How to measure the Coastal Currents of Yeosu?

1. Where is Yeosu?

Yeosu is a city in South Jeolla Province, South Korea. It is a coastal city situated along the southern coast of the Korean Peninsula, facing the South Sea (Korea Strait). Yeosu is known for its magnificent natural beauty, which boasts a long, indented coastline with numerous bays, islands, and peninsulas.

The landscape of this city is in perfect harmony between sea and land. With a number of beaches, like Odongdo Beach, it is a beach paradise for many tourists. Being abundant in maritime history, there is also a well brisked port which plays an important role in trade and fishing. Many locals are into different trades: fishing, shipbuilding, and tourism. Yeosu is also very famous for its seafood; therefore, a wide variety of fresh fish and shellfish characterizes the local cuisine.

The South Sea off Yeosu is a warm water sea with a rich marine ecosystem. It is a home to a variety of fish, including mackerel, tuna, and anchovy. Its coastal waters are a habitat for extensive beds of seaweed and other marine plants. The sea has a great influence on the local climate, carrying in warm and humid air and moderating the temperature.

2. What is the status of the coastal currents around Yeosu?

The coastal currents of Yeosu are caused by a combination of factors. The Tsushima Current is the dominant ocean current, generally in warm water that moves north through the Korea Strait. The current conveys warm, nutrient rich waters with highly significant contributions to the marine ecosystem in this region and within the current in the coastlines.

Other important factors are tidal currents. Yeosu has a high tidal range, and due to the ebb and flow of the tides, complex current patterns arise. The shape of the coastline and underwater topography is also very important. Bays, islands, and underwater ridges can make the currents change direction and speed. Besides, wind patterns, especially seasonal winds, might force surface currents or mix layers of water.

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

Surface Drifting Buoy Method: One of the most common methods for observing surface current is a surface drifting buoy. This buoy would be released in the water, and then the movement is tracked over a certain period of time using GPS or another tracking system. This method, however, also has a lot of restrictions. It only gives information about the surface current and can be influenced by wind and waves. For example, if a strong wind happens to blow the buoy in a different direction than where the actual current is going, it could result in wrong measurements with regards to direction and speed.

Anchor Boat Method: For measuring the current, an anchored boat can be used. Different instruments are lowered from the anchored boat into the water for recording the current at various depth levels. While this provides more detailed measurements depth wise, it again has its drawbacks. One major disadvantage is that the measurement area is restricted to one fixed position of the boat that may not capture the variability of the currents in a large coastal area.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP profiler method is an advanced and efficient way of measuring the coastal currents. 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. They are less affected by surface disturbances and can operate continuously for long periods, giving a more accurate picture of the current structure.

4. How do ADCPs using the Doppler principle work?

ADCPs depend on the Doppler principle. They emit high frequency acoustic pulses into the water. Whenever these pulses interact with moving water particles, it results in the change in frequency of the reflected pulses. If the water particles move towards the ADCP meter, they return a signal with a frequency higher than what was emitted by the device. If moving away, they return lower.

Multiple transducers fitted on the ADCP flow meter send and receive signals at different angles. By analyzing the Doppler shifts from different directions and at different depths, the device is able to calculate the three dimensional velocity of the water that is, the horizontal and vertical components of the velocity, hence giving a very good understanding of the current structure and behavior.

5. What is required for high quality measurement of Yeosu coastal currents?

For high quality measurement of the coastal currents near Yeosu, equipment reliability must be based on good materials. The marine environment includes saltwater, a potential exposure to storms, and the influence of tides; it needs a strong casing. It should be of a compact size to ensure that the deployment and recovery processes are easy, particularly because of the complex coastline with its bays and islands.

A lightweight design is preferred because it makes the equipment more manageable during installation and maintenance. Low power consumption is necessary for long term and autonomous operation. Cost effectiveness is also a requirement to enable large scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is very important to resist the corrosive action of seawater. Besides, it is strong and durable to bear the pressure of water at different depths. Its lightweight nature makes it more convenient for various deployment methods.

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

Equipment selection for current measurement at Yeosu shall be selected in terms of purpose of use: For vessels that navigate or are involved in short term research, ship mounted ADCPs would be the proper option, as they could provide real time current information on a voyage.

For the measurement near the seabed, such as in studying sediment transport or benthic ecology, a bottom mounted ADCP is preferred. It can capture the details of the near bottom current. If long term and wide area monitoring of the coastal current is required, a buoy type ADCP current profiler is ideal.

For the water depths up to 70m, a 600kHz ADCP is quite adequate. If the depth is up to 110m, then 300kHz would be more appropriate, and for deeper waters those that might be near Yeosu, for instance, with a depth exceeding 1000m, then 75kHz is recommended.

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.