How do we measure the coastal currents of Zhoushan?

1. Where is Zhoushan?

Zhoushan is a particular archipelago city in the People's Republic of China, Zhejiang Province, and it lies in the East China Sea. It represents a wide variety of islands because it is a unique geographic entity.

Zhoushan has a subtropical monsoon climate with a hot and humid summer, while winters are warm. Such rainfall and pleasant climate provide abundant flora and fauna within the area. On each island, there are a lot of lush vegetations such as forests and grasslands that add to the charm of nature of the place.

Geographically, the location of the city in the East China Sea simply means that it acts as the focused hub for aquatic activities. Native people of this area have an attachment with the sea since fishing and shipping have been a part of their lives for centuries. Zhoushan is also famous for its port economy with its ports acting significantly in domestic and international trade.

The sea area surrounding Zhoushan is complicated, with a number of sea channels and bays. The bottom topography is varied with underwater ridges, shoals, and troughs. In addition to determining the distribution of marine resources, these features control the flow of water. The islands themselves take part in influencing the coastal currents as water is deflected and channeled around them.

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

Many factors shape the coastal currents around Zhoushan. The leading influence is that of the monsoon winds, which is very great. During summer, this southeast monsoon brings warm and moist air into the area, which may advance the surface waters and, in turn, alter the direction and strength of the coastal currents. During Winter, the Northwest Monsoon Alters Current Patterns.

One important factor is topography of the seabed. Often, underwater ridges and troughs can act in steering the water in different directions at different speeds. The shallow water areas, like shoals, can result in slow-moving currents, while deeper troughs may have stronger and more complicated flows.

However, tides also play an important role. The East China Sea experiences tidal rise and fall, which may create strong tidal currents. Generally speaking, the extreme strength of tidal currents manifests around narrow channels between islands and estuaries. They are fairly important in sediment transportation, nutrients, and marine organisms, all of which directly affect the marine ecosystem and coastal geology.

Besides, the interaction with larger-scale ocean currents from the Taiwan Strait and elsewhere might also alter the coastal currents off Zhoushan. Such oceanic currents can also bring in water masses with different temperatures and salinity that further influence the local dynamics of the current.

3. How to Observe the Coastal Water Flow of Zhoushan?

It goes without saying that the precise measurement of coastal currents at Zhoushan has much to offer in serving a number of needs related to human activities: marine safety, management of fisheries, and scientific studies. Until recently, techniques that use buoys and current meters have been the popular ones. Traditional techniques, on the other hand, have serious drawbacks when considering their accuracy and extent of coverage.

Since the invention of the acoustic doppler flow meter, which is more advanced and convenient for measuring coastal currents, many other types of current meters have fallen out of use. ADCPs based on the Doppler principle are able to measure water flow velocity.

3.1 How do ADCPs using the Doppler principle work?​

The principle behind an Acoustic Doppler Current Profiler(ADCP) is that it first emits sound waves into the water. These sound waves scatter off the moving particles in water, like suspended sediments and small organisms. In the process, these particles shift the frequency of reflected sound waves due to their movement in water. This frequency shift is proportional to the velocity of the water current.

The ADCP current profiler emits and receives sound waves from a transducer array in several directions. The reflected waves from multiple directions can thus be analyzed for frequency shifts by the ADCP flow meter to compute the current's speed and direction at various depths. This enables the reconstruction of the three-dimensional structure of currents.

3.2 What is required for high-quality measurement of Zhoushan coastal currents?

Equipment reliability is the first and foremost thing that has to be considered in measuring the coastal currents of Zhoushan for high quality. The ADCP meter must be manufactured with materials that will help it overcome the unfriendly marine environment .

Titanium alloy is a very good material for making the casing of the ADCP profiler. This is highly corrosion-resistant; hence, suitable in the salt-water environment of the coast. The material resists seawater and marine organism corrosion performance for a long period, hence allowing good equipment performance. Titanium alloy is also solid yet lightweight. The strength allows it to undergo the physical stresses present within the marine environment, while the lightweight allows for easy manipulation and installation.

These characteristics include small size and light weight, low power consumption, and low cost, in addition to material reliability. A compact and lightweight ADCP current meter is therefore more convenient to carry and deploy, allowing measurements in a greater number of locations than might otherwise be possible. Low power consumption allows the ADCP to operate for longer without the need for frequent battery replacement or large power supplies. Cost-effectiveness is vital for large-scale deployment and will also enable the monitoring of the coastal area in greater detail.

3.3 How to Choose the right equipment for current measurement?

Selection of proper equipment for measurement of coastal currents in Zhoushan depends upon various factors. The intended application of the instrument is one of the key factors.

If the discharge is measured from a vessel that is in motion, the ship-mounted ADCP is ideal. Real current data can be gathered from the vessel as it moves along a coast in continuous current monitoring.

A bottom-mounted ADCP is called for when the measurement needs to be conducted from a fixed location on the seabed, installed at a point and providing long-term stable measurements in that location.

This buoy-mounted ADCP is used in open water or where a fixed installation is not practicable. This has a larger area of current measurement and can transmit data wirelessly.

Regarding the frequency to be used, different frequencies are suited for different water depths. A 600 kHz ADCP is generally suited for water depths up to 70 meters, while a 300 kHz ADCP is suited for waters between 70 to 110 meters in depth. To go even deeper-to 1000 meters in depth-a 75 kHz shall be considered.

When it comes to choosing an ADCP brand, well - known international brands such as Teledyne RDI, Nortek, and Sontek are popular options. However, for those seeking a cost - effective yet high - quality alternative, the China Sonar PandaADCP is worth considering. Made entirely of titanium alloy, it combines durability and reliability with an excellent price - performance 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.