How do we measure the coastal currents of Putian?

1. Where is Putian?

Putian, with its charm, is nestled in Fujian Province, China, and faces an equally strikingly beautiful coastline. This happens to be one of those places where the beauty of nature and cultural heritage go hand in glove.

Geographically, Putian is strategically located along the southeastern coastline, having a coastline that borders the Taiwan Strait and presents magnificent scenes of blue ocean waters. The climate within this city is mild and subtropical, with warm temperatures throughout the year, accompanied by substantial rainfall amounts.

Putian is enriched with cultural traditions. Local people are proud of their unique heritage combined with traditional Chinese culture and local folks' customs. Equally famous, the city is also famous for religious sites such as the Meizhou Island Mazu Temple, which is very famous among pilgrims from around the world.

There are several important water areas around Putian. To the east, the Taiwan Strait is an important shipping route with rich marine resources. The strait currents and tides have a great effect on the shaping of the local marine environment.

The shoreline consists of sandy beaches, rocky cliffs, and small islands. Such features create an environment for the development of tourism or outdoor activities. Ports and harbors present a scene of heavy action and economic endeavor in trade and transport at large.

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

The coastal currents around Putian are influenced by a myriad of factors: first, the influence of the monsoon climate predominates. In summer, the general circulation of air is from the southeast, carrying a lot of warmth and moisture which may affect the direction and strength of the coastal currents. During winter, the general weather condition is made up of a northwest monsoon.

The bottom relief also plays a decisive role. An uneven seafloor, to say the least, with so many depths and contours, is an additional cause for variation in flow. Where the trenches are deep and submarine canyons are plenty, the currents are more powerful; where it is shallow, the flow can be slower.

Other factors would include tides. Due to the regular rise and fall of tides in the Taiwan Strait, water is pushed in and out of the coastal areas of Putian, thereby creating tidal currents. These might have a great impact on shipping, fishing, and other marine activities.

Further, human activities like dredging, construction of ports and harbors, and discharge of pollutants will also impact the coastal currents of a region. All these activities will definitely change the flow of the water and impact the sensitive balance of the marine ecosystem.

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

It is urgent to measure the coastal current in Putian for marine environment description and the safety of shipping and other activities. Traditional measuring methods have been used for many years, including buoy, drifter, and current meter. However, there are some disadvantages of these methods in the aspects of accuracy and coverage.

Recently, it has become possible to conduct more effective and accessible measurement of coastal currents using ADCP current meter. The Doppler effect principle has been applied in ADCP current profiler for measuring the velocity of water flow.

3.1 Principle of ADCP using the Doppler effect

The Acoustic Doppler Current Profiler(ADCP) emit sound waves into the water. Particles within the water, such as suspended sediment or small organisms, reflect these sound waves. Due to the movement of these particles, the frequency of the reflected sound waves is shifted, which has a relation with the velocity of the water flow. It would be possible to get, from the frequency shift analysis, the speed and direction of the current at different depths.

The ADCP current are commonly of the transducer array that may be mounted on a vessel, a buoy, or fixed structure. The transducer array sends and receives sound waves in various directions to make three-dimensional measurements of current.

3.2 What's needed for high-quality measurement of Putian coastal currents?

For the correct measurement of the coastal currents in Putian, a number of factors have to be taken into consideration. First, there is the question of the reliability of the equipment itself. The ADCP doppler needs to be made from materials that are resistant to the harsh marine conditions.

The material composition of titanium alloy would be ideal for ADCP flow meter ​casings, since it resists corrosion at a very good rate, is solid yet light. It would also resist the corrosive action of salt water and marine organisms and would continue for a long period. With its strength and light weight, it would easily be manipulated and installed.

Besides material reliability, other factors that are important include small size, low weight, low power consumption, and low cost. Small and lightweight ADCP meter is more easily deployed and may be used in more applications. Low power consumption permits operation for a longer life on battery or alternative power, such as solar panel power. Low cost enables deployment of more ADCP to achieve widespread coverage of a coastal area.

3.3 How to Choose the right equipment for current measurement?

Several factors have to be put into consideration in choosing the right ADCP profiler to measure Putian currents. First and foremost, there is a need to consider the intended application of the equipment. For instance, if the measurement is to be carried out from a vessel, there is a probability that a ship-mounted ADCP will be the best option. Ship-mounted ADCP can deliver real-time data of the current a vessel moves through the water.

The ADCP would suit for mounting on the bottom of the seabed if the measurement needs to be conducted at a fixed location. By using bottom-mounted ADCP, long-term measurements of the current can be acquired without every-day maintenance.

When the measurement is supposed to go in open water, the ADCP should be mounted on a buoy. Buoy-mounted ADCP are capable of providing data on the current over a wide area.

Another important aspect is the frequency of the ADCP itself, whereby different frequencies suit different water depths. Shallow waters up to 70 meters normally require a 600 kHz ADCP. In deeper ones, say up to 110 meters, a 300 kHz ADCP may be in order. The most adequate for waters as deep as up to 1000 meters is typically 75 kHz ADCP.

The selection of an ADCP brand could be from renowned Teledyne RDI, Nortek, or Sontek. However, a highly cost-effective option with high quality is the China Sonar PandaADCP. The all-titanium alloy used in the manufacture provides excellent durability and reliability for this series. Advanced in technology and competitive pricing enables an incredible value for money. For more information about the China Sonar PandaADCP, please visit: https://china-sonar.com.

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