How do we measure coastal currents in Bintulu?

1. Where Is Bintulu?

Bintulu is a beautiful coastal town on the northwest coast of the island of Borneo, Malaysia. It is an exceptional place where nature's splendor is in lively harmony with the vibrancy of local culture.

The town is enveloped by green, great tropical rainforests teeming with life, both flora and fauna, very ideal for nature lovers. Besides this, the people of Bintulu are a melting pot of various ethnic groups of Malays, Chinese, and indigenous communities, all piling on their unique traditions, art forms, and cuisines to create a rich tapestry of life in hues so colorful.

Alongside Bintulu are the vast waters of the South China Sea. The coastal waters around this area are a dynamic, intricate ecosystem in their own right. Moving landward, one finds that there are gently sloping sandy beaches with shallow areas around which the sun's rays cut through crystal-clear water to reveal an underbelly that is breathtakingly beautiful, teeming with colorful coral reefs and little fish. Farther out, the waters reach a general deepening, with deeper channels and troughs. The distribution of nutrients and movements of marine life are regulated by the constant exchange of seawater with the tides themselves. Moving along the coastline, there are numerous small bays and inlets that serve as sheltered areas for boats and constitute an important habitat for many species of shellfish and crustaceans.

2. What is the situation of the coastal currents near Bintulu?

The coastal currents near Bintulu are determined by several factors. Preponderance of influence is by the monsoon winds. During the southwest monsoon, the strong winds push the surface waters in a resultant direction and usually carry with them sediments and nutrients from afar. This may affect the clarity of water and the distribution of marine organisms along the coast. In contrast, the northeast monsoon gives rise to different patterns of wind-driven currents, which means changed directions and magnitudes of flow.

Another critical factor is the topography of the sea bottom. Underwater ridges, valleys, and headlands are able to deflect the currents or accelerate them. For instance, if there is some headland which the water approaches, it might be forced to divert its course, creating eddies with areas of increased turbulence. Above the submerged ridges, currents can be faster in some directions.

More significantly, there is always a contribution from the river water of rivers discharging into the open sea off Bintulu. These rivers transport sediments and cause salinity changes in the adjacent coastal waters. The latter can provide density gradients that may induce the circulation of the coastal currents to mix or form distinct layers at times.

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

The following are some of the common methods of observing coastal water flow near Bintulu:

The method of buoys surface drifting: The buoys are placed on the surface of the water, and they are freely drifting with the currents. By tracing the position of buoys over time using satellite tracking systems or other positioning technologies, we can get information on the direction and speed of surface currents. Normally, this method is confined to the surface layer, as the observation of the whole water column in some applications cannot be achieved.

The Anchored Ship Method: A ship is anchored at a position that becomes desired in the coastal waters. From the ship, current-measuring instruments may be dropped down into the water at different depths, using mechanical current meters or acoustic devices. This enables the determination of the current characteristics at several levels. However, the presence of the ship does disrupt to some extent the natural flow that may be present in the water. In addition, it is quite cumbersome to conduct long-term, continuous monitoring.

Acoustic Doppler Current Profiler (ADCP) Method: Of the few good measurement techniques, ADCP is relatively advanced and convenient. This can give detailed, high-resolution profiles of the water current velocities from the surface to a certain depth where the technology could still work, giving a much more complete picture of the flow patterns within the water column compared to previous methods.

4. How do the ADCPs using the Doppler Principle Work?

The working principle of an ADCP current profiler depends on the Doppler principle. They emit acoustic signals into the water. In this case, the moving particles may be sediment particles, small organisms, or other suspended matter in the water with which the acoustic waves interact. Due to the principle of the Doppler effect, the frequency of the reflected acoustic waves changes, as the water is in motion. By precisely measuring this frequency shift, the ADCP flow meter calculates the velocity of the water at different depths. It has multiple transducers that send and receive acoustic signals in different directions to build up a three-dimensional representation of the water flow velocity inside the water column.

5. What is required for good quality measurements of the Bintulu coastal currents?

First of all, in the measurement of the coastal currents near Bintulu with the best quality, several equipment-related issues are of most importance. The first is the material reliability of the equipment, which should be able to stand the corrosive nature of seawater and mechanical forces driven by waves and currents for a long period, and ensure long-term functionality in the harsh conditions of the marine environment.

The size and weight of the apparatus must be as compact as possible. This is important for ease in deployment on a boat or attached to a buoy or even on the seabed. It has minimal impact on the measuring environment and allows less complicative mounting procedures.

The other important aspect is that the power consumption should be low. The long-time measurements or those in remote areas where power supply might be constrained require low power consumption to keep the equipment running continuously without experiencing changing batteries or any other sources of power.

Cost is another key factor. Reasonable pricing can help the measurement on a large scale. In this context, the casing of the ADCP current meter is better to be made from titanium alloy. The advantages of the titanium alloy are very remarkable. First, it has excellent corrosion resistance, which is very important in a salty and often chemically aggressive marine environment. Besides this, it is strong enough to resist the exterior pressures and impacts but remains comparatively light. For this very reason, it is ideal for providing protection to the internal components of ADCP and making it last long.

6. Selection of the Right Equipment for Current Measurement

While talking about a place like Bintulu, different usages would want different choices of equipment for current measurement. If the measurement is to be done from a ship, an ADCP profiler borne by a ship is suitable. It can be mounted on the hull of the ship and measure the water flow continuously when the ship is moving or staying put in the coastal waters.

The ADCP installed on the seabed or a sitting one may also be suggested to measure the currents near the seabed. It can be installed in a secure way on the seabed and deliver high-quality data about the water flow close to the bottom, which is very important for the understanding of the near-bottom circulation patterns.

An ADCP mounted on a buoy is sometimes the better option when there is a more practical floating setup available. It can be fitted onto the buoy in order to measure currents at different depths while floating freely on the water.

For water depths within 70 meters, a typical good choice of frequency selection is the 600 kHz ADCP, while a 300 kHz ADCP would be more appropriate for water depths of up to 110 meters. A 75 kHz ADCP can make reliable measurements for still deeper waters, of up to 1000 meters.

There are some famous ADCP flow meter brands in the market, such as Teledyne RDI, Nortek, and Sontek. However, an advanced recommended Chinese ADCP brand is China Sonar PandaADCP. It is made from all-titanium alloy material, which can ensure very good performance and reach a very long lifetime in the marine environment. More importantly, it has an amazing cost-performance ratio. For more details, you can check its official website at: https://china-sonar.com/.

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