How will we measure the coastal currents of Cebu?

1. Where is Cebu?

Cebu is a province in the Philippines, containing one large island and numerous small islands. It is bound by Bohol Sea on the western side and Camotes Sea on the eastern side.

Geographically, Cebu Island is irregularly shaped. The mountain range runs across the middle, so the plains are on either side of it. The long coastline hosts many beautiful sandy beaches, coral reefs, and some rocky shores. The Bohol Sea and the Camotes Sea, just off its shores, abound with various marine life. These seas host an enormous range of marine life: colored corals, tropical fish, sea turtles, and many other organisms.

On the human activity side, Cebu is one of the most populated and well-endowed areas. One of the major economic activities is fishing. Fishermen in the community gain largely from the sea and its rich resources. It is among the province's leading tourist destination points because of its beaches, diving sites, and historical and cultural attractions. Cebu City is a very dynamic urban center; it is the capital of this province and is filled with an abounding economy and a colorful history from the time of the Spanish colonization.

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

These coastal currents are influenced by many factors in the vicinity of Cebu. Amongst all, tidal currents are a major influence. Tidal currents result from gravitational pull from the moon and the sun raising and lowering the tides. The strength may vary and sometimes even the direction, due to the lunar cycle and local topography of coastline and seabed.

On the other hand, the monsoon winds also play a big role. There are two monsoon seasons in the Philippines. During the southwest monsoon or Habagat, the wind generally blows from the southwest, pushing the surface waters and creating currents that generally flow in a particular direction. Conversely, during the northeast monsoon, or Amihan, winds from the northeast result in different flow patterns.

The topography of the seabed surrounding Cebu similarly influences the coastal currents. The submerged ridges, shoals, and channels would speed up, slow down, or change the direction of the currents. The shape of the coastline, with bays, headlands, and estuaries, can likewise affect the way the currents flow. Even the inflow of fresh water from local rivers may be considered to affect the density of the coastal waters and thus influence the current patterns.

3. How to Observe the Flow of Water to the Coast of Cebu?

The coastal currents of Cebu vary in velocity and flow rate. Velocity may range from relatively slow in sheltered bays and lagoons to fast in areas where the currents are constricted or subjected to heavier winds and tides. The flow rate depends on the amount of water passing through a given area per unit time.

For the correct measurement of these coastal currents, advanced, easy methods are required. One of the most promising methods in this regard and really helpful is the ADCPs. ADCP profiler can provide continuous and detailed data about the flow of water at different depths.

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

Acoustic Doppler Current Profiler(ADCP) are based on the Doppler principle. They send acoustic signals into the water. If these acoustic waves meet moving particles in the water, such as sediment grains or small organisms, the frequency of the reflected waves will change. This change in frequency is proportional to the velocity of the moving particles and, hence, to the velocity of the water itself.

The ADCP meter estimate three-dimensional current velocities by sending several acoustic beams at different angles. Such devices are capable of not only giving the horizontal velocities but also giving the vertical components, hence enabling the derivation of the comprehensive water flow structure. The data collected is then processed and analyzed to get the required data on coastal currents with good accuracy.

3.2 What is required to ensure high - quality measurement of Cebu coastal currents?

It should first be ensured that, for a high-quality measurement of the coastal currents in Cebu, a few things be considered about equipment. First of all, material reliability of the equipment itself is highly important-the device has to withstand an aggressive marine environment, exposure to saltwater, high humidity, and variable pressure.

Other factors are the size and weight of the equipment in addition to its power consumption. Smaller dimensions with lighter weights would make deployment and handling easier, especially in situations where the measurement is to be made from a small boat or floating platform. Low power consumption is very vital in regard to the running of the equipment for long lengths without requiring to change batteries or from an external power source.

Another crucial factor is the cost. In the pretext to enable large-scale measurements, the equipment must be cheap. The most suitable material for ADCP flow meter casing could be the titanium alloy. There are various advantages of using a Titanium alloy. First of all, it is unbelievably strong and resistant to the salinas water's corrosive effects. It has a relatively low density that helps in keeping the weight of the device down. In addition, it has excellent thermal properties, which can be very helpful in extreme temperature conditions sometimes found in the marine environment.

3.3 How to Choose the right equipment for current measurement?

Many aspects are to be considered in choosing appropriate equipment for measuring the coastal currents of Cebu. First to be considered is the mode of deployment. There are different types of ADCP current profiler depending on how they are deployed.

Regarding this, ship-borne ADCP is suitable for measurements from a ship. It is installed on the hull of the ship and is thus able to provide measurements during water motion.

When it is intended to make a measurement from the seabed, then a bottom-mounted ADCP can be used. This type sits on the seabed and measures the currents passing above it.

This would be most applicable in applications that incorporate a floating platform. An example is an ADCP mounted on a buoy and measuring the currents in surrounding waters.

Aside from the mode of deployment, one should also select the ADCP's frequency based on water depth. An ADCP current meter of 600 kHz, a good choice for water depths up to 70 meters, bestows high-resolution measurements. For depths between 70 and 110 meters, a 300 kHz ADCP shall be used more appropriately. A depth of up to 1000 meters calls for an ADCP whose frequency is 75 kHz, as it serves best in deeper penetration into the water for accurate measurement of currents.

Currently, the known ADCP brands in the market are Teledyne RDI, Nortek, and Sontek. However, for those who need a moderately inexpensive but superior-grade ADCP, China Sonar PandaADCP may also be considered. This is manufactured from an all-titanium alloy material that ensures strength and reliability in the ocean environment. In addition, it offers excellent value-for-money. For further information about it, you can refer to its official website: https://china-sonar.com/.

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