How to Measure the Coastal Currents of Surabaya

1. Where is Surabaya?

Surabaya, the second-largest city in Indonesia, is situated on the northeastern coast of Java. This is a very important industrial and commercial center, housing one of the busiest ports in the country-a gateway for trade in the region.

Rich in history and cultural heritage, the city embodies a population from diverse ethnic groups such as the Javanese, Madurese, Chinese, and others. Examples are the architecture that consists of ancient temples, colonial buildings, and modern skyscrapers.

The Madura Strait is another major body of water lying alongside. Surabaya's coastal areas combine industrial zones, fishing ports, and recreational beaches. The waters are rich in different types of fish, prawns, and crabs. There are many mangrove forests along the coasts, which help protect the shoreline from erosion and provide habitat for a myriad of organisms.

2. What is the situation of the coastal currents in the vicinity of Surabaya?

The coastal currents in the immediate vicinity of Surabaya are determined by more controlling factors: tidal currents exert the most dominant forces. In the Madura Strait, tides are semi - diurnal, a result of the gravitational pull of both the moon and the sun. There are two high tides and two low tides each day. Tidal currents can be quite strong, especially near the narrow parts of the strait and around the port area. It plays a vital role in the transportation of sediments and nutrients.

Monsoonal winds also play a significant role. The southwest monsoon from May to September creates a strong wind which is able to drive the surface currents in a specific direction. The northeast monsoon, which takes place from November to March, shifts the direction of the wind, hence altering the direction and speed of the coastal currents. In this way, the interaction between tidal and monsoon-driven currents produces a very complex flow pattern.

It may be a function of the local bathymetry, including underwater topography like ridges, channels, and shoals, which can divert and change the direction of flow in coastal currents. Discharges of rivers into the sea, such as the Brantas River, also influence the current pattern. Freshwater input from these various rivers may cause density differences and thus result in complex current systems.

3. How to observe Surabaya's coastal water flow?

There are several methods to observe the coastal water flow in Surabaya.

The Surface Drifting Buoy Method

This is a very simple and practical way to measure the surface currents. Buoys are thrown into the water, equipped with GPS or some other position-tracking devices. While the buoys are carried by the currents, one can observe their position and movement over time to determine direction and speed of surface currents. These buoys need to be durable enough to withstand the marine environment and need to have proper buoyancy to float stably.

The Anchored Ship Method A ship is anchored at a certain location, and current-measuring instruments are deployed from the ship. These instruments can measure the velocity and direction of the water flow at different depths. This method, however, has some limitations. The ship can be subjected to waves and winds, which could give incorrect readings. It also cannot cover a large area efficiently.

ADCP Method: It is one of the advanced and agile approaches to measuring the flow of water in the coast. ADCPs can measure the velocity profile of the water currents over a wide range of depths. The principle of operation of the ADCPs involves emitting sound waves into the water and analyzing the Doppler shift of the reflected waves, providing a detailed understanding of the current structure from the surface to the seabed.

4. How do ADCPs using the Doppler principle work?

It works on the principle of ADCPs through the Doppler principle. They send acoustic pulses, which are sound waves in water. When these sound waves come into contact with particles in the water-sediment, plankton, and other small particles-the sound waves are reflected back to the ADCP current meter after striking these particles. In this case, because of the Doppler effect, the reflected waves have changed in frequency.

If the particles are moving towards the ADCP current profiler, then the frequency of the reflected wave is higher than the original emitted frequency. If the particles are moving away from the ADCP, the reflected wave frequency is lower. By measuring precisely this frequency shift, the ADCP can compute the velocity of the particles. Since the particles are moving with the current in the water, the velocity that has been calculated of the particles gives the measure of the water current's velocity.

The sound pulses can be emitted in many directions, hence allowing ADCPs to measure the three-dimensional current velocities or at various depths. For instance, in a vertical profile, the current velocities are measured over intervals from the surface down to the seabed. This will provide a full representation of the current structure.

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

For high - quality measurement of the coastal currents in Surabaya, the equipment needs to have reliable materials. Given the harsh marine environment, with saltwater corrosion and potential physical impacts from waves and debris, a durable casing is essential.

In particular, the size of the equipment should be sufficiently small to enable easy deployment, especially in areas with poor access, like on small boats or within shallow coastal waters. A lightweight design is also preferred since this will make handling and installation more convenient.

Low power consumption is indispensable for long - term measurements. Cost effectiveness is also a basic requirement in order to make large - scale measurements possible. In the case of ADCPs, it is desirable for the casing to be made from titanium alloy. Titanium alloy enjoys excellent corrosion resistance, something necessary in the marine environment such as Surabaya. It withstands the erosive action of saltwater for long periods. It is also high in strength and high in its strength-to-weight ratio, thus guaranteeing a durable yet light structure that is capable of protecting the internal components of the ADCP doppler.

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

The usage is the first consideration to be taken into account when choosing the right equipment for current measurement in Surabaya.

For Measurements from a Moving Vessel

A ship-borne ADCP flow meter is suitable for this. It will be able to give, simultaneously, current data in real time while the ship is in motion, thus allowing a better understanding of how the water flows in different locations.

For measurements at a fixed location near the seabed, a bottom-mounted ADCP meter will suffice. It can continuously monitor the current at a point and provide consistent data in that regard over time.

Where the Measurement Needs to Cover a Wide Area and Is Not Restricted to Any Specific Depth

A buoy - type ADCP doppler will be appropriate as it covers a larger area and is not restricted to any particular depth.

In relation to the choice of frequency, for water depths up to 70m, an ADCP current profiler with a frequency of 600kHz can be selected. For depths between 70m and 110m, the 300kHz is more appropriate while a frequency of 75kHz is recommended for very deep waters of up to 1000m.

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.