How can we measure the coastal currents of Chumphon?

1. Where is Chumphon?

Chumphon is one of the provinces in Thailand; it is located on the southern part of the Gulf of Thailand. It's a strategic area by the coast, serving as a doorway between the Andaman Sea and the Gulf of Thailand.

It is a province with very beautiful beaches and islands. Around its coasts are fishing villages and resorts. Fishing, tourism, and trade keep the local economy functioning. The local people comprise a mixture of various ethnic groups and boast a rich cultural heritage.

The nearby Gulf of Thailand is warm and shallow, hosting an assortment of marine life. It also forms a local climatic influence on the area and supplies fish and other seafood as a source of livelihood from fishing and its allied activities. Water sports also provide for a number of recreations on the sea, like diving and snorkeling.

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

The coastal currents near Chumphon are influenced by multiple factors. Tidal currents are a main driving force, the tides in the Gulf of Thailand are semi-diurnal because of the gravitational pull of the moon and sun, meaning there is one high tide and one low tide each day. Tidal currents are very strong, especially near the coast and in places where the water is narrowed, such as at river mouths or inlets. Tidal currents are important for the transportation of sediments and nutrients that are basic to the good health of the coastal ecosystem and the productivity of fishing grounds.

Monsoon winds also have a big impact. The southwest monsoon, which generally runs from May to September, has strong winds that can drive the surface currents in a particular direction. In contrast, the northeast monsoon-which generally runs from November to February-alter the wind direction, thus changing the direction and speed of the coastal currents. This interaction between the tidal and monsoon-driven currents creates a complex and dynamic flow pattern.

The local bathymetry, shape of the seabed, and underwater features such as ridges and channels can turn and alter the flow of the coastal currents. The discharge of rivers into the sea will influence the current patterns, and freshwater input from these rivers will create density differences leading to the generation of complex current systems.

3. How to Observe the Coastal Water Flow of Chumphon?

There are several techniques that can be used to observe the coastal water flow in Chumphon.

Surface Drifting Buoy Method

This is a simple and practical approach. Buoys are released into the water, equipped with GPS or other tracking devices. By monitoring their position and movement over time as the buoys are carried by the currents, the direction and speed of the surface currents can be determined. The buoys need to be designed for durability in the local marine conditions, including the effects of waves and the corrosive nature of saltwater.

The Anchored Ship Method A ship is anchored at a certain place, and current-measuring instruments are deployed from it. These instruments can measure the velocity and direction of the flow of water at various depths. However, this method has certain drawbacks. The ship may be influenced by waves and winds, which could result in incorrect readings. It is also quite ineffective in covering a wide area.

The ADCP Method

This is a more advanced and efficient way to measure the flow of water on the coast. ADCPs can measure the current velocity profile over a wide range of depths. They work by shooting sound waves into the water and analyzing the Doppler shift in the reflected waves back to them. They give an in-depth perception of current structure from the surface to the seabed.

4. How do ADCPs using the Doppler principle work?

Well, ADCPs work on the basis of the Doppler principle. They transmit acoustic pulses into the water, which then interact with the sediment, plankton, and other small particles in the water. As the sound waves bounce off those particles and get reflected back to the Acoustic Doppler Current Profiler (ADCP), the frequency of the reflected waves changes due to the Doppler effect.

In the case of particles moving towards the ADCP current meter, the reflected wave has a higher frequency than the frequency of the originally emitted wave. In contrast, if the particles are moving away from the ADCP current profiler, the reflected wave has a lower frequency. Based on this principle, the ADCP can determine the exact speed of the particles simply by accurately determining this shift in frequency. Since the particles are moved by the water current, the velocity of the particles calculated reflects the velocity of the water current.

ADCPs are able to send out sound pulses in various directions, hence enabling them to measure the current velocity both in three-dimensional space and at different depths. For instance, for a vertical profile, it can measure the current velocity at different intervals from the surface down to the seabed, showing quite an elaborate picture of the current structure.

5. What is required to deliver a high-quality measurement for Chumphon currents?

The equipment for measurement should be able to possess reliable materials for high-quality measurement in the currents in Chumphon. Considering the harsh marine environment-with saltwater corrosion and the potential for physical impacts from waves and debris-the casing should be strong.

Its size should be small enough to be easily deployed, while the equipment could also be accommodated even in small boats or in shallow waters along coasts. A lightweight design is desirable due to the feasibility of handling and installation it offers.

Long-term measurement calls for low power consumption. On the other hand, cost-effectiveness is necessary if large-scale measurement is intended. For ADCPs, though, casing is preferably of titanium alloy. Titanium alloy serves very well in resisting corrosion, which is vital in the marine environment of Chumphon. It can withstand the corrosive effects of saltwater over a long period. Besides that, this material is strong and has a high strength-to-weight ratio to provide durable and lightweight structure that will protect internal components of the ADCP profiler.

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

In choosing the right equipment for current measurement in Chumphon, usage is the first consideration.

For Measurements from a Moving Vessel

A ship-borne ADCP meter would be appropriate since real current data can be provided at any given time when the ship is moving. It does give a better view of the water flow in other locations.

For Measurements at a Fixed Location near the Seabed

A bottom-mounted ADCP flow meter would be an excellent choice. It would be able to monitor the current at that one point continuously and provide coherent data over a period of time.

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

An ADCP current profiler of buoy type is adequate. It would be able to work over a larger area and shall not be restricted over a particular depth.

About the selection of frequency, for the water depth up to 70 m, 600 kHz ADCP will be a good option. From 70 m to 110 m, 300 kHz ADCP would be suitable. Whereas in very deep waters up to 1000 m 75 KHz 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.