How to Measure Coastal Currents in Leyte island

1. Where is Leyte?

Leyte is an island in the Visayas region of the Philippines. It belongs to the central part of the country, bounded by the Leyte Gulf on the west and the Philippine Sea on the east.

Geographically, Leyte presents a diverse landscape. It contains mountain ranges in the interior and wide coastal plains along its periphery. Quite a long coastline with sandy beaches, rocky shores, and mangrove forests forms part of it. The Leyte Gulf is a large body of water that provides sheltered anchorage and makes up part of the important maritime activities of the island. The waters surrounding it are rich in marine life. The presence of coral reefs hosting a diversity of fish and other organisms.

Another significant human activity on this isle is fishing, which represents an important industry. Local fishermen find rich supplies both in the Leyte Gulf and the seas around it. Certain parts of the island are used for agriculture. Among the crops grown here are coconut and rice. Leyte plays an important part in history, particularly the Second World War. Tourism is slowly but surely creeping up as people enjoy the natural aspects of this island and the historical events related to it.

2. What is the condition of the coastal currents near Leyte?

The coastal currents near Leyte have several influences. One of the strongest forces that affect these currents is tidal currents. The gravitational pull of the moon and the sun causes the tides to ebb and flow, creating tidal currents. Tidal currents, depending on the lunar cycle and the local topography along the coastline and its seabed, can be stronger or softer at certain periods in each month.

The monsoon winds are also importantly involved. There are two monsoon seasons over the Philippines: during the southwest monsoon or Habagat, which has wind generally blowing from the southwest, pushes the surface waters and leads to a current that in general acts in a specific direction, while during the northeast monsoon, winds from the northeast result in different flow patterns.

The topography of the seabed around Leyte, similarly, affects the coastal currents. The underwater ridges, shoals, and channels may be causing acceleration or deceleration of the current or its direction change. The shape of the coastline - bays, headlands, estuaries, and so on - has an impact on the nature of the flow in the currents. Inflow of fresh water from the local rivers can affect the density of the coastal waters and influence the pattern of the currents.

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

The coastal currents around Leyte have peculiarities of their own with regard to velocity and flow rate. Velocity can be relatively slow in sheltered bays and lagoons while it can be quite fast in regions where the current is obstructed or wherever winds and tides are stronger. On the other hand, the flow rate is determined by the volume of water passing an area for every unit time.

The measurement of these coastal currents will require new, easy methods that are accurate. One of the methods that proved to be very efficient is the ADCP current profiler. They can give flow details of water at different depths continuously.

3.1 How do the ADCPs using the principle of Doppler work?

The operating principle of Acoustic Doppler Current Profiler(ADCP) is based on the Doppler principle. Each ADCP emits its acoustic signals into the water. As these acoustic waves reflect off the moving particles in the water, the frequency of the reflected waves changes. This frequency shift is proportional to the velocity of the moving particles and hence, by extension, the velocity of the water.

With ADCP current meter sending out multiple acoustic beams at different angles, they are able to measure three-dimensional velocity of the water. They can measure not only the horizontal velocity but also vertical velocity components, hence enabling a full realization of the structure of water flow. The obtained data is thereafter processed and analyzed for an accurate information provision on the currents in that particular coast.

3.2 What is required for high - quality measurement of the currents in Leyte coast?

In regard to equipment, there are several factors to be considered in the measurement of high-quality coastal currents near Leyte. First and foremost, there is a need to take into consideration the material reliability of the equipment. The device applied in the study area should be resistant to the marine environment, putting into consideration saltwater, high humidity as well as pressure variations.

Other important parameters are size, weight, and power consumption. Smaller size and lighter weight mean easier deployment and handling, especially if the measurement has to be done from a small boat or floating platform. Low power consumption will keep the equipment running for a longer period of time without frequent changes of batteries or other extra power sources.

Another important factor is the cost. In order to be able to make large-scale measurements, the equipment needs to be affordable. One of the materials that is very suitable for ADCP flow meter casing is a titanium alloy. The advantages with the titanium alloy are several. For example, it is extremely strong and durable and able to resist the corrosive effects of saltwater, while at the same time having relatively low density, which helps in keeping the overall weight of the device down. Besides, it has excellent thermal properties, which may be useful in an extreme temperature condition of the marine environment.

3.3 How to Choose the right equipment for current measurement?

Several aspects will go into determining the appropriate equipment in measuring the coastal currents of Leyte. First, there is the mode of deployment. The ADCPs available are different depending on the deployment mode.

Carried on a ship, the ADCP meter could be mounted on the hull of the ship and make continuous measurements while the ship is in motion in water.

If the measurement is to be done from the seabed, then the bottom-mounted ADCP can be used. This type of ADCP is placed on the seabed and measures the currents passing above it.

For those applications carried out with the use of a floating platform, an ADCP profiler on a buoy is the solution. Thus, an ADCP can be attached to a buoy and carry out the measurement of currents in the surrounding water.

Besides the mode of deployment, the frequency of the ADCP should also be selected according to the depth of water. Basically, with water depths of as high as 70 meters, a normal good job is done through a 600 kHz ADCP, which offers high-resolution measurements. For higher water depths-which are between 70 to 110 meters-a 300 kHz ADCP can be more appropriate. On much deeper waters-say, up to 1000 meters-a 75 kHz is preferred because it would allow reasonably deeper penetration into the water for the currents to be measured with good accuracy.

Famous brands in the market for ADCPs include Teledyne RDI, Nortek, and Sontek. However, a very cost-effective option with excellent quality is the China Sonar PandaADCP. Made from all-titanium alloy material, this ensures it will be durable enough to bear the marine conditions, besides being an extremely high value-for-money gadget. More about it can be read from its website: https://china-sonar.com/.

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