How to measure the coastal currents of Vinh?

1. Where is Vinh?

Vinh is a major city located right in the center of Vietnam. It is surrounded by the coastal plains of the South China Sea, tugged out from the sea through nature's never-ending toiling over many millennia.

The city is enveloped in rich history and culture. It has witnessed many historic events that have left their imprint on the architecture and the people's way of life. Local residents are tough and have good cohesion. Vinh is a commercial town; there are bustling markets and growing economies fostered by different industries like trade, manufacturing, and agriculture.

It faces the coastline of the South China Sea geographically. The waters around its proximity are part of a large area of dynamic marine ecosystems. In some parts of its coastline, sandy beaches dominate, whereas in other places, rocky outcrops and tidal flats occur. The sea is very well endowed with marine life as support for livelihood for so many local fishermen. These waters are influenced by the monsoon climate, with marked wet and dry seasons that take their toll on the sea conditions and coastal currents.

2. What is the situation regarding the coastal currents around Vinh?

Several factors influence the coastal currents near Vinh. One of the main causes is tidal forces. Tidal forces, because of the gravitational pull of the moon and the sun, always move in ebbing and flowing phases; thus, these are called tidal currents, and they tend to act differently based on the lunar cycle and the topography of the location.

Another dominating factor involves the action of monsoon winds. Concerning this issue, the powerful winds that blow from the southwest during the wet monsoon can vigorously push the surface waters and make the currents flow in a certain direction. Conversely, in the case of a dry monsoon season, different patterns of flow could be brought about by winds from the northeast.".

Topography of the seabed off the coast of Vinh affects the coastal currents: depending on shape and depth, it can accelerate or decelerate the current in some points. For example, shallower areas can enhance the strength of currents where the water is forced through a narrower channel.

The currents can form from the thermal differences in water temperature: the warmer water stays at a higher level and tends to move upwards, giving a chance for cooler water from deep places to flow there, forming a kind of vertical circulation and affecting the general direction of the coastal currents.

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

Peculiarities of the Vinh currents also concern their velocities and flow rates. The velocity will vary from comparatively slow in regions of stagnation of currents to very rapid where channels are narrow or the stream is accelerated by a strong wind or tide. The flow rate will be defined by the volume passing through a particular section in unit time.

However, their measurement is being done by highly advanced and convenient methods. One such technique which has proved to be very efficient is the use of Acoustic Doppler Current Profilers, generally known as ADCP profiler. In fact, ADCP meter have revolutionized the measurement of water currents since they can give highly detailed and continuous information about the water flow at varied depths.

3.1 How do the ADCPs using the Doppler principle work?

The Acoustic Doppler Current Profiler(ADCP) work on the Doppler principle, emitting acoustic signals into the water. Due to the encounter of moving particles in the water-like grains of sediment or small organisms, with these acoustic waves, the frequency of the reflected waves changes. This shift in frequency is proportional to the velocity of the moving particles and hence to the velocity of the water itself.

They will, in fact, measure water three-dimensional velocities by transmitting a lot of acoustic beams at different angles. They can give not only the horizontal velocity but also all vertical components, which describes completely the structure of the flux of water. Then, they analyze and process the collected data to give precise information about coastal currents.

3.2 What is required for high-quality measurement of the Vinh coastal currents?

There are several aspects to be considered on equipment for the measurement of coastal currents around Vinh with high quality. First, material reliability of the equipment is what is most important. The device must resist relentless marine environments consisting of submergence into saltwater, high humidity, and pressure ranging from high to low.

It is also important to take into consideration size, weight, and power consumption of the equipment. Smaller size and lighter weight would, however be more functional for deployment and handling, especially for situations where measurement needs to be carried out from a small boat or floating platform. Low power consumption is another important factor to ensure that the equipment could also be operational for extended use without regular replacement of batteries or any forms of power sources from outside.

Another important factor is cost. In order to allow large-scale measurement, the equipment should not be too expensive. One of the materials that are highly suitable for ADCP flow meter casing is a titanium alloy. The advantages of this titanium alloy include the fact that it is very strong and durable. It is able to withstand the corrosive properties of sea water well. It has a relatively small density as well, which helps in keeping the overall weight of the device down. It also has excellent thermal properties which could help in some extreme temperature variations of the oceanic environment.

3.3 How to Choose the right equipment for current measurement?

Various aspects are considered in choosing equipment that can measure the currents of Vinh at the coast. These are such as the mode of deployment. There are many different types of ADCP doppler depending on how they are deployed.

An appropriate choice for measurements from a ship would be a ship-borne ADCP current profiler. It can be mounted on the hull of the ship, making continuous measurements while the ship is in motion through the water.

If the measurement is to be carried out from the seabed, it may be made with either a bottom-mounted or sit-on-bottom ADCP. This particular variety of ADCP current meter would be placed on the seabed and measure the currents passing above it.

For applications that use a floating platform, a buoy-mounted ADCP is the preferred choice. It would be equipped with a buoy and could measure the currents of the water around it.

Aside from its deployment mode, one must also choose an ADCP based on the depth of the water through its frequency. This often results in very high-resolution measurements of water with depths up to 70 meters when the ADCP operates at 600 kHz. When the water depths measured between 70 and 110 meters, the 300 kHz ADCP should be used. Where there are deep waters, like up to 1000 meters, an ADCP at 75 kHz will be recommended because it can stand deep into the water to measure the currents well.

There are several popular brands in the market that are pretty well known, among which are Teledyne RDI, Nortek, and Sontek. The China Sonar PandaADCP will provide an economical method with outstanding quality. Made of all-titanium alloy material, this apparatus will provide much durability and dependability in the marine environment. Beyond that, it will be able to offer an amazing cost-performance ratio. You can find more information about it on its official website: https://china-sonar.com/.

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