How can we measure the Coastal Currents of Tomakomai?

1. Where is Tomakomai?

Tomakomai is a city in Hokkaido, Japan. It's located on the southern coast of Hokkaido, facing the Pacific Ocean. The city is an important port and industrial center, with a diverse economy that includes fishing, shipping, and manufacturing.

The Pacific Ocean off Tomakomai is very rich in marine resources. It provides a variety of fish, including salmon, tuna, and squid. There are also great seaweed beds and shellfish grounds. The local fishing industry benefits from these resources, while the port is used for both domestic and international trade.

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

Various factors influence the coastal currents near Tomakomai. First, there is the Oyashio Current. This cold current, which streams from the Arctic region, brings cold water and nutrients that affect the temperature and distribution of marine life.

It is also affected by the Kuroshio Extension. Interaction of Oyashio Current with the Kuroshio Extension gives birth to a rather complicated pattern of current. And, finally, the tidal constituent is of importance. The range of tide is specific for Tomakomai; ebb and flow result in development of rather complex patterns of flow.

Shape of coastline and submarine topography are very important: bays, headlands, submarine ridges may be used to bend the currents, changing their direction and speed. The wind, mainly the seasonal winds like the trade winds, could push the surface currents and mix different layers.

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

Surface Drifting Buoy Method

A surface-drifting buoy might be deployed in the water where a surface current would then be observed. The buoy movement may then be tracked by various GPS or other tracking systems at later times.

However, this method has several drawbacks. It gives only the surface current, and it is subjected to wind and waves. For instance, if the buoy is blown by a strong wind sideways from the actual current, it may give incorrect measures of the direction and speed of the current.

Anchor-Boat Method

It is possible to measure the current with an anchored boat. From this, instruments are lowered into the water to measure the current at different depths.

While this gives a more detailed depth - wise measurement, it has disadvantages. The fixed position of the boat limits the area of measurement, and this might 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 sophisticated and efficient in the measurement of 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 gives a better profile of the current from surface to seabed. ADCPs 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 work on the principle of the Doppler effect. They transmit high-frequency acoustic pulses into the water. Whenever these pulses encounter moving water particles, the frequency of the reflected pulses shifts. When the water particles are moving toward the ADCP meter, the reflected signal frequency is higher than the emitted signal, and vice versa when they are moving away.

The ADCP current profiler has multiple transducers, each transmitting and receiving signals at a different angle. The device can then calculate the three-dimensional velocity of the water by taking into account the Doppler shifts at different directions and depths, and thus the horizontal and vertical components of the velocity, giving an in-depth insight into the structure and behavior of the current.

5. What is necessary to make high-quality measurements of Tomakomai coastal currents?

The equipment should possess reliable materials for high measurement quality of the coastal currents around Tomakomai. Since these are in the marine environment, where there is saltwater, occasional exposure to storms, tidal, and ocean currents that may exert their influence, a casing that is not easily broken should be used. The device should also be small in size; this is very important given the coastal geography with bays and beaches.

A lightweight design is preferable as it makes the equipment more manageable during installation and maintenance. Low power consumption is crucial for long - term and autonomous operation. Cost-effectiveness is also important to enable large - scale measurements.

The casing of ADCPs should be made from titanium alloy. Titanium alloy is resistant to corrosion, which is necessary in sea water that corrodes a lot. It is strong and durable to stand the pressure of the 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?

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

If measurements are near the seabed, as would be for studying sediment transport or benthic ecology, a bottom-mounted ADCP is better. It can capture the detail of the near-bottom current. If long-term and wide-area monitoring of the coastal current is needed, a buoy-type ADCP is ideal.

In general, for water depths up to 70m, a 600kHz ADCP will be a good choice, while up to 110m the most appropriate would be a 300kHz ADCP, and for deeper waters, as may be encountered near Tomakomai, greater than 1000m for instance, a 75kHz ADCP would be most suitable.

There are well-known ADCP 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.