How do we estimate the coastal currents of Ubatuba?

1. Where is Ubatuba?

Ubatuba is a beach resort in the state of São Paulo, Brazil. Roughly at 23°29′S 45°05′W, it runs along the Atlantic Ocean for over 100 kilometers of shoreline. This location is most renowned for natural splendor, featuring a wide range of coastline scenery. Ubatuba's beaches are some of its most striking attractions, ranging from extensive sand beaches to tiny secluded coves. The beaches are not only attractive to tourists but also play important ecological roles, such as providing breeding grounds for sea turtles and homes to many shore-dwelling creatures.

Geologically, the area surrounding Ubatuba is characterized by a combination of ancient metamorphic and igneous rocks capped by sedimentary deposits. Seafloor found offshore and in coastal proximity displays complex bathymetry. The shorelines are afflicted with shallow zones adjacent to the coasts, gradually increasing in depth farther offshore. Structures present at underwater locations include sandbars, channels, and coral reefs which are small in size. The coral reefs are significant even though less noticeable as some zones within tropical regimes but vital in a marine society residing herein. They provide a very broad spectrum of fish, crustaceans, and mollusks with shelter, and also impact the coastal currents. The release of small rivers and streams into the sea impacts the salinity and density of coastal water as well as influences the municipality.

Ubatuba is highly historic. There were indigenous people, such as the Tupinambá, who originally occupied the area. Their nautical and continental knowledge was passed down through the generations. The Portuguese colonizers arrived in the 16th century with novel farming and commercial methods. Gradually, Ubatuba emerged as a key coastal settlement. Fishing and agriculture were its initial economic activities. But tourism is the main economic activity of the region in the last few decades due to the area's picturesque beaches and pristine waters.

2. In what state are the coastal currents surrounding Ubatuba?

Coastal currents along Ubatuba are determined by a complex combination of a number of variables. One of the most significant ocean currents of the Atlantic Ocean, the South Equatorial Current, is an important factor. Upon approaching the Brazilian coast, it interacts with local topography and bathymetry. In the region of Ubatuba, the South Equatorial Current might split into a number of minor streams. These branches are then influenced by the shape of the coastline, submarine topography, and freshwater discharge from adjacent rivers.

Tides in the Atlantic Ocean play a critical role. The semi-diurnal tidal regime causes recurring water-level fluctuations. Spring tides experience greater gravitational pull by the sun and moon, so the tidal currents are more powerful. These tidal currents interact with the South Equatorial Current and local coastal geometry. Ebb and flow of the tides may cause water to flow in and out of the estuaries and bays in Ubatuba, producing intricate circulation patterns. Tides can also produce rip currents, which are strong, narrow currents flowing away from the shore. Rip currents pose danger to beachgoers and are an important consideration for coastal safety.

Local winds in the region, mainly the southeasterly trade winds, also influence the coastal currents. They can push surface waters in one direction and create a wind - driven current. The wind - driven current interacts with the South Equatorial Current and the tidal currents. For example, during strong wind periods, surface waters in the region of Ubatuba may be forced ashore or seaward by wind direction. Bathymetry on the seafloor near Ubatuba, sandbars, channels, and the coral reef system can redirect or block the flow of currents. Coral reefs can serve as barriers, making the water go around them, which can alter the direction and velocity of the current.

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

Surface Drifting Buoy Method

The surface drifting buoy method is a conventional method of observing coastal water flow. Scientists release buoys with tracking devices into the water. By tracking the drift of such buoys over time, they can determine the velocity and direction of the surface currents. This technique has certain limitations, however. It provides information on the surface layer of the water column, and it is extremely susceptible to wind interference by the buoys. In Ubatuba, the complex pattern of the winds and the presence of bays and estuaries can complicate the results obtained with the use of surface drifting buoys. The wind will tend to push the buoys in a course that is not representative of the real course the currents below them are taking.

