How can we measure the coastal currents of Concarneau?

1. Where is Concarneau?

Concarneau, a charming town that lies on the southern coast of Brittany in northwestern France, is a place where the allure of the sea seamlessly blends with rich cultural heritage. Nestled along the Bay of Biscay, this coastal gem is embraced by the Atlantic Ocean, creating a unique marine landscape.

It is a well-known town due to its very well-preserved medieval fortified Ville Close listed with UNESCO, the "Enclosed City", with winding cobblestone streets between ancient stone buildings and the ramparts giving it all fantastic views of the waters in its vicinity. Local people have been very attached to the sea; fishing has always been one of their oldest traditions and industries. The port of Concarneau is busy, full of fishing vessels of all sizes whose hulls bob gently in the water.

The Bay of Biscay is a large body of water lying adjacent to Concarneau. It is characterized by its relatively large expanse and is influenced by the broader currents of the Atlantic Ocean. Marine life ranges from the small fish species that form the base of the food chain to the larger pelagic fish. Different seabirds can also be found along the coastal waters of Concarneau, further enhancing the diverse and dynamic ecosystem.

2. What is the situation of the coastal currents near Concarneau?

A few preceptors are responsible for the characteristics of the coastal currents around Concarneau. Tidal forces, for one, are a major influence. There are semi-diurnal tides around the Bay of Biscay-that is, a pair of high and low tides. These tides are responsible for the ebb and flood carried by the water in and out of the coasts, creating strong currents.

Moreover, the current is modified by the topography of the coastline around Concarneau. An irregular, indented shoreline which contains numerous bays and inlets can easily cause divergence and convergence of the current that, at times, alters its direction. For example, narrow channels between islands or peninsulas will decrease the width, hence increase the speed of the current.

Wind, on the other hand, is another very crucial factor. The prevailing winds from the Atlantic can push the surface waters, creating wind-driven currents. Westerly winds, common in this area, can push the surface waters to the east, which then interact with the tidal currents. Furthermore, the Atlantic Ocean large-scale oceanic circulation patterns, such as the North Atlantic Drift, extend well to drive coastal currents around Concarneau, although its immediate effect is somewhat modified by local bathymetry and tidal forces.

3. How to monitor the current conditions of Concarneau Coastal Current?

Surface Drift Buoy Method

One of the traditional methods of observing coastal water flow involves the use of surface drift buoys. The design of such buoys allows them to float on the surface of the water and essentially move with currents. They are equipped with sensors, including GPS for position tracking. A buoy determines the position at regular periods, from which the direction and speed of the current on the surface are established. However, this can only give information about the surface currents and may not be a true representation of the currents at different levels.

Anchored Ship Method

This method can be done by anchoring the ship, mostly keeping it stationary in one location. Current meters are lowered from the ship at different depths to measure the velocity of water. This method can provide a more detailed profile of the currents at different depths near the ship. However, it is limited in terms of spatial coverage. The measurements are only representative of the area around the ship, and it can be time-consuming and expensive to move the ship to different locations for comprehensive data collection.

Acoustic Doppler Current Profiler (ADCP) Method

In more recent and advanced methods of measuring coastal currents, the method has become more handy with the introduction of the Acoustic Doppler Current Profiler, ADCP. The ADCPs measure the water velocity at more than one depth simultaneously and give a detailed vertical profile of the currents. They can also be deployed from ships, moored to the seafloor, or attached to buoys, offering greater flexibility in data collection. This allows for both a broader outlook of the general view of the system, from top surface waters well into deeper ones.

4. How do Doppler Principle applying ADCPs Work?

The principle of operation of ADCPs is based on the Doppler principle. They send acoustic signals into the water. Acoustic signals reflected from small particles suspended in the water (like plankton, sediment, or bubbles) return to the instrument. When the water is in motion, a frequency shift in the reflected acoustic signals occurs.

Particularly, the frequency of the reflected signal is higher than the emitted one if the particles move towards the ADCP-a so-called positive Doppler shift. In contrast, when particles are moving away from the ADCP, the frequency of the reflected signal is lower-a so-called negative Doppler shift. By measuring such frequency shifts, the velocity of the water at various depths is calculated by the ADCP.

To do so, the ADCP current meter divides the water column into several layers, or bins. Each bin corresponds to a particular depth range. From the analysis of the Doppler shifts of the acoustic signals reflected from each bin, the ADCP can determine the velocity of the water within that particular depth range. A fine vertical profile of the current velocity is thus attained.

5. What is required for high-quality measurement of currents at Concarneau coasts?

Reliability

Measurement of coastal current is extremely a sensitive one in nature; for that, it requires high dependability. A marine atmosphere always contains saltwater, high humidity, and sometimes strong waves; which may hamper the reliability of measuring