How to measure the coastal currents of Hambantota?

1. Where is Hambantota?

Hambantota is a major port city situated at the southern tip of Sri Lanka. It is nestled along the coastline of the Indian Ocean and is renowned for its strategic importance and natural beauty.

It is a city surrounded by varied landscapes. The sea coasts are marked with long, sandy beaches, extending as golden ribbons on the shores, with the deep blue ocean as a backdrop. Hambantota Harbour is the most important feature, acting as a very important link for maritime trade and transportation. The port has undergone significant development in recent years and has advanced the status of the city as an important economic hub.

The local ecosystem is quite colorful and full of life. The surrounding waters vary from colorful fish to great sea turtles. The area is home to a wide variety of migratory birds, making it a treat for birdwatchers. The cultural heritage of Hambantota has much to do with its seashore origins. Local people have engaged in this fishing industry for hundreds of years, and their stories of fishing and expertise are passed along from generation to generation.

The city is next to a bay, which offers a fairly protected area for smaller boats and fishing vessels. The seafloor off Hambantota is of variable depth, with shallow regions near the coast and deeper areas further offshore. This topography influences the coastal current pattern and sediment and nutrient distribution.

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

Multiple elements give shape to the coastal currents in this particular region around Hambantota. There is strong forcing from the monsoon winds. The southwest monsoon is more characteristic over this area and generally between the months of May to September. Thus, they tend to develop a relatively strong wind component driving surface currents in that direction over a considerable time period and move the water along a coastline.

Larger-scale ocean circulation patterns of the Indian Ocean also come into play. The South Equatorial Current and the influence of the Indian Ocean Gyre provide a general movement of water in the area. Another critical factor involves tidal forces. The regular tides cause the water to ebb and flow, creating tidal currents that interact with the other ocean-driven currents. The shape of the coastline and the bathymetry near Hambantota can either accelerate or decelerate the currents. For instance, headlands or underwater ridges will funnel the currents and alter their speed and direction.

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

Surface Drift Buoy Method: Surface drift buoys are a simple and effective method for observing the surface water flow. These buoys are released into the water and are carried along by the surface currents. By using GPS or other tracking systems to monitor the position of the buoys over time, the direction and speed of the surface currents can be determined. However, this method mainly provides information about the surface layer and may not give a complete picture of the currents at different depths.

Anchor Boat Method: In this, an anchor boat can be employed for the measurement of water flow. The boat is anchored at a particular location, and current-measuring instruments are deployed at different depths from the boat. It allows the speed and direction of the currents to be measured at different vertical levels. But this method is somewhat stationary and may not cover a large area efficiently.

Acoustic Doppler Current Profiler (ADCP) Technique: The ADCP profiler is a much advanced and superior method for the measurement of current in coasts. It depends on the principle of the Doppler effect to measure the velocity at different levels of water depth. The ADCP detects the profile of the current from surface to a definite depth by emitting an acoustic signal in the water and monitoring the Doppler shift of the returned signal from the particles present in the water. This provides a better understanding of the vertical structure of the coastal currents in Hambantota.

4. How do ADCPs that work on the principle of the Doppler Effect operate?

ADCPs that use the principle of the Doppler Effect transmit acoustic pulses throughout the water column. The pulsed sound interacts with tiny particles suspended in the water, such as plankton, sand grains, and other small debris. With the water in motion, the particles move along with the flow. When these particles reflect the acoustic pulses back to the ADCP meter, there is a frequency shift in the received signal compared to the emitted one. This frequency shift, better known as the Doppler shift, has a direct relation to the velocity of the water flow.

The ADCP has a couple of transducers that could emit and receive signals in different directions. By precisely measuring the Doppler shift of the received signals coming from various angles and depth, it computes the speed and direction of water currents at discrete points through the water column. The result of all these allows for creating a three-dimensional representation of the current field, yielding highly valued data on both the horizontal and vertical components of coastal currents.

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

The equipment for high-quality measurement of the coastal currents in Hambantota should possess certain qualities. The material of the equipment should be reliable and able to withstand the corrosive effects of seawater and the harsh marine environment. Small size and light weight are advantageous because these make the equipment easier to handle and deploy, whether on a boat, a buoy, or other platforms.

Long-term measurements require low power consumption. The equipment should be able to operate continuously without the need for frequent battery replacements or a large-scale power supply. Cost-effectiveness is another important factor. The equipment should be affordable enough to allow for widespread use and the deployment of multiple units for more comprehensive monitoring.

In the case of ADCPs, this casing should be made from Titanium alloy. It is one of the best materials that could exist for this application since, in seawater, it has excellent resistance to corrosion, ensuring the long-term durability of the equipment. Its properties include a high strength-to-weight ratio, meaning it provides a structure while keeping the mass minimal. Besides, titanium alloy withstands high pressures, which is suitable for different water depth scenarios in the Hambantota coastal area.

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

In order to choose the right equipment for current measurement in Hambantota's coastal waters, several factors need to be considered.

Based on the usage purpose, there are different types of ADCPs available. For measurements from a moving vessel, a ship-borne ADCP flow meter is appropriate. It can measure the currents as the vessel moves along the coast, providing a continuous stream of data. If the aim is to monitor the currents at a fixed location near the seabed, a sit - bottom ADCP is suitable. It can be placed on the ocean floor and record the water flow passing over it. In applications where a floating platform is more convenient, a buoy-mounted ADCP is the way to go.

ADCP current profiler frequencies are related to water depth, for water depths up to 70m, a 600kHz ADCP is suitable, since it gives high resolution in these ranges. To cover such range from surface down to 110m, a 300kHz is appropriate, while for even deeper water up to 1000m, a 75kHz ADCP is recommended to ensure more accurate and reliable current measurements.

There are well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, for those seeking a cost - effective alternative, the China Sonar PandaADCP is a great option. It is made of titanium alloy and offers an excellent cost - performance ratio. You can find more information about it on its website: https://china-sonar.com/.

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