How to measure Malacca Coastal Currents?

1. Where is Malacca?

Malacca is a state in Malaysia and is located along the southwest coast of the Malay Peninsula. It is bordered by the Strait of Malacca, which is among the most important and busiest shipping lanes in the world.

Malacca City boasts a very rich historical and multi-ethnic background. Centuries ago, it was a major trading port and was influenced by the various cultures of Malays, Chinese, Indians, and Europeans. The architecture of Malacca depicts this varied history from colonial buildings, ancient temples, down to the traditional Malay houses.

The neighboring Strait of Malacca is a narrow body of water that connects the Indian Ocean and the South China Sea. The coasts in Malacca comprise a combination of fishing villages, ports, and holidaying spots. Marine resources include fish, shellfish, and planktons of all kinds. There are mangrove forests on the coasts that protect the shoreline from erosion by preventing the land from being washed away and provide a habitat to a lot of species.

2. What about the situation of the coastal currents near Malacca?

The coastal currents near Malacca are influenced by many variables. Tidal currents are a dominant factor. Gravitational pull of the moon and the sun causes the tide in the Strait of Malacca to be semi - diurnal. This means there are two high tides and two low tides each day. The tidal currents are powerful, especially in the narrow parts of the strait and near the coast. These kinds of currents are of great help in transporting sediments and nutrients within the area.

Monsoons contribute much to this process. From May to September, the south-west monsoon is dominating with strong winds capable of driving the surface currents in one direction. From November to March, the north-east monsoon happens, changing the wind directions and therefore the direction and speed of coastal currents. The interactions between tidal and monsoon-driven currents yield a dynamic and complex flow pattern.

These waters may be deflected, and their configuration altered, by the local bathymetry: underwater ridges, channels, and shoals. Discharge of rivers and streams into the strait may also alter current patterns. Freshwater input, for instance, may establish density contrasts that can provide the potentiating conditions for complex current systems to develop.

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

It can be seen that there are a number of ways to observe Malacca coastal water flow. One of the simple and practical approaches is a surface-drifting buoy. Buoys are discharged into the water with GPS or any other tracking devices. As buoys are carried by currents, their movements over time can be monitored to determine the direction and speed of surface currents.

In the anchored ship method, the ship will be anchored at a point, and the flow of water at different depths is measured using the current-measuring instruments. It has a few limitations. This method is likely to be affected by waves and winds. This could lead to inaccurate measurements. Further, this is not a very efficient way of covering a large area.

The Acoustic Doppler Current Profiler (ADCP) method is an advanced technique for the measurement of flow in coastal water. The ADCPs are able to measure the velocity profile of currents within water over quite large depth ranges. They work by emitting sound waves into the water and then analyzing the reflected waves for the Doppler shift. This gives great detail about the current structure from surface to seabed.

4. How do ADCPs using the Doppler principle work?

A Doppler principal is used in the generation of acoustic pulses or sound waves into water to operate an ADCP current profiler. These sound waves interact with some particles in the water, mostly sediment and plankton, or any other small-size particles that may be present therein. As such, when the sound waves reflect back to the ADCP after interaction with those particles, the frequency of the reflected waves changes due to the Doppler effect.

The frequency of the reflected wave will be higher than the originally emitted frequency when the particles are moving towards the ADCP current meter. In return, if the particles are moving away from the ADCP, then the frequency of the reflected wave is going to be lower. The ADCP flow meter will be able to calculate the velocity of the particles by taking this frequency shift measurement very precisely. Since the particles are moving with the water current, the calculated particle velocity provides the velocity of the water current.

They can transmit sound pulses in various directions; thus, ADCPs are capable of measuring the current three-dimensional velocity and that of multiple depths. For example, vertical profiling of current measurements can be made over intervals ranging from the surface to the seabed for a full view of current structure.

5. What is required for high-quality measurement of currents off Malacca?

The equipment should be made from reliable materials for high-quality measurements of coastal currents in Malacca. A durable casing is needed because salinity in seawater, potential corrosion, and physical impacts caused by waves or floating debris can easily occur.

The equipment size should be small enough to be easily deployable, especially in places with limited access, such as in small boats or shallow coastal waters. The lightweight design is also advantageous for much easier handling and installation.

Low power consumption is necessary for long-term measurements. Cost-effectiveness is another significant factor in enabling large-scale measurements. For the ADCP profiler in this case, the casing should be made from titanium alloy. For Malacca, where the ADCPs will face a saltwater marine environment, there can hardly be any better resistant corrosion material than a titanium alloy. It can provide resistance to corrosive saltwater for a longer period of time. This further benefits from strength and a high strength-to-weight ratio, thus obtaining a durable, lightweight structure that is able to bear all unfavorable conditions inside the ADCP.

6. Selection of Appropriate Equipment for Current Measurement

The first and foremost thing to consider for the selection of the right equipment for current measurement in Malacca will be the usage: a ship-borne ADCP would be appropriate for measurements from a moving vessel. It would offer real current data as the ship is moving.

Bottom-mounted ADCPs should be used for fixed location measurements near the seabed. It continuously monitors the current at a point.

When the area of measurement is large and does not fall under any fixed depth, then a buoy-type ADCP is appropriate for the application.

Frequency Choice: The chosen frequency can be a 600kHz ADCP for water depths up to 70m, though for greater than 70 to 110m, a better choice will be a 300kHz ADCP, and for very deep waters of up to 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 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.