How to measure the coastal currents of Bangkok?

1. Where is Bangkok?

Bangkok is the capital city of Thailand, located in the central part of the country. As a noncoastal city in the proper definition of a coastal city, it is connected to the sea through a very elaborate network of rivers and canals that lead down to the Gulf of Thailand.

It is a vibrant metropolis city that is famous for having the most beautiful temples, which include the Grand Palace and Wat Arun. The city is also an economic and cultural center with very heterogeneous residents who include people from all over Thailand and a considerable amount of expatriates. Bangkok's architecture blends between traditional Thai and modern skyscrapers.

The Chao Phraya River courses through the very center of Bangkok. By its channel, as well as several of its distributaries, it provides a significant transportation and trade route, and sometimes part of daily life. The river is a busy artery, with watercraft of every description, from traditional long-tail boats to great freight vessels. Ultimately, this water flows into the Gulf of Thailand via the Chao Phraya and contributes to the general movement of water within the given area.

The nearby Gulf of Thailand is shallow and warm. It is rich in marine life and serves as an important area for fishing and other maritime activities. The sea also contributes to the climate and weather patterns of the Bangkok region by its influence on air humidity and temperature.

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

Multiple factors affect coastal currents near Bangkok, though it is not placed directly on the coast. The large tidal currents are a dominant influence. The tides in the Gulf of Thailand are semi - diurnal, due to the gravitational pull from the moon and the sun. These tidal movements can change the water level and flow rate of the rivers and canals connecting Bangkok to the sea. Tidal currents can be felt far inland, especially during high-tide periods when the water from the sea pushes upstream.

The monsoon winds likewise create an effect. The southwest monsoon brings heavy rainfall during the months of May to September, thus affecting the water flow in the rivers and canals. The wind-driven currents within the Gulf of Thailand during this period may influence the general patterns of water movement. On the other hand, the northeast monsoon, which blows from November to February, causes changes in the wind direction and thus the direction and speed of the coastal and riverine currents.

Another important factor is the discharge of the Chao Phraya River and its tributaries. The volume of water from the city and its catchment area flowing into the sea may also be responsible for causing density gradients to alter the pattern of coastal currents. The local bathymetry, which includes the shape of the seabed in the Gulf of Thailand and the channels through which the river water flows, can redirect and modify the flow of the coastal and river-influenced currents.

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

There are a few ways to observe the water flow that eventually connects to the coastal area from Bangkok.

The Surface Drifting Buoy Method

It can be applied in the rivers and canals closer to the sea. Buoys are released into the water and tracked by GPS or other tracking devices. Because the buoys are in the current and move with them, their position and trajectory over time can be measured to determine the direction and magnitude of surface currents. The buoys must be fabricated for resistance against the local water conditions, flow rate, debris, and salinity - closer to the sea.

Anchored Ship Method

A ship may be anchored near the mouth of the rivers where they meet the sea. Current-measuring instruments may be deployed from the ship to measure the water flow at various depths. This method also has some limitation, Besides, the ship may be subjected to waves and winds, hence giving incorrect measures. It is also not very efficient to cover a large area, especially in the context of a wide - spread river - canal network like that of Bangkok.

The Acoustic Doppler Current Profiler (ADCP) Method

It is more advanced and efficient ways of measuring the water flow. The ADCPs can be installed in the rivers, canals, and near the coastal areas. They emit sound waves into the water and analyze the Doppler shift of the reflected waves, thereby offering a very accurate insight into the current structure from surface to seabed. An ADCP current meter is able to measure the velocity profile of water currents over a wide range of depth.

4. How do ADCPs using the Doppler principle work?

In operation, ADCPs utilize the Doppler principle whereby acoustic pulses or sound waves are sent through the water. Such sound waves interact with particles in the water, like sediment, plankton, and other small particles. When the sound waves have interacted with these particles and are reflected back to the ADCP current profiler, the frequency of the reflected waves is changed by the Doppler effect.

If these particles are moving toward the ADCP flow meter, then the frequency of the reflected wave is higher than the original emitted frequency. Conversely, if the particles are moving away from the ADCP meter, the frequency of the reflected wave is lower. By precisely measuring this frequency shift, the ADCP is able to calculate the velocity of the particles. As the particles are in motion with the water current, the calculated velocity of the particles gives the velocity of water current.

They can emit sound pulses in various directions, thus measuring the current velocity in three-dimensional space and depth. Such would have the ability to measure the current velocities at various intervals from the surface to the seabed in a vertical profile for a complete picture of the structure of the current.

5. What is required to obtain high-quality measurements of currents along the coast of Bangkok?

Equipment made of reliable materials is needed for high-quality measurement of the water flow related to the coastal area from Bangkok. It is expected that there would be a pretty complex water environment, ranging from fresh to saltwater, with probable debris inside and different flow rates; therefore, the casing should be durable enough.

The size of the equipment should be small enough to be easily deployed in rivers and canals as well as in coastal areas. A lightweight design is also important because it enhances convenience in handling and installation, particularly in areas where access may be limited, such as in small boats or in narrow waterways.

Low power consumption is highly essential for long - term measurements. Cost-effectiveness is also crucial for allowing large-scale measurements. In the case of the ADCPs, the casing is preferably made from titanium alloy. Titanium alloy has very excellent corrosion resistance, important in water environment surroundings like Bangkok. It resists well the corrosive effects of saltwater and any potential chemical and physical effects from the river water. It is also strong and has a high strength-to-weight ratio, thus providing a durable and lightweight structure able to protect the internal components of the ADCP meter.

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

While choosing the appropriate equipment for current measurement, taking into perspective Bangkok's water network and its connection with the coast, the usage should be considered first.

For Measurements from a Moving Vessel

The ADCP profiler which is ship-borne can be suitable for conducting the measurements in rivers and canals while the vessel is in motion. It provides real current data in real time and helps in understanding how water flow changes with location as the ship moves on.

For Measurements at Fixed Locations near Seabed

A bottom-mounted ADCP flow meter would serve better for the purpose. It could be used to continuously monitor the current at a point, say, at the river mouth or in some particular area of the coastal waters. Bottom-mounted ADCPs can provide consistent measurements over time and are suitable for applications involving longer-term studies.

When the Measurements Have to Cover a Wide Area and Are Not Confined to a Particular Depth The buoy-type ADCP would be adequate. It has a better coverage area and is not confined to any particular depth. In relation to the widespread water network in Bangkok, a buoy-type ADCP current profiler can be used in the rivers closer to the sea or at coastal areas to capture a more general view of the flow of water.

Frequency Choice: For water depths up to 70m, one can well use a 600kHz ADCP. For the depth of 70-110m, 300kHz ADCP may be used. In very deep waters of up to a depth of 1000m, the suitable instrument is a 75kHz ADCP.

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.