How do we measure the coastal currents of Torres?

1. Where is Torres?

Torres is a city in Rio Grande do Sul state, Brazil, on the country's southern coast. Torres is located at the mouth of the Jacuí River, where the river flows into the Atlantic Ocean. Torres' location provides it with a unique geographical and ecologic significance.

Geographically, the region is diversified by a diverse landscape. The coast has extensive stretches of sandy beaches, some of which are renowned for being tranquil and naturally scenic. Such beaches are not only visited by visitors but also bear major sea turtle nesting sites. The coastal dune belts offer natural barriers against coastal erosion and support an array of vegetation species that have learned to cope with the harsh coastal environments.

Back country, Torres is controlled by the Jacuí River, one of the largest in southern Brazil. The river's valley is rich and farmed for several decades. Surrounding areas have grasslands and tracts of original forests, which provide housing for a good mix of animals, including birds of different types, small animals, and reptiles.

Culturally, Torres is not poor in terms of history. Native tribes inhabited the region initially, followed by Portuguese colonizers in the 18th century. They have left an indelible mark on native architecture, cuisine, and local culture. It has been generations since fishing was a traditional profession in Torres, and the locals of the town form the bulk of the working class. The newly caught fish and seafood from the nearby waters are not only sold locally but also come in handy when cooking a delicious local meal.

Tourism has grown consistently in Torres in recent years. The town combines natural and cultural sites, its beaches and the Jacuí River on the one side, and historical sites and festivals on the other side. The seafood festival every year, for example, attracts tourists from all corners of the world to taste the local cuisine, hear live music, and watch traditional dances.

2. How are the coastal currents around Torres?

The coastal currents around Torres are decided by an involved interaction of a variety of factors. The tidal forces are a fundamental influence. The standard ebb and flow of tides in the region generate significant water movement. Seawater floods into the estuary formed by the Jacuí River at high tide, and the water floods back out into the ocean at low tide. These tidal currents are quite strong, especially in the narrow channels near the river mouth. They play a significant role in sediment, nutrient, and marine life transportation, which directly affects the local marine ecosystem.

The wind systems also affect the coastal currents significantly. The prevailing southeast winds are common in this part of Brazil. These winds can force surface water down the beach and create longshore currents. The velocity and direction of the longshore currents are functions of the strength and frequency of the wind. Stronger winds will produce stronger longshore currents, which can transport sand along the beach and occasionally lead to beach erosion or accretion elsewhere.

The discharge of the Jacuí River is also essential. The massive quantity of freshwater released from the river to the sea can create a floating plume that extends on the coastline. The plume can alter the density and salinity of the coastal waters, which in turn influence the current patterns. The blending of the river-borne freshwater with the ocean's saltwater can lead to the formation of complex flow patterns, like the formation of estuarine circulation cells.

3. How to monitor the coastal water flow of Torres?

Surface Drift Buoy Method

One of the traditional ways of monitoring coastal water flow is the use of surface drift buoys. These are tracking buoys, either GPS or satellite transmitters. Once put into the ocean, they emit signals at regular intervals. By tracking the path of these buoys over time, scientists can measure the speed and direction of the surface flow. Surface drift buoys have one weakness. They are highly wind and wave dependent. They make the buoys deviate from the actual path of the current and thus provide incorrect measurements. They measure only the surface layer of the water column and not the subsurface currents.

Anchored Ship Method

Anchored ship method utilizes a stationary ship as a platform for measuring the current. Scientists submerge current meters from the ship at different depths to estimate the velocity and direction of the current. The method gives a more detailed vertical profile of the current than surface drift buoys. The method is, however, labor - intensive and time - consuming. The ship can also disturb the natural course of the current, and the measurements can be taken at a single point only. Adverse weather conditions, such as strong winds and turbulent waves, can make deployment and maintenance of the equipment challenging or even impossible.

Acoustic Doppler Current Profiler (ADCP) Method

Acoustic Doppler Current Profiler (ADCP) has been established as a newer and more reliable method to quantify coastal currents near Torres. ADCPs can provide high-resolution velocity data of currents at multiple depths in the water column.

4. On what Doppler principle are ADCPs founded and how do they function?

ADCPs are founded on the Doppler principle. They discharge sound waves into water. Upon these sound waves impacting particles of the water, such as suspended sediment or minor sea creatures, part of the energy of sound returns towards the ADCP profiler. If the particles are moving with the current downstream, the Doppler frequency of the scattered sound wave will not equal the frequency of the transmitted sound wave. This frequency difference, the Doppler shift, is directly proportional to the velocity of the particles and therefore the current velocity.

Most ADCPs employ more than one beam, typically four, to measure the Doppler shift from more than one direction. By measuring the Doppler shifts of these few beams, the ADCP can calculate the three-dimensional velocity of the current at various depths. The depth at which the current is measured varies with the frequency of the employed sound waves by the ADCP. ADCPs with higher frequency are better suited for shallow-water measurements as they provide greater resolution but a reduced range. Lower-frequency ADCPs penetrate deeper into the water column but with lower resolution.

5. What is needed for high-quality measurement of Torres coastal currents?

In order to measure the coastal currents of Torres at high quality, several traits are needed in the measurement instrument. The material reliability is the most important thing. The equipment must be resistant to the marine environment, with its exposure to saltwater, strong currents, and unpredictable weather. Corrosion - resistant materials play a critical role in ensuring the long - term operation of the equipment. For ADCPs, the casing material is critical. Titanium alloy is a suitable choice for ADCP casings used in Torres' coastal waters. Titanium alloy is extremely corrosion-resistant, which is key to resisting corrosive action over extended periods. It is lightweight and strong as well, possessing a good trade-off between ruggedness and being easy to deploy.

Size, weight, and power usage also play important factors. Smaller and lighter gear is simpler to deploy, especially in remote or hard - to - reach situations. Low power consumption devices can sustain operation over a longer time without requiring continuous replacement or charging of batteries, an aspect significant in long-term monitoring ventures. Economical factors also matter a lot. The equipment needs to be inexpensive so as to accommodate wide-scale measurement and intensive collection of data. High-cost equipment can limit the number of measuring points, reducing the accuracy and representativeness of the data.

6. How to Choose the Right Equipment for Current Measurement?

Determining by Usage

The use of the proper equipment for measuring current will depend on the use. If the ADCP is being used on a moving ship, a ship-mounted ADCP is the proper choice. This ADCP can sample the current continuously as the ship moves across the water, providing a profile of the current along the ship's track.

For fixed-point measurements over long term, a bottom-mounted (or sit-on-the-bottom) ADCP would be appropriate. They are fixed to the seabed and have the capability of collecting current data at a single location for an extended period.

If the measurement of the current is to be done in a more mobile and larger scale, a buoy-mounted ADCP can be utilized. They are fixed on floating buoys and can be set to drift along with the current, collecting information as they go.

Choosing the Right Frequency

The frequency of the ADCP also comes into play. A 600kHz ADCP can be used to measure currents in up to 70m deep water. It provides very high-resolution measurements in shallow to moderate-depth waters. One can use a 300kHz ADCP for up to 110m depth, while a 75kHz ADCP is designed for much deeper water, up to 1000m. The frequency to be applied relies on the expected depth of the water where the current measurements are to be recorded.

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 supplier 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.