How do we measure the coastal currents of General Santos?

1. Where is General Santos?

General Santos is a highly advanced urban city found in the southernmost part of the Philippines. It is located on the island of Mindanao and is one of the country's major urban centers for the area.

Geographically, it is situated on land fronting the Sarangani Bay. This is the wide and significant body of water that offers a natural harbor and a rich fishing ground. The waters of Sarangani Bay are teeming with life, from different species of fish, crustaceans, and mollusks. The coastline of the bay is a combination of sandy beaches and mangrove forests. These sandy beaches provide a venue for open swimming and sunbathing among locals and tourists. In contrast, the mangrove forests serve very important ecological purposes. They help protect the coasts from further erosion, serve as a hatchery for juvenile fish, and assist in purifying the water through filtration of pollutants.

On its human aspect, General Santos is a highly active city with quite a diverse population. It is known as the "Tuna Capital of the Philippines" due to its more progressive tuna industry. The city's port is a big hub for vessels of fishing and cargo line vessels, facilitating the exchange of trade and commerce. The local culture is a mixture of the different ethnic groups, which include the B'laan and Maguindanaoan. The city teems with vibrant markets where fresh seafood can be found, along with local handicrafts and all sorts of agricultural products. Festivals somehow play a significant part in the local culture, purporting the richness of the city's heritage and the bountiful harvests from the sea and land.

2. What is the condition of the currents along the coasts near General Santos?

The general condition of the currents along its coasts is guided principally by a couple of factors: Tides are a basic ingredient that molded the form of movements these currents have. The tide in the area is semi-diurnal. There are, therefore, two high tides and two low tides each day. During high tide, waters from both the bay and the open sea flood towards the shore, carrying nutrients and sediments in their path. These nutrients support richly diverse marine life in the area. During the low tide, the waters recede to expose large areas of the seabed and totally change the direction and speed of the coastal currents.

These winds themselves play an important role. The prevailing wind conditions in the area are a result of the monsoon winds, which are further subdivided into the southwest monsoon-wind Habagat and the northeast monsoon- Amihan. The Habagat, or southwest wind, can drive the current in a particular direction, usually northeast. This is usually reversed or moderated by the Amihan winds blowing from the northeast. These winds can be held responsible for upwelling events, too. Upwelling is a process wherein winds push the surface waters away, allowing colder and nutrient-rich waters deeper below to rise to the surface. This is a very vital process in the productivity of the marine ecosystem because it provides added nutrients for the phytoplankton and other primary producers.

Another important factor is the topography of the seabed off General Santos. Underwater ridges, channels, and shoals can partly divert and accelerate the currents. This might be illustrated by the action of a submarine ridge that splits or converges the currents to form areas of different current velocities. This is in addition to the shape of the coastline, bays, and headlands that change the flow of the currents. They usually break on headlands or around them because currents tend to be deflected around headlands, which provides areas of stronger flow on one side and often calmer waters on the other. Aside from that, inflow of freshwater from rivers and streams in the area can make variations in salinity and density of the coastal waters, which in turn affects the currents.

3. How to observe the coastal water flow of General Santos?

In order to accurately measure the velocity and flow rate, it is necessary to properly determine the coastal currents of General Santos. There are some drawbacks to previous methods measuring current, but Acoustic Doppler Current Profiler(ADCP) is more advanced and handy for the job.

3.1 How do ADCPs using the Doppler principle work?

The basic principle behind ADCPs - the Doppler principle. They send acoustic signals down the water column. The interaction occurs with the suspended particles, such as plankton and sediment, in the water. Those particles move due to the water current. This generates a frequency change of the reflected acoustic signal with respect to the original emitted signal. This frequency shift is called Doppler shift and depends linearly on the particles' velocity and hence the water current's velocity.

ADCP current profiler generally emit several beams of acoustic signals at several angles. Thereby, they can measure the three-dimensional velocity of the water current. Analyzing the Doppler shifts with the several beams allows the ADCP current meter to provide a detailed profile of the currents in the flow both in horizontal and vertical directions of the water column. Data gained could then be utilised in determining the flow rate of the respective currents. This is quite imperative in various applications in the study of marine navigation, coastal engineering, and environmental studies.

3.2 What is required for quality measurement of general Santos coastal currents?

For quality measurement of the coastal current around General Santos, several equipment requirements have to be satisfied. First, the ADCP material must be reliable. It should be able to survive extreme marine conditions: from being in salty water, through high pressure at depths, to impacts by floating debris.

Another important consideration is size and weight for the ADCP flow meter: smaller and lighter is easier to deploy and handle. If, for example, it is to be installed on a boat or buoy, then a lighter ADCP shall be more practical. Another key consideration is the power consumption, especially for long-term measurements. It enables the device to operate continuously without frequent changing of batteries or a huge power supply.

The other important factor is cost-effectiveness. In order to implement wide-range measurement, the ADCP should be reasonably priced. The casing of the ADCP meter should be made from titanium alloy. Titanium alloy has good resistance to corrosion and can stand well in seawater and therefore in the saltwater of marine, which corrodes metals very fast. It has strong and durable qualities, too, which can bear the pressure and tension of underwater working. The relatively low density is quite helpful to keep the overall weight of the ADCP down, which can be convenient in terms of its deployment.

3.3 How to Choose the right equipment for current measurement?

Selection of appropriate equipment to conduct the measurement of the coastal currents of General Santos needs to consider several factors.

There are several types of ADCP profiler, depending on the method of deployment. The shipborne ADCP is mounted on a ship and is used in those surveys where the ship can travel along the coast. Such type of ADCP allows the study of coastal currents in a wide range over a big area.

Sit-on-bottom ADCP is a device mounted on the bottom that provides continuous measurements of the currents passing over it while placed on the seabed. It is ideal for monitoring specific locations such as near a coastal structure or an area of particular interest for marine ecological studies.

The buoy acoustic doppler flow meter is mounted on a buoy and can float freely in the water, measuring the currents around it. This is advantageous in areas difficult to access by ships or areas needing continuous monitoring from a fixed position in the water, such as in open waters near the coast of General Santos.

In addition to the deployment method, the ADCP frequency will be important also. For water depths up to 70 meters, the 600 kHz can be a good option for an acoustic doppler velocity meter. This resolution allows for high-resolution measurement capabilities for shallower waters. A 300 kHz is a good choice for deeper waters, such as those up to 110 meters. It reaches an ideal balance between resolution and depth of penetration. The ADCP is intended to water as deep as 1000 meters, operating at 75 kHz. Since it works at a lower frequency, it can bore deeper into the water column in order to measure the currents.

There are well - known ADCP brands like Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option with good quality, the China Sonar PandaADCP is worth considering. It is made of all - titanium alloy material, which not only ensures its durability and resistance to the marine environment but also provides an incredible cost - performance ratio. You can find more information about this product on their website: https://china-sonar.com/.

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