How can we measure the coastal currents of Davao?

1. Where is Davao?

Davao is a thriving and ebullient city located in the southernmost part of the Philippines on the island of Mindanao. It is a place which amalgamates natural grandeur along with a rich tapestry of human activity and culture.

Davao is a geographic entity blessed with diverse land forms. To the east lies the blue waters of the Davao Gulf-a major body of water and a very important component in the ecology and economy of the region. Relatively tranquil waters characterize the gulf, making it suitable as a haven for several marine species and, therefore, a favorite destination for fishing as well as water-based recreation activities.

Aside from these, it is ringed by lush mountains and rolling hills that contribute to the city's scenic beauty. These natural barriers create a picturesque backdrop and influence the local climate; thus, a unique microclimate that is conducive to almost all kinds of flora and fauna growth is realized.

On the human culture side, Davao is a melting pot. It shelters a heterogeneous population with the different ethnic groups, namely the Bagobo, Mandaya, and Mansaka, who contributed to the rich culture of the city. The center of the city houses teeming markets selling everything from various traditional handicrafts to the fresh local produce of the day. Davao also has its list of festivals, with the Kadayawan Festival being one of them, where the culture of the city is reflected through colorful processions and music and dance events.

2. What are the coastal currents near Davao?

Coastal currents in the vicinity of Davao arise due to several causes. The most overriding agent that decides the nature of movement of these currents is that of tides. The semi-diurnal tides in the area cause regular ebb and flow of the waters. During high tide, the sea waters rush towards the shore, carrying with them nutrients and sediments so important for the nourishment of marine organisms. During low tide, the waters recede to expose parts of the seabed and generally alter the direction and speed of the coastal currents.

Winds also play a decisive role. In the place, the winds are of the monsoon type, precisely the southwest monsoon or Habagat and northeast monsoon or Amihan. The Habagat winds can drive the coastal currents in one direction, with the Amihan winds usually reversing or changing this flow. These winds may bring about upwelling, where deep, nutrient-rich waters reach the surface, consequently having an enormous impact on the local marine ecosystem.

Another important factor is the topography of the seabed off Davao. The underwater ridges, channels, and shoals will be able to change the direction of currents and speed them up. The shape of the coastline, bays, and headlands around it will modify the flow of the currents. For instance, currents can be deflected around a headland, creating areas of stronger flow on one side and calmer waters on the other. Also, freshwater intake from the rivers and streams in that area affects the salinity and density of the waters along its coasts, which is affecting the movement of the currents.

3. How to Observe the Davao Coastal Water Flow?

For proper measurement of the coastal currents of Davao, determination of the velocity and flow rate is highly important. The earlier methods of current measurement had their inefficiencies, but this recent one has been much advanced and handy: the Acoustic Doppler Current Profiler (ADCP).

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

Based on the principle of the Doppler, ADCP profiler work. They send acoustic signals down the water column. The signals interact, among others, with plankton and sediment particles in suspension in the water. These particles are transported by the water current, which, in return, changes the frequency of the reflected acoustic signal with respect to the emitted one. This change in frequency is what is called the Doppler shift, and is directly proportional to the velocity of the particles and therefore to that of the water current.

Typically, ADCPs are designed to transmit several beams of acoustic signals at different angles. Therefore, the current velocity may be measured in three dimensions by an ADCP meter. A properly analyzed Doppler shift from multiple beams can provide a detailed profile of how currents are flowing both horizontally and vertically within the column of water. This will make it possible to calculate the flow rate of the currents along the coast from the data collected, which, in turn, can be used in marine navigation, coastal engineering, and environmental studies.

3.2 What's needed for High-quality Measurement of Davao Coastal Currents?

Several equipment requirements have to be met so that high - quality measurement of the coastal currents near Davao can be measured. First, the material used for ADCP has to be reliable. It should be able to withstand the harsh marine environment, including saltwater, high pressure at a different depth level, and impact from floating debris.

Important criteria are the size and weight of the ADCP flow meter. The smaller and lighter devices are easily deployed and handled. For instance, in case it is to be installed on board a boat or on a buoy, the lighter an ADCP current profiler, the more practical. This is important, especially for long-term measurements. Low power consumption is also a very important criterion. In this way, the device can operate continuously without frequent battery replacements or large power supply.

Another important aspect involves cost-effectiveness. The price of the doppler current profiler should be such that large-scale measurements are possible. In this connection, the casing of the ADCP should preferably be made of titanium alloy. Corrosion Resistance: The metal is very resistant to corrosion and hence particularly well-suited for marine work in saltwater because such an environment can easily corrode many metals in relatively short periods. It is strong and tough, capable of withstanding pressure and stresses imposed during underwater operations. Its low relative density is also advantageous for ease of deployment, keeping the overall weight of the ADCP relatively low.

3.3 How to Choose the right equipment for current measurement?

Choosing the right equipment to measure the coastal currents of Davao needs some careful considerations on a few aspects.

According to the deployment method, there are several kinds of ADCP current meter. The ship-borne ADCP is installed on a ship and applies to those surveys where the ship can navigate along the coast. For this kind of ADCP, the range of view for the coastal currents can be very wide over a big area.

A sit-on-bottom ADCP continuously measures the currents passing over it while mounted on the bottom. 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-mounted acoustic current meter is attached to a buoy and, therefore, can float freely in the water while measuring the currents around it. This is an advantage for areas that are difficult to reach by ship or when one needs continuous monitoring from a fixed position in the water, such as the open waters near the coast of Davao.

Aside from the deployment method, another highly relevant factor is the frequency of the acoustic doppler flow meter itself. For water depths up to 70 meters, the best choice would be a 600 kHz ADCP. In such frequency, the measurements are highly resolved for shallower waters. Where there is a requirement for water depths up to 110 meters, an ADCP of 300 kHz would do. It compromises between resolution and depth of penetration. Equally deep waters of 1000 meters warrant the use of the 75 kHz ADCP. This can penetrate deeper into the water column 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.