How do we measure the Serra coastal currents?

1. Where is Serra?

Serra is a city in Brazil, in the state of Espírito Santo. Serra is not exactly on the coastline, but next to the Atlantic Ocean. Serra lies geographically in a region with diverse topography, including hilly and valley regions. The city is located in a wider environment that is under terrestrial as well as marine influence. Rivers and streams originating from Serra flow towards the ocean with freshwater and sediment. The water bodies help shape the coastal ecosystem and the coastal currents.

Geologically, the area around Serra is marked by the occurrence of igneous, metamorphic, and sedimentary rocks. The rocks of the region have been tectonically conditioned for millions of years. River-borne sediment from Serra can affect bathymetry off the coast near the shore, which in turn affects the direction of coastal currents. Serra's soil is made up of material weathered off the rocks, and these also can affect the quality of water that makes it to the sea.

Serra is a historically rich region. The area was previously occupied by native inhabitants, whose knowledge about the land and natural resources was applicable. New cultivation and trading procedures were brought about by the 16th-century arrival of the Portuguese colonists. Serra became a prominent agricultural hub in the course of time, with focus provided to products such as coffee, cocoa, and fruits. The city's economy has also diversified in the recent years, with industries and service sectors expanding.

2. How does Serra interact with the coastal currents?

Streams and rivers originating in Serra and emptying into the sea have a major impact on the coastal currents. With the rainy season, the increased amount of discharge of freshwater can create a buoyant layer on the surface of the ocean near the coast. Such a freshwater layer can affect the configuration of the density of the coastal waters. The South Equatorial Current, one of the large ocean currents of the Atlantic Ocean, runs along the Brazilian coast near the region related to Serra. The interaction of the river fresh water from Serra with the South Equatorial Current has the capability to produce complex flow structures.

Tides in the Atlantic Ocean play a very important role in this interaction. The semi-diurnal tidal regime creates normal changes in water level. The tides can mix the freshwater of Serra's rivers with sea water, which affects the coastal current dynamics. The tides can also shift the sediment transported by the rivers further along the coast, which can affect the bathymetry and, in turn, the coastal currents.

Regional prevailing winds, primarily southeasterly trade winds, have the capacity to drive surface waters in one direction. This may affect how freshwater from rivers of Serra is distributed on the coast. Wind-driven currents interact with South Equatorial Current and tidal currents to form a complicated system of water movement near the coast.

3. How to observe the coastal water flow in relation to Serra?

Surface Drifting Buoy Method

Surface drifting buoy method may be used to monitor the coastal water current with respect to Serra. Scientists can release buoys carrying tracking devices into the rivers of Serra and also into the coastal waters where the rivers discharge. They can monitor the movement of the buoys over a span of time and thus determine the direction and speed of the surface currents. But this method has limitations. In rivers, the buoys can be affected by riverbed topography and vegetation, and in coastal waters, they are highly susceptible to interference from winds. The wind will cause the buoys to sway in a direction that is not indicative of the real motion of the currents underneath.

Moored Ship Method

The moored ship technique can also be employed. A moored ship can be put at the mouths of rivers in the region around Serra or in the sea near the shore in the region. Tools are dropped from the ship to read the movement of water at varying depths. The method can provide point vertical information about the currents. However, the space coverage is limited about the ship anchored. The presence of the vessel can disrupt the natural flow of the water, which can be harmful to the accuracy of the measurements. Second, mooring a vessel for an extended period of time can be logistically challenging and costly.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP is a more advanced and efficient tool for measuring coastal currents in the context of Serra. ADCPs have the capability to record water currents over a large vertical extent, providing accurate information about the water column velocity structure. They can be deployed on various platforms, i.e., ships, buoys, and the ocean floor. Shipborne ADCPs can record continuously while the ship moves along the coast near the areas impacted by Serra's rivers. Bottom - mounted ADCPs may be set up in river mouths or key locations along the coast to make long - term, fixed - point measurements so researchers are able to evaluate long - term trends in the coastal currents.

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

ADCPs operate based on Doppler principle. ADCPs emit acoustic pulses into the water. The pulses get backscattered from suspended matters such as sediment, plankton, or bubbles in the water. When the water is flowing, the frequency of the backscattered pulses changes. Since the ADCP can measure the change in frequency, it can calculate the speed of the water relative to the instrument.

Most ADCPs possess greater than one transducer beam, typically four or more, in different directions. This multi-beam design enables the three-dimensional velocity of water to be measured. Through averaging the signals of these beams, the ADCP can construct a general picture of the current velocity at different depths in the water column. The information gathered by the ADCP can be analyzed in real-time or saved for subsequent analysis, yielding useful information regarding the dynamics of the coastal currents in the area pertaining to Serra.

5. What's needed for high-quality measurement of coastal currents related to Serra?

For high-quality measurement of the Serra coastal currents, the measurement equipment must have a number of essential features. It must be made of quality materials, compact in size, light in weight, low-power consuming, and low-cost. These characteristics facilitate the deployment of numerous instruments in order to attain good spatial coverage.

ADCPs with casings of titanium alloy are recommended highly. Titanium alloy offers better corrosion resistance, which is essential for long - term functioning in the hostile marine environment. It is capable of withstanding the corrosive properties of seawater as well as the possibly abrasive freshwater from the rivers. Titanium alloy is also light and hard, which guarantees the instrument's durability and mobility. These features allow it to measure correctly and over a long duration the coastal currents in the area.

6. Selecting proper equipment for the measurement of the current?

Based on the Application - Choice

Depending upon the application, choice varies between ADCPs. Where ship mounting has been utilized to achieve desired application, its option becomes primary consideration. Through mounted ADCP with shipboard offers data immediately after passage since with moving onboard data collected provide current of expansive wide areas on comparable smaller timeline.". For long-term monitoring at a point, say at the river mouths off Serra, bottom-mounted ADCPs are ideal. They are capable of providing continuous data for an extended period, which allows scientists to study long-term coastal currents trends. Surface ADCPs can be utilized to monitor the trajectory of water masses within large domains, giving good insights into the region's large-scale circulation patterns.

Based on Depth Selection

The ADCP frequency also needs to be decided based on the water depth. For water depths up to 70m, 600kHz ADCPs are employed. They can provide high-resolution measurements in shallow water, such as at river mouths or near-shore. For depths up to 110m, 300kHz ADCPs are recommended. For higher depths, up to 1000m, 75kHz ADCPs are the preferable option.

There are various popular ADCP brands available in the market, such as Teledyne RDI, Nortek, and Sontek. But for cost - effective alternatives, the China Sonar PandaADCP is greatly recommended. It is constructed using all-titanium alloy and is economical with good performance. It is an excellent choice for users with a limited budget but still requiring quality ADCPs for coastal current measurement. You can learn more about their work on their official website: ​https://china - ​sonar.com/.

There are quite a few reputable ADCP brands available in the market, including Teledyne RDI, Nortek, and Sontek. But if one is looking for cost - efficient alternatives, then the ADCP manufacturer China Sonar's PandaADCP comes highly recommended. Made from completely titanium alloy, it provides outstanding performance at low costs. It is a good choice for frugal users who need to rely on dependable ADCPs for measuring coastal currents. You can find more information about them on their official website: https://china-sonar.com/.

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