How to measure the coastal currents of Tianjin?

1. Where is Tianjin?

Tianjin is a major municipality in north China, directly abutting the coast of the Bohai Sea. The city serves as one of the most integral economic centres, transportation hubs, and hosts rich history and multi-culture.

Tianjin has a warm-temperate continental monsoon climate: hot and humid summers, cold and dry winters. In Tianjin, many rivers cross the city, and a coastal position predetermines the role of trade and shipping. There is a lot of ports, estuaries, and tidal flats on the Tianjin coastline.

The Bohai Sea is the most important part of Tianjin's maritime activities, situated right beside it. The sea floor topography is rather complicated around Tianjin, because in several places very near the shore, the water is shallow, like in estuaries and tidal flats, while it is pretty deep a little further away from the coast. Factors affecting the waters include river discharges, tides, and oceanic currents from the Bohai Sea.

2. What is the state of the coastal currents near Tianjin?

The coastal currents near Tianjin are influenced by many factors. First, there is the effect brought about by the monsoon climate. For instance, during summer, the southeast monsoon is able to drive the surface waters, influencing the direction and strength of the coastal currents. During winter, the northwest monsoon does alter the current patterns.

The contribution of river discharges, especially the Haihe River, is not negligible. The freshwater and sediment outflows may develop complex current patterns, generally induced by differences in density between the river water and seawater. Estuarine circulation can bring about an interaction between river and sea that may influence the distribution of sediments and nutrients.

The topography of the sea floor is another major factor. Underwater ridges, troughs, and shoals deflect the water in different directions and at different speeds. Relatively slow-moving currents might show in shallow areas, such as tidal flats, while stronger and more complex flows are possible in deeper regions.

Tides are another important factor. The Bohai Sea has regular tides; thus, big tidal currents may form due to its features. Tidal currents around the estuary and in the narrow channel may reach a very high value. They provide a very essential role in the transportation of sediments, nutrients, and marine organisms and influence coastal erosion and sediment deposition processes.

Besides, it is also modified by interaction with the larger-scale ocean currents from the Bohai Sea and other adjacent regions. The additional impact of these oceanic currents could bring in water masses with different temperatures and salinity levels, affecting the local dynamics of currents.

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

The accurate measurement of the coastal currents in Tianjin makes the sea safe for marine usages such as port operations and fishery management. Besides, it contributes to environmental protection. Conventionally, observations were performed by buoy and current meters. However, these observation methods are limited by poor accuracy and low area coverage.

Acoustic Doppler Current Profiler(ADCP) is a more advanced and convenient way of making the measurements. ADCP profiler measure the velocity of water flow using the Doppler principle.

3.1 Working of ADCPs Using Doppler Principle

ADCP meter transmit sound waves into the water column. The transmitted sound waves scatter off moving particles in the water, such as suspended sediments and small organisms. Due to the movement of these particles, the frequency of the returned sound waves is shifted. The frequency shift is proportional to the water velocity.

The transducer array of ADCP flow meter emits and receives sound waves in multiple different directions. By analyzing multiple directional frequency shifts of the reflected waves, the ADCP doppler can calculate speed and direction at different depths of the current. This gives three-dimensional information on the current structure.

3.2 What is necessary for the high-quality measurement of Tianjin coastal currents?

Different factors have to be put into consideration in the measurement of the coastal currents in Tianjin in high quality. The equipment used has to be highly reliable. The ADCP current profiler, therefore, has to be made of materials that can withstand the harsh marine environment.

Titanium alloy is thus a very good material used in making the casings of ADCP current meter. These are highly corrosion-resistant, something which is of importance at the salt-water environment of the coast. It is resistant to the corrosive effects of seawater and marine organisms, which could be very deleterious and may affect the performance of equipment in the long run. Besides strength in corrosion resistance, the alloying of titanium is both strong yet light. Its strength is sufficient to bear physical stresses in the marine environment, while the light weight makes handling and installation of parts lighter.

Besides material reliability, other characteristics such as small size, low weight, low power consumption, and low cost are welcome. A compact and lightweight ADCP current is much easier to handle during transport and deployment; consequently, measurements can be performed in a more diversified range of places. Low power consumption allows longer operation without frequent battery replacement or a large power supply. The cost-effectiveness allows it to be deployed in large scales which in turn provides more comprehensive monitoring of the coastal area.

3.3 How to Choose the right equipment for current measurement?

In choosing the appropriate equipment for the measurement of the coastal currents in Tianjin, several factors have to be taken into consideration. The intended use of the equipment is a key factor:.

In this regard, measurements from a vessel in motion would be better provided by the ADCP mounted on a ship. It would provide real-time data on the current as the vessel moves down the coast and thus would monitor the current conditions.

If the measurement is to be carried out at a fixed point on the seabed, a bottom-mounted ADCP shall be applied. This can be installed at a defined position and yield stable, long-term measurements of the current at the point in question.

An ADCP fixed on a buoy is applied when the location of operation is in open water or in places where a fixed installation might be impracticable. In an ADCP mounted on a buoy, measurement of current over a larger area is measured and wirelessly transmits the data.

As to the choice of frequency, different frequencies apply for different water depths. In general, a 600 kHz ADCP will suffice for water as deep as 70 meters, while the 300 kHz would be better for a depth of 70 to 110 meters. To go deeper, up to 1000 meters, the 75 kHz is the one which has to 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 ChinaSonar 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.