How can we measure the coastal currents of Pattani?

Learn about methods to measure coastal currents in Pattani, including ADCP usage. Discover factors affecting currents and equipment selection for accurate measurement.

1. Location and Coastal Characteristics

Pattani is a southern Thai province situated on the east coast of the Malay Peninsula, with a shoreline open to the Gulf of Thailand. The area has a very long coastline, with sandy beaches and lively fishing communities. The number of fisheries and aquaculture leans considerably in this local economy. This region is well-endowed with rich cultural heritage, further supported by a very diverse population comprising Thai-Malays and other ethnic groups.

The nearby sea, the Gulf of Thailand, is a warm and shallow body of water. It provides valuable habitat for myriad marine species, such as fish, shellfish, and coral reefs. The sea has strong relevance to the local climate and the livelihood of so many people who depend on fishing and related activities.

2. Factors Affecting Coastal Currents

Tidal Currents: Tides in the Gulf of Thailand are semi-diurnal. Due to gravitational pull from the moon and the sun, two high and two low tides occur every day. Tidal currents along the coast of Pattani may be pretty strong, particularly in river mouths and inlets. These currents are very important in carrying sediments and nutrients, vital for the health of the coastal ecosystem and productivity of fishing grounds.

Monsoons: Strong winds from the southwest monsoon between May and September can drive surface currents in a certain direction. Subsequently, the northeast monsoon changes the direction of the wind from November to February, therefore the direction and speed of coastal currents. Interaction of the tidal and monsoon-driven currents produces a complex dynamic flow pattern.

Local Bathymetry: The shape of the seabed with underwater features such as ridges, channels, and shoals are capable of changing the direction and modifying the flow in coastal currents. Similarly, discharge from local rivers to the sea modifies the current patterns. The freshwater input by such rivers can create density differences that may cause complex current systems to form.

3. Methods for Observing the Flow of Water in Coasts

Surface Drifting Buoy Method

This is a very simple and realistic method for measuring surface currents. Buoys are discharged into the water and fitted with GPS or other tracking devices. Because the buoys will travel with the currents, their position and movement over time can be monitored to determine the direction and speed of the surface currents. The design of these buoys should be such that they can withstand the local marine conditions, including those of waves and the salinity of seawater.

Anchored ShipMethod

A ship is anchored at a particular position nearshore, and current-measuring instruments are discharged from the ship. The measuring instruments will be capable of determining the velocity and direction of the flow of water at various depths. However, this methodology also has some limitations. The ship will be subjected to waves and winds, which might cause inaccuracies in measurement. It will also not be efficient for large areas.

Acoustic Doppler Current Profiler (ADCP) Method

Ability to measure flow in the coastal waters more proficiently. The main purpose of an ADCP current meter is measuring the velocity profile of water currents over a wide range of depths. Their mode of operation is through the emission of sound waves into the water, and they monitor the Doppler shift of the reflected waves back to them, hence giving a proper idea about the structure of the current right from the surface to the seabed.

4. Principles of Operation of ADCPs Using the Doppler Principle

The operation of an Acoustic Doppler Current Profiler (ADCP) is based on the principle of the Doppler effect. ADCPs emit acoustic pulses, that is, sets of sound waves, into the water. These 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 are reflected back to the ADCP, the frequency of the reflected waves changes due to the Doppler effect.

If the particles are moving towards the ADCP flow meter, then the frequency of the reflected wave is higher than the original emitted frequency.

Conversely, when the particles are moving away from the ADCP meter, the frequency of the reflected wave becomes lower. By measuring this frequency shift precisely, it will be possible for the ADCP to calculate the velocity of the particles. Because the particles are in movement with the current of water, the calculated velocity of said particles is a result of the water current's velocity. They can emit sound pulses in various directions and are hence capable of measuring the current velocity in three - dimensional space and at different depths. For instance, vertically, it will get the velocity of the current at different intervals from the surface to the seabed. The result obtained gives a full picture of the current structure.

5. Requirements for High - Quality Measurement of Coastal Currents

The equipment should contain reliable materials for the high-quality measurement of the coastal currents in Pattani. Since the marine environment is very harsh, with saltwater corrosion and potential physical impacts from waves and debris, a casing that is durable will be important. The size of equipment needs to be compact enough to allow easy deployment, in particular, when access is minimal, as it would be from small boats or in shallow coastal waters. A light design is also advantageous since it allows lighter and more convenient handling and installation.

Low power consumption is critical for long-term measurements.

Cost-effectiveness is likewise important in enabling large-scale measurements. In the case of the ADCP profiler, the casing should be made from titanium alloy. Titanium alloy has outstanding corrosion resistance, which is critical in the marine environment of Pattani. It resists the corrosive action of saltwater for a long time. Besides this, it is strong with a high strength-to-weight ratio and will provide a solid yet light structure able to protect the internal parts of the ADCP profiler.

6. Selecting the Correct Equipment to Measure Current

For Measurements from a Moving Vessel

A ship - borne ADCP meter would be appropriate. This gives current in real time as the ship is moving, thus enabling the better understanding of the water flow in different locations.

For Measurements at a Fixed Location near the Seabed

A bottom - mounted ADCP flow meter is a good option. It can continuously monitor the current at a specific point, providing consistent data over time.

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

It will be appropriate to use ADCP current profiler of a buoy-type. It may cover a more significant area and is not limited to a particular depth.

From the viewpoint of frequency selection for water depths up to 70m, a 600kHz ADCP can have an excellent performance. Further, for depths between 70m to 110m, 300kHz ADCP is more ideal. For very deep waters up to 1000m, a 75kHz ADCP is recommended.

There are 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 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.

Brandmodel
Teledyne RDIOcean Surveyor ADCP , Pinnacle ADCP , Sentinel V ADCP , Workhorse II Monitor ADCP, Workhorse II Sentinel ADCP, Workhorse II Mariner ADCP, Workhorse Long Ranger ADCP, RiverPro , RiverRay , StreamPro  , ChannelMaster  etc.
NORTEKEco, Signature VM Ocean, Signature ADCP, AWAC ADCP, Aquadopp Profiler etc.
SonTek SonTek-RS5, SonTek-M9, SonTek-SL, SonTek-IQ, etc.
China SonarPandaADCP-DR-600KPandaADCP-SC-300K, PandaADCP-DR-75K-PHASED, PandaADCP-DR-300K, PandaADCP-SC-600K etc.
Jack Law November 22, 2024
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