How to measure the coastal currents of Phetchaburi?

1. Where is Phetchaburi?

Phetchaburi is a province of Thailand, located on the western shore of the Gulf of Thailand. Beauty both in history and nature abounds within this province. Ancient temples and palaces reflect the glorious eras of this province.

The coastline of Phetchaburi presents a mix of sandy beaches and fishing villages. The mainstay of the local economy is fishing, agriculture, and tourism. People here are closely affiliated with the sea and land. The beaches here, such as Cha - am Beach, are popular with both domestic and foreign tourists.

The nearby Gulf of Thailand is a warm and comparably shallow body of water. It is a haven for diverse marine life. Various fish species, shellfish, and other organisms are supported in the waters. Mangrove forests along the coast are very important to protect the shoreline from erosion and provide a habitat for many species.

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

There are many factors that influence the situation of the coastal currents near Phetchaburi. The most significant ones are tidal currents. Because of gravitational pull by the moon and the sun, tides in the Gulf of Thailand are semi-diurnal. This is to say, there is one low tide and one high tide throughout the day. Tidal currents can be very strong, particularly near the coast and in regions where the water is funneled, as near river mouths. They are very important mechanisms of sediment transport and also for the resuspension of nutrients.

Monsoon winds also play a major role. The southwest monsoon between May and September has strong winds that drive the surface currents in a particular direction. The northeast monsoon, between November and February, changes the wind direction and thus the direction and speed of the coastal currents. This interaction between tidal and monsoon-driven currents sets up a complex and dynamic flow pattern.

The shape of the bottom, besides underwater relief, such as ridges and channels, may cause the coastal currents to bend and alter their flow. The discharge of rivers into the sea will also have an effect on the pattern of currents. The freshwater input from these rivers can create density differences that lead to the formation of complex current systems.

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

There are several methods to observe the coastal water flow in Phetchaburi.

The Surface Drifting Buoy Method

In principle, this is quite straightforward and a pragmatic approach. The buoys are deployed into the water, and each has fitted GPS or other trackers. Since the buoys would travel on the movements of the currents, it would be possible to learn the position of the buoys over time and, hence, the direction and speed of the surface currents. The buoys would have to be designed for the local marine conditions with respect to wave effects and the corrosive nature of saltwater.

The Anchored Ship Method: A ship is anchored at a particular point and current-measuring instruments are lowered from it. These instruments can measure the water flow velocity and direction at various depths. However, this technique suffers from a few drawbacks. The ship may be influenced by waves and winds, which could give incorrect measurements. It is also pretty inefficient for area coverage.

The Acoustic Doppler Current Profiler (ADCP) Method: A more advanced and thus efficient measurement for the flow of the coastal water can be obtained by the use of an ADCP current meter. ADCPs are capable of measuring the velocity profile in water currents over a wide range of depths. The sound waves emitted into the water by the instrument are reflected and further analyzed for the Doppler shift in it. This gives them an in-depth overview of the current structure from the surface right to the seabed.

4. How do ADCPs using the Doppler principle work?

The ADCPs apply the Doppler principle: They send acoustic pulses-sound waves-into the water. The sound waves reflect off particles in the water, like sediment, plankton, and other small particles. When these sound waves come back to the ADCP current profiler, having bounced off these particles, the frequency of the reflected waves has changed because of the Doppler effect.

If the particles are moving towards the ADCP flow meter, then the frequency of the reflected wave is higher than the originally emitted frequency. On the other hand, if the particles are moving away from the ADCP profiler, then the frequency of the reflected wave is lower. The ADCP computes the velocity of the particles simply by making a very precise measurement of this frequency shift. Since the particles are in motion with water current, the calculated velocity of the particles will give an estimation of the water current velocity.

They can emit sound pulses in several directions and, thereby, measure the three-dimensional current velocity and the variations thereof with depth. For instance, a vertical profile provides the velocity of flow at several intervals from the surface to the seabed, in order to provide a comprehensive picture of the current structure.

5. What is required for high-quality measurement of the Phetchaburi coastal current?

The equipment should be made of reliable materials for high-quality measurement of the currents in Phetchaburi Province. Due to the harsh conditions in the sea, such as saltwater corrosion and probable physical impacts from waves and debris, casings should be durable.

The size of the equipment should be small enough to be easily deployed, especially in areas with limited access such as in small boats or in shallow coastal waters. A lightweight design is also desirable because it provides easiness for handling and installation.

Long-term measurements require low power consumption. Cost-effectiveness is also necessary to enable large-scale measurements. In the case of ADCPs, the casing is preferably made of titanium alloy. This provides very good corrosion resistance, which is extremely important in the marine environment of Phetchaburi. It can stand up to the corrosive effects of saltwater over a very long period. This is strong and has a high strength-to-weight ratio, thus providing durability and light weightiness that allows protection for the internal components of the ADCP profiler.

6. How to Select Appropriate Equipment for Current Measurement?

While selecting appropriate equipment for the measurement of current in Phetchaburi, the first point to be considered is the usage.

For Measurements from a Moving Vessel

For this purpose, a ship-borne ADCP meter can be used. It can facilitate current data in real time when the ship is underway. This will help view the water flow in various locations more clearly.

For Measurements at a Fixed Location near the Seabed A bottom-mounted ADCP current profiler is suitable. It will be able to monitor the current at that one point continuously and hence provide steady data for that point over time.

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

A buoy-type ADCP flow meter will be appropriate because it can provide more extensive area and has no certain restriction concerning the depth.

The frequency selection: for water depths up to 70 m, a suitable option is the 600 kHz ADCP. If the depth ranges between 70 m to 110 m then, 300 kHz ADCP would be suitable. For quite deep waters up to 1000 m, a 75 kHz ADCP is advisable.

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.