How can we measure the Coastal Currents of Pathein?

1. Where is Pathein?

Pathein is a city in Myanmar, in the Ayeyarwady Region. It is an important coastal city that faces the Bay of Bengal. The city is a bustling center of activities, while its rich cultural heritage is influenced by its marine location.

The area around Pathein features a flat coastal plain. The city itself has its quaint charm, with its pagodas and colonial-era buildings. The local people are engaged in occupations such as fishing, agriculture, and trade. The Bay of Bengal lying adjacent to Pathein is a vast expanse of water that is subject to the strong forces of nature. It is known for its seasonal cyclones and heavy tidal movements.

The waters are filled with a lively variety of marine life. Mangrove forests line parts of the coast, serving as a buffer against storms while providing a habitat for a number of species. The estuaries and creeks in the area, too, serve an important purpose in the local ecosystem, as they form a place where fish and other such aquatic organisms come to breed.

2. What is the condition of the coastal currents near Pathein?

A large number of factors shape the coastal currents near Pathein. The monsoon winds play a major role. During the southwest monsoon, heavy winds push surface waters, and then very strong currents may influence shipping and fishing there. Another dominant force is the tidal currents. Large tidal ranges characterize the Bay of Bengal; the ebb and flow of the tides can give rise to complex current patterns.

The freshwater discharge from the Ayeyarwady River, among other smaller local rivers, contributes to changes in the levels of salinity and density of coastal waters, thus having an interaction with current flow. The general shape of the coastline and the underwater topography are of great importance. The presence of sandbars, shoals, and channels can cause the currents to diverge, converge, or form eddies.

3. How to Observe the Coastal Water Flow in Pathein?

Surface Drifting Buoy Method: This includes releasing a buoy into the water and following its path. From the path of the buoy, it is possible to get an approximation of direction and speed of the surface current. However, there are several drawbacks to this approach. The movement of the buoy can be considerably affected by wind and wave actions, while it provides information only on the surface layer of water. This can happen when, for instance, a strong wind coming from another direction than the current might push the buoy off course, therefore giving incorrect readings of the currents.

Anchormethod-Boat: A boat is anchored in a certain position and from which the current-measuring instruments are deployed. This allows measurement at various depths. But this has also serious disadvantages. One fixed position of the boat restricts the area in which the measurements can be taken, and it may not capture the full variability of the currents in a large coastal area.

Acoustic Doppler Current Profiler (ADCP) Method: ADCP is a much newer and more efficient method of measurement for coastal currents. It sends out acoustic signals and calculates the Doppler shift of the reflected signal to obtain the velocity of water at different depth levels. This allows for a more complex profiling of the current, from surface to seabed. They are also less affected by surface disturbances and thus can be run continuously over long durations.

4. How do ADCPs using the Doppler principle work?

The basic principle of operation of ADCPs is the Doppler effect. They emit an acoustic pulse into the water. Due to interactions with moving water particles, the frequency of the reflected pulses is shifted. If the water particles are moving toward the ADCP, then the frequency of the reflected signal is higher than the frequency of the emitted one, and vice versa, if they are moving away.

The ADCP has multiple transducers that send and receive signals at different angles. By analyzing the Doppler shifts from different directions and at different depths, the device can calculate the three - dimensional velocity of the water. This means it can determine the horizontal and vertical components of the velocity, providing a detailed understanding of the current's structure and behavior.

5. What is required for high-quality measurement of Pathein coastal currents?

The equipment for the measurement of the coastal currents around Pathein should be made of reliable materials. Since the marine environment is so harsh, with saltwater, high humidity, and the possible presence of storms, it needs a casing that can protect it. The size of this equipment should be small to allow for easy deployment and retrieval, particularly around areas with a complicated coastal landscape.

A lightweight design is preferred since it makes the equipment more manageable during installation and maintenance. Low power consumption is essential for long-term and autonomous operations. Cost-effectiveness is also necessary for allowing large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, vital for withstanding the corrosive effects seawater can cause. It's tough and durable, able to handle the pressure of the water at different depths. Its lightweight makes it more convenient for several ways of deployment.

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

First, it would be considered to design what the equipment is used for. If the measurement is for a vessel's navigation or short-term research, a ship-mounted ADCP should be appropriate. It gives real-time current information during the voyage.

For measurements near the seabed, such as for studying sediment transport or benthic ecology, a bottom-mounted ADCP is preferable; it can capture the details of the near-bottom current. If long-term and wide-area monitoring of the coastal current is required, a buoy-type ADCP will be ideal.

Frequency-Regarding the frequency of ADCPs, for water depths up to 70m, the 600kHz ADCP will be good to go. For depths up to 110m, it would be more appropriate to use a 300kHz ADCP. For deeper waters, which might be found near Pathein, such as areas with more than 1000m, a 75kHz ADCP is recommended.

There are well - known ADCP 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 an excellent cost - performance ratio. You can find more information on their website: ​https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and moels.