How do we measure the coastal currents of Ilhéus?

1. Where is Ilhéus?

Ilhéus is a city in the southern Bahian state of Brazil on the Atlantic coast. At coordinates approximately 14°49′S 39°04′W, it is one of the area's major coastal cities. The city's coastline features a combination of beautiful beaches, rocky headlands, and small estuaries. These features of the coastline, apart from the aesthetic appeal of the region, also serve significant roles within the ecosystem. The beaches, for instance, provide habitat for nesting sea turtles, whereas the estuaries are home to over three hundred species of fish that live there as their nurseries.

Geologically, the region of Ilhéus consists of a mixture of low-coast plains and very old sedimentary rock formations. The coastal seafloor is extremely intricate in its bathymetry with irregular depths and a combination of underwater features such as sandbars, channels, and coral reefs. The coral reefs, while smaller than in some tropical regions, are still rich in a vast array of sea life. They also serve as natural breakwaters, protecting the coast from erosion and providing room for countless numbers of fish, crustaceans, and mollusks. Ilhéus city is also impacted by the stream and river runoff into the sea, impacting the density of the coastal water along with the salinity of the water.

Ilhéus also experienced some history with which it was blessed. It initially had indigenous inhabitants such as the Tupinambá people. The Portuguese later arrived to colonize during the 16th century and laid the structures of Ilhéus city as it exists today. In earlier centuries, the city was a major hub for cocoa manufacturing and export following the introduction of cocoa in the region in the 18th century. This had brought economic prosperity and expansion of culture. The contemporary economy of Ilhéus revolves around diversified industries like tourism, agriculture (of which cocoa cultivation was among the most notable of them), and services.

2. What are the coastal currents off Ilhéus?

Offshore currents at Ilhéus are controlled by an interaction of a great many factors. Among the dominant controls is the South Equatorial Current, one of the biggest of the ocean currents in the Atlantic Ocean. It is a warm, west-flowing current that hugs the Brazilian coast and, upon reaching close to Ilhéus, interacts with the topography and bathymetry of the area. The South Equatorial Current can be divided into local currents as it approaches the coastline, creating an intricate pattern of coastal currents.

Atlantic Ocean tides play a special significance. The semi-diurnal tidal cycle creates repeat water-level cycles. The increased gravitational pull by the sun and moon during spring tides results in stronger tidal currents. The tidal flows mix with coastal geometry and the South Equatorial Current in the area and guide the overall coastal water direction. Tides will also be contributing to creating rip currents, their narrow flow streams of moving water offshore of the beach at high velocity. Rip currents pose peril to swimmers and are an integral part of coastal safety. Local winds, blowing as southeasterly trade winds, also impact the coastal currents.

Wind will drive surface water in one direction and create a wind-driven current. The wind-driven current also meets the South Equatorial Current and tidal currents, further adding to the pattern of water flow. Seabed bathymetry off Ilhéus, such as sandbars, channels, and coral reefs, can either direct or disorient the flow of the currents. Coral reefs, however, can create a barrier, and the water will run around them, whereas channels can accelerate the current.

3. How to track the coastal water flow of Ilhéus?

Surface Drifting Buoy Method

The surface drifting buoy technique is a standard method of tracking coastal water flow. Scientists release buoys equipped with tracking units into the sea. By tracing the movement of buoys over time, scientists can determine the direction and speed of the surface currents. However, this technique has certain limitations. It only provides information about the surface layer of the water column, and the buoys are highly susceptible to interference by wind. The buoys may be deflected by the wind in a manner that does not represent the true direction of motion of the underlying currents.

Moored Ship Method

The moored ship method involves using a fixed ship as a platform for current measurements. The sensors are released from the ship to make measurements of water flow at varying depths. The method has a few disadvantages though it can produce accurate vertical current profiles. It is limited by spatial coverage that is only restricted to the very local area in the vicinity of the moored ship, and the natural flow of water will be distorted through the effect introduced by the vessel. In addition, having a ship tied up for an extended period of time can be logistically complex and costly.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP has emerged as an increasingly sophisticated and efficient tool for coastal current measurement. ADCPs can measure water currents over a wide vertical range with high-resolution data on the velocity structure of the water column. ADCPs can be installed on a range of platforms, from ships to buoys to the seafloor. Ship - mounted ADCPs are capable of making continuous measurements as the ship is moving, measuring a broad area in a relatively short time. Bottom - mounted ADCPs can provide long - term, fixed - point measurements, allowing researchers to monitor long - term trends in the coastal currents.

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

ADCPs operate on the principle of Doppler. They transmit acoustic signals into the water. These acoustic signals bounce off particles suspended in the water such as sediment, plankton, or air bubbles. When the water is moving, the frequency of these returning signals is altered. From this altered frequency, the ADCP determines the relative speed of the water relative to the instrument.

Most ADCPs have a number of transducer beams, typically four or more, at different angles. The multi-beam setup allows the three-dimensional velocity of the water to be calculated. When the signals of the beams are summed, the ADCP can construct a full image of the current velocity at different depths in the water column. The information collected by the ADCP can be analyzed in real-time or saved for later analysis, providing valuable information regarding the dynamics of the coastal currents.

5. What is needed for good-quality measurement of Ilhéus coastal currents?

In order to measure accurately the coastal currents of Ilhéus, measuring instruments must possess some important characteristics. They must be built of long-lasting materials, with compact dimensions, light weight, low power consumption, and inexpensive costs. Such attributes allow large quantities of instruments to be put out, resulting in full spatial coverage.

Titanium alloy casings ADCPs are highly advised. Titanium alloy has excellent corrosion resistance, which is essential for long - term exposure to the challenging marine environment. It is also resistant to the corrosive nature of saltwater, thereby safeguarding the ADCP's internal components against corrosion. Titanium alloy is also strong and yet lightweight, providing support for instrument durability and maneuverability. The properties combined provide accurate and long - term measurement of the coastal currents off Ilhéus.

6. How to Choose the Appropriate equipment for current measurement?

According to Usage Choice

The ADCP to choose is determined by its use. For ship measurement, ship-mounted ADCPs are best suited. They can transmit real-time data as the ship moves through water and covers a large distance in a short time span. For long - term, fixed - point monitoring, bottom - mounted ADCPs are preferable. They can provide continuous data over a long period of time, which allows researchers to study long - term trends of the coastal currents. Floating ADCPs work best in monitoring the motion of huge water masses over huge distances and providing informative inputs to large - scale circulation patterns.

Choice Based on Depth

The ADCP frequency should also be decided based on the water depth. For depths below 70m, 600kHz ADCPs are preferable. They can provide high-resolution measurements in shallow waters. For depths of up to 110m, 300kHz ADCPs are suitable. For deeper waters, up to 1000m, 75kHz ADCPs are the preferable option.

Some of the known ADCP brands in the market are Sontek, Nortek, and Teledyne RDI. For those who need cost - friendly ones, one of the highly recommended ADCP supplier China Sonar's PandaADCP made of pure titanium alloy is affordable and has great performance. It is perfect for budget - friendly users but still need good quality ADCPs utilized for coastal currents measurement. You can find out more about them on their official website: https://china-sonar.com/.

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