How do we measure the coastal currents of Guaratuba?

1. Where is Guaratuba?

Guaratuba, that intriguing city in Paraná state in Brazil, is an Atlantic jewel on the nation's Atlantic coast. Its name reportedly of Tupi origin, bestowing on this Atlantic jewel an aura of mystery and cultural refinement. Guaratuba is situated geographically approximately 90 kilometers southeast of Curitiba, the Paraná state capital. Along a beautiful stretch of Atlantic Ocean, the municipality runs miles, anointed by rock but scenic coast.

The region possesses a unique topography. The Serra do Mar mountain range, parallel to the seashore, is a beautiful scenery for the seashores of Guaratuba. The mountains add not only beauty to the landscape but also to the local climate and weather. It lies near the Ilha do Mel (Island of Honey), a holiday island. The island, whose waters are crystal clear, forested, and rich in historical sites, is accessed by boat tour from Guaratuba.

Guaratuba town is a cultured town. It has existed for centuries, and remnants of its history are evident in the architecture, customs, and way of life of the town. The town's population itself is a mix of indigenous, Portuguese, and other European influences. Fishing is a hereditary business that has been around for generations, and the fishing villages in the town are a testament to this enduring history. The multicolored fishing boats scattered across the harbor are not only a pragmatic livelihood aid but a town jewel as well.

Guaratuba Bay upon which the town is located is a natural wonder. The bay is sheltered, and it is an excellent place for a range of water sports. The serene waters are perfect for boating, kayaking, and stand-up paddleboard. The mangrove forests within the region are also an essential ecosystem that provides a home to a diverse range of flora and fauna. Mangroves act as a natural coastal barrier against erosion and maintain the ecological balance of the region.

2. What is the state of the coastal currents at Guaratuba?

Off Guaratuba, coastal currents are controlled by a number of factors. Wind conditions are the dominant control. Prevailing winds in the region that typically blow from the southeast have the capacity to push the surface waters, creating longshore currents along the coast parallel to the coast. Longshore currents are the primary agents of sediment transport along the coast, and as such, beach formation and stability of the coastline.

Tidal forces are significant as well. The rise and fall of tides within Guaratuba Bay on a daily basis causes water to enter and exit, and therefore tidal currents are produced. They are very powerful, especially during spring tides when the combined force of gravity of the sun and moon is in their direction. Tidal currents possess the ability to transport nutrients and marine organisms, with some effect on the marine ecosystem of the region.

The seafloor topography, or the bathymetry of the area, is also an important factor to consider. The presence of shallow reefs, deep channels, and varying seabed slopes can deflect and redirect the flow of the currents. For example, nearshore reefs may be barriers, splitting or deflecting the current. The depth of the water also determines the speed of the current, with deeper water possessing stronger and more stable currents.

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

Surface Drift Buoy Method

One of the traditional means of monitoring coastal water flow is using surface drift buoys. These floating objects are released into the sea. With tracking technology onboard, they transmit signals via satellite or radio as they float along with the current. By taking the position of the buoy at regular intervals, scientists can calculate the direction and speed of the surface current. This method is not perfect, however. Surface drift buoys are highly sensitive to waves and wind, which causes them to wander away from the actual course of the current. They also only provide data about the surface ocean layer, not subsurface currents.

Anchored Ship Method

The ship-anchored technique involves mooring a vessel in one place. From the anchored location, current meters are lowered to different depths. The meters record the velocity and direction of the current at the different depths. Although this technique gives more accurate information about the vertical profile of the current compared to surface drift buoys, it is labor - intensive and time - consuming. The presence of the vessel can also disrupt the normal current flow, and measurements are limited to a point.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) has revolutionized coastal current measurements. ADCPs are now the tool of preference for oceanographers charting the waters off Guaratuba. ADCPs can provide a comprehensive image of the current velocity at a number of depths of the water column.

4. How do ADCPs working on the Doppler principle operate?

ADCPs operate on the basis of the Doppler principle. ADCPs emit sound waves into the water. When these sound waves encounter particles within the water, such as suspended sediment or tiny marine life, some of the energy of the sound is bounced back to the ADCP flow mete. If the particles are being transported by the current, the frequency of the back-scattered sound wave will differ from that of the original sound wave. This difference, or Doppler shift, varies directly with the velocity of the particles and therefore the current's velocity.

Many ADCPs utilize multiple beams, typically four, to calculate the Doppler shift from various directions. By looking at these shifts, the ADCP meter will be able to calculate the three-dimensional velocity of the current at numerous depths. Depth from where the measurement of current is taking place is dependent on frequency of sound waves utilized by ADCP. There are high-frequency and low-frequency ADCPs available. High frequencies of ADCP would be ideal for shallow measurements of water, while low frequency is suitable to reach deeper inside the water body.

5. What is required to make high - quality measurement of Guaratuba coastal currents?

To accurately and of good quality measure the coastal currents of Guaratuba, there are several considerations regarding equipment. Material reliability is most important. The equipment should be strong enough to withstand the corrosive marine environment, such as saltwater exposure, high currents, and high waves. Corrosion-resistant material should be employed so that the device lasts longer.

Size, weight, and power consumption are considerations as well. Lighter and more compact gear is simpler to deploy, especially in remote or hard - to - reach areas. Low - power - consumption gear can operate for extended durations without the need for constant battery replacement or recharging, which is essential for extended - duration monitoring operations. Cost - effectiveness is also an important consideration. In order to enable large - scale measurements and large data collection, the equipment should be cost - effective. Costly equipment may limit the number of points of measurement, thus reducing the completeness of the data.

For ADCPs, the casing material is a point of consideration. Titanium alloy is a suitable casing material for ADCPs to be deployed in Guaratuba's coastal waters. Titanium alloy is resistant to corrosion, and this is ideal for enduring corrosive saltwater action over an extended period. It is also strong yet lightweight, offering the best balance of longevity and ease of deployment. The use of titanium alloy in ADCP casing can go a long way to sustaining the life and performance of the device in the turbulent coastal conditions of Guaratuba.

6. How to Choose the Right Equipment for Current Measurement?

By Determining through Usage

The selection of suitable equipment for measurement of current depends on the use. For measurement at sea on a moving ship, where an ADCP is mounted on a ship, the most appropriate would be a ship-mounted ADCP. This type of ADCP can continuously measure the current while the ship travels, providing a profile of current along the track of the ship.

For fixed - point, long - term measurements, a bottom - mounted (or sit - on - the - bottom) ADCP can be used. They are mounted on the seabed and are able to collect current data over a long time at a particular location.

If it is desired to sample the more mobile and larger current, a buoy-mounted ADCP can be used. These are installed on floating buoys and may ride with the current, sampling en route.

Choosing the Right Frequency

The ADCP frequency is also something to consider. A 600kHz ADCP can be used to sample currents in water depths of up to 70m. It gives relatively high-resolution measurements at shallow-to-moderate water depths. A 300kHz ADCP is employed for depths up to 110m, but a 75kHz ADCP is employed at much deeper depths, to 1000m. Choosing the right frequency is associated with the assumed water depth where the currents are going to be measured.

There are some popular ADCP brands available in the market, including Teledyne RDI, Nortek, and Sontek. But for those who are looking for an affordable option without compromising on quality, the ADCP supplier China Sonar's PandaADCP is a great option. Composed entirely of titanium alloy, it provides high endurance in the sea environment. The most notable thing about it is its very high cost - performance ratio. It is a budget ADCP with reliable current measurement functionality. For more information, you can visit their site at https://china-sonar.com/.

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