How to measure the Coastal Currents of Kedah?

1. Where is Kedah?

Kedah is a state of Malaysia and is located in the north-western part of the country. Its western border is the Strait of Malacca, while towards the north lies Thailand. The state is renowned for its rich history and cultural heritage that dates back to centuries.

Kedah has varied landscapes comprising rich, arable plains, limestone hills, and a lovely coastline. The administrative capital is Alor Setar, the largest urban centre in the state. The culture of the Kedah people is quite unique but has strong elements of Malay tradition. Agriculture, particularly paddy cultivation, plays a major role in the local economy.

The nearby Strait of Malacca, separating the Indian Ocean from the South China Sea, is one waterway that is really important. Village-like fishing harbors and busy coastal communities line the coast of this place. These waters are teeming with shoals of fish, prawns, and crabs. Sandy beaches, mangrove forests, and mudflats are common along the coastline. These mangroves give a natural nursery to many marine organisms and help act as a barrier against coastal erosion and storm surges.

2. What is the state of the coastal currents off Kedah?

The coastal currents off Kedah rely on a combination of: tidal currents as the dominant element in influence. It is natural that the gravitational pull of the moon and the sun should raise and lower the tides of the Strait of Malacca to a semi-diurnal pattern with two high and two low tides each day. These tidal currents can be quite strong, especially near the coasts and in narrow channels.

Monsoon winds also contribute to a great extent. The southwest monsoon, which is usually predominant between the months of May and September, contributes to strong winds to constitute a well-defined direction in the surface current. Contrarily, northeast monsoon, during the period of November-March, functions differently to vary both the speed and direction of coastal currents.

Local bathymetry, or underwater topography in the form of seamounts, ridges, and channels, could deflect and alter the flow in these coastal currents. Discharge into the sea from rivers, such as Sungai Muda in Kedah, would also contribute to these coastal currents. Freshwater from these rivers mixes with seawater, creating differences in densities that could result in complex current patterns.

3. How can the water flow on the Kedah coast be observed?

A lot of the coastal water flow in Kedah can be observed through various means. The most common one is the surface drifting buoy technique. Essentially, buoys are deployed on the water and fitted with GPS or any other devices that will be able to show their location in a readable manner. Carried by the currents, their movements are then monitored over time, which then defines the direction and speed of the surface currents.

In an anchored ship method, a ship is anchored at a point, and the current-measuring instruments of the ship take the water flow from top to bottom. However, this technique has a few drawbacks. The ship may be prone to waves or winds, which could lead to less accuracy in the measurement, and it's really not efficient for large areas.

This is, however, done in a more efficient manner with the ADCP method. ADCPs measure the velocity profile of water currents throughout the range of depths. They function by emitting sound waves into the water and analyzing the Doppler shift in the waves that bounce back. This therefore provides a detailed understanding of the structure of the current right from the surface to the seabed.

4. How do ADCPs using the Doppler principle work?

Acoustic Doppler Current Profiler (ADCP) work on the principle of the Doppler principle. They send acoustic pulses-a form of sound waves-through the water. The sound waves scatter off particles in the water, which include sediment, plankton, and other small particles in the water. The reflected waves have a change in frequency due to a phenomenon called the Doppler effect when these sound waves are reflected back to the ADCP flow meter.

With particles moving towards the ADCP profiler, the reflected wave has a higher frequency than the original emitted frequency. Particles that are moving away from the ADCP reflect back with lower frequencies. The shift in frequency, due to this principle, is what the ADCP measures with high accuracy in order to calculate the velocity of the particles. Since the particles move with the flow of water, the particle velocity calculated will be a measure of the velocity of the water current. ADCP meter can emit sound pulses in more than one direction. Hence, they can measure three-dimensional current velocity in various depths to give a good profile of the structure of the current.

5. Fine measurement of Kedah coastal currents requires:

Such measurement of the coastal currents of Kedah requires equipment with reliable materials for their making; it needs to be strong enough to overcome saltwater corrosion and possible physical impacts due to waves or other floating debris. The casing should be made tough to resist such impacts. The size and weight of the equipment should be suitable. Because a small size appliance is easier to install; particular locations like in small boats or in shallow coastal waters will have limited access. Because a lightweight device is more handy, and installation is less of a hassle.

Long term measurement requires low power consumption of the device. Cost-effectiveness is yet another advantage enabling large-scale measurements. In the case of ADCP current profiler, casing is preferably of titanium alloy. This is because titanium alloy has excellent corrosion resistance, which would be highly essential in the marine environment of Kedah. It also can provide great resistance against the effects of saltwater for a considerable period of time. The strength and high strength-to-weight ratio deliver a lightweight and robust structure that would protect the internal components of the ADCP current meter.

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

First of all, usage will be considered for selecting the right equipment for the current measurement in Kedah. When it is necessary to make measurements from a moving vessel, then it would be sufficient to use a ship-borne ADCP. Further, this is also capable of carrying out real current data while the ship is in motion so that a better understanding of water flow in different locations can be known. If the measurements must be from a fixed location near the seabed, a bottom-mounted ADCP will suffice. It can monitor the current continuously at a point and provide consistent data for any amount of time. A buoy-type ADCP is appropriate if the measurements must cover a wide area and are not restricted to any particular depth.

Frequency selection: up to 70m of water depth can use 600kHz ADCP while 70-110m depth requires 300kHz ADCP, and for very deep waters, up to 1000m, a frequency of 75kHz will be more appropriate.

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.