How do we measure the currents off the coast of Songkhla?

1. Where is Songkhla?

Songkhla is a southern province of Thailand. It is located on the eastern coast of the Malay Peninsula and borders the Gulf of Thailand. The city is renowned for its lovely beaches, among them Samila Beach, which serves as a strong tourist attraction.

It is also an important economic hub, serving as a hub for fishing, trade, and manufacturing. Songkhla is home to a large fishing port, and fishing remains a key source of income for residents. People in the locality include Thai, Malay, and Chinese; thus, the area has a rich cultural heritage in terms of ethnicity.

The nearby Gulf of Thailand is a relatively shallow, warm body of water that sustains adequate marine life; there are various fish, shellfish, and coral reefs. The sea modifies the local climate and supports water-based recreational activities such as swimming, snorkeling, and sailing.

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

The various coastal currents off Songkhla are induced by more than one factor.

Tidal Currents

The tide in the Gulf of Thailand is semi - diurnal. Gravitational pulls by the moon and the sun result in two high tides and two low tides in a day. Tidal currents might be very strong and are channeled by the coastline or constricted around river mouths or inlets. These currents are very important for sediment and nutrient transport, which is vital for the health of the coastal ecosystem and thus for fishing grounds productivity.

Monsoon Winds

From May to September, the southwest monsoon brings strong winds that can drive the surface currents in a particular direction. From November to February the northeast monsoon 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.

Local Bathymetry

The form of the bottom of the sea and the underwater relief with ridges and channels will contribute to the deviation and modification of the coastline currents. Discharging rivers also may act on the current patterns in view. In addition, freshwater input provided by these rivers produces variations in density that give rise to the development of complex systems of currents.

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

There are a few ways to monitor the current flow of the water in Songkhla.

The Surface Drifting Buoy Method

This is fairly straightforward and workable. Buoys are deployed in the water and fitted with GPS or other position-tracking devices. When the buoys are moved by the currents, their location and travel over time can be observed and the direction and velocity of the surface currents estimated. The buoys must be constructed to be resilient against the local marine conditions - specifically the wave action and corrosive nature of salt water.

The Anchored Ship Method

The ship is anchored at a place with current-measuring instruments deployed from it. Such instruments can be used for measuring the velocity and direction of the flow of water at different depths. There are certain drawbacks to this method, though. The ship may be subjected to waves and winds, due to which the measurements may not be quite accurate. Besides, it is not very effective in covering a big area.

The Acoustic Doppler Current Profiler (ADCP) Method

This provides a more recent and effective approach towards measuring coastal water flow. ADCPs can measure the velocity profile of water currents over a wide range of depths. They work by emitting sound waves into the water and analyzing the Doppler shift of the reflected waves. This gives a better comprehension of the current structure from surface to seabed in much detail.

4. How do ADCPs using the Doppler principle work?

ADCPs rely on the principle of the Doppler effect. They send acoustic pulses, or simply sound waves, into the water. In water, there are particles such as sediment, plankton, and other small particles that these waves will be in contact with. When the sound waves bounce off these particles and are reflected back to the Acoustic Doppler Current Profiler (ADCP), the frequency of the reflected waves changes owing to the Doppler effect.

If the particles are moving towards the ADCP current meter, then the frequency of the reflected wave is higher than the emitted one. On the other hand, if the particles are moving away from the ADCP meter, then the frequency of the reflected wave is lower. By accurately measuring this frequency shift, the ADCP can determine the velocity of the particles. Since these particles are in the movement along with water current, the obtained velocity of the particles will give the water current velocity.

They can emit sound pulses in several directions; thus, ADCPs can measure current velocity in three - dimensional space and at different depths. For instance, in a vertical profile, they are able to estimate the current velocity at different intervals from the surface to the seabed and provide a comprehensive view of the current structure.

5. What's needed for high - quality measurement of Songkhla coastal currents?

To provide high-quality measurement of the coastal currents in Songkhla, the equipment should be made from reliable materials. In an aggressive marine environment, with saltwater corrosion and possible physical influences due to waves and floating debris, casing durability is important.

The size of the equipment should be small enough to be easily deployed, especially in areas that are hard to access, such as on small boats and shallow coastal waters. The design should also be lightweight for easier handling and installation.

Low power consumption will enable long-term measurements. It should also be cost-effective to allow large-scale measurements. In the case of ADCPs, the casing is preferably made of titanium alloy. Titanium alloy provides excellent corrosion resistance, essential in the marine environment of Songkhla. It resists the corrosive effects of saltwater for an extended time. It is also strong with a high strength-to-weight ratio and would provide a strong and lightweight structure that could protect the internal components of the ADCP profiler.

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

While selecting appropriate equipment for the measurement of current in Songkhla, usage is considered the first factor.

For Measurements from a Moving Vessel

In these situations, a ship-borne ADCP meter may be deployed. This could offer immediate real-time current data as the vessel cruises, thus developing good knowledge of the water flow in various locations.

For Measurements at a Fixed Location near the Seabed

A bottom-mounted ADCP flow meter would be a good option. It can monitor the current continuously at the same point and provide consistent data for a longer period of time.

For Measurements which have to Cover a Larger Area and are not Restricted to any Particular Depth

An ADCP current profiler of buoy type is suitable. It can cover a wider area and also it is not confined to any particular depth.

Choice of frequency: Up to 70 m depth of water, 600kHz ADCP can be used. From 70 m to 110 m water depth, one can use 300kHz ADCP. In very deep water, up to 1000 m, 75 kHz ADCP can be used.

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.