How are the coastal currents of Nam Định to be measured?

1. Where is Nam Định?

Nam Định is a city and an advantageously placed town in the Red River Delta region of the country of Vietnam. The city nestles amongst the green, rich plains created by deposits of the Red River over many, many centuries. The city is rich in cultural heritage and history dating from ancient times, with an abundant local community.

It has a strategic location geographically along the coastline of the Gulf of Tonkin. The coastline of Nam Định contains fishing villages and has sandy beaches in certain areas. Adjacent waters have a part of a complex marine ecosystem. There are large areas of mudflats and shallow coastal areas inhabited by a diverse range of shellfish and other invertebrates. These areas provide vital feeding and breeding sites for many species of birds.

Fishing is the great industry in regard to human activities here. The local fishermen are totally familiar with the sea and its rhythm. Tourism has developed recently in this city, receiving visitors who come for its beaches and to experience the culture of the coastal area. The Gulf of Tonkin, off Nam Định, represents a semi-enclosed sea area, influenced both by the freshwater inflow from the Red River and from the tidal movements of the South China Sea.

2. What about the coastal currents near Nam Định?

Various variables interact to determine the characteristics of the currents in general off Nam Định. Tidal currents are the most prevalent. Due to gravitational pull from both the moon and the sun, the tide rises and falls to form various currents that can differ in their intensity and direction. The semi-enclosed nature of the Gulf of Tonkin may make these tidal currents more complicated in comparison with open ocean areas.

Another great contribution is the input of fresh water from the Red River. The discharge of this river develops a density-gradient-driven current. Because of the less dense fresh water floating over the denser salt water, there is the tendency to create overlayer flow that influences the general pattern of current in the coastal currents.

Other significant influences are currents due to wind. During various seasons, the very same monsoon winds crossing the area might push the surface waters and result in the currents. The more substantial surface currents of the wet monsoon season can be advected by southwest winds, while during the dry monsoon season, winds from the northeast might give another regional net flow direction.

3. How to Observe the Coastal Water Flow of Nam Định?

The velocities and flow rates vary within different ranges concerning the coastal currents in Nam Định. The speed is slow near the shoreline, especially when the flow was braked by a lot of sediment deposition and complicated topography, but relatively fast where the flow concentrated, such as channels or zones that are probably affected by stronger wind and tide conditions. The flow rate is influenced by the width and depth of the coastal area along with the combined effect of all factors driving the currents.

Acoustic Doppler Current Profilers are among the effective advanced methods for observation in these coastal currents. They are able to give substantial information with depthwise accuracy in the water flow.

3.1 How do ADCPs using the principle of the Doppler work?

Acoustic Doppler Current Profiler(ADCP) work on the principle of the Doppler effect. They send acoustic signals into the water. These get scattered by the moving particles in the water that could be plankton or even suspended sediment. These reflected waves of acoustic waves, reflected back by these moving particles, have a different frequency from the incident waves. The shift in frequency depends directly upon the velocity of these moving particles and in turn upon water velocity.

With more acoustic beams at different angles, ADCP current meter can measure three-dimensional water velocity. In other words, they are able to find the horizontal and vertical components of the velocity, which allows them to give a complete description of the structure of the water flow. After processing, the data obtained from measurement provides useful information about coastal currents.

3.2 What's required for high - quality measurement of Nam Định coastal currents?

The measuring equipment would need to meet some requirements for high-quality measurement of the coastal currents near Nam Định. The reliability of the material used must be able to hold against the harsh marine environment of the currents. It should be resistant to saltwater corrosion, humid conditions, and temperature fluctuation.

Besides, it should be small in size and light in weight to make its setup easy. A lightweight device is more convenient in installation on various platforms such as on boats, buoys, or even on the seabed. The power consumption should be sufficiently low to allow for long-term operation by avoiding frequent battery replacement or the need to use a complex power supply system. Finally, it should be cost-effective for large-scale measurement purposes.

The casing for ADCP current profiler is preferably made from titanium alloy. Titanium alloy is highly resistant to corrosion, which is cardinal in a salt-water environment. Besides its relatively low density that keeps its weight low, it is strong, resilient to the mechanical stresses the equipment experiences within the marine environment, while it also provides good thermal conductivity, useful in the temperature-variable conditions at sea.

3.3 How to Choose the right equipment for current measurement?

The method of deployment is another important thing in the selection of equipment in Nam Định. There are different kinds of ADCP doppler for different uses.

For ship - based measurements, there is an ADCP flow meter that can be installed on the ship. This one measures the current as the ship travels in the water.

If the measurement is to be done from the seabed, then a bottom-mounted ADCP profiler will be appropriate. Being placed on the seabed, it measures the currents passing above it.

A buoy-mounted ADCP would be the way to go for measurements using a floating platform in the form of a buoy. It can measure the currents around the buoy.

In terms of frequency selection, a 600kHz ADCP provides high-resolution measurements for a water depth up to 70m. For a water depth within the range of 70-110m, it is more appropriate to use a 300kHz ADCP. When it comes to up to 1000m in deeper waters, a 75kHz ADCP is best suited because it can penetrate deeper with greater accuracy to measure the currents.

Among the ADCP meter brands, well - known ones include Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option with excellent quality, the China Sonar PandaADCP is a good choice. It is made of all - titanium alloy and offers an excellent price - performance ratio. You can visit https://china-sonar.com/ for more details.

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