How to measure the coastal currents of Da Nang?

1. Where is Da Nang?

Da Nang is a crowded and attractive seaside city in the central area of Vietnam. It is situated with the Truong Son Mountain Range to the west, the South China Sea to the east, and a beautiful scenery of mountains meeting the sea.

Geographically, it enjoys a premier location on the coastline of the South China Sea. It is a city whose coastline stretches over a distance with continuous sandy beaches, which are renowned for their pristine beauty. Some of the popular beaches in Vietnam, such as My Khe Beach, lie here and house many tourists across the globe.

In human respects, Da Nang has a rich history and a very diversified population. Centuries of an important trading port left its cultural imprints reflecting a number of different civilizations-from Chinese to French and Vietnamese. Local people are famous for their hospitality and entrepreneurial spirit. In the last years, the town grew as one of the most important tourist destinations, with a well-developing hospitality and service industry.

The waters off Da Nang form part of the large, dynamic marine ecosystem of the South China Sea. Indeed, the sea offers a marvellous diversity of marine life, including many types of multicoloured fish, coral reefs, and different types of shellfish. Its waters are affected by the monsoon climate with pronounced wet and dry seasons that impact conditions within the sea and coastal currents.

2. What condition do the coastal currents face around Da Nang?

The general nature of the coastal currents around Da Nang is contributed by several factors. First, there is the effect caused by the tidal current. The tides are the targets of gravitational pull by the moon and the sun, which results in ebbs and flows. This will lead to the advancement of the currents, which are often variable, while the strengths and directions depend on the lunar cycle and the local topography.

Monsoon winds are also a very influencing agent in this case. In the wet monsoon period, it can be strong winds blowing from the southwest, which might act like an agent of pushing the surface waters to allow the currents to flow in a particular direction. While during the dry season, the winds blowing from the northeast can determine different flow.

The topography of the seabed near Da Nang also influences the coastal currents. Its shape and depth might accelerate or decelerate it in some places. For instance, shallower depths may reveal stronger currents where water is forced to go through a narrower channel.

Differences in temperature within the water could also create currents. Warmer water near the surface may be replaced by cooler water from deeper layers as it rises, developing a vertical circulation that can influence the overall flow of the coastal currents.

3. How to Observe the Coastal Water Flow of Da Nang?

In the Da Nang coastal currents, it has certain peculiar characteristics relating to its velocity and flow rate. The velocity remains relatively low in some areas that are really calm, although it tends to be quite fast in areas where the currents may be constricted or strongly influenced by winds or tides. Its flow rate is determined by the volume of water that passes through a given area per unit time.

To measure these currents along coastlines accurately, advanced and convenient methods are needed. One of such advanced and highly effective ways is using Acoustic Doppler Current Profiler(ADCP) The ADCP profiler have been revolutionary in measuring the water current because it can give detailed and continuous data on the flow of water at varied depths.

3.1 Working of ADCPs based on the principle of Doppler

The operating principle of ADCP profiler relies on the Doppler principle. They send acoustic signals into the water. As these acoustic waves encounter moving particles within the water-like sediment grains or small organisms, the frequency of the reflected waves changes. This frequency shift is proportional to the velocity of the moving particles and, by extension, the flow velocity itself.

ADCP meter make it possible to determine the velocity of water in three dimensions by sending out several acoustic beams at different angles. The sensors can measure not only the horizontal but also the vertical components of flow velocity, thus giving a complete understanding of the water flow structure. Data logged is post-processed and analyzed for information on coastal currents.

3.2 What is necessary to perform high-quality measurement of Da Nang coastal currents?

Basically, while implementing high-quality measurement of the coastal currents around Da Nang, several aspects should be considered in reference to equipment. First and foremost, the reliability of the material of equipment stands paramount. The device should be resistant to harsh conditions in a marine environment because it could face exposition to salt water, high humidity, and variable pressures.

The other important aspects are the size and weight of the equipment and the power consumption. Smaller size and lighter weight make its deployment and handling easier, particularly under conditions when the measurement has to be made from a small boat or floating platform. Low power consumption is a must to enable the equipment to operate for extended periods without frequent replacement of batteries or getting power from external sources.

Cost is also an important issue. For large-scale measurement, the equipment should be inexpensive. One material highly suitable for the casing of ADCP flow meter is titanium alloy. There are a number of reasons that can be identified as to why the use of titanium alloy is so advantageous. First of all, it is tremendously strong and resilient, able to resist the corrosive effects of saltwater. Its density is also relatively low, helping to keep the overall weight of the device down. Besides that, it has great thermal properties that might favor the sometimes extreme temperature conditions of marine media.

3.3 How to Choose the right equipment for current measurement?

Several factors should, therefore, be put into consideration when selecting the appropriate equipment for measuring the coastal currents of Da Nang. First to be considered is the mode of deployment. Depending on how they are deployed, there are different types of ADCP doppler available.

An ADCP current profiler can be used for making measurements from a ship. An ADCP installed on the hull of a ship has the capability to give continuous measurements while the ship is in motion through the water.

If the measurement is to be made from the seabed, it is better to use a bottom-mounted or sit-on-bottom ADCP. This kind of ADCP current meter will sit on the seabed and measure currents that pass above it.

In applications with floating platforms, ADCP mounted on a buoy is the way to go. It can be attached to a buoy and measure the currents in the water surrounding it.

Besides the mode of deployment, the frequency of the ADCP too has got to be selected based on the water depth. Whereas a 600 kHz ADCP can be quite all right for water up to a depth of about 70 m because it offers fairly high-resolution measurements, for the case where the depth extends beyond 70 to as high as 110 m, a 300 kHz ADCP would best be suitable. And in the case of deeper waters, say starting from 1000 meters going downwards, a 75 kHz ADCP is the most desirable since it will be in a position to penetrate quite deeper into the water to measure currents quite effectively.

The famous brands of ADCP current on the market are Teledyne RDI, Nortek, and Sontek. But if you want to have excellent quality with a cost-effective price, then there is China Sonar PandaADCP. All of its alloy materials were made from all-titanium alloy, which means that it can last really long and be reliable in a marine atmosphere. Moreover, it has a tremendous cost-to-performance ratio. For further information, you are welcome to enter their official website: https://china-sonar.com/.

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