How to measure coastal currents of Mamberamo?

1. Where is Mamberamo?

Mamberamo River is situated in Papua, Indonesia. It is a big and important river that flows through a vast and relatively big undeveloped region. The area round Mamberamo is generally made up of tropical rainforests and a big variety of flora and fauna.

It finally discharges into the Pacific Ocean. The river's discharge close to its mouth marks the transition between its freshwater environment and the ocean's saltwater. The adjacent coastal area is under the direct influence of the river's discharges, enriched with a huge quantity of sediments and nutrient content. The Pacific Ocean facing this shore is a vast, dynamic body of water with strong waves and intricate systems of currents.

The local population in the Mamberamo region includes indigenous tribes who have a traditional way of life that is intertwined with the river and the surrounding forest. Fishing is an important activity, both in the river and in the coastal areas.

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

Several factors affect coastal currents near Mamberamo. Tidal currents have a very important part to play. The gravitational pull of the moon and the sun influences tides in the Pacific Ocean off the mouth of the Mamberamo. Due to this, tidal currents may be strong in many instances and varied in their direction according as the tide is high, full, ebbing, or low. The nature of the river's outflow interacting with tidal currents creates quite a complex pattern.

The wind patterns also have a strong influence. The trade winds, as well as other seasonal winds, are able to drive the surface currents. Furthermore, the local topography and shape of the coastline may further modify how the winds act upon the currents. Local bathymetry, or shape of the seabed around the estuary and down the coast, can also deflect and alter the flow of the coastal currents. Another important factor is the discharge of the Mamberamo River into the ocean. The freshwater input from the river may create density differences and thereby affect the current patterns.

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

There are several methods to observe the coastal water flow near Mamberamo.

The Surface Drifting Buoy Method

Simple and straightforward, buoys are deployed in the water and fitted with GPS or other position-tracking devices. By knowing the position of the buoys over time, the direction and speed of the surface currents can be calculated as the buoys are carried by the currents. The buoys must be designed for the local marine conditions, including strong wave action and possibly fresh water from the river affecting the buoy's performance.

The Anchored Ship Method

A ship is anchored at a certain site near the coast or in the estuary, and current-measuring instruments are deployed from the ship. Such instruments could measure the velocity of the flow of water and the direction at different depths. However, this method also has some drawbacks. The ship is subjected to oscillation due to waves and winds, and that could lead to erroneous recordings. Additionally, it is not very effective in covering a large area.

ADCP Method

This is a more advanced and efficient way of measuring the flow of water in the coast. The ADCPs can measure the velocity profile of water currents over a wide range of depths. They emit sound waves into the water and analyze 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?

ADCPs apply the principle of the Doppler. They send acoustic pulses or sound waves into the water. The sound waves will be in contact with particles in the water, which may include sediment, plankton, and other little particles. The waves reflected from these particles to the ADCP current meter have a changed frequency due to the Doppler effect.

If the particles are moving towards the ADCP current profiler, then the frequency of the reflected wave is higher than the original frequency it emitted. On the other hand, if particles are moving away from the ADCP, the frequency of the reflected wave is lower. By measuring this frequency shift precisely, the ADCP can calculate the velocity of the particles. Since the particles are moving with the water current, the calculated velocity of the particles is a measure of the water current velocity.

ADCPs are able to transmit sound pulses in several directions, providing them with the capability of measuring current velocity in three-dimensional space and at disparate depths. For instance, in a vertical profile, they may measure current velocity at varied intervals right from the surface to the seabed, thereby painting a full picture of the current structure.

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

For the good quality measurement of the coastal currents near Mamberamo, all its equipment should be made of reliable materials. A durable casing will be required because of the salty, corrosive seawater environment and possible physical impacts by waves and other floating debris.

The size of equipment should be small enough to be easily deployed, particularly when one has to consider areas without good access, such as small boats or shallow coastal waters. A light weight is desirable too because it leads to more convenient handling and facilitates installation.

Low power consumption is highly relevant for long-term measurements. Cost-effectiveness is another important feature in enabling large-scale measurements. In ADCPs, the casing could be made from titanium alloy. It has excellent resistance to corrosion, which is crucial in seawater conditions at Mamberamo. The material could resist for a long period of time against the corrosive action of saltwater. Its toughness and a good strength-to-weight ratio supply a structure that is robust yet lightweight to house the internal parts of the ADCP profiler.

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

While choosing the right equipment for current measurement over Mamberamo, the usage is the first consideration.

For Measurements from a Moving Vessel

A ship-borne ADCP meter is suitable. It can provide real-time current data while the ship is in motion, thus enabling a better understanding of the water flow in different locations.

Measurements at a Fixed Location near the Seabed

The bottom-mounted ADCP flow meter can serve as a decent option. This will be able to continuously monitor the current at a point and give consistent data for a long time.

Measurements That Need to Cover a Wide Area and Are Not Restricted to a Specific Depth

A buoy-type ADCP current profiler would be appropriate because it would cover a much larger area and is not limited to any particular depth.

For the choice of frequency, for water depths up to 70m, a 600kHz ADCP is appropriate; for further ranges between 70m to 110m, a 300kHz ADCP is better; and for very deep waters 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 models.