How do we measure the Vitória coastal currents?

1. Where is Vitória?

Vitória, capital city of the Brazilian state of Espírito Santo, is located strategically along the eastern coast of Brazil on the Atlantic Ocean. It is roughly at 20°14′S 40°17′W and is a working coastal city. The shoreline of the city is a continuous interface between sea and land and consists of a variety of sandy beaches, rocky headlands, and an expansive natural bay, the Bay of Vitória. The bay is not only a crucial port but also a notable feature of the coastal scenery of the region.

Geologically, the region around Vitória is a mélange of old igneous and metamorphic rocks capped by sedimentary deposits. The seabed close to the beach is varied in terms of bathymetry. There are shallow waters close to the beach, deepening as one moves towards the beach from more distance from the coast. There are some underwater structures like sandbars, channels, and minor deposits of coral reefs. These coral reefs, although not so frequent as in certain tropical refuges, have an integral role to play in the sea environment of this region. They provide shelter for a vast array of fish, crustaceans, and mollusks and help stabilize the coastal currents. The city is also subject to drainage from several small rivers and streams into the sea, which impinges on the salinity and density of the sea water off the coast.

Vitória has a rich and diverse history. There were native tribes in the area, including the Tupinambá. Their presence left a profound mark on the local sea and land folklore, traditions, and culture. Portuguese colonists arrived in the 16th century and formed a colony that grew into the city of Vitória. Throughout the centuries, the city has remained a commercial center, with its port as a gateway to exchanging commodities between the rest of the world and Brazil. Currently, the economy of Vitória is diversified, with manufacturing, services, and tourism being prominent contributors.

2. How powerful are the coastal currents off Vitória?

Coastal currents off Vitória are the result of complex interaction of several factors. Among them, there is a significant ocean current in the Atlantic Ocean, namely, the South Equatorial Current, whose impact is dominant. As it is moving towards the Brazilian coast, it interacts with the local bathymetry and with the topography. Along the coast of Vitória, the South Equatorial Current could divide into smaller currents. These would be deflected by the shape of the coast, the Bay of Vitória, and submarine topography beneath the seafloor.

The Atlantic Ocean's tides are extremely significant. The semi-diurnal tidal cycle produces recurring oscillations in water heights. The tidal currents are significantly larger at spring tides when the combined gravitational attraction of the sun and moon is highest. The tidal currents are supplemented by the South Equatorial Current and coastal morphology. The rising and falling tide may drive water in and out of the Vitória Bay, creating complex patterns of circulation. Tides can also create rip currents, thin, fast currents that move off the beach. Rip currents can be dangerous to swimmers and are an important part of beach safety.

Wind of primary concern to the region, mostly the southeasterly trade wind, also impacts coastal currents. Wind can cause surface water to be pushed in a certain direction and, thereby, create a wind-driven current. The wind-driven current is joined by the South Equatorial Current and tidal currents. For instance, in strong winds, the surface waters along Vitória are driven onto or offshore depending on the direction of the wind. Bathymetry of the ocean floor off Vitória, including sandbars, channels, and coral reefs, may channel or obstruct the flow of the currents. Coral reefs, for instance, can create a barrier with the water circulating around them and potentially changing the direction and the velocity of the current.

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

Surface Drifting Buoy Method

The surface drifting buoy method is an ancient technique of observing coastal water flow. Scientists release buoys with tracking devices into the ocean. From analyzing the movement of such buoys over a certain time duration, they are able to deduce the velocity and direction of the surface current. The method is not disadvantageless, though. It only provides information of the surface level of the column of water and is highly responsive to wind disruption. Wind may shift the buoys from one direction not necessarily being the true direction of travel of the base currents. For the case of Vitória, the complex pattern of winds and the presence of the bay could make even the surface drifting buoys' data more difficult to interpret.

Moored Ship Method

The moored ship method utilizes a moored ship as a platform to quantify currents. Equipment is deployed from the ship to measure the flow of water at various depths. Though this technique has the ability to present high-resolution vertical profiles of the currents, it is not without several shortcomings. The coverage area is only where the moored ship is situated. Within a big and dynamic coastal area such as Vitória, such constrained coverage will likely not present an accurate indication of the entire coastal current system. The presence of the ship might also distort the natural current flow of the water, influencing the precision of the measurements. In addition, holding a vessel berthed for a long period may be logistically complex and costly, especially in a busy port city such as Vitória.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP is now a more advanced and useful tool for measuring coastal currents. ADCPs are able to estimate water currents in a broad range of vertical height, providing accurate information on the velocity structure of the water column. They may be mounted on various platforms, including ships, buoys, and the seafloor. Ship-mounted ADCPs are able to continuously measure while a ship moves, covering a vast area in a relatively short amount of time. In Vitória, a ship-mounted ADCP may be used to map the coastal currents around and within the Bay of Vitória, providing valuable information on the complex flow patterns. Bottom - mounted ADCPs can be deployed at strategic locations, e.g., at the entrance to the bay or above areas with large underwater features, for making long - term, fixed - point measurements. This allows scientists to examine long - term trends in coastal currents.

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

ADCPs operate on the Doppler principle. They transmit acoustic pulses into the water. The pulses bounce off suspended particles such as sediment, plankton, or bubbles in the water. When the water is in motion, the frequency of the returned pulses is changed. By measuring this change in frequency, the ADCP can calculate the velocity of the water relative to the instrument.

Most ADCPs have multiple transducer beams, typically four or more, arranged at different angles. This multi-beam arrangement enables the three-dimensional velocity of the water to be measured. By combining the signals of the beams, the ADCP is able to construct a general image of the current velocity at different depths in the water column. The ADCP data can be processed in real-time or stored for later analysis. In use for Vitória's coastal currents, ADCP data can provide researchers with the capability to examine the interaction between the South Equatorial Current, tides, and wind-driven currents at different depths and give valuable insights into the dynamics of the coastal waters as a whole.

5. What does it take for high-quality measurement of Vitória coastal currents?

Equipment that is geared for high-quality measurement of Vitória's coastal currents should possess the following vital characteristics. It must be made using reliable material, with infinitesimal measurements, a light weight, minimal power consumption, and minimal costs. These facilitate the availability of a multitude of devices whose placement ensures exemplary spatial coverage.

ADCPs with titanium alloy casings are strongly recommended. Titanium alloy is highly resistant to corrosion, which is crucial for the long-term deployment in the hostile marine environment. It can resist the corrosive effect of saltwater so that the internal components of the ADCP are protected from corrosion. Titanium alloy is also strong and lightweight and provides the strength and portability of the instrument. For a crowded coastal metropolis like Vitória, whose deployment site access might be limited, portability of the device is a definite advantage. With the combination of these features, it is possible to measure currents along the coastline around Vitória accurately and over long periods of time.

6. Selection of correct equipment for measurement of currents

Usage-wise

The ADCP choice changes depending on use. For measurements from ships, ship-mounted ADCPs are the most appropriate. They are able to provide real-time information as the ship moves across the water, surveying a large area in a short time. In Vitória, this proves useful to quickly map the coastal currents surrounding and within the bay. For sustained observation at one point, bottom-mounted ADCPs are more appropriate. They are able to pass data continuously over a long period of time, allowing the researchers to track long - term coastal current trends. For example, placing a bottom - mounted ADCP near the mouth of Bay of Vitória can allow them to track changes in tidal and other currents over months or years. Floating ADCPs are useful to monitor the movement of water bodies over a wide area and are highly informative of large-scale pattern circulation. Floating ADCPs may be used to study how the South Equatorial Current interacts with the regional coast currents for Vitória.

Selection Based on Depth

Based on the depth of water, the frequency of the ADCP also needs consideration. For less than 70m depths, 600kHz ADCPs can be used. They can record high-resolution measurements in shallow areas, such as along the shores or in the inner part of the Bay of Vitória. For depths up to 110m, 300kHz ADCPs can be used. The frequency is best for moderate-depth areas, such as the outer part of the bay. For greater depths, to 1000m, 75kHz ADCPs are more desirable. Although the waters along Vitória are not typically very deep, in some offshore areas or channels, these lower-frequency ADCPs may be required to measure the currents at deeper depths accurate

There are a number of well - known brands for ADCP in the market, including Teledyne RDI, Nortek, and Sontek. Yet, for those who want cost - effective ADCPs, the ADCP supplier China Sonar's PandaADCP is most recommended. With a body composed of pure titanium alloy, it provides superior performance at a low price. It is most suitable for cost - saving users but still need high - quality ADCPs to measure coastal currents. You can get more information on them on their official website: https://china-sonar.com/.

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