How can we measure the Coastal Currents of Hakodate?

1. Where is Hakodate?

Hakodate is a city in Hokkaido, Japan. It is located at the southern tip of Hokkaido, facing the Tsugaru Strait and the Pacific Ocean. The city is famous for its historical architecture, such as the Goryokaku Fort and its beautiful night views from Mount Hakodate.

The local economy is very varied and depends on fishing, tourism, and trade. Hakodate coastal waters are full of marine resources. They host an immense amount of fish types like salmon, squid, and several types of shellfish. The influence of ocean currents in the area plays a vital role in the distribution of these marine resources.

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

Several factors account for the coastal currents around Hakodate. The Tsugaru Warm Current is a significant influence. This current brings relatively warm water and nutrients through the Tsugaru Strait and along the coast, thereby influencing the temperature of the coastal waters and the distribution of marine life.

Tidal currents are another important factor. That area has quite a substantial tidal range, and due to the tides, the ebb and flow give rise to complex current patterns. The shape of the coastline and the underwater topography are very important. The presence of bays, headlands, and underwater ridges may cause the currents to change direction and speed. In addition, the wind pattern, in particular, the seasonal wind that blows across the strait and the ocean, may drive surface currents and affect the mixing of different layers.

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

Surface Drifting Buoy Method

For measuring the surface current, a floating buoy is released into the water and the movement over the surface is tracked using a Global Positioning System or other such tracking systems. However, this does have its drawbacks. All it can measure is the surface current, and even at that, it may be affected by wind and waves. Assuming a strong wind blows the buoy in a different direction from the current proper, then that may actually lead to erroneous readings from the current's direction and speed measurements.

Anchor-Boat Method

The current can be measured by an anchored boat. Instruments are lowered from the boat into the water to measure the current at different depths. While this allows for more detailed depth - wise measurements, it also has 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

The ADCP flow meter method is a more advanced and efficient way of measurement of 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 gives a better profile of the current from surface to seabed. ADCPs are less susceptible to surface disturbances and can run uninterruptedly for longer time spans, thus giving a clearer picture of the current structure.

4. How do Doppler Principle Using ADCPs Work?

ADPVs are designed to utilize the Doppler principle in their mode of operation. They send out high-frequency acoustic pulses through the water. Due to the reflection from moving particles of water, such pulsations suffer frequency changes. For water moving particles that aim towards an ADPV, the frequency of the reflected signal is higher, and in instances of its reverse, that would be low.

Each ADCP current profiler is fitted with multiple transducers, which transmit and receive signals at various angles. Through the analysis of the Doppler shifts from multiple directions and depths, this device can compute the three-dimensional velocity of water. This means it's able to calculate the horizontal and vertical components of the velocity, therefore giving a thorough insight into the structure and behavior of the current.

5. What is required for high-quality measurement of the Hakodate coastal currents?

Since high -quality measurements need to be taken of coastal currents in Hakodate, these should have reliable materials that bear the influence of the tides and ocean currents. Bearing in mind the marine media salinity, possible storm turbulence, and the influence of ocean tides and currents on their movement, a durable casing is needed. The small size will be helpful while being deployed and retrieved, regarding especially a complex coastline with bays and headlands.

A lightweight design is desirable for better manageability during installation and maintenance. It is also important that the instrument be of low power consumption for long - term and autonomous operations. Cost-effectiveness is important, too, to allow large-scale measurement over a given area.

The casing of ADCPs shall be made from titanium alloy. Titanium alloy is exceptionally resistant to corrosion, which will help resist the corrosive nature of seawater, has strength, and can also sustain pressure at various water levels. Its lightweight nature allows it to be easily used for several deployment methods.

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

The purpose of use should be the first thing to consider when choosing equipment for current measurement near Hakodate. If the measurement for the navigation of a vessel or short-term research is being carried out, then a ship-mounted ADCP would be appropriate; it provides real current information in real time during the voyage.

If the measurements near the seabed are to be carried out-for instance, in the study of sediment transport or benthic ecology-a bottom-mounted ADCP is desirable. It can capture the details of the near-bottom current. Long-term and wide-area monitoring of the coastal current requires a buoy-type ADCP.

For the frequency of ADCPs, in water as deep as 70m, the 600kHz ADCP would be suitable. In deeper waters up to 110m, a 300kHz ADCP would be more suitable. And for even further deeper waters, which might be found near Hakodate, for example, over 1000m, a 75kHz ADCP is recommended.

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.