How to measure the Coastal Currents of Goheung?

1. Where is Tongyeong?

Tongyeong is a city that falls under the South Gyeongsang Province in the nation of South Korea. Located on the southern extremity of the Korean peninsula overlooking the South Sea commonly called Korea Strait, the place is highly beautiful along its coastline and has various traces relating to its enriched maritime history.

The city is renowned for its numerous islands and islets, which are scattered like jewels across the sea. These islands not only add to the scenic charm but also play a crucial role in shaping the local marine environment. The coastline of Tongyeong is characterized by a mix of rocky shores, sandy beaches, and small coves.

The local population is very much engaged in fishing and tourism. Fishing thrives because of the great volume of marine life in its waters. Its ports are filled with fishing boats and small vessels. Besides fishing, Tongyeong is a tourist city. Its islands offer opportunities for boating, diving, and exploring unique coastal ecosystems.

The South Sea off Tongyeong is a warm water sea where many kinds of fish, including sea bream, mackerel, and anchovy, live. The sea supports wide beds of seaweed and shellfish, too. Its warm waters and rich marine resources make the local economy and food culture vibrant. It influences the local climate: during summer, sea breezes bring mild winds into this area, and during winter, it warms the temperatures.

2. What is the state of the coastal currents in front of Tongyeong?

The coastal currents of Tongyeong are influenced by many different factors. The major ocean current in the area is the Tsushima Current, a warm water current that generally flows northward through the Korea Strait. It brings in warm and nutrient rich water, which is one of the major contributors to the local marine ecosystem and influences the coastal currents.

Tidal currents are another important influence. There is quite a large tidal range at Tongyeong, and the rise and fall of the tides creates complex current patterns. First, the shape of the coastline and underwater topography are significant. Islands, channels, and shoals can cause the current to bend and change its speed. For instance, the water might flow faster through channels between islands or be deflected by a submerged shoal. Besides, the wind patterns, especially the seasonal winds, can drive surface currents and affect the mixing of different water layers.

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

Surface Drifting Buoy Method: A surface drifting buoy can be released into the water to observe the surface current. The buoy's movement is tracked over time using GPS or other tracking systems. However, this method has limitations. It only provides information about the surface current and can be affected by wind and waves. For instance, if a strong wind blows the buoy in a different direction from the actual current, it may result in incorrect measurements of the direction and speed of the current.

Anchor Boat Method: The current could be measured by an anchored boat. The instruments used to measure current are lowered into the water from the boat at various depths. Although this is more representative depth wise than the preceding method, it also presents some drawbacks. The fixed boat position limits the area that can be measured, probably not catching the full variability in a large coastal area.

ADCP Method: This is the more sophisticated and efficient way of measurement of the coastal currents. ADCPs emit an acoustic signal into the water and measure the Doppler shift of the reflected signals to calculate the velocity of the water at different depths. It yields a very comprehensive profile of the current from the surface to the seabed. Being less affected by surface disturbances, ADCPs can be used continuously over long periods, thereby giving a more realistic picture of the current structure.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They transmit high frequency acoustic pulses into the water. When these pulses interact with moving water particles, the frequency of the reflected pulses changes. If the water particles are moving towards the ADCP profiler, the frequency of the reflected signal is higher than the emitted signal; if they are moving away, it is lower.

The ADCP meter has several transducers that transmit and receive signals at different angles. Through the analysis of the Doppler shifts from various directions and at different depths, the device can compute the three dimensional velocity of the water. That means it can determine the horizontal and vertical components of the velocity, hence providing an insight into the structure and behavior of the current in great detail.

5. What will be required for good quality measurement of coastal currents around Tongyeong?

For high quality measurement of the coastal currents near Tongyeong, the equipment should be manufactured with reliable materials. Considering the marine environment, including saltwater, potential exposure to storms, and the influence of tides, a durable casing is essential. The size of the equipment should be small to enable easy deployment and retrieval, especially in view of the complex coastal landscape with its islands and coves.

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

The housing for ADCPs is preferably to be made from titanium alloy. Titanium alloy is highly resistance to corrosion, which is essential for the corrosive effects caused by seawater. Besides, it is strong, durable, and able to withstand pressures of water at different levels. Its lightweight nature makes it more convenient for various deployment methods.

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

Equipment for the measurement of current near Tongyeong shall be selected by taking into consideration the purpose of use: in case the measurement is to be utilized for a vessel's navigation or for short term research, the ship mounted ADCP flow meter shall be the suitable one, as it offers real time current information throughout the voyage.

For measurements near the seabed, as in the case of studies on sediment transport or benthic ecology, a bottom mounted ADCP is preferred. This can capture the details of the near bottom current. If one needs to monitor the coastal current over a long period and/or over a wide area, a buoy type ADCP current profiler is ideal.

Regarding the frequency of ADCPs, for water depths up to 70m, the 600kHz ADCP is an appropriate selection, while the 300kHz ADCP will be relevant for up to 110m depth. A 75kHz ADCP can be recommended for the really deep waters that might exist near Tongyeong with depth over 1000 meters or so.

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.