How to Measure Coastal Currents of Ranong?

1. Where is Ranong?

Location and Coastal Features

Ranong is a southern province in Thailand and borders the Andaman Sea. It is strategically positioned in the coast, proximate to the border with Myanmar. The area boasts of beautiful shores, islands, and hot springs.

The economy of this province is very diversified, with fishing, tourism, and commerce being major sectors. Fishing villages line the coastline, with sea ports in several locations. This Andaman Sea here is a warm, rich body of water filled with fish, shellfish, and coral reefs. It also plays an important role in regulating the local climate, thus providing great resources for fishing and tourist industries.

Factors Affecting Coastal Currents

Tidal Currents: The tide in the Andaman Sea has a pattern, induced by the gravitational forces of the moon and the sun. Tidal currents can be strong, especially in constricted areas, which may include narrow channels between islands or off river mouths. Such currents are important in the transport of sediments and nutrients that maintain the health of the coastal ecosystem and the productivity of fisheries.

Monsoon Winds: The southwest monsoon (May to September) brings strong winds that drive the surface currents in a particular direction. In contrast, the northeast monsoon carries changes in the wind direction and likewise changes the direction and speed of coastal currents from November to February. The interaction between tidal and monsoon-driven currents gives rise to an intricately complex flow pattern.

Local Bathymetry: This is the general shape of the ocean floor that can have underwater features such as ridges, channels, and shoals. These can alter the direction and shape of the coastal currents. Discharge of local rivers into the sea can also affect current patterns. Freshwater input from these rivers may create density differences, sometimes giving rise to quite complex current systems.

2. Methods to Observe Coastal Water Flow

Surface Drifting Buoy Method

This is a fairly simple, practical method. Buoys are set in the water, with GPS or other types of tracking devices on board. The buoys shift with currents; their position and journey over time can be followed to estimate the direction and speed of the surface currents. It would be necessary to design the buoys in such a way that they are able to withstand local marine conditions, including those from wave action and the corrosive action of saltwater.

Anchored Ship Method

A ship is anchored at a certain place near the shore and current-measuring instruments are thrown out of the ship. These instruments can measure the velocity and direction of the flow of water at various depths. There are a few drawbacks to this approach, though. The ship may be subjected to wave actions and winds, which could result in inaccuracies. It is also not very effective in covering a large area.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP offered a more intelligent and useful continuous measurement of the flow of water on the coast. Generally, the ADCPs are able to measure with a great deal of accuracy the profile of water current velocity over an unusually large range of depths. They work by sending out sound waves into the water and then analyzing the Doppler shift of the reflected waves. This further provides the detailed understanding of the structure of the current right from the surface to the seabed in great detail.

3. Principle of Operation of ADCPs Using the Doppler Principle

The ADCPs operate based on the principle of the Doppler effect: they send acoustic pulses, which refer to sound waves, into the water. The emitted sound waves interact with particles in the water, such as sediment, plankton, and other small particles. When the sound waves bounce off these particles and get reflected back to the ADCP current profiler, the frequency of the reflected waves changes because of the Doppler effect.

If the particles are going towards the ADCP flow meter, then the frequency of the reflected wave is higher than that emitted originally.

On the other hand, if the particle velocities are in the opposite direction from the ADCP profiler, the frequency of the reflected wave will be lower. With a fair measurement of this Doppler frequency shift, the velocity of the particles can be determined. Since these particles are in essence moving with the water current, the calculated velocity of the particles is a measure of water current velocity. ADCPs are also capable of emitting sound pulses in more than one direction, enabling them to measure the current velocity in three-dimensional space and at different depths. A vertical profile, for example, may measure the current velocity along a number of evenly spaced intervals from the surface to the seabed in order to build up a clear comprehensive picture of the current structure.

5. Requirements for High Quality Measurement of Coastal Currents

The equipment for measurement of coastal currents in Ranong should be made from materials whose quality can be assured to obtain quality measurements. Since the marine environment is very harsh, with corrosion from saltwater and possible physical impacts due to waves or other floating debris, protection by casing will be needed.

The size of the equipment has to be small enough that it is easily deployed, in particular when access is poor, such as in small boats or in shallow coastal waters. A light design is even more convenient for handling and installation.

Long - term measurements call for low power consumption.

Another important requirement, especially for large - scale measurements, is cost-effectiveness. Therefore, the casing in ADCPs is preferably made from a titanium alloy. The reason is that titanium alloy has outstanding corrosion resistance, which is required, particularly in the Ranong marine environment. This can resist the action of salt water for a long period. Besides, it is solid and also includes a high strength-to-weight ratio; thus, offering a strong yet light structure able to protect internal components within the ADCP current meter.

6. Choice of Suitable Equipment to Measure Current

For Measurement while in Motion in a Vessel

It can be measured by a ship -borne ADCP. The real time current data obtained from the moving ship would give a good understanding of the water flow in different locations.

For Measurement from a Fixed Location near the Seabed

One would find a bottom-mounted ADCP appropriate. It is continuously monitoring the current at one point and can provide steady data over a time period.

For Measurements that Need to Cover a Wide Area and Are Not Restricted to a Specific Depth

A buoy -type ADCP is appropriate because it can cover a larger area and is not limited to any particular depth.

Considering the frequency of choice, for water depth of up to 70m, 600kHz ADCP is an excellent choice. In cases of water depth ranging from 70m to 110m, the best choice is 300kHz; for very deep waters with a maximum of up to 1000 meters, the recommended frequency for an ADCP is 75kHz.

There are well - known ADCP 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 and offers a great 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.