How to measure coastal currents of Ho Chi Minh City?

1. Where is Ho Chi Minh City?

Ho Chi Minh City, previously named Saigon, is the biggest city in Vietnam, located in the south of this country. Although it cannot be regarded as a seaside city like some other cities in Vietnam, which face the open ocean, it is fairly close to the South China Sea.

Geographically, it is located on the flat and fertile Mekong Delta plain that it has gained through sediment deposits carried along by the Mekong River. The city itself is a busy metropolis with various types of people and a booming economy. This constitutes one of the largest centers for commerce, industry, and tourism in the country.

The nearby waters in the South China Sea off Ho Chi Minh City form part of a complex marine ecosystem. Within the coastline, there are muddy coasts, mangrove forests, and other small parts of sandy beaches further away. The sea is dominated by the outflow of the Mekong River, with the release into the sea of enormous volumes of fresh water, which mixes in a given area with saltwater. This estuary area is very rich in biodiversity since many species of fish and crustaceans, among other species of marine organisms, are concentrated here.

Of the anthropogenic uses, fishing is a well-known industry along the coasts facing Ho Chi Minh City. The local fishermen depend on the rich marine resources for sustenance. Besides, the port facilities available in the city are highly essential for international trade, with ships continuously arriving and leaving the port, carrying goods to and from other parts of the world.

2. What about the condition of coastal currents around Ho Chi Minh City?

Various elements act together to outline the features of the coastal currents near Ho Chi Minh City. First, there is the discharge of the Mekong River. The enormous volume of fresh water poured into the sea provokes the creation of a current caused by the difference in density. The fresh waters, less heavy compared to the seawater, tend to circulate over the heavier salt water, hence determining the overall circulation pattern of the coastal currents.

Tidal currents also play an important role. The tides, through the gravitational pull of the moon and the sun, cause the tides to ebb and flow, generating tidal currents. These tidal currents can vary in strength and direction depending on the lunar cycle and the local topography of the estuarine area.

Another important factor is the monsoon winds. In the wet season, strong winds blow from the southwest and thus press upon the surface waters so as to create currents in a particular direction. While in the dry season, the winds from the northeast are believed to give way to quite different flow.

Another characteristic that influences the currents along the coast is the topography of the seabed around the estuarine area. The relief of the bottom can accelerate or decelerate the currents in certain areas. For example, in places where the bottom relief is shallower, the currents will be stronger because the water goes through a more narrow channel.

3. How to Observe the Ho Chi Minh City Coastal Water Flow?

In general, the velocity and flow rate are particular for the coastal currents in Ho Chi Minh City. The velocities vary from relatively slow in some sheltered areas of the estuarine zone to relatively fast where the currents are constricted or under stronger winds and tides. The flow rate depends on the volume of water passing through a certain area per unit time.

Accurate measurement of these currents requires modern and easy means. Of these, one of the most practical approaches is based on an Acoustic Doppler Current Profilers, or simply ADCPs. ADCPs are capable of providing, in great detail and continuously, the flow of water at different depths.

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

The operating principle for the Acoustic Doppler Current Profiler(ADCP) is based on the Doppler principle. They send acoustic signals into the water. As a result of the contact between these acoustic waves and the moving particles in the water, such as sediment grains or small organisms, the frequency of the reflected waves changes. The shift in frequency, therefore, depends linearly upon the velocity of the moving particles and thus, in this case, the velocity of the water.

With several transmitted acoustic beams in different directions, ADCP current meter can measure the three-dimensional velocity of the water. Measuring the horizontal and vertical components of the velocity becomes possible, hence giving a full insight into the structure of the water flow. The data collected further undergoes processing and analysis to get accurate information about coastal currents.

3.2 What is needed to have high-quality measurement of Ho Chi Minh City coastal currents?

High-quality measurement of the Ho Chi Minh City Coastal Currents will consider a few aspects regarding the equipment. First and foremost, material reliability of the equipment has to be put in place. The device should be made in such a way that it resists the harsh marine environments characterized by saltwater, high humidity, and fluctuating pressures.

Besides power consumption, other important factors in the equipment are size and weight. Smaller size and lighter weight would involve ease of deployment and handling, particularly when the measurement needs to be done from a small boat or floating platform. Low power consumption would mean longer operational time without frequent battery replacements or external power sources.

Another important factor is the cost. It must be reasonably affordable in order to enable large-scale measurements. One highly suitable material for the casing of ADCP current profiler is the alloy of titanium. The alloy of titanium has many advantages. It is immensely strong and durable, capable of withstanding the corrosive effects of saltwater. It also has comparatively low density, which helps keep the overall weight of the device down. In addition, the excellent thermal properties could be useful in the extreme conditions of temperature found sometimes in the marine environment.

3.3 How to Choose the right equipment for current measurement?

The following are the aspects to be considered in choosing the appropriate equipment for measuring coastal currents at Ho Chi Minh City. First, there is the mode of deployment. In regard to deployment, there exist different types of ADCP doppler.

In providing measurements from a ship, a ship-borne ADCP is appropriate. This can be installed on the hull of the ship and deliver continuous measurement as the ship moves through the water.

If the measurement is from the seabed, then the bottom-mounted or sit-on-bottom ADCP should be used. This ADCP flow meter rests on the seabed and measures currents passing above it.

For the application involving the usage of a floating platform, one may use a buoy-mounted ADCP meter. It can be installed on a buoy and measure currents in the surrounding water.

Besides the mode of deployment, the ADCP profiler frequency also must be selected as a function of the water depth. For depth ranges up to 70 meters, the frequency of 600 kHz ADCP is quite suitable, as it provides high-resolution measurements. A 300 kHz ADCP is more appropriate for water depths ranging from 70 to 110 meters. In the case of even deeper waters, such as up to 1000 meters, a 75 kHz ADCP offers the added advantage of deeper water penetration in order for proper current measurements.

For instance, there are quite a few well-known ADCP brands in the market, including Teledyne RDI, Nortek, and Sontek. However, China Sonar PandaADCP remains the best choice for its value. It has very good quality and is processed with all-titanium alloy material, hence durable and dependable in ocean environments. Besides, it has an incredibly good 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.