How can we measure the Coastal Currents of Busan?

1. Where is Busan?

Busan is a lively and energetic metropolis that lies in the southeastern part of South Korea. It is a significant port city located along the shores of the South Sea (Korea Strait). The topography of the city is an interesting juxtaposition of modern skyscrapers, sandy beaches, and a busy harbor.

The beach of Haeundae in Busan is renowned over the world for its gentle sand and transparent water, which magnetizes numerous tourists each year. It houses people of varied backgrounds, and everyone earns a living by indulging in a number of day-to-day businesses. Its strategic positioning makes Busan a center of international trade and shipping activities.

Busan has one of the largest and busiest ports in the world, with millions of tons of cargo being handled in containers, bulk goods, and automobiles. The local economy is deeply connected with sea activities. It also hosts an important cultural heritage, as ancient temples and traditional markets find their place alongside modern shopping malls and entertainment complexes.

The South Sea near Busan is a warm-water body that has enormous marine life. It provides a shelter for several species of fish, such as mackerel, tuna, and sardines. The sea also has enormous beds of seaweed and shellfish. Warm currents and the presence of the Nakdong River delta near Busan have enhanced the rich biodiversity of the coastal waters. The coastal area is very important, not only in fisheries but also in yachting and other sea-related sports.

2. What is the condition of the coastal currents near Busan?

In the area near Busan, there are many factors that have been influencing the coastal currents. The main ocean current in this region is the Tsushima Current-a warm-water current flowing generally northward through the Korea Strait. It carries in a large amount of warm and nutrient-rich water, highly influencing the local marine ecosystem and coastal currents.

Tidal currents are another dominant factor. Busan has quite a large tidal range, while the ebb and flood induce complex current patterns. These shapes of the coastline and its bottom topography are quite vital. The presence of port facilities, the breakwaters, and even the Nakdong River delta has an effect of either diverting, converging, or eddying. Also, the intrusion of the Nakdong River alters the salinity and density in the coastal waters, therefore it affects the flow of the currents. Wind patterns, mainly the seasonal winds such as the monsoon winds, can be seen driving surface currents, which eventually affect mixing at different levels of water.

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

Surface - drifting buoy method: This buoy is released into the water to observe the surface current. Its movement is tracked by the GPS or other tracking system over time. However, the limitation of this method remains. It only provides information regarding the surface current and sometimes becomes victimized by wind and wave. This would happen, for example, when strong wind in some other direction than the current pushes the buoy away from the real direction of current, hence making wrong estimations of its speed and direction.

Anchor - Boat Method: This is another method of measurement, wherein an anchored boat measures the current. Instruments to measure the current are lowered from the boat into the water at various depths. While this does have its advantages of being able to make more detailed depth-wise measurements, it also has its disadvantages. Because the boat remains in one fixed position, only a limited area of measurement can be obtained, and large coastal areas may not represent the full variability of the currents.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP current meter method has several advantages in measuring coastal currents with better efficiency. Basically, the ADCPs send out acoustic signals into the water and, based on the Doppler shift of the reflected signal, determine the velocity of the water at each depth. In such a way, it would also provide an appropriate profile from the surface to the bottom for the current. Because ADCPs are less affected by surface disturbances, they are able to operate continuously for longer periods with a truer indication of current structure.

4. How do the ADCPs using the principle of the Doppler work?

The operating principle of ADCPs is based on the Doppler effect. They send high-frequency acoustic pulses into the water. Due to interaction with moving water particles, the frequency of reflected pulses is different. When the movement of the water particles is toward the ADCP current profiler, the frequency of the reflected signal is higher than that emitted, and vice versa.

Each ADCP profiler has several transducers, which transmit and receive the signals at various angles. As it analyzes the Doppler shift coming from several directions, along with several depths, a calculation of three-dimensional velocities of water can be derived-the horizontal and vertical components that make up its speed provide information about the detailed structure of the current.

5. What is required to measure Busan coastal currents with high accuracy?

The equipment should be made with reliable materials for high-quality measurement of the coastal currents around Busan. The casing needs to be robust, considering that it is a marine environment with saltwater, potential storms, and tides. The size of the equipment should be small for easy deployment and retrieval, considering the complex coastal landscape of beaches, ports, and river deltas.

A lightweight design is preferred since this makes the equipment more manageable during installation and maintenance. Low power consumption is required for long-term and autonomous operation. Cost-effectiveness is also important to allow for large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy is resistance to corrosion, which is a very critical factor in its survival against the corrosive sea and saltwater. Besides, it is strong and resilient enough to bear the water pressure at different levels. It is lightweight, hence easier for various deployment methods.

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

When selecting equipment for current measurement near Busan, the first consideration should be the purpose of the equipment. If the measurement is to be used for navigation on a vessel or for short-term research, then a ship-mounted ADCP meter is adequate. It provides real-time current information during the voyage.

A bottom-mounted ADCP would be preferred for measurements near the seabed, such as in studies of sediment transport or benthic ecology. It will be able to capture the details of the near-bottom current. In cases where long-term and wide-area monitoring of the coastal current is required, a buoy-type ADCP flow meter would be ideal.

Considering ADCP current profiler frequencies, in water up to 70m, a 600kHz ADCP would be quite effective; for water up to 110m, the instrument would be a 300kHz ADCP. In deep water, like those which might be found near Busan-areas of over 1000 meters, for instance-a 75kHz unit should work well.

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.