Moored Ship Method

The moored ship method includes the use of a ship that stays stationary and acts as a platform for measurements of currents. Devices are released from the ship to measure currents at various depths. While this method can record fine vertical profiles of currents, it has a number of disadvantages. The spatial coverage is limited only around the moored ship. In a vast and dynamic coastal environment like Ubatuba, this limited coverage may not capture the overall coastal current patterns. The existence of a ship will also disrupt the natural flow of the water and can affect measurement accuracy. Also, having a ship anchored for an extended period of time could be logistically infeasible and costly.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP profiler has gained usage as a more advanced and efficient method to measure coastal currents. ADCPs can measure currents in water over a broad vertical range, providing detailed information on the velocity structure of the water column. ADCPs can be deployed on various platforms, including ships, buoys, and the seafloor. Ship-mounted ADCPs can collect data continuously as the ship moves, sampling a wide area in a relatively short amount of time. In Ubatuba, a ship-mounted ADCP can be used to survey the coastal currents along the long coast, providing an indication of the complex patterns of flow. Bottom-mounted ADCPs can be placed in key locations, e.g., at bay entrances or over areas of significant underwater topography, to provide long-term, fixed-point measurements. This allows researchers to study long-term currents within coastal waters.

4. How do ADCPs operating on the Doppler principle work?

ADCPs operate based on the Doppler principle. ADCPs emit sound pulses into water. Acoustic pulses bounce back from suspended substances like sediment, plankton, or bubbles present in water. When water moves, the reflected signals change their frequency. Using this frequency shift, the ADCP is able to determine water velocity with respect to the sensor.

Most ADCPs consist of multiple transducer beams, typically four or more, positioned at different angles. The multi - beam setup enables the three - dimensional velocity of water to be calculated. By adding up the signals from the beams, the ADCP can reconstruct a full picture of the current velocity at different depths in the water column. The ADCP current profiler data can be operated on - line in real - time or stored to be processed later. For Ubatuba coastal currents, ADCP data can help explain how South Equatorial Current, tides, and wind - driven currents interact with different depths so that effective information of the whole dynamics of coastal waters can be ascertained.

5. What are the requirements for high-quality measurement of Ubatuba coastal currents?

To facilitate high-quality measurement of Ubatuba's coastal currents, the measuring instruments need to possess some very significant properties. They should be made of reliable materials, possess small dimensions, low weight, low energy consumption, and low cost. These properties allow a large number of instruments to be used so that there can be full spatial coverage.

ADCPs made from titanium alloy casings are strongly encouraged. Titanium alloy is very resistant to corrosion, which is ideal for long-term exposure to the corrosive marine atmosphere. It resists the corrosive effect of seawater and shields the internal devices of the ADCP against damage. It is also durable and lightweight, with the assurance of the instrument's endurance and portability. In a coastal site like Ubatuba, where the nearness to deployment sites may vary, the instrument portability proves to be a big advantage. This combination of attributes offers effective and long-term measurement of the currents at the coastal areas near Ubatuba.

6. Choosing the appropriate equipment for current measurement?

Usage-Based Selection

The choice of ADCP depends on the desired application. For ship - based measurements, ship - mounted ADCPs are optimal. They are able to produce real - time data as the vessel moves through the water, covering a wide area in a relatively short time. For Ubatuba, it is useful for quickly mapping coastal currents along the long coastline. For fixed - point, extended - term observation, bottom - mounted ADCPs are preferable. They can provide continuous data for months or years, allowing researchers to study long - term trends in the coastal currents. For example, placing a bottom - mounted ADCP near the mouth of a bay in Ubatuba can allow researchers to track the tidal and other current changes for months or years. Floating ADCPs are advantageous in the observation of the movement of water masses over vast regions, providing valuable information about large-scale circulation patterns. For Ubatuba, floating ADCPs can be utilized to study how the South Equatorial Current interacts with local coastal currents in a larger context.

Depth-Based Selection

The ADCP frequency also needs to be determined based on the depth of the water. For depths less than 70m, 600kHz ADCPs are appropriate. They can provide high-resolution measurements in shallow water conditions, such as in the beaches or inner bays. For depths up to 110m, 300kHz ADCPs are recommended. This frequency range is suitable for areas with moderate depth, such as outer bays or general coastlines. For the deeper waters to 1000m, 75kHz ADCPs are the correct selection. Although the waters off Ubatuba are generally not very deep, in some offshore areas or channels, these lower-frequency ADCPs must be employed in order to effectively measure the currents at greater depths.

Several popular brands of ADCPs are available in the market, such as Teledyne RDI, Nortek, and Sontek. Yet, for those who are looking for cost - effective solutions, the ADCP flow meter China Sonar's PandaADCP is greatly recommended. It is made of pure titanium alloy and provides great performance at a reasonable price. It is a great option for users who are budget - friendly but still need quality ADCPs for coastal current measurements. You can learn more about them on their official website: https://china-sonar.com/.

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