How to Measure the Coastal Currents of Semarang?

1. Where is Semarang?

Semarang is a major city in Central Java, Indonesia. The city is on the north coast of Java and is essentially an important port city. The city has historical architecture, very vibrant street life, and a blend of Javanese and Dutch colonial cultures.

The coast of Semarang is a very busy port; this is a place of shipping and trade in the region. The city's location on the Java Sea makes it a strategic point for maritime activities. There are also some natural coastal features like beaches and fishing villages. The local population engages in fishing and other marine-related activities, which are an important part of the local economy.

The Java Sea, which faces the land, houses many living species of saltwater fish, shellfish, and coral. The mangrove forests on the coast provide the important function of protecting the shoreline from erosion conditions and a home for many organisms, including small fish and birds.

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

Multiple factors interact to effect change in the coastal currents near Semarang. Tidal current tends to be one of the most dominant factors. The tides of the Java Sea are semi-diurnal-a result of the gravitational pull of the moon and the sun. In simple terms, this means there is a repetition of two high tides and two low tides every day. Tidal currents may be very strong, especially near the coastline and where the water is constricted, for example around the entrance to the port. These currents are significant for sediment and nutrient transport.

Monsoon winds also have a major impact. From May to September, the southwest monsoon brings strong winds that can drive the surface currents in a particular direction. The northeast monsoon from November to March changes the wind direction and therefore the direction and speed of the coastal currents. The tidal and monsoon driven currents interact in a way that generates a very complicated flow.

In such a case, the dispersion of the coasts, for example, ridges, channels, and shoals, can divert and alter the coastal current flow. River discharge can also contribute to altering the current pattern. This can include the freshwater input from these rivers, leading to density contrasts in the water that promote more complex current systems.

3. How to observe the Semarang coastal water flow?

There are a few ways to observe the flow of coastal water in Semarang.

The Surface Drifting Buoy Method

This is an easy and practical way. Buoys are released into the water and have GPS or any other tracking devices. This buoy will be carried by currents, and movement over time can be tracked to determine the directions and speeds of surface currents. The buoys can be produced with durable materials that can withstand the marine atmosphere, with various sizes according to the requirements. For instance, smaller-size buoys may be utilized for more precise short-term measurements in specified areas while larger buoys covering a wider area can carry more advanced sensors.

Anchored Ship Method

It involves anchoring one ship at a place and then measuring the water flow with current-measuring instruments at different depths. This method also has several limitations. The ship may be influenced by waves and winds, which may eventually result in incorrect measurements. It is also not that effective in covering a wide area. The instruments used may include current meters that measure the speed and direction of the water at a particular point. These meters work on different principles, such as mechanical rotation or electromagnetic induction, depending on the design.

The Acoustic Doppler Current Profiler (ADCP) Method

This is one of the more advanced and efficient ways of measuring the flow of water in a coastline. ADCPs can measure the profile of water current velocities in a range from very shallow to very deep. Simply put, they work by sending out sound waves into the water and then analyzing the Doppler shift in the waves that return. This gives a very good indication of current structure from the surface to the seabed with great detail. Usually, ADCPs are mounted on boats, buoys, or even on the seabed, depending on the purpose.

4. How do ADCPs using the principle of Doppler work?

The ADCPs apply the principle of the Doppler effect to function. They emit acoustic pulses, which are basically sound waves, into the water. Particles in the water-like sediment, plankton, and other small particles-interact with these sound waves. Whenever the reflected sound waves bounce off the mentioned particles and get back to the ADCP current meter, the frequency of the reflected waves changes due to the Doppler effect.

If the particles are moving towards the ADCP current profiler, the frequency of the reflected wave is higher than the emitted one. On the other hand, if the particles are moving away from the ADCP, the frequency of the reflected wave is lower. The ADCP measures this frequency shift accurately and from that computes the velocity. Since the particles are moving with the current of the water, the velocity calculated for the particles provides the measure of the water current's velocity.

These ADCPs can emit sound pulses in multiple directions. Because of this, they can measure the current velocity in three - dimensional space and at different depths. Such a profiler would record the current velocity in a vertical profile over a certain interval between the surface and seabed, giving a picture of the current structure.

5. What's needed for high - quality measurement of Semarang coastal currents?

The measuring of the coastal currents in Semarang should be of high quality; thus, the equipment has to be made of reliable materials. Since the seas are very harsh, with saltwater corrosion and possible physical impacts from waves and debris, one will need a casing that can support it. It has to be resistant to the corrosive actions of the seawater over quite some time and should not allow internal components to damage easily.

The size of the equipment should be small enough for easy deployment, in particular in areas of limited access, such as in small boats or in shallow coastal waters. It should be of lightweight design to enable convenient handling and installation.

Low power consumption is required for long - term measurements. Cost - effectiveness shall allow for large - scale measurements. The material used is required to be made of Titanium alloy in casing. Titanium alloy has good corrosion resistance, which plays an important factor in the marine area of Semarang. It shows great resistance to saltwater effects that might take a very long time. Besides, it is strong and with high strength-to-weight ratio, yielding durability and lightness of weight that protects internal components of the ADCP doppler.

6. How to Choose the Right Equipment for Current Measurement?

In choosing the right equipment for current measurement in Semarang, the first consideration is usage.

For Measurements from a Moving Vessel

An ADCP doppler deployed on a ship is adequate. During the process, the ship could be traveling, as there can be real-time current data. The current's flow will be seen relatively well in various spots where the vessel travels over. The shipborne ADCP profiler must, therefore, be robust for the movement and various vibrations of the ship and give correct readings.

For Measurements at a Fixed Location near the Seabed

A bottom-mounted ADCP meter would be a good option. It can monitor the current continuously at a point. This type of ADCP profiler is usually much more stable and can provide regular data over time. It has to be installed and fixed on the seabed properly to avoid displacement by currents or any other means.

For Measurements that Need to Cover a Wide Area and are not Restricted to a Specific Depth

A buoy - type ADCP profiler is appropriate. It can cover a larger area and is not limited to a particular depth. The buoy - type ADCP current profiler should be designed to float stably and carry the necessary sensors and communication devices to transmit the data back to the shore or a receiving station.

Regarding the frequency choice, for a water depth up to 70m, one should choose a 600kHz ADCP. For 70-110m, a 300kHz ADCP is more advisable. For very deep waters of up to 1000m, a 75kHz ADCP is recommended.

There are well - known ADCP current meter 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.