How can We Estimate the Coastal Currents of Wakayama?

1. Location of Wakayama

Wakayama is a prefecture located in Kansai, Honshu Island of Japan. It is basically a coastal area that fronts the Pacific Ocean and Kii Channel. The city of Wakayama is a popular destination due to its beautiful nature: mountains, forests, and beaches.

The local economy is supported by a combination of fishing, agriculture, and tourism. The coastal waters are rich in marine resources. The Pacific Ocean near Wakayama is home to a variety of fish species such as tuna, bonito, and mackerel. There are also extensive beds of seaweed and shellfish. The warm Kuroshio Current has a significant influence on the local climate and marine ecosystem, bringing in warm water and nutrients.

2. What is the condition of the coastal currents off Wakayama?

The coastal currents off Wakayama are determined by many different factors. The Kuroshio Current is one of the dominant ones. This warm ocean current that moves northward brings in warm and nutrient-rich water, affecting the local marine life and the overall current patterns.

Tidal currents are also important. The tide varies regularly with reasonable tidal range, the rise and fall of which form the pattern of complicated currents in Wakayama. First, there is a consideration of coastline and underwater topography. This might induce currents to alter course and speed due to underwater ridges, bays, and headlands. Water can be observed flowing much quicker around headlands, deflecting into bays. Besides, the wind patterns, especially the seasonal winds like the trade winds, may push the surface current and mix different layers of water.

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

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 technique also has its limitations. It does not give any information about the current, apart from the surface one. It is also affected by wind and waves. For example, if a strong wind blows on the buoy in a direction different from the actual one, it can lead to inaccurate measurements of the direction and speed of that current.

Anchor-Boat Method: Current can be measured using an anchored boat. Instruments for measurement of current are lowered from the boat in the water at different depths. Although this allows for more detailed depthwise measurements, it also has its drawbacks. 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.

ADCP Method: This is a far more sophisticated and effective way of measuring coastal currents. ADCPs send acoustic signals into the water and detect the Doppler shift in the signals that bounce back to estimate the water velocity at various depths. It allows a finer profile of the current right from the surface down to the seabed. They are less affected by surface disturbance and can operate continuously for long periods to provide a more accurate picture of the current structure.

4. How do ADCPs using the Doppler principle work?

The operation of ADCPs is based on the Doppler effect. They emit high-frequency acoustic pulses into the water. As these pulses encounter and interact with moving water particles, the frequency of the reflected pulses changes. When the water particles are moving towards the ADCP current meter, the frequency of the reflected signal is higher than that emitted; if they are moving away, it is lower.

In operation, ADCP current profiler with more than one transducer, it sends and receives signals at different angles. The analysis of Doppler shifts in the different directions and at depth enables the device to compute three-dimensional velocity. This means the horizontal and vertical components of the velocity, giving detailed insight into the current structure and behavior.

5. What is necessary for high-quality measurement of Wakayama coastal currents?

The equipment should be made of reliable materials for high-quality measurement of the coastal currents around Wakayama. A durable casing will be required because of the marine environment, with saltwater, potential exposure to storms, and the influence of tides and ocean currents. The size of the equipment should be small for easy deployment and retrieval, especially in the complex coastal landscape with its bays and beaches.

A lightweight design is preferred, as 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 important to enable large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is vital for withstanding the corrosive effects of seawater. It is also strong and durable, capable of withstanding the pressure of the 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?

If there is any measurement near Wakayama, then equipment should be chosen according to purpose: a ship-mounted ADCP in case of measurement for navigation or short-term research of vessels. It provides real current information in a voyage in real time.

An ADCP installed on the bottom is required if a measuring program is for near - seabed measurements, including studies of sediment transport and/or benthic ecology. It should bring back much better detail of the near-bottom current. A buoy -type ADCP is ideal in providing long-term and wide-area coastal currents.

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

There are well-known ADCP profiler 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.