How to measure the coastal currents of Haiphong?

1. Where is Haiphong?

Haiphong City is one of the vibrant and significant cities in Northern Vietnam. It is a major port city with substantial historical and cultural significance.

Geographically, it is located along the coast of the Gulf of Tonkin, part of the South China Sea. The city is evergreen and is surrounded by that particular area of the fertile plains that further expand inland. The sand on its shores is white and beautiful, and the coastline of this area stretches over a good distance.

The social outlook of Haiphong is very posh; it's a city of busy people and a metropolis, generally. Its inhabitants are warm hosts and good workers. From the historical point of view, there was much trade and commerce in that city; all these factors helped this city grow and advance up to this date. At the same time, it is an industrious hub related to manufacturing and fisheries.

This city draws a lot of its vitality from the Gulf of Tonkin that lies on its doorstep. In turn, this gulf is rich in sea life and therefore a very important fishing area. The waters are quite tranquil in some areas, whereas in other areas, there is significant tidal shift and current. The sea is very important to the local economy here because shipping and trading activities through sea transport connect it to other parts of the world. This way, Haiphong remains in contact with the rest of the world.

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

There are several influences on the coastal currents around Haiphong. First, the most dominant ones are the tides. The gravitational pull of the moon and the sun causes the level of the sea to change, therefore inducing tidal currents. These tidal currents can be more or less strong according to the phase of the tide.

These monsoon winds exert a great influence on coastal currents, too. Throughout the wet monsoon season, winds blowing from the south-west may push the surface waters and create any-direction currents. In comparison, the winds from the north-east during the dry monsoon season cause other types of flow.

Still, coastal currents are further modified by bottom conditions of the sea floor off Haiphong. Bottom topography, in particular, accelerates or retards currents at certain places. For example, at places where depths reduce, currents might be stronger because water is simply forced to pass through a narrower passage.

These currents could also be partially created according to the temperature differences of the water. Warmer water near the surface may tend to rise and be replaced by cooler water from deeper layers, creating a vertical circulation that can influence the overall flow of the coastal currents.

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

Some of the characteristics of Haiphong coastal currents include velocity and flow rate. The velocity might be somewhat slow in some areas, mainly in calm regions, while being quite fast in constricted regions or influenced by strong winds or tides. The flow rate is basically dependent upon the volume of water passing through a given area per unit time.

For measuring these coastal currents accurately, methods that are advanced and convenient need to be devised. One of the very convenient methods that have proved to be very effective in measuring them is the Acoustic Doppler Current Profilers, commonly known as ADCP flow meter. These ADCP meter proved to be a revolution in the measurement of water currents as they have the capacity to provide detailed and continuous information on the flow of water at variable depths.

3.1 How do the ADCPs employing the Principle of Doppler work?

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

In sending out multiple acoustic beams at differing angles, the ADCP profiler is able to determine the three-dimensional components of the water's velocity. For instance, they can establish the vertical velocity components in addition to horizontal ones, allowing for a full understanding of the structure of water flow. The data is then processed and analyzed to provide correct information concerning the currents of the coast.

3.2 What is needed for high-quality measurement of Haiphong coastal currents?

The main requirements to be fulfilled by the equipment for high-quality measurements of coastal currents around Haiphong concern several aspects. First, material reliability of the device itself plays a major role. The device should be resistant to marine environmental impacts such as saltwater, high humidity, and different kinds of pressure.

The size, weight, and power consumption of the equipment also matter: it should be smaller in size and lighter in weight to make deployment and manipulation easier, especially when, in many instances, the measurement has to be done from a small boat or floating platform. Low power consumption shall enable the equipment to run for several hours on a single charge without frequently changing or seeking external power sources.

Another very relevant issue is that of cost. In order to enable large-scale measurements, it needs to be inexpensive equipment. One of the very appropriate materials which the casing of an ADCP doppler may be made from is an alloy of titanium. It has a number of beneficial properties: it is very strong and resistant, and thus well capable of standing the salinity of water; the density is relatively low, which helps keep the general weight of the device low as well. It also possesses excellent thermal properties, possibly useful in the sometimes extreme temperature conditions of the marine environment.

3.3 How to choose the right equipment for current measurement?

A number of aspects shall be considered in choosing appropriate equipment for the measurement of Haiphong's coastal currents. First, the mode by which instruments shall be deployed has to be chosen. Depending on the deployment mode, there is an array of choice for ADCP current profiler.

In the case of a measurement from a ship, one proper variant would be an ADCP. It can be mounted on the hull of a ship and give continuous measurement when the ship is moving in water.

If the measurement is to be done from the seabed, then one can use bottom-mounted or sit-on-bottom ADCP. Such an ADCP is placed on the seabed and measures current that passes above it.

The ADCP fixed on a buoy is perfect for applications involving a floating platform; it can be fixed to a buoy and measure the currents in the surrounding waters.

Again, besides the mode of deployment, the frequency of the ADCP also needs to be selected based on the water depth. For waters as deep as 70 meters, a typical ADCP of 600 kHz will often work well since it will give high-resolution measurements. For depths from 70 to 110 meters, a typical ADCP of 300 kHz is used. And for greater water depths, such as as high as 1000 meters, a typical ADCP of 75 kHz is considered good since it can penetrate more deeply into the water to accurately measure the currents.

There are some very famous brands of ADCPs in the market, such as Teledyne RDI, Nortek, and Sontek. In recent decades, people seeking an economical but quality product may refer to the China Sonar PandaADCP. The all-titanium alloy material ensures its good reliability in the marine environment. Besides, it offers an incredible cost-performance ratio. You can find more information about it from its official website: https://china-sonar.com/.

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