How do we measure the coastal currents of Samut Sakhon?

1. Where is Samut Sakhon?

Samut Sakhon is a province in Thailand, situated on the Gulf of Thailand. It has an important history and a dynamic economy. The province is specifically famous for its fishing and aquaculture industries. Essentially, both businesses are based on its coasts and canals.

The city of Samut Sakhon is a busy metropolis where traditional Thai fishing boats share the same waters as modern aquaculture establishments. The inhabitants of this province are very much involved with activities related to fishing, and their culture is closely linked with the sea. There is also quite a varied mix of ethnic groups in the area, adding to a very special cultural weave.

The Gulf of Thailand, lying just nearby, is shallow and warm. Many types of fish, shellfish, and crustaceans find their home in this body of water. The sea is not only a source of livelihood through fishing but an important part of the local ecosystem. Mangrove forests line the coasts, serving to protect the shoreline against erosion and providing a habitat for many organisms.

2. What is the situation of the coastal currents in Samut Sakhon?

Coastal Currents around Samut Sakhon are influenced by several factors. The most dominant force is that of tidal currents. In the Gulf of Thailand, the tide is semi-diurnal due to the gravitational pull of both the moon and the sun. This means that each day there is one high tide and one low tide. Tidal currents can be quite strong, especially near the coast and in areas where the water is constricted, such as near river mouths and canals. These currents play an important role in the transportation of sediments and nutrients that are fundamental for the good health of the coastal ecosystem and productivity of fishing grounds.

Monsoon winds, too, play a decisive role. The southwest monsoon, between May and September, provides strong winds capable of driving the surface currents in a specific direction. The NE monsoon between November and February changes the wind direction and thereby the direction and speed of the coastal currents. This interacting between tidal and monsoon-driven currents creates a complex and dynamic flow pattern.

The shape of the bottom and any underwater features such as ridges and channels can cause local bathymetry to redirect and alter the flow in coastal currents. The discharge from rivers and canals into the sea may also have an impact on the pattern of currents. Input of fresh water from such sources can create density differences that may give rise to the formation of complex current systems.

3. How to Observe the Coastal Water Flow of Samut Sakhon?

There are a few methods to observe the coastal water flow in Samut Sakhon.

The Surface Drifting Buoy Method

This is a rather straightforward and practical method. Buoys, that have been fitted with GPS or other devices which allow for tracking, are sent into the water. As the buoys move with the currents, it would be possible to monitor their position and movement over time to determine the direction and speed of the surface currents. Buoys should be constructed in such a way that they can survive the marine conditions predominant in the area of study, including the wave actions and the chemical corrosion from saltwater.

The Anchored Ship Method A ship is kept anchored at a specific location and current-measuring instruments are in water from the ship. They can measure the velocity and direction of the flow of water at different depths. Limitations of this method are that the ship may be subjected to waves and winds and therefore inaccurate measurement would result. Also, this will not be very effective in covering a major area.

The Acoustic Doppler Current Profiler (ADCP) Method

This is one more advanced and effective way of measuring the flow of water on the coast. The ADCP current meter can record the current water velocity profile across a wide depth range. It works by sending sound waves into the water and analyzing the Doppler shift of the waves reflected back through it. Further, a comprehensive perception of the structure of the current, right from the surface to the seabed, is achieved.

4. How do ADCPs using the Doppler principle work?

ADCPs basically work on the principle of the Doppler effect. They send out acoustic pulses, or simply sound waves, into the water. When these sound waves encounter particles, which may include sediment, plankton, and other minute particles in the water, they interact with it. If the sound waves finally get reflected back to the Acoustic Doppler Current Profiler (ADCP) after having encountered those particles, the frequency of the reflected waves is changed by the Doppler effect.

The frequency of the reflected wave is higher compared to the original emitted frequency if the particles are moving towards the ADCP flow meter, and the reverse occurs if they are moving away from the ADCP. Precise measurements of this frequency shift enable the ADCP to find 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.

Some ADCPs can project their sound pulses in several directions and thus measure the three-dimensional current velocity, and even its variation with depth. For instance, in the case of a vertical profile, the current velocity at different steps from the surface to the seabed is obtained, developing a complete picture of the current structure.

5. What is required for good quality measurement of the Samut Sakhon coastal currents?

The measuring equipment at Samut Sakhon should have good quality in terms of reliable materials. In view of the hostile marine environment where saltwater will corrode the device and physical impacts may be caused by waves or debris, the equipment casing needs to be durable.

The size of the equipment must be small enough to be easily deployed, particularly at places that are difficult to access, including small boats or shallow coastal waters. A lightweight design is beneficial, too, since it makes access more convenient, as well as handling and installation.

Low power consumption is an important criterion for long-term measurements. Cost-effectiveness is also very important in order to enable large-scale measurements. In case of ADCPs, the casing is desired to be made of Titanium alloy. Titanium alloy owns a great ability for anti-corrosion, which is crucial in the marine environment of Samut Sakhon. It can withstand the corrosive effects of salt water for a long time. It is also strong with a high strength-to-weight ratio, offering a durable and lightweight structure to protect the internal components of the ADCP meter.

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

Selection of the proper equipment in the measurement of current in Samut Sakhon depends on the usage.

For Measurements from a Moving Vessel

Ship-borne ADCP meter would be appropriate in this case. It will be able to give current information in real time while the ship is in motion; hence, it offers a finer description of water flow at various points.

For Measurements at a Fixed Location near the Seabed

A bottom-mounted ADCP flow meter would be quite adequate for that purpose. The current could be continuously monitored at the same point and thus give consistent data over a period of time.

For Measurements that Need to Cover a Wide Area and are not Restricted to a Specific Depth A buoy - type ADCP current profiler is suitable. It can cover a larger area and is not limited to a particular depth.

For selecting the frequency, a 600kHz ADCP should be used for water depths up to 70m; for 70-110m depth, a 300kHz ADCP can be used; and up to 1000m for very deep waters, a 75kHz 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.