How do we quantify São Mateus's coastal currents?

1. Where is São Mateus?

São Mateus is a municipality in Espírito Santo, Brazil, along the Atlantic Ocean. Located at approximately 18°40′S 39°50′W, it has a very good coastal location. The city's coastline is a mixture of beautiful beaches, rocky headlands, and small estuaries. These beach landforms not only beautify São Mateus but serve critical roles within the local ecosystem as well. The beaches, for instance, serve as crucial nesting grounds for sea turtles, and the estuaries function as nurseries for numerous fish.

Geologically, the São Mateus region is marked by a combination of low coastal plains and ancient sedimentary rock structures. The seabed off the coast is of complex bathymetry, in depth and made up of a range of underwater features such as sandbars, channels, and small coral reefs. Although the coral reefs are not as extensive as some of the tropical regions, they remain high in marine biodiversity. They act as natural breakwaters, which protect the coast from erosion and create the home of different species of fish, crustaceans, and mollusks. The city is also influenced by the drainage of small rivers and streams into the sea, which affects the salinity and specific gravity of the sea waters.

São Mateus has a rich and storied history. The indigenous people who occupied the region initially were the Tupinambá people. Portuguese colonizers arrived in the region in the 16th century and established a settlement that developed into the city of São Mateus. Over the centuries, the city has been a major center for coffee, sugar, and other crop cultivation and export. The economy of São Mateus today is driven by a diverse set of sectors such as services, manufacturing, and tourism.

2. What are the coastal currents surrounding São Mateus?

The coastal currents surrounding São Mateus are shaped by an advanced combination of different factors. One of the dominating influences is the South Equatório Current which is one of the major ocean currents in the Atlantic Ocean. It is the hot, westerly flow toward the Brazilian coast; as it approaches São Mateus, its pathway is disturbed by local topography and bathymetry. This might produce complicated coastal flow by the branching of coastal currents close to the coast near the site.

Tidal influence of the Atlantic Ocean is very strong. The semi-diurnal tidal regime generates cyclic water-level variations. At spring tides, the stronger gravitational attraction of the sun and moon results in more intense tidal currents. These tidal currents interact with the South Equatorial Current and local coast geometry to determine the net coastal-water movement. The tides are also capable of generating rip currents, which are strong, narrow moving currents away from the coast. Rip currents are dangerous to bathers and are a prime consideration in coastal safety.

Regional prevailing winds, mostly the southeasterly trade winds, also affect the coastal currents. These winds can force surface waters in one direction, and this creates a wind-driven current. The current driven by the wind interacts with the South Equatorial Current and tidal currents, further complicating the pattern of water movement. The seabed bathymetry off São Mateus, made up of sandbars, channels, and coral reefs, has the ability to channel or break the flow of the currents. Coral reefs, for example, can act as barriers, making the water move around them, while channels are able to accelerate the current.

3. How can the coastal water current of São Mateus be monitored?

Surface Drifting Buoy Method

Surface drifting buoy method is a traditional means of monitoring surface water current of the coast. Scientists release tracking devices attached buoys to the sea. By observing how the buoys drift after some time, they can derive the direction and speed of surface currents. Surface drifting buoy method has its own disadvantages, though. It is only able to provide information in relation to the surface layer of the water column, and buoys are highly susceptible to wind interference. The buoys can be displaced by wind in a manner that does not represent the movement of the bottom currents.

Moored Ship Method

The moored ship method involves utilizing a ship acted as a measuring platform for current measurements. Measuring instruments are dropped from the ship to measure the flow of water at varying depths. This method can produce high-resolution vertical profiles of the currents but is not without some disadvantages. Spatial coverage is limited to the vicinity of the anchored ship, and the presence of the ship has the potential to disrupt the natural flow of water, which may affect the measurements' accuracy. Also, mooring a ship for an extended period of time may be logistically complex and costly.

Acoustic Doppler Current Profiler (ADCP) Technique

ADCP is now a more advanced and efficient technique for coastal current measurement. ADCPs can measure water currents over a large vertical range, providing detailed information on the velocity structure of the water column. ADCPs can be deployed on a variety of platforms, including ships, buoys, and the seafloor. Ship - mounted ADCPs can collect information continuously while traveling, covering a broad extent within a reasonable time frame. Bottom - mounted ADCPs will provide long - term, settled - spot estimation, and that is the way that researchers can analyze the long - term patterns of coastal currents.

4. How do Doppler principle-based ADCPs work?

ADCPs operate on the Doppler principle. They emit acoustic waves into the water. Acoustic waves bounce off suspended material such as sediment, plankton, or water bubbles. For flowing water, the frequency of the backscattered signals is shifted. From this frequency shift, the ADCP can make an estimate of the water velocity relative to the instrument.

Most ADCPs consist of more than one transducer beam, often four or more, positioned in different directions. Through the multi-beam arrangement, they can measure three-dimensional water velocity. From a combination of signals of the beams, the ADCP is able to provide a total description of the current velocity at different depths across the water column. Data obtained from the ADCP can either be analyzed in real-time or reserved for later use, providing valuable information on the dynamics of the coastal currents.

5. What does one need for high-quality measurement of São Mateus coastal currents?

For precise measurement of São Mateus' coastal currents, the measurement equipment should have certain specific features. It should be built in a way that it is made of strong materials, has small size, is light in weight, has less power demand, and is economical. All these features allow many instruments to be deployed in order to achieve total spatial coverage.

Titanium alloy case ADCPs are highly recommended. Titanium alloy has better corrosion resistance, as it is necessary to withstand the extreme marine environment in the long term. Titanium alloy can also withstand corrosive action of seawater to prevent degrading the inner components of the ADCP. Titanium alloy is also light in weight and resistant, as they guarantee durability in the instrument along with convenient portability. This combination of properties allows for accurate and sustained measurements of the coastal currents off São Mateus.

6. Selecting the right equipment for current measurement

Choice Based on Application

The choice of ADCP depends on where it will be used. Ship-mounted ADCPs are the ideal choice for ship-borne measurements. They can supply real-time information as the vessel travels through the water, sweeping a large area in a relatively short period. For fixed - point long - term monitoring, bottom - mounted ADCPs are better. They can supply continuous data over a long period, enabling researchers to investigate long - term trends in the coastal currents. Floating ADCPs may be used to track water mass movement over large areas and be highly useful to large-scale circulation patterns information.

The ADCP frequency should also be determined depending on the water depth. For less than 70m water depths, 600kHz ADCPs are suitable. They can have high-resolution measurement in shallow seas. For 110m maximum depth, 300kHz ADCPs are appropriate. For waters with greater depth, up to 1000m, 75kHz ADCPs are suitable.

There are various established ADCP brands available in the market, including Teledyne RDI, Nortek, and Sontek. But for individuals looking for budget - friendly solutions, the ADCP supplier China Sonar's PandaADCP is highly recommended. Constructed of pure titanium alloy, it performs well without the high price tag. It is a good fit for frugal users who need dependable ADCPs for coastal current measurement. Additional information can be found on their website: https://china-sonar.com/.

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