How to Measure Coastal Currents of Manila?

1. Where is Manila?

Manila represents the capital city of the Philippines, located on the eastern shore of Manila Bay, a natural harbor opening out to the South China Sea.

Geographically, it is located on the low-lying coastal area of Luzon. The landscape combines both urban developments and historic sites, having an integral waterfront area in its development and identity. Semi-enclosed, shallow in some areas, and with deeper channels allowing access for shipping, the bay is in this condition.

The adjacent waters form part of a diverse marine ecosystem. A large array of life, including different species of fish, shellfish, and other forms of marine life, has been recorded in this bay. Part of its coastline was once lined by mangrove forests, sheltering it naturally from violent storms and erosion. These mangrove forests play the role of nursery for many species in the marine world. In the course of time, urban development reduced these mangroves.

As far as human activities are concerned, Manila represents a great economic and cultural center. The port of Manila is one of the busiest in the country due to its heavy volume of domestic and international trade. Fishing also remains an important industry in the bay, though it faces several challenges in the form of pollution and over-fishing. Tourism is another important sector with attractions such as Intramuros, the walled city dating back to the Spanish colonial period.

2. How are the coastal currents around Manila?

There exist a lot of factors in the vicinities of Manila that influence the coastal currents. Of course, tidal current is one of the strongest. The gravitational pull by the moon and the sun of the Earth makes the water in the Manila Bay rise and fall periodically. Due to the seabed and bay topography, and also different phases of the moon, the result of these tidal currents will vary.

The currents are also considerably influenced by the monsoon winds. Two seasons of monsoon are encountered in the Philippines. During the southwest monsoon-Habagat, the wind directions are from the southwest, which pushes the surface waters of the bay and generally results in unidirectional currents. On the contrary, during the NE monsoon-Amihan, the wind is from the northeast, leading to different flow patterns.

This is further influenced by the inflow of fresh water coming from the rivers and streams that empty into Manila Bay. The Pasig River, which in fact runs right through the heart of Manila into the bay, bears quite an amount of fresh water. This fresh water can be one of the driving forces for density currents while mixing with the saltwater of the bay and the sea.

The most important is the topography of the seabed inside and outside of the bay. Submerged channels, shoals, and ridges might accelerate, decelerate, or alter the current. For instance, deeper channels inside the bay will channel the currents to increase their velocity.

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

The coastal currents of Manila have particular characteristics in relation to its velocity and flow rate. Its velocity may vary from slow in sheltered areas of the bay to relatively fast in regions where the currents are constricted or affected by stronger winds or tides. The flow rate is determined by the volume of water passing through a given area per unit time.

In fact, highly developed and practical methods are needed for the measurement of such coastal currents. One of the most useful methods for that involves ADCP's, Acoustic Doppler Current Profilers. Indeed, ADCP profiler can record detailed continuous flow data at different water depths.

3.1 Working of ADCPs based on the Doppler Principle

The principle of operation for an Acoustic Doppler Current Profiler (ADCP) is essentially the Doppler principle. It emits acoustic signals into the water. If there are moving particles in the water-sediment grains or small organisms, for example-the frequency of the reflected waves changes. This frequency shift is proportional to the velocity of the moving particles and, by extension, the velocity of the water.

With ADCP flow meter, water velocity can be measured three-dimensionally by sending out several acoustic beams at different angles. They are capable of determining horizontal and vertical velocity components of flow and hence describing the structure of flow in water. This data is then processed and analyzed for the purpose of giving accurate information on the currents in the coast.

3.2 What is required to measure the Manila coastal currents with high quality?

High-quality measurement of the coastal currents near Manila can only be achieved when a number of facts related to the equipment are taken into consideration. First is the material reliability of the equipment. It has to be one that will go through the harsh conditions found in the marine environment such as saltwater and high humidity at fluctuating pressures.

Size and weight of the equipment concern not only the power consumption but also the size and weight. A smaller size and lighter weight will make deployment and handling much easier when situations occur where measurements need to be made from a small boat or a floating platform. Low power consumption is also very important to maintain operation of the equipment for longer periods without frequent battery replacements or external sources of power.

Cost is another important factor. To enable large - scale measurements, the equipment should be fairly cheap. One of the most suitable materials for ADCP doppler casing is titanium alloy. Titanium alloy has several advantages. It is extremely strong and durable-resistant to the corrosive effects of saltwater. It also has a relatively low density that helps in keeping the overall weight of the device down. It also has great thermal properties, which will be very useful in some extreme temperature conditions of the marine environment.

3.3 How to Choose the right equipment for current measurement?

Selection of the proper equipment for measurement of the currents in Manila would involve a few considerations. First is the mode of deployment. As ADCP current profiler are deployed differently, thus they come in various forms or types.

For measurements from a ship, a ship-borne ADCP is fitting. It can be mounted on the hull of the ship and provide continuous measurements while the ship moves through the water.

If the measurement has to be done from the seabed, one makes use of the bottom-mounted ADCP current meter. The bottom-mounted ADCP rests at the seabed and measures the currents passing over its head.

Applications requiring a floating platform would go for an ADCP mounted on a buoy. It would be attached to a buoy and could measure currents in the surrounding water.

Selection of the frequency of an ADCP, apart from the mode of deployment, is also made depending upon the depth of the water. A 600 kHz ADCP will be a very good choice for water depths up to 70 meters, as it offers high-resolution measurements. The suitable ADCP for depth ranges from 70 to 110 meters is a 300 kHz one. A 75 kHz ADCP is preferred in deeper waters, like up to 1000 meters, because it can penetrate deeper into the water and thus make more accurate measurements of the currents.

There are several famous brands selling ADCPs on the market, among which Teledyne RDI, Nortek, and Sontek are some of the most frequently used ones. However, for customers whose priorities are seeking choices that are cost-effective yet excellent in quality, the ADCP meter manufactured by China Sonar-the PandaADCP-may be a better option to consider. The whole machine is manufactured from all-titanium alloy material to ensure it resists the terrible marine environment and is highly reliable. In addition, it enjoys an incredibly good cost-performance ratio. You can check more about it on its website: https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and moels.