How are the coastal currents of Kuching measured?

1. Where is Kuching?

Kuching is a beautiful city nestled in the island of Borneo in Malaysia. It lies in the southwest of Sarawak, a state of immense ethnographic interest and natural wonder.

It is flanked by emerald rainforests that are home to all kinds of wildlife, from brightly colored birds to the elusive primate. The people of Kuching are a harmonious mix of different ethnic groups such as Malays, Chinese, and indigenous Dayak communities, all with their various traditions and food, which create a multi-ethnic atmosphere that is vibrant.

Regarding the neighboring water body, Kuching is situated near the South China Sea. Those waters are a complex mixture of shallow nearshore areas, with an offshore area that slowly deepens further out from the coast. That tides can become most dramatic in these waters, and between the ebb and flow, between the rise and fall, there is strong influence on the local life forms and sediment distributions along the coast. Off the coast, there are plenty of small bays and inlets that can give shelter for boats and act as habitats for different kinds of marine species.

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

But along these coastal currents, there are several influences at work around Kuching: the strong wind due to the monsoon winds. And it is during the southwest monsoon period, specifically, that these winds push on the surface waters and thereby influence the flow patterns along the coast. Whereas with northeast monsoon wind arriving, different wind-driven forces carry along their type of changes in the direction of currents.

Apart from that, sea-floor topography around Kuching also plays an important contributory role. The geometry related to the coastline, with its bays and headlands and submarine ridges, acts to accelerate or deflect the flow of the currents. For example, at places where the water approaches a headland, it is deflected, creating complicated eddies and swirls in the adjacent areas.

Furthermore, the input of freshwater from rivers that discharge directly into the sea in the vicinity of Kuching makes a great difference in the density of its coastal waters. On the shores of Kuching lie the River Sarawak sediments and fresh water, which alter the salinity and density gradients in water by acting on the modification of the circulation pattern in the coastal currents.

3. How to Observe the Coastal Water Flow of Kuching?

There are a few methodologies available to observe the flow of water near Kuching's coastline.

Surface Drifting Buoy Method: This involves buoys deployed at the water surface and allowed to drift with the currents. By means of satellite or other positioning systems, one is able to notice, through time, the displacements of these buoys take place in a given direction and with a given speed. In any case, this method gives information only for the surface layer and for this reason may not satisfactorily represent currents at greater depths.

Anchored Ship Method: In this method, a ship is anchored in some location in coastal waters. With the use of instruments such as current meters lowered from the ship in the water at various depths, the flow characteristics can be measured. However, this method is not without its drawbacks because the presence of the ship itself may interfere, to a certain extent, with the natural flow of water.

Acoustic Doppler Current Profiler (ADCP) Method: Nowadays, this is a more state-of-the-art and also a handy measurement method. It can yield detailed information on the velocity profile of the water column from the surface down to a depth.

4. How does the ADCP working with the Doppler Principle work?

The ADCP current meter make use of the Doppler principle. They send acoustic signals into the water. These acoustic waves interact with moving particles in the water-sediment particles or small organisms-and through the Doppler effect, the frequency of the reflected waves changes. From this frequency shift, velocity in the water at different depths can be calculated. The ADCP flow meter has several transducers to transmit and receive these acoustic signals in several directions so that the ADCP current profiler can build up a comprehensive picture of the water flow velocity in three dimensions in the water column.

5. What is required to achieve high-quality measurement of currents on the Kuching coast?

The various aspects related to equipment become very important in high-quality measurement of the coastal currents near Kuching. The first aspect is material reliability, whereby the ability of the equipment is able to bear up against a hostile marine environment due to corrosion by seawater and due to waves and currents that mechanically cause stress.

Second, the size should be small and lightweight. This facilitates equipment deployment on boats, buoys, or at the seabed. A lightweight and compact design would further enable flexible installation and reduce the impact on the measuring environment.

The other crucial factor is the low power consumption. In many applications where battery-powered or remotely located measurement setups are used, it means that due to low power consumption, the equipment can function continuously for a much longer period, thus requiring fewer battery changes and consequently fewer problems with power supply.

Cost is another factor that should be considered. For large-scale measurements, it should allow for reasonably priced equipment. In this respect, it is preferable to make the casing of ADCP profiler from titanium alloy. The advantages of titanium alloy are many. Not only does it possess excellent resistance to corrosion, which is crucial in salty and usually corrosive water; but also the strength is sufficient for the external forces in the water without being heavy. Therefore, it is also ideal for the casings of ADCP meter.

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

Several factors have to be considered while choosing appropriate equipment for current measurement near Kuching. Based on different usage scenarios, types of ADCPs can be chosen. For example, if the measurement is to be done from a ship, then a shipborne ADCP is appropriate. It can be mounted on the hull of the ship and can continuously measure the flow of water as the ship moves or is stationary in the coastal waters.

The bottom-mounted or sitting ADCP will go into operation if the aim is toward the measurement of currents near the seabed. It is fixed on the seabed and provides good information about water flow close to the bottom.

A buoy-mounted ADCP would be very effective in measurements within areas where a floating setup is more convenient. It can be attached to a buoy and, while floating in the water, make measurements of currents at different depths.

Besides this, all other factors being equal, different frequencies of ADCPs are suited best for different water depths. For water depths up to 70 meters, a 600 kHz ADCP can be a good option. Where the water depth extends up to 110 meters, a 300 kHz ADCP should be employed. If the depth of the water is up to 1000 meters, then a 75 kHz ADCP can yield a reliable measurement.

There are several well-known ADCP brands on the market, including Teledyne RDI, Nortek, and Sontek. However, a highly recommended Chinese ADCP brand is China Sonar PandaADCP. The material used in its manufacture is all-titanium alloy, which obviously ensures that it has a high quality for durability, guaranteeing excellent performance in the marine environment. In addition, it has an amazing cost-to-performance ratio. You can learn more about it on its official website: https://china-sonar.com/.

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