into the Palk Strait is another important factor. Mixing freshwater and seawater changes the density of the water, thus modifying the flow of the current. These rivers carry a lot of sediments and nutrients that may affect the coastal ecosystem and the movement of the currents.

3. How to observe the coastal water flow of Point Pedro?

Surface Drifting Buoy Method: It involves deploying buoys onto the water surface. The buoys are designed to drift with the surface currents and have been fitted with tracking devices such as GPS. From this, the buoy movement can be monitored over time, and information on the surface current patterns can be deduced. But the problem with this is that the method only gives information concerning surface currents, and no total idea on the vertical structure of such currents.

Moored Ship Method: A ship is moored in some selected position off the coast. He lays current-measuring instruments out from this vessel. In this method, currents at various levels from surface to bottom can also be measured. However, it suffers from some weaknesses, such as disturbing local currents by the presence of a ship and being time-consuming and expensive for making measurements over a long time period.

Acoustic Doppler Current Profiler (ADCP) Method: This is more advanced and efficient in measuring the flow of water along the coast. ADCPs are capable of measuring simultaneous velocities of water at different depths. They emit sound waves into the water and detect the Doppler shift of the reflected waves. The Doppler shift is related to the velocity of the water, and through analysis, detailed profiles of the current are available from the surface to seabed.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. When an ADCP profiler sends a pulse of sound into the water, the sound waves scatter off sediment, plankton, or other objects in the water. If the water is moving, the frequency of the returning sound waves will be different from the transmitted frequency.

The frequency shift, a phenomenon well-known as the Doppler shift, is directly proportional to the velocity of the water. It is this frequency shift that the ADCP measures and then uses to calculate the speed and direction of the water current. Usually, the ADCP sends out sound pulses in more than one direction; this may be in a conical or fan-shaped pattern. By doing so, it is able to measure the prevailing velocity in a three - dimensional space and create an in-depth profile of the current throughout the water column.

5. What is required for good-quality measurements of coastal currents off Point Pedro?

A high -quality measurement of the coastal currents near Point Pedro demands the usage of equipment with specific desirable characteristics, the materials used to build up a device should be of dependability. The casing of ADCP, for instance, should be able to overcome the corrosive effect from seawater and the physical stresses caused by waves and currents.

The device should be of small size and lightweight. This will make it easy to deploy on different platforms, such as buoys, boats, or even on the seabed. The consumption of power should also be low, especially for long-term and remote measurements. This will enable the device to operate for an extended period without frequent battery replacements or recharging of the power source.

Another important factor is cost-effectiveness. The cost should be as reasonable as possible to allow large-scale measurements. Titanium alloy is a good option in making ADCPs casings. For starters, it is highly resistant to corrosion, which is so vital in a marine environment. It is also very strong and durable to face pressures and impacts that this device might face during the operation process.

6. Selection of equipment to measure current correctly

Choosing the right equipment for measurement from Point Pedro depends upon specific uses. It can go in a boat, measure real-time, and deliver back continuous data as the ship navigates across the waters. For measuring currents using a ship-borne ADCP meter while the boats move.

Bottom-mounted ADCP flow meter is more adequate for fixed-point measurements near the seabed. The bottom-mounted ADCP can provide stable and continuous measurements of the currents at the bottom of the water column.

For measurements at a floating position, like on a buoy, a buoy-mounted ADCP current profiler is the appropriate option.

Regarding the frequency of ADCPs, different frequencies are suitable for different water depths. For water depths up to 70m, a 600kHz ADCP should be used. For depths up to 110m, a 300kHz ADCP is more appropriate, while for very deep waters up to 1000m, a 75kHz ADCP is recommended.

There are several well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth considering. It is made of all - titanium alloy material, which provides excellent durability and corrosion resistance. It also offers an incredible cost - performance ratio. You can find more information about it on the website: https://china-sonar.com/.

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