How to Measure Coastal Currents of Narathiwat?

1. Where is Narathiwat？

Location and Coastal Features

Narathiwat is a southern province of Thailand, situated on the Malay Peninsula bordering the Gulf of Thailand. It boasts a nice coastline with sandy beaches and mangrove forests. The place is rich in natural beauty and is host to various marine and coastal ecosystems.

The local economy is sustained through fishing, farming, and trade. Fishing is fairly important, considering access to the Gulf of Thailand. Here, the immediate community is much more closely affiliated with the sea and land, both largely comprised of mixed ethnic groups to form quite a unique cultural landscape.

The nearby Gulf of Thailand is a warm and moderately shallow body of water. It serves as a home to several marine species, ranging from fish and shellfish to other species. It is also responsible for regulating the local climate and allows activities in the form of water to be related to fishing and tourism.

2. Factors Affecting Coastal Currents

Tidal Currents: Tides within the Gulf of Thailand are semi-diurnal; the gravitational pull of both the moon and the sun causes two high tides and two low tides each day. The tidal currents are pretty strong, especially near coastal areas and in places with a constriction of water, such as near river mouths or inlets. These currents already mean a lot regarding the transport of sediments and nutrients that are important to maintain good health in the coastal ecosystem and for the productivity in fishing grounds.

Monsoon winds: There are strong winds due to the southwest monsoon from May to September that can drive the surface currents in a particular direction. The NE monsoon changes the wind direction from November to February and thus the direction and speed of coastal currents. The interaction between tidal and monsoon-driven currents gives rise to a complex and dynamic flow pattern.

Local Bathymetry: The shape of the seabed and the presence of underwater features such as ridges, channels, and shoals can redirect and modify the flow of the coastal currents. The discharge of local rivers into the sea contributes in modifying the current patterns. The freshwater input from these rivers can create density differences that lead to the formation of complex current systems.

3. Methods for Observing Coastal Water Flow

Surface Drifting Buoy Method

A simple and practical approach. Buoys are released into the water, fitted with GPS or other tracking devices. By knowing the movement of buoys carried by the currents over some time, the position and movement can be monitored and analyzed to establish the direction and speed of surface currents. The buoys should be designed to handle the local marine conditions related to the effects of waves and the corrosive nature of saltwater. - Anchored Ship Method A ship is anchored at a certain place and current-measuring instruments are released from it. These measuring instruments are capable of measuring the velocity and direction of the flow of water at different levels. However, this method has some drawbacks. The ship may be subject to waves and winds. Therefore, there is a possibility of inaccuracy in the measurement. This method is also not too effective to cover a vast area.

Acoustic Doppler Current Profiler (ADCP) Method

It is a more sophisticated and effective means of measurement of coastal water flow. ADCPs are capable of measuring the velocity profile in water currents over an extensive range of depths. They operate by emitting sound waves into the water and analyzing the Doppler shift of the reflected waves. Further, this will provide detailed knowledge of current structure from surface to seabed.

4. How ADCPs Using the Doppler Principle Work

ADCPs work on the principle of Doppler. They send out acoustic pulses or simply sound waves into the water. The sound waves scatter off particles in the water, such as sediment, plankton, and other small particles in the flow. If these sound waves are reflected back to the ADCP after bouncing off these particles, the frequency of the reflected waves shifts due to a Doppler effect. Since the particles are moving toward the ADCP profiler, the reflected wave has a higher frequency than that of the original emitted frequency.

Conversely, when the particles move away from the ADCP flow meter, the frequency of the reflected wave is lower. The ADCP accurately calculates this frequency shift to determine the velocity of particles. Since the particles are in motion along with the water current, the velocity thus estimated of the particles would be that of the water current's velocity. ADCPs can emit sound pulses in multiple directions, allowing them to measure current velocity in three - dimensional space and different depths. As in the vertical profile, for example, they are able to establish the speed of flow in periodic intervals from the surface all the way to the seabed, giving a very comprehensive picture of the current structure.

5. Requirements for High-Quality Measurement of Coastal Currents

To measure high-quality coastal currents in Narathiwat, the equipment must be made from reliable materials. The sea environment is really tough, salty water corrodes rapidly, and physical impacts can be brought by waves and various floating debris; a casing should be durable, not easily broken or cracked.

The size of the equipment should be small enough to be easily deployed in areas most difficult to reach, such as in small boats or shallow coastal waters. A lightweight design is also desirable for convenience in handling and installing the instruments.

Low power consumption is an important advantage for long - term measurements.

Cost - effectiveness is also important to make large - scale measurements feasible. For ADCPs, the casing is preferably made from Titanium alloy. The marine environment of Narathiwat makes good corrosion resistance an absolute necessity. It can also tolerate the corrosive nature of saltwater for a long period of time. It is strong, with a very high strength-to-weight ratio, thus providing a formidable yet light structure which can protect the internal components of the ADCP current profiler. 

6. Selection of Appropriate Equipment to Measure Current

For Measurements While on a Moving Vessel

A ship - borne ADCP would be appropriate. It would be able to provide current in "real time" while the ship is in motion and thus give a better understanding of the flow of water at varied locations.

For Measurements at a Fixed Location near the Seabed

A bottom-mounted ADCP would be a good option for this purpose. It will continuously monitor the current at that one point, with consistent data through time.

For Measurements that Must Cover a Wide Area and are not Restricted to a Specific Depth

Buoy type ADCP will be suitable, as it can cover a more significant area and are not confined to any particular depth. 

The frequency choice: For the water to the depth of 70m, 600kHz works quite well. For the depths between 70m to 110m, one should go with 300kHz ADCP and for very deep waters to 1000m, 75kHz is quite suitable.

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.