How can we measure the Incheon Coastal Currents?

1. Where is Incheon?

Incheon is one of the major cities of South Korea and is situated in the northwest of the country, being a coastal city that overlooks the Yellow Sea. It is well renowned for its strategic importance as a port city and for playing a major role in international trade and transportation.

The cityscape of Incheon is both modern and full of nature. It has a big and busy port, one of the busiest in Asia. The facilities in the port handle a lot of cargo, from containers to bulk cargo and many industrial products. Besides the port, there are beautiful beaches and coastal parks in Incheon. The local people of Incheon are involved in a wide range of activities, such as shipping, fishing, and tourism.

The Yellow Sea close to Incheon is considered a semi enclosed sea, quite shallow in a lot of parts with its peculiar marine life. A large population consists of fish such as flatfish, anchovies, and small sharks, extensive beds of seaweed, and shellfish. These extreme changes in water levels largely define the tides around Incheon. The tidal range is quite big, and the ebb and flow of the tides affect the local environment and the behavior of the coastal currents.

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

The coastal currents around the city of Incheon are also influenced by many factors. Tidally induced currents are one of the major forces. Because of the Yellow Sea's great tidal rise, the water moves out of and into the coasts rhythmically. The fall and rise of the sea level due to tides create very complicated current systems.

The shape of the coastline and the underwater topography also play a crucial role. In the coastline of Incheon, there are bays, estuaries, and channels. The underwater sandbars and shoals, along with these features, may cause the currents to diverge, converge, or even form eddies. Inflow from rivers and other freshwater sources can also influence the salinity and density of the coastal waters, affecting the current flow. Besides, the wind patterns, especially the seasonal winds from the northwest and southeast, may drive the surface currents and affect the mixing of different layers of water.

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

Surface Drifting Buoy Method: A surface drifting buoy can be released into the water to observe the surface current. The movement of the buoy is followed for a certain amount of time using a GPS or other tracking systems. However, this method also has some limitations. This can only give information of the surface current and may be affected by wind and waves. For instance, if a strong wind sends the buoy in a direction different from the actual current, it will result in error measurements of the direction and speed of the current.

Anchor Boat Method: In this, the current can be measured by an anchored boat. Instruments are lowered from it in the water at different depths to measure the current. While this allows more detailed depth wise measurements, it also has drawbacks. The fixed position of a boat restricts the area of measurement, and it may not capture the full variability of the currents in a large coastal area.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP current meter is a more sophisticated and efficient technique for measuring coastal currents. The ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals to calculate the velocity of water at different depths. This provides a more comprehensive profile of the current from the surface to the seabed. Because ADCPs are less affected by surface disturbances, they can operate continuously for long periods and give a more accurate picture of the current structure.

4. How do ADCPs using the Doppler principle work?

These instruments use the principle of the Doppler effect. ADCPs send out high frequency acoustic pulses in the water. The frequency changes when these pulses reflect off the moving water particles. In the case of movement of water particles towards the transducer, the reflected signal has a higher frequency compared with the emitted one, whereas if they are moving away from the transducer, the frequency is lower.

The ADCP current profiler has a set of multiple transducers that transmit and receive signals at different angles. By analyzing the Doppler shifts coming from different directions and different depths, the device will be able to calculate the three dimensional velocity of the water. That means it calculates the horizontal and vertical components of the velocity, allowing detailed insight into the structure and behavior of the current.

5. What's required for the high quality measurement of Incheon coastal currents?

Measurements for high quality coastal currents at Incheon require equipment possessing good, reliable materials. If operated on saltwater, with much exposure to storms and under the influence of tides and river inflows, there has to be a casing. The size of the equipment also must be small in size so that deployment and retrieval operations can be easily carried out, particularly over this unique coastal topography characterized by so many ports, bays, and channels.

A lightweight design is preferable as it makes the equipment more manageable during installation and maintenance. Low power consumption is crucial for long term and autonomous operation. Cost effectiveness is also important to enable large scale measurements.

The casing of ADCPs shall preferably be of Titanium alloy. Because it offers an outstandingly high degree of resistance against corrosion, which is quite critical with sea water's exposure, the alloy is quite robust to resist water pressure at respective levels of depth, besides its light mass that can enable convenient manipulations with several methods.

6. How to Choose the right equipment for current measurement?

When choosing equipment for current measurement near Incheon, the purpose of use has to be considered first. If it is for the navigation of a vessel or short term research, then a ship mounted ADCP flow meter will be a good option. It gives real time current information during the voyage.

For measurements near the seabed, such as the study of sediment transport or benthic ecology, a bottom mounted ADCP is preferable. It captures the details of the near bottom current. If one intends to conduct long term, wide area monitoring of coastal currents, then a buoy type ADCP current profiler would be ideal.

In the light of ADCPs frequency, ADCP with a 600 kHz frequency would serve better in a depth up to 70 m. In this way, an ADCP operating on a 300 kHz frequency could apply for a water body as deep as 110 meters, and a 75 kHz version for depths well above 1000 meters.

There are well known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth considering. It is made of all titanium alloy material and offers an excellent cost performance ratio. You can find more information on their website: https://china-sonar.com/.

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