How to measure the Coastal Currents of Gimhae?

1. Where is Gimhae?

Gimhae is a city in the province of Gyeongsangnam-do, South Korea, and is located on the southeastern coast of the Korean Peninsula. It is a city full of historic and natural beauty.

The area surrounding Gimhae is of diverse landscapes, a long coastline with sandy beaches, tidal flats, and small fishing harbors. There are many historical and cultural sites within the city. During ancient times, Gimhae was an important center and the birthplace of the Gaya Confederacy. Ruins and artifacts from this era can still be found and attract history enthusiasts from far and wide.

Their main activities in life are fishing, farming, and other occupations. Also, with its coastal location, it means that the sea will play a major part in the local economy and in people's lives. A main river of South Korea, Nakdong River, is facing the sea near Gimhae, influencing the water condition along the coasts.

The sea off Gimhae, a part of the South Sea or Korea Strait, is a warm water body. All types of marine organisms are found, including various fish species: mullet, flounder, and anchovy. The coastal waters are host to vast beds of seaweed and shellfish. The warm waters and rich marine resources contribute to a vibrant fishing industry and also attract tourists interested in coastal activities such as beach-going and seafood tasting.

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

Multiple factors account for the variation in coastal currents around Gimhae. Major ocean currents in the area play a major role. The Korea Strait is dominated by the Tsushima Current, a warm-water current normally flowing northwards. The current brings in warm, nutrient-rich water that highly influences the local marine ecosystem and the coastal currents.

Tidal currents are also a major factor. The tidal range is quite large in the area, and the ebb and flood of the tides create very complicated current patterns. The shape of the coastline and the underwater topography are important determinants. The presence of shallow areas, such as tidal flats, and underwater channels can cause the currents to change direction and speed. Inflow from the Nakdong River affects the salinity and density of the coastal waters, which again can affect the current flow. The wind patterns, especially the seasonal winds, may drive surface currents and affect the mixing of different water layers.

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

Surface Drifting Buoy Method: A buoy, which floats on the surface and is free to drift, is deployed in the water. The motion of the buoy is followed with time by using GPS or any other tracking system. This method, however, has its own drawbacks. First, it gives information on the surface current alone and may be influenced by wind and waves. For instance, if a strong wind blows the buoy in another direction from the real current, then it results in incorrect measurement of the direction and speed of the current.

Anchor-Boat Method: Currents can be measured by an anchored boat. Instruments for measuring the current are lowered from the anchored boat into the water at different depths. While this enables more detailed depthwise measurements, it also has disadvantages. The fixed position of the 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 method is more advanced and efficient in 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. Thus, ADCPs will be less affected by surface disturbances and can run for long, continuous periods without interruption for a better depiction of current structure.

4. How does an ADCP work, using the principle of Doppler?

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

In its construction, the ADCP flow meter contains multiple transducers that send and receive signals at different angles. This device calculates the three-dimensional velocity of the water through the analysis of Doppler shifts from different directions and at different depths. By this, it means being able to determine the horizontal and vertical components of the velocity, providing a close outlook on the structure and behavior of the current.

5. What’s needed for high - quality measurement of Gimhae coastal currents?

The equipment should have reliable materials for high-quality measurement of the coastal currents at Gimhae. Given the marine environment with saltwater, potential exposure to storms, and the influence of tides, casing will be durable. The equipment size should be small, easily deployable, retrievable, and specially applicable in the complex coastal landscape with beaches, tidal flats, and harbors.

A lightweight design is preferable because it makes the equipment easier to handle during installation and maintenance. Low power consumption allows for long-term and autonomous operation. Cost-effectiveness is also necessary for enabling large-scale measurements.

The casing of ADCPs should be made from titanium alloy. Titanium alloy is a good resistant material to corrosion, which is very much essential to resist the corrosive action of seawater. It is strong and resilient enough to bear the water pressure at different levels of depth. Its lightweight quality also makes it more employable with various deployment techniques.

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

First, when choosing equipment for current measurement near Gimhae, consider the purpose of use. If the measurement is for a vessel's navigation or short-term research, a ship-mounted ADCP flow meter is suitable. It provides real-time current information during the voyage.

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

Regarding the frequency of ADCPs, for water depths up to 70m, a 600kHz ADCP is a good choice. For depths up to 110m, a 300kHz ADCP is more appropriate. And for deeper waters that might be found near Gimhae, such as areas with a depth over 1000m, a 75kHz ADCP 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.