How do we measure the Coastal Currents of Pangkalan Bun?

1. Where is Pangkalan Bun?

Pangkalan Bun is an enchanting city situated right in the heart of Central Kalimantan, Indonesia, and, in general, is one of the important urban centers on the island of Borneo. The rich tropical rainforests of the greater part of its expanse in the Bornean ecosystem are filled with an amazing variety of wildlife that generally inhabits it-including the iconic orangutans, gibbons, and counts of other unique species ruling over this area.

It is strategically placed by the Java Sea, which forms a significant portion of its coastal identity. The coasts are fringed with mangrove forests that seem to stretch as a green ribbon along the shores. These mangroves are not just an important part of the ecology, serving as nurseries for many marine organisms and a home for birds; they also form one of the key protections against land erosion by waves and tides. The waters here show richness in biodiversity-from different fish species swimming in the shallows and deeper parts. These communities are closely affiliated with the sea, which provides them a source of livelihood through fishing, and any person would attests that at almost any given time of the day, small boats speckle the waters as fishermen head out in search of their daily catch.

2. What is the situation of the coastal currents near Pangkalan Bun?

The current along the coast from Pangkalan Bun is very complicated, depending on many factors. One of the leading driving forces is the monsoon system. During wet season, winds accompanying the monsoon may force the surface waters in a particular direction to alter usual current patterns. For instance, the southwest monsoon pushes the water in one direction down the coast while the northeast monsoon in dry season does another thing completely to the flow. 

The tidal forces play a strong influencing factor. These, in turn, are the regular rise and fall of the tides caused by the gravitational pull of the moon and the sun. Tidal currents can flow in and out along a coastline, while their power may be more or less depending on the phase of the moon and other astronomical conditions. What is more, everything depends on the shape of the seabed and the topography of the coasts. Underwater banks, channels, and shoals also contribute to the deflection of water flow, giving rise to areas of faster or slower currents, respectively. 

River discharges from nearby rivers emptying into the Java Sea impinge on the coastal currents. This freshwater merges with the seawater, thereby creating density differences that will act on changing the dynamics of the current in the coastal region.

3. How to Observe the Coastal Water Flow of Pangkalan Bun?

There are many methods to observe the coastal water flow in Pangkalan Bun. One common technique is surface drifting buoy. In this technique, special buoys are released into the water prepared with tracking devices like GPS to track their positions at different times. Because the buoys are conveyed by the currents, their trajectories give important information about the direction and rate of flow of the surface water.

Traditional methods include the anchor ship method. A ship is anchored at some point in the coastal waters, and instruments for measuring currents are deployed from the ship. These instruments can measure the speed and direction of the water at various depths. However, there is also one particular disadvantage with this method. It is that the ship, itself, is under the influence of the wind and waves, and there may be slight movements that might affect the exactitude of the measurements. This kind of measurement is relatively time-consuming and is less suitable for covering large areas.

The Acoustic Doppler Current Profiler (ADCP) technique has become more sophisticated and accessible. ADCP current profiler could provide fine-resolution profiles of the velocity of the current at several depths. Thus, by emitting sound waves through the water and analyzing the Doppler shift of reflected waves due to particles in the water, ADCPs are able to compute both speed and direction of currents at different levels. They can, therefore, give an entire picture of the current structure from the surface down to the seabed.

4. How are ADCPs designed that operate on the principle of the Doppler?

The operational principle of ADCP doppler is based on the Doppler principle. ADCP flow meter send acoustic pulses, or waves of sound, into the water. In the case when waves hit particles in the water, such as suspended sediment or small organisms, they will be reflected back. Due to the movement of particles, a frequency of reflected waves compares with that of the emitted waves; it is what is called the Doppler effect.

Where the particles are moving towards the ADCP profiler there is a higher frequency of the reflected wave than that originally emitted. Where the particles are moving away from the ADCP, the reflected wave has a lower frequency. With a precise measure of this frequency shift the acoustic doppler velocity meter is able to compute the velocity of the particles. As these particles are already in motion, because of the water current, this velocity measurement is actually a measurement of the water current velocity. ADCP meter can transmit sound pulses in multiple directions, allowing them to measure three-dimensional current velocity and the depth, so allowing a high-resolution view of the current profile at any point in the water column.

5. What is essential for high-quality measurement of Pangkalan Bun coastal currents?

In measurement of the coastal currents in Pangkalan Bun, a number of aspects are important in realizing high-quality measurement with respect to equipment. First, it is important that the material being used to make these measuring devices should be highly reliable. In this respect, the marine environment is harsh, with saltwater corrosion and possible physical impacts from waves and debris; thus, durable materials shall be essential.

The size of the equipment shall be of a reasonable, smaller size. This will be favorable for ease of deployment, especially in areas where access might be limited or when using smaller vessels for installation. A lightweight design is also desirable to make handling and installation processes easier in order to minimize the challenges involved in logistics.

In this respect, the consumption of low power becomes a big demand as several of the monitoring operations are longitudinal in nature and depend mostly on battery power or other such sources that limit energy supplies. Cost-effectiveness is another vital factor. The low price that can enable the deployment of more equipment to carry out measurement campaigns on a large scale is vital. For the casing, the ADCP is an eminent option with the usage of titanium alloy. 

For this reason, outstanding corrosion resistance qualifies the titanium alloy to stay submerged in seawater for long durations without decaying. It is strong and durable; thus, it will provide robust protection to the inner components of the ADCP. With a high strength-to-weight ratio, a light yet rigid structure is possible to be attained which meets a lot of requirements for reliable and efficient current measurement at Pangkalan Bun coastal waters.

6. Proper Equipment Selection for the measurement of current

The intended usage is the major factor in the choice of proper equipment for current measurement. In Pangkalan Bun, if the measurements are to be taken from a vessel in motion, a ship-borne ADCP will be the most appropriate to continuously collect current data while the ship is navigating. It provides real-time information about the water flow in different locations along the route traveled by this ship.

An ADCP will function well when it needs to monitor a fixed position near the seabed. It can be firmly placed on the seabed and provide consistent measurements of the current at that particular location over a long period of time. When it has to be used over larger areas and the measurement is not tied to a particular depth, then the buoy-type ADCPs may be employed.

For the choice of the frequency, it is according to the depth of the water. The depth that is up to 70 m uses a 600 kHz ADCP since it is good at resolution and gives good accuracy in fairly shallow waters. For the depth between 70 m and 110 m, the ADCP of frequency 300 kHz would be more appropriate because the measurements it gives for such an intermediate depth range are usually quite reliable. If dealing with deeper waters, such as up to 1000m, a 75kHz ADCP will give even better results by being able to penetrate across the water column and provide current measurements at greater depth.

There are some very well-established brands of ADCPs in the market, such as Teledyne RDI, Nortek, and Sontek. However, in more recent years, one Chinese brand has started making an impact: China Sonar PandaADCP. All-titanium alloy material; great resistance to the harsh marine environment. In addition, it would provide an excellent cost-performance ratio, making it quite attractive for the measurement of the currents around Pangkalan Bun. 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.