How are the coastal currents of Surat Thani to be measured?

1. Where is Surat Thani?

Surat Thani is one of the southern provinces in Thailand. It faces the Gulf of Thailand and has some beautiful islands, Koh Samui, Koh Phangan, and Koh Tao. These islands are well-known for their white-sand beaches, waters with perfect clarity, and a pulsating nightlife.

The province also has a massive fishing industry. The local economy is a mixture of tourism, fishing, and agriculture. The land portion comprises rich natural resources and has an ethnically diverse population that includes the Thai people and other ethnic minorities.

The nearby Gulf of Thailand is a warm and comparatively shallow body of water, offering a comfortable environment for countless marine animals, such as brightly colored fish, shellfish, and coral reefs. The sea plays a crucial role in the local climate and provides many opportunities for water-based activities such as diving and snorkeling.

2. What is the condition of the coastal currents near Surat Thani?

Various factors influence the coastal currents near Surat Thani. Tidal current influence is a dominant effect. The tide in the Gulf of Thailand has a semi-diurnal pattern due to gravitational influences of the moon and the sun; hence, there are two high tides and two low tides per day. Tidal currents may be very strong, particularly near coastlines and in places where the water is restricted, as it is near river mouths or inlets. These are important for sediment and nutrient transport and are thus crucial to coastal ecosystem health and fishing ground productivity.

Monsoon winds also have a major impact. The southwest monsoon, which occurs from May to September, brings strong winds that can drive the surface currents in a particular direction. The northeast monsoon, from November to February, changes the wind direction and thus the direction and speed of the coastal currents. The interaction between the tidal and monsoon - driven currents creates a complex and dynamic flow pattern.

The local bottom topography may act to deviate and alter the coastal current flow due to its shape, whether it's plain or having underwater features like submarine ridges and submarine channels. Surface currents may be affected by river discharges into the ocean. The freshwater added through these river discharges may create density differences leading to the formation of complex current systems.

3. How to Observe Coastal Water Flow of Surat Thani?

There are several ways to observe the coastal water flow in Surat Thani.

Surface Drifting Buoy Method

This is quite straightforward and useful. Buoys are deployed into the water, while their position and movement over time could be tracked using GPS or any other tracking mechanisms when moved by the currents to work out a direction and speed of the surface currents. The buoys must be designed such that they would be able to withstand the local conditions in the sea, including the wave actions and the corrosive nature of saltwater.

The Anchored Ship Method A ship is anchored at a particular site, and current-measuring instruments are deployed from the ship. These instruments could measure the velocity and direction of the water flow at various depths. This method, however, has a few disadvantages. The ship may be subjected to waves and winds, which can distort the measurement. It is also pretty inefficient to cover a large area using this method.

The ADCP Method

This is a more advanced and efficient way of measuring the flow of water in the coast. It can measure the profile of the water current's velocity over a wide range of depths. The ADCPs emit sound waves into the water to analyze the Doppler shift of the reflected waves, enabling a comprehensive understanding of the structure of the current from surface to seabed.

4. How do ADCPs using the Doppler principle work?

The ADCPs are based on the Doppler principle. They emit acoustic pulses, or simply sound waves, into the water. This energy intersects with particles in the water-sediment, plankton, and other small particles. When this energy is reflected back to the Acoustic Doppler Current Profiler (ADCP), the frequency of the reflected waves changes because of the Doppler effect.

If the particles are moving towards the ADCP current meter, the frequency of the reflected wave is higher than the originally emitted frequency. On the contrary, if it is moving away from the ADCP, the frequency of the reflected wave becomes lower. Precise measurement of this frequency shift allows the ADCP to calculate the velocity of the particles. Since the particles are moving with the water current, the calculated velocity of the particles is a measure of the water current velocity.

ADCPs are able to send pulses of sound in various directions and hence give the three-dimensional current velocity and at depth intervals. For instance, in a vertical profile, they are able to measure current velocity from near the surface to the seabed at various intervals, thus giving a complete picture of the current structure.

5. What is required for good quality measurement of Surat Thani coastal currents?

The measuring equipment for high-quality measurement of coastal currents in Surat Thani must be fabricated with materials that are reliable. With saltwater corrosion and the possible physical impacts by waves or debris, a casing should be durable.

The size of the equipment should be small enough to be easily deployed, especially in areas that are not very accessible, such as on small boats or in shallow coastal waters. A lightweight design is also very useful because it allows the device to be more conveniently handled and installed.

Low power consumption is crucial for long-term measurements. Cost-effectiveness is very necessary to allow the making of large-scale measurements. In the case of ADCPs, the casing is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is vital in the marine environment of Surat Thani. It can support the corrosive effect of salt water for a long time. It is also strong and has a high strength-to-weight ratio, which gives a durable yet light structure that can protect the internal components of the ADCP profiler.

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

Selection of the right equipment for current measurement in Surat Thani should be based on the usage.

For Measurements from a Moving Vessel

A ship-borne ADCP meter will be appropriate. Real current data can be obtained while the ship is moving, thus enabling 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 continuously monitors the current at a point and provides regular data over time.

For measurements that must cover a wide area and aren't restricted to a particular depth, a buoy - type ADCP current meter is appropriate. It covers a larger area and isn't limited to a particular depth.

For water depths up to 70m, a choice of frequency such as 600kHz is ideal. For those with water depths between 70m and 110m, a 300kHz ADCP is relatively better. For very deep waters with depth up to 1000m, a 75kHz ADCP is recommended.

There are well - known ADCP current profiler 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.