How do we measure the São Francisco do Sul coastal currents?

1. Where is São Francisco do Sul?

São Francisco do Sul is a coastal municipality of the state of Santa Catarina, Brazil. It occupies the top position at the country's southern coast, along the Atlantic Ocean. Because of its prime location, it has grown into a significant hub for several economic and maritime endeavors.

Geographically, the region is varied. The coastline is a mix of sandy beaches, rocky outcrops, and small bays. The beaches are sandy and clear water, and they attract tourists from both within Brazil and abroad. The municipality also features several islands, which add to its natural appeal. The islands are usually surrounded by rich coral reefs, providing a habitat to a variety of marine life.

In terms of human settlement, São Francisco do Sul has a long history. It is as old as the 17th century and has developed into a vibrant community ever since. There exists a tradition of close contact with the sea among the indigenous people in the form of fishing and shipbuilding. One of the greatest ports in the southern region is the São Francisco do Sul port. It is one of the major points of entry for import and export trade, exporting and importing a wide range of commodities such as agricultural products, industrial goods, and construction materials.

The city also has a rich cultural heritage. It is dotted with old buildings, including colonial-era mansions and churches. These buildings reflect the signature of Portuguese settlers, who settled in the area centuries back. The local festivals, which are typically focused on the sea and culture of fishing, reflect the people's identity. For example, the fishing festival every year celebrates the local fishermen's expertise and involves traditional music, dance, and cuisine.

2. What are the coastal currents off São Francisco do Sul?

Coastal currents off São Francisco do Sul are created by a combination of factors. The tidal forces are a fundamental force. The regular ebb and flow of the tide in the region create significant movement of water. During high tide, seawater flows into the estuaries and bays, and during low tide, the water flows back into the ocean. These tidal currents are usually extremely strong, especially in estuary mouths and in constricted channels. They carry sediment, nutrients, and marine organisms, which in turn affect the local ecosystem.

Wind patterns also have a major impact. Dominic southeast winds are common in the area. The winds have the power of pushing surface water along the shoreline and causing longshore currents. The speed and direction of the longshore currents change by the proximity to the wind force and direction. They can support or counter the tidal currents, resulting in complex flow patterns. For instance, in the case of extremely strong southeasterly winds, longshore currents will carry enormous amounts of sand along the beach, sometimes causing erosion or accretion of the beach elsewhere.

Another important effect is the influence of river discharges. Although São Francisco do Sul does not have a major river like other coastal regions, there are small streams and rivers that flow into the ocean locally. The fresh water from such sources may have an effect on the salinity and density of the coastal water, and the latter can alter the current pattern. The outflow of river water can create a buoyant plume running along the coast, blending with the tidal and wind-driven current.

3. How to observe the coastal water flow of São Francisco do Sul?

Surface Drift Buoy Method

One of the traditional ways of measuring coastal water current is by laying surface drift buoys. These are sea-dropped, floating devices. Equipped with current monitoring equipment such as GPS or satellite transmitters, they send signals at regular intervals. By monitoring the movement of these buoys over time, scientists can ascertain the speed and direction of the surface current. However, this method has certain drawbacks. Surface drift buoys are very susceptible to wind and wave effects. Strong winds will drive the buoys far off the actual course of the current, and the findings will be inaccurate. They provide data about only the surface water column, without observing the subsurface currents.

Anchored Ship Method

Anchored ship technique is a method that employs a stationary ship as a platform to record current. Current meters are lowered from the ship at different levels to record the speed and direction of the current. The method gives a more detailed vertical profile of the current compared to the surface drift buoy technique. The method is, however, labor - intensive and time - consuming. The presence of the ship will also disrupt the natural course of the current, and readings are limited to a single point. Inclement weather in the form of strong winds and high waves will jeopardize the mounting and functioning of the equipment.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) has been shown to be a more advanced and reliable method of measuring coastal currents off São Francisco do Sul. ADCPs have the ability to provide high-resolution current velocity observations at multiple levels in the water column.

4. How do Doppler principle ADCPs work?

ADCPs operate on the principle of the Doppler principle. They release sound waves into the water. When these sound waves strike particles in the water, like suspended sediment or small aquatic animals, some of the sound energy is bent back toward the ADCP. If particles are moving with the flow, the frequency of the bent sound wave will differ from that of the emitted sound wave. This difference in frequency, or Doppler shift, is directly proportional to the velocity of the particles and, hence, the velocity of the current.

The majority of ADCPs use multiple beams, typically four, to measure the Doppler shift in different directions. By analyzing the Doppler shifts from the multiple beams, the ADCP can calculate the three - dimensional current velocity at different depths. The point at which the current is taken is a function of the frequency of the sound waves used by the ADCP flow meter. Higher-frequency ADCPs are better suited to shallow-water measurements since they provide higher resolution but lower range. Lower-frequency ADCPs travel deeper into the water column but provide lower resolution.

5. What is needed for high-quality measurement of São Francisco do Sul coastal currents?

Several qualities are needed in the measurement gear for high-quality measurement of São Francisco do Sul's coastal currents. Material reliability is paramount. The gear must be able to withstand the corrosive marine environment, such as exposure to seawater, high currents, and varying weather conditions. Corrosion - resistant materials are necessary to ensure the long - term functioning of the device. For ADCPs, the casing material is a critical consideration. Titanium alloy is a suitable choice for ADCP casings in São Francisco do Sul coastal waters. Titanium alloy is highly corrosion resistant, which is required to withstand the corrosive action of saltwater in the long term. It is also strong and light, with a good compromise between toughness and ease of deployment.

Power consumption, size, and weight are also essential factors. Smaller and lighter equipment is more convenient to deploy, particularly in remote or inaccessible locations. Low - power - consuming equipment can operate for extended periods without the need for frequent replacement or recharging of batteries, which is essential for long - term monitoring projects. The cost - effectiveness factor is also of prime importance. In order to enable large - scale measurements and complete data collection, the equipment should be inexpensive. Costly equipment may limit the number of measurement points, reducing the accuracy and representativeness of data.

6. How to Choose Suitable Equipment for Current Measurement?

Determination by Usage

The choice of suitable equipment for current measurement is an application - dependent one. In case of mounting the ADCP on a moving vessel to make ship - based measurements, the ship - mounted ADCP is an ideal choice. This type of ADCP is able to continuously measure the current as the ship moves along through the water, providing a profile of the current along the ship's track.

For long - term, fixed - point measurements, a bottom - mounted (or sit - on - the - bottom) ADCP can be employed. They are bottom - mounted and are capable of measuring current data for an extended period at a point.

If it is desired to measure the current in a more mobile and dispersed way, a buoy-mounted ADCP may be utilized. These are mounted on floating buoys and may travel with the current, gathering data as they go.

Selecting the Correct Frequency

The frequency of the ADCP is also a consideration. A 600kHz ADCP can be employed to measure currents in up to 70m water depths. It makes fairly high-resolution measurements in shallow-to-moderate-depth waters. A 300kHz ADCP is capable of making measurements up to a depth of 110m, whereas a 75kHz ADCP can make measurements up to a depth of 1000m. The frequency has to be chosen based on the likely depth of water where current measurements are to be taken.

There are various well-known companies of ADCPs in the market, e.g., Teledyne RDI, Nortek, and Sontek. But for users in search of affordable alternatives, the ADCP supplier China Sonar's PandaADCP comes very highly recommended. Constructed from pure titanium alloy, it achieves high performance at very reasonable prices. It is a perfect option for users who are budget - sensitive yet still need to use quality ADCPs to measure coastal currents. More information about them can be accessed on their website: https://china-sonar.com/.

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