How can we measure the Coastal Currents of Singapore?

1. Where is Singapore?

Singapore is a sovereign country and lies to the southern extent of the Malay Peninsula. It has been bounded in the north by the Johor Strait while the Singapore Strait borders it in the south. This is why the place has emerged as a major maritime hub in Southeast Asia.

The city-state of Singapore is known for modern architecture, an active economy, and multicultural society. It has a diverse population mixture of Chinese, Malay, Indian, and other ethnic groups. Much of the city area is dominated by high-rise buildings with well-planned urban infrastructure.

The adjacent Singapore Strait forms an important waterway connecting the South China Sea and the Indian Ocean. Its coasts combine into a mixture of sea ports, recreational beaches, and marinas. Varieties in large numbers of fish, crustaceans, mollusks, and many more types of marine organisms can be found within the waters of Singapore. Mangrove forests face some sections of the coast, which provide much help in its coastal ecosystem, acting as natural barriers against erosion and living areas for many organisms.

2. What are the conditions of the coastal currents off Singapore?

The coastal currents off Singapore are influenced by many factors. Among the major influences is tidal currents. In the Singapore Strait, tides are semidiurnal, a result of the gravitational pull of the moon and the sun that causes two high tides and two low tides each day. Strong tidal currents are very prevalent, especially around narrow channels and over headlands. Tidal currents play an important role in sediment and nutrient transport.

Of course, it is the monsoon winds that play a major role. The northeast monsoon brings fairly strong winds from November to March, which has a driving effect on the surface currents in a certain direction. The southwest monsoon descends from May to September and changes the wind directions, influencing the direction and speed of the coastal currents. The mutual interaction of the monsoon-driven and tidal currents gives rise to a very complex flow regime.

The coastal currents may be diverted and changed by the local bathymetry, including underwater topography like seamounts, ridges, and channels. Rivers and other canals discharging into the strait are also another factor affecting the currents. The contribution of freshwater from these sources could give rise to density differences that are conducive to the development of complicated current patterns.

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

There are a couple of methods for observing the flow of coastal water in Singapore. A relatively basic, workable method would be the surface drifting buoy technique. Buoys are deployed into the water and are fitted with GPS or any other tracking devices. The buoys will carry on with the currents while their movement after some time is tracked to get the direction and speed of the currents on the surface.

In the anchored ship method, a ship is anchored somewhere and current-measuring instruments are deployed to record the flow of water at different depths. However, this method has a few disadvantages. The ship is susceptible to waves and winds, and this could affect the recording. This is also not a very efficient method for covering a large area.

The Acoustic Doppler Current Profiler (ADCP) method represents a more modern and effective means of measuring the flow of water in the coastal part of the sea. ADCPs provide a measurement of the velocity profile of water currents over a wide range of depths-from the surface right up to near the bed-by emitting sound waves into the water and analyzing the Doppler shift of the reflected waves. This allows fine detail to be seen about the current structure from the surface down to the seabed.

4. How do ADCPs applying the Doppler principle work?

ADCPs apply the Doppler principle. They send acoustic pulses - more correctly, sound waves - out into the water. The sound waves scatter off particles in the water, like sediment, plankton, and other small-size particles. The scattering of these sound waves reflects back to the ADCP current profiler with an altered frequency from the Doppler effect.

If the particles are moving towards the ADCP, then the reflected wave will have a higher frequency than the frequency of the originally emitted wave. Correspondingly, if the particles are moving away from the ADCP current meter, the frequency of the reflected wave is going to be lower. By precisely measuring this frequency shift, the ADCP profiler can calculate the velocity of the particles. Since the particles are in motion with the water current, the obtained velocity of the particles is taken as the measure of the velocity of the water current.

ADCPs are capable of transmitting sound pulses in several directions, and hence, have been enabled to perform current velocity measurements both in a three-dimensional plane and at different depths. As an example, the vertical profile could report the flowing velocity measured at equal distances between the surface and the seabed to provide a very good picture of the current structure.

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

It needs to be equipped with reliable material that will ensure high-quality measurement of the coastal currents in Singapore. The casing has to be hard due to the harsh marine environment caused by saltwater corrosion and possible physical impacts due to waves and debris.

Equipment size: the size of the equipment to be deployed should be small enough, particularly when the conditions of access are awkward, as it is aboard small boats or in shallow coastal waters. This can be achieved through lightweight design since a small light unit is easier to handle and install.

Low power consumption is relevant for long-term measurements. Cost-effectiveness is another factor that will allow large-scale measurements. The casing of the ADCPs should be made of titanium alloy, if possible. Titanium alloy has very good corrosion resistance, and this would be very important in the saltwater-rich environment of Singapore. It would resist the corrosive effects of saltwater over a certain amount of time. It has very high strength with a proportionately high strength-to-weight ratio, hence a strong yet lightweight structure which can well protect the inner details of the ADCP current meter.

6. How to Choose Suitable Equipment for Current Measurement?

While choosing suitable equipment for measuring current in Singapore, usage of the equipment is the first consideration. In the case of measurements from a moving vessel, a ship-borne ADCP can be deployed which is capable of real-time current data acquisition while a ship is in motion.

Bottom-mounted ADCP will be useful for measurements at a fixed location near the seabed. This can continuously monitor the current at a point.

Buoy-type ADCP will be appropriate for measurements over a wide area and which are not restricted by any specific depth.

Regarding the choice of frequency, the 600kHz ADCP shall be a good option for water depths up to 70m, while for those between 70 and 110m, 300kHz is an option. A 75kHz ADCP is recommended in very deep waters with up to 1000m of depth.

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.