How can the coastal currents of Zhangzhou be measured?

1. Where is Zhangzhou?

Zhangzhou is a captivating city in southeastern Fujian Province, China. Being at sea, it enjoys a privileged position regarding its location, with an exceptionally handsome coastal physiography.

This city is with a lot of natural beauty. On the east, this city was bordered with Taiwan Strait, therefore it has an extended and curvy coastline. The waters of the Taiwan Strait are an integral part of Zhangzhou City's definition: it provides not only a source of livelihood through fishing and marine-related industries but also a place of natural wonder.

Zhangzhou boasts a pleasant subtropical monsoon climate with mild temperatures throughout the year and plentiful rainfall. Such a condition has brought up a richly variegated ecosystem, housing most tropical and subtropical plants. Cultural heritage is also comparatively rich, with the city's history reaching as far back as hundreds of years ago. The native people here have their particular way of life, which unites traditional fishing and farmers' cultures.

The sandy beaches and rocky shores form a beautiful coastline for Zhangzhou. Added to this are small coves, which all combine to create a haven for tourists seeking fun in the sun, sea, and sand. Off its coast lie a few islands and islets, further enhancing its beauty. Certain islands harbor special wildlife and give opportunities to observe and study nature for eco-tourism.

2. What are the conditions of the coastal currents around Zhangzhou?

Various processes might influence the coastal currents of Zhangzhou. The winds of monsoon origin are the first factor contributing to it. During the summer months, the southeast monsoon blows with a flow of warm and moist air. This might act on the surface waters and alter the direction and strength of the coastal currents. During winter, it is the turn of the northwest monsoon that changes the pattern of the current.

Topography is also very important from that aspect, of the seafloor. It can produce changes not just in speed but also in direction. Features on the ocean floor like underwater ridges, valleys, and shallows might create eddies, areas of convergence or divergence, which consequently would also influence the flow of the currents along the coast.

Other contributing factors include tides. Because of the periodic rise and fall of the tides in the Taiwan Strait, it has wild fluctuations in coastal currents. In some places, tidal currents are pretty strong and thus control navigation and marine organisms' distribution, especially around estuaries and narrow channels.

The proximity to the open ocean and the interaction with the larger-scale ocean currents in the South China Sea and the East China Sea are also influencing the coastal currents near Zhangzhou. In such a case, this larger oceanic circulation can bring in water masses of different temperatures and salinity levels, further modifying the dynamics of local currents.

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

Precise measurements of the Zhangzhou coastal currents are of great importance for at least three purposes: marine resource utilization, coast protection, and the study of the local marine ecosystem. Whereas in the past measurements of coastal currents by surface buoys and series of fixed current meters have been performed, several advanced techniques are available nowadays.

One of these sophisticated approaches involves Acoustic Doppler Current Profilers or ADCP current meter. The ADCP current profiler are very efficient in measuring the velocity and direction of the coastal currents at various depths.

3.1 How does the application of the Doppler principle work in ADCP?

Acoustic Doppler Current Profiler(ADCP) rely on the principle of the Doppler effect. These instruments transmit sound waves into the water at a known frequency. When the sound waves run into moving particles in the water, such as sediment or small organisms, the frequency of the waves that bounce back changes. This change in frequency is directly proportional to the velocity of the particles and thus the current.

Through the processing of the Doppler shift in the returned sound waves, it becomes possible for an ADCP doppler to find out the current speed and direction for various depths. A single transducer array, part of an ADCP profiler, sends and receives sound waves in several directions in such a way that the three-dimensional measurement of the current is taken. 

3.2 What is necessary to obtain high-quality Zhangzhou coastal currents measurement?

In trying to obtain quality measurements of the coastal currents in Zhangzhou, there are several factors that have to be put into consideration. First, there is the aspect of equipment reliability. The ADCP meter should be made with materials that can resist the harsh marine environment.

Titanium alloy is one of the most appropriate materials for making ADCP profiler casings. There are several advantages accrued to the use of this material for the casings of ADCP. First, it is highly resistant to corrosion due to the salty nature of sea water along the coast. It resists seawater and marine organisms' chemical aggressiveness, hence it allows the equipment to work for a long time. The second reason is that the titanium alloy is resistant yet lightweight. While its strength is able to resist such physical stress in the ocean environment, its light weight makes manipulation and installation easy, especially when the situation demands the installation of equipment in hard-to-reach areas.

Apart from material quality, the other features are small in size, low weight, low power consumption, and at a low cost. A small and lightweight ADCP is easier to be carried and deployed; thus, it measures more places. Low power consumption can enable it to operate longer without replacing batteries or a large power supply. Cost-effectiveness for large-scale deployment will enable more general monitoring of the coastal area.

3.3 How to Choose the right equipment for current measurement?

Selection of appropriate equipment for the measurement of the coastal currents in Zhangzhou would depend on many aspects. The first and foremost thing to be considered is the purpose for which the equipment is to be used.

This would apply to measurements from a moving vessel. A ship-mounted ADCP would, therefore, be applicable in such a case. It gives real-time current data as the ship moves along the coast and, therefore, enables continuous surveying of the current conditions.

If the measurement required is at a certain position on the seabed, then it is your choice of bottom-mounted ADCP. A bottom-mounted unit can be installed in a fixed point and provide long-term stable measurements of current at that particular point.

An ADCP buoy is suited to open water applications or where fixed installations are not possible. It has measurement of current over a greater area with wireless data transmission.

Frequency Selection: Varying depths of water require the use of different frequencies. For up to 70 m of water depth, a 600 kHz ADCP will normally suffice, from 70 to 110 m depth, a 300 kHz ADCP is preferred, while for deeper water applications up to 1000 m, a 75 kHz ADCP would be more relevant.

The popular brands of ADCP on the international scene include Teledyne RDI, Nortek, and Sontek. However, if one is seeking a good alternative that is cost-effective and yet quality, then the China Sonar PandaADCP is what that investigation will bear out. It is a device made wholly out of titanium alloy; thus, this ADCP guarantees durability and reliability with an excellent price-to-value ratio. You can find more information about it at https://china-sonar.com.

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