How are coastal currents in Vietnam measured?

1. What is the situation like in respect to the coastal currents of Vietnam?

The coastal currents around Vietnam are part of an interacting combination of forces. On the contradictory side, Vietnam faces rather along coastline along with both the South China Sea and the Gulf of Thailand. Monsoon winds, oceanic circulation, tides, and complicated bathymetry of the continental shelf and seas in the neighborhood influence the waters in this region.

The monsoon winds serve as the primary driving force in surface currents. During the season of the northeast monsoon, which is from November to April, people enjoy cooler and drier winds from the northeast, while during the southwest monsoon season, from May to October, they enjoy warmer and more humid winds coming from the southwest. When these winds blow, they usually bring changes either in direction or in strength into the coastal current.

Equally important are oceanic circulation patterns. While the warm Kuroshio Current moves northward along the eastern coast of Vietnam, the cooler South China Sea Current moves in different directions depending upon the season. Interaction between those currents and coastal waters of Vietnam presents a complicated system of currents.

Another important factor involves the tides; in some regions, tidal ranges are large and could create strong tidal currents that may interfere with shipping and fishing and other coastal activities.

The seabed bathymetry also influences coastal currents. Shallow areas, reefs, and submarine canyons can speed up, slow down, or change the direction of the flow.

2. What are the factors influencing the coastal water flow of Vietnam?

Such factors prevail as the most influential in the coastal water flow of Vietnam:

Monsoon Winds: As it was said above, the monsoon winds are the main cause for surface currents. Due to large seasonal variations in wind direction and strength, the latter causes significant changes in coastal currents.

The oceanic circulation is comprised of large-scale circulation patterns, which include the Kuroshio Currents and the South China Sea Current transporting dissimilar water masses carrying different temperatures and salinity. These currents interact with the coastal waters of Vietnam and exchange effects on the local current systems.

Tides: The tidal forces give rise to periodic ups and downs in water levels, developing tidal currents. The tides have different magnitudes at different times of the day for different coastal regions.

Bathymetry: The geometry of the ocean floor strongly influences the currents over any given coastline. Flow can be channeled through narrow channels and over shallow banks, rounded by deep canyons.

River Discharge: The vast volume of river water from the mainland of Vietnam into the sea, such as the Mekong River and the Red River, can impose its effects on coastal currents. The discharge of fresh water changes the salinity and temperature of the coastal waters, creating current patterns within the locality.

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

Measuring the current in the coastal waters of Vietnam will be very helpful in marine environmental analysis, storm surge forecasting, and coastal resource management. Many techniques are available to observe coastal currents, among which ADCP is widely used during the last two decades because of accuracy and convenience in operation.

3.1 Principle of Operation of Doppler Principle-based ADCP

The general design of an ADCP includes a set of transducers. These transduce, send out, and receive sound waves. One of the most usual mountings for the transducer array is to attach them to a ship, buoy, or any other platform. Through the movement of this platform within water, the ADCP measure the velocity of the water related to the platform. By subtracting the velocity of the platform from the measured water velocity, the true velocity of the current can be ascertained.

3.2 What is required to make a high-quality measurement of Vietnam coastal currents? 

The features needed to conduct a high-quality measurement of coastal currents in Vietnam are explained as follows:

Reliability: The measuring equipment needs to be reliable and strong enough to stand against such difficult conditions found in the sea. Resistance to corrosion, shock, and vibration is an added advantage in these situations.

Compact Size and Lightweight: Small size and lightweight equipment is quite easy to handle and deploy at every kind of remote or inaccessible areas.

Low Power Consumption: Of course, it is an important factor when there are very long-term deployments, as well as when one tries to optimize economically and ecologically the measurement system.

Low Cost: This is important in many measurement campaigns, especially if a huge quantity of data is to be collected. Indeed, if the cost allows the running of several tens or hundreds of equivalent measuring equipment, it increases the spatial and/or temporal representativity of the database.

The ADCP current meter shell is manufactured from titanium alloy material. It has many advantages: high strength, corrosion resistance, lightweight, and it can operate well in ocean conditions. These advantages make the titanium alloy an ideal material for oceanic applications since it withstands such harsh oceanic conditions, hence offering long-term protection to the sensitive electronics inside the ADCP flow meter.

3.3 How to Choose the right equipment for current measurement?

For the selection of appropriate equipment for coastline currents in Vietnam, a number of variables need to be emphasized, such as:

Intended use: Identify the intended application of the measurement. If the currents are to be measured from a ship, a shipboard ADCP could suit very well. If you want measurements over a longer period at one fixed location, a bottom-mounted or buoy-mounted ADCP may suit better.

Frequency selection: different frequencies suit different water depths. For shallow waters near the coast, a higher frequency ADCP may suffice for up to 70 meters. In deeper waters, lower frequency ADCP-for example, 300 kHz or 75 kHz-may be required.

Last but not least, talking about the ADCP brands, there are quite a number of well-recognized manufacturers in the market. Some of the popular brands include Teledyne RDI, Nortek, Sontek, and China Sonar etc. The PandaADCP from China Sonar offers a mix of high quality with all-titanium alloy construction and unbeatable value for money. For more details, one can visit the China Sonar website at https://china-sonar.com/.

Following is the list of some of the popular ADCP brands along with their models