How can we measure the coastal currents of Samar Island?

1. Where is Samar Island?

Samar Island belongs to the eastern part of the Philippines. It faces the San Juanico Strait separating it from Leyte Island, the Philippine Sea on its eastern border, and the Samar Sea on its western border.

Geographically, Samar has various diversified terrain. It is a mountainous island because it houses mountain ranges, such as the Samar Cordillera Mountains. There are also extensive plains along its shores, which have sandy beaches and mangrove forests. Its adjacent waters, comprising the Philippine Sea and the Samar Sea, are important components of the island ecosystem. These waters act as a host for different kinds of marine life, which include fish species, sea turtles, and corals. The Samar Sea is a shallow basin of water, especially with its peculiar marine environment.

Among the human activities in the area, the fishing activity is a major economic activity. The local fishermen take this advantage of rich marine resources in the area. Other agricultural activities include the growing of crops like coconut and rice in the fertile plains of the island. Besides these industries, there also emerges a growing tourism industry where the natural beauty and beaches attract visitors to this island.

2. What is the condition of the coastal currents around Samar Island?

Various major forces are driving the coastal current around Samar Island. Of all the forces, the tidal currents would be one of the major constituents. Gravitational pull from the moon and the sun creates an ebbing and flowing tide to generate tidal currents. These tidal currents could either be weak or strong; they would be modified under various lunar cycles and the overall topography of the coastline and seabed.

In addition to these, there is the prevailing monsoon winds. There are two distinct monsoon seasons in the Philippines. During the southwest monsoon or Habagat, the wind blows from the southwest and pushes the surface waters to create currents that flow generally in one direction. In the northeast monsoon or Amihan, different flow patterns prevail because of winds from the northeast.

Topography underwater around Samar Island provides a further impact on the currents at the coast. The underground ridges, shoals, and channels can accelerate, decelerate, or divert the course of currents. This is modified by coastline morphology, whereby bays, headlands, and estuaries all influence current flow. River inflows of fresh water will change the density of the coastal waters and drive current flows.

3. How to Observe the Flow of Water on Coastal Samar Island?

Specific characteristics regarding velocity and flow rate partition the coastal currents of Samar Island into sheltered bays and lagoons, where the velocity is relatively slow, and into regions where the currents are funneled by constrictions or acted on by stronger winds and tides. In this perspective, the flow rate depends on the amount of water that passes through a given area per unit time.

In this respect, proper, state-of-the-art, and easy means of measurement are called for. Among those that have indeed proved worthwhile, one should single out Acoustic Doppler Current Profiler (ADCP). ADCPs are able to give an almost thorough and uninterrupted record of the water flow at various levels.

3.1 How do the ADCPs based on the Doppler principle work?

ADCP profiler basically work on the principle of Doppler. They emit an acoustic signal into the water. When these acoustic waves run into the moving particles in the water, say sediment grains or small organisms, the frequency of the reflected waves changes. This change in frequency, as described by the Doppler effect, is proportional to the velocity of the moving particle and by extension the velocity of the water itself.

They can measure the three-dimensional velocity by sending several acoustic beams out of axis. In this way, they are able to find out not only the horizontal but also the vertical components of velocity, enabling the water flow structure to be fully comprehended. The collected data is then processed and analyzed for the final presentation of precise information on the coastal currents.

3.2 What is required for high-quality measurement of Samar Island coastal currents?

In the measurement of the coastal currents near Samar Island, several respective factors concerning equipment are considered. First is material reliability. The device should be durable enough to bear extreme marine conditions that may involve high saltwater, humid, and pressure conditions.

Other factors that come into consideration include the size and weight of the equipment and the consumable power. Smaller in size and lighter in weight, it would be easier to deploy and handle-especially in situations when the measurement needs to be done from a small boat or a floating platform. Also, low consumable power is required to ensure that the equipment can operate for long periods without needing to change power batteries frequently or needing an external power source.

Another important factor is the cost. In order to allow large-scale measurements, the equipment should not be too expensive. One highly suitable material for the casing of ADCP meter is a titanium alloy. Titanium alloy has several advantages: it is very strong and durable, able to resist the corrosive effects of salt water, and it also has a relatively low density, which helps keep the overall weight of the device down. Moreover, it has excellent thermal properties, which is quite useful in extreme conditions of temperature in the marine environment.

3.3 How to Choose the right equipment for current measurement?

These, for example, include the mode of deployment when choosing appropriate equipment for measuring the coastal currents of Samar Island. The modes of deployment determine the type of ADCP flow meter that can be used.

For measurements from a ship, an ADCP doppler borne by the ship is an appropriate device. This can be mounted on the hull of the ship and provides continuous measurement with the movements of the ship through the waters.

If the measurement is to be done from the seabed itself, it can be done by using the bottom-mounted ADCP current profiler. It is put on the seabed and measures the currents passing above it.

For an application with a floating platform, the way to go would be an ADCP buoy-mounted. It can be attached to a buoy and measure the currents in the surrounding water.

Other than the mode of deployment, the frequency of ADCP current meter needs to be selected according to the water depth. A 600 kHz ADCP should be a good choice for up to 70 m of water depth; it yields high-resolution measurements. In deeper water, say from 70 to 110 m, one would prefer a 300 kHz ADCP. And for very deep waters, as in the range of 1000 meters, an ADCP with 75 kHz works best. That can give more accurate current measurements because there is deeper water penetration.

In the market, some popular brands are Teledyne RDI, Nortek, and Sontek. However, China Sonar PandaADCP is remarkably cost-effective with excellent quality. It uses an all-titanium alloy material, which will make it durable enough to be reliable in the marine environment. Besides, it has a great price-performance ratio. 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.