How to measure the Coastal Currents of Riau Islands?

1. Where is Riau Islands?

The Riau Islands are located in the South China Sea and the Strait of Malacca. Geographically, they compose a very strategic part of Southeast Asia. The islands are dispersed over a wide area of water, comprising a large maritime region.

The Riau Islands are home to ethnic variety. A native would be described as a combination of the major ethnic groups, namely Malays, Chinese, and Bugis. Because of this, the islands have long been involved in trade and sailing. The rather lively ports and coastal communities reflect this fact.

As for the surrounding waters, to the east is found the major body of water-the South China Sea. It is reputedly known for its complicated conditions with regards to oceanography. To the west, the Strait of Malacca represents one of the most congested shipping lanes in the world. Coastal areas along the Riau Islands are dominated by thick mangrove forests. Mangroves act not only as a shield in these areas against coastal erosion but also provide a very important habitat for many marine and terrestrial species. The waters around the islands are teeming with life-from colorful coral reefs that support a diverse range of fish and invertebrates to the migratory paths of larger marine mammals.

2. Current state of the currents around Riau Islands:

Many factors influence the coastal currents round the Riau Islands. Among these, tidal currents are a major factor. The gravitational pull of the moon and the sun influences the tidal system. The semi-diurnal tides in the South China Sea and the Strait of Malacca provide a rhythmic ebb and flow of water along the coast. The tidal currents can be quite strong, especially through narrow straits and channels.

In particular, the monsoon winds have a strong effect. The southwest wind of this season forces the surface waters in one direction, which therefore influences the current patterns. The northeast monsoon has an opposite effect on resultant coastal currents, many times altering their direction and velocity. In addition to these factors, the local bathymetry, seafloor topography including seamounts, trenches, and shoals, locally deflects and modifies the flow of the coastal currents.

Another source of influence on the island coastal currents could be fresh water inflow from rivers and estuaries on the islands. The mixing of fresh and salt water can lead to density differences, hence quite complex current systems. In addition, shipping traffic in the Strait of Malacca may contribute a minor perturbation. Large ships can create wakes and disturb the near-surface water flow in some local region.

3. How to Observe the Riau Islands Coastal Water Flow?

There is a variety of ways to observe the flow of water along coasts in the Riau Islands. A simple technique is the surface drifting buoy. Buoys are set onto the surface of the water and installed with GPS or other tracking devices. As the buoys are conveyed by the currents, their movement can be monitored over time to determine the direction and speed of the surface currents.

This will involve anchoring the ship in a given location; besides this, the current meters will be used to measure the flow of water at different depths. The disadvantage of this method is that it is liable to be affected by waves and winds that may result in erroneous measurement. Besides that, it is not efficient for field coverage:.

The second, more sophisticated and efficient way is the method of Acoustic Doppler Current Profiler (ADCP). ADCPs measure the velocity profile of water currents over a depth range by transmitting sound waves through the water and interpreting the Doppler shift of the returned waves. In this way, a very accurate image of the current structure from the surface down to the seabed is obtained.

4. How do ADCPs using the Doppler principle work?

The ADCP current profiler work on the principle of the Doppler Principle. They send acoustic pulses into the water. The interaction of these pulses takes place with particles in water-sediment, plankton, or even other small particles. The point at which the sound waves reflect back after hitting such particles, due to the Doppler effect, there is a shift in the frequency of the reflected waves.

If the particles are moving towards the ADCP current meter, then the frequency of the reflected wave is higher than the frequency of the emitted wave. In case of movement away from the ADCP flow meter, the frequency of the reflected wave is lower. By detecting the frequency shift of the reflected waves, the ADCP meter is able to calculate the velocity of the particles. Since the particles are moving with the current, the velocity of the particles is related to the velocity of the water current. ADCP profiler can emit sound pulses in different directions and can measure the current velocity in three - dimensional space and at different depths.

5. What's needed for high - quality measurement of Riau Islands coastal currents?

The equipment needed for high-quality measurements of the coastal currents of the Riau Islands should be made of reliable materials. In particular, the casings of equipment need to withstand a hostile marine environment due to saltwater corrosion and physical impacts caused by waves and debris. Small size and light weight are highly beneficial features. In particular, when access is limited-as it can be in small boats or in shallow coastal waters-a small-sized device is easier to deploy. A lightweight device also means more comfort for handling and installing it.

Long-term measurements are only possible with low power consumption. Cost-efficiency is another decisive factor, especially in large-scale measurement quantities. In the case of the ADCPs, the casing could be made preferably from titanium alloy. Another advantage of the Titanium alloy is that it has excellent resistance to corrosion, which plays a very important role in the marine environment of the Riau Islands. It is able to keep its integrity over a long period in saltwater. It is strong and with a high strength-to-weight ratio provides durable and light structure.

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

The first consideration in choosing the right equipment for current measurement in the Riau Islands is usage. Ship-borne ADCPs can be used for the measurement of currents from a moving vessel. In fact, this would be able to provide real-time current data during the time the ship is in motion. The bottom-mounted ADCP would be an excellent option for the measurements at a fixed location near the seabed. It can continuously monitor the current at a specific point. For the measurements that must cover a wide area and are not limited to a particular depth, a buoy-type ADCP is adequate.

On the selection of frequency, for water up to 70m, there could be a good selection of a 600kHz ADCP. For depths between 70m to 110m, a 300kHz ADCP would be adequate. In the case of very deep waters of up to 1000m, a 75kHz ADCP would be preferred.

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 a great cost - performance ratio. You can find more information about it on the website: https://china-sonar.com/.

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