How to measure the coastal currents of Sandakan?

1. Where is Sandakan?

Sandakan is a coastal city and lies in the state of Sabah, Malaysia. It has great historical and natural importance.

Nestled on the eastern coast of Borneo, Sandakan nestles between the Sulu Sea. Rainforests abound with peculiar wildlife, such as orangutans and innumerable species of birds. Also, local communities are a fusion of various ethnicities: Chinese, Malays, the indigenous Kadazan - Dusun, and Bajau. The diverse cultures add to a rich tapestry of traditions, languages, and cuisines common to this area.

The shallow, adjoining Sulu Sea is also a dynamic body of water. Fine-grain sandy beaches and shallow lagoons characterize the shorelines. Most of these lagoons host various coastal marine organisms and serve as juvenile nurseries for a number of fish species. The nearshore seabed consists of sand with coral reefs. The coral reefs, part of the coastal ecosystem, give shelter and food to umpteen colored fishes and other sea animals. Further out into the Sulu Sea, the water is deeper, and there are shipping lanes and fishing grounds that support the local economy.

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

The nature of coastal currents around Sandakan is determined by various factors. In this regard, there is the influence of monsoon winds. During the southwest monsoon, it would push the surface waters in a specific direction, which could alter the distribution of nutrients or sediments and hence determine growth and distribution of life in the sea. The currents which changed during the northeast monsoon usually created another pattern in the movement of water in the area, sometimes shifting direction and speed of currents.

The underwater topography further contributes to the behavior of the coastal currents, converging, diverging, or being deflected by the underwater ridges, headlands, and bays. For example, the currents speed up around a headland, thus forming areas of strong tidal streams. Coral reefs also participate in the modification of current flow, in that they may retard the water or change its direction, hence making particular micro -habitats for marine organisms.

The other ingredient includes freshwater input from rivers and streams around the area. These freshwater can alter the salinity of the coastal waters. The resulting differences in density may develop different layers of water and affect the vertical movement of the currents.

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

It involves placing buoys on the water surface and letting them drift with currents. Employing satellite-based tracking systems to monitor buoy movements enables information to be acquired on the direction and speed of surface currents. However, data obtained with this method are mainly limited to the surface layer and cannot give an exact representation of the current structure in the entire water column.

The Anchored Ship Method A ship is anchored in coastal waters, and from it, current-measuring instruments are dropped into the water to measure the characteristic of the current at various levels. The proximity of the ship could interfere with the natural flow of the water. Continuous long-term monitoring is more time-consuming and less effective.

Acoustic Doppler Current Profiler ADCP Method: Being relatively more advanced and at the same time convenient in measurement, ADCP profiler gives a detailed profile of the velocities of the current right from the surface down to some depth, hence giving an overview of the flow pattern in a column of water.

4. How do ADCPs using the Doppler principle work?

The Acoustic Doppler Current Profiler (ADCP) work on the basis of the Doppler principle. They emit acoustic signals into the water. These acoustic pulses come in contact with those particles in water which are in motion, such as sediment particles and small organisms. Since the water is in motion, there is a frequency shift in the reflected pulses by the Doppler effect in them. This frequency shift is measured by the ADCP flow meter in order to compute the velocity at various depths in water. Multiple transducers fit on the instrument that can send and receive acoustic signals in many directions and thus enable the measurement of the three-dimensional velocity structure of the water column.

5. What is needed for a high-quality measurement of Sandakan coastal currents?

The equipment must be made of reliable materials for high-quality measurement of the coastal currents near Sandakan. It has to withstand the corrosive effect of seawater and mechanical forces by waves and currents. Small size and light weight are advantageous because that makes deploying on a boat, buoy, or at the seabed much easier.

The power consumption shall be low, especially for long-term measurements in remote locations. Another important aspect is that it should be cost-effective; in order to perform measurements at large scale, the equipment has to be available at low cost. The ADCP meter housing shall preferably be made from Titanium alloy. Some of the interesting characteristics of Titanium alloy are that it shows outstanding corrosion resistance, which, in general, is important within the marine environment. It is also sturdy and long-lasting to withstand the unforgiving elements at sea, without being too heavy.

6. How to choose proper equipment for current measurement?

It might be desirable to employ equipment for current measurement according to the usage scenario near Sandakan. The most preferred ship-mounted ADCP can be deployed on the hull of a ship and measure currents while the ship is sailing or stationery.

A bottom-sitting ADCP would be a good choice for the measurement of currents near the seabed, which can easily be put on the seabed and provide pretty accurate measurements of currents near the bottom.

A buoy-mounted ADCP is appropriate for floating applications. It can be attached to a buoy and measure currents at different depths while floating.

Frequency - For water depth up to 70m, a 600kHz ADCP is often sufficient. From 110m, a 300kHz ADCP is a better option, and while depths reach 1000m, a 75kHz ADCP can be deployed with relatively good measurements.

There are several well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a highly recommended Chinese ADCP brand is China Sonar PandaADCP. It is made of all - titanium alloy material, ensuring excellent performance and durability in the marine environment. It also offers an outstanding cost - performance ratio. You can find more information on its website: https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and moels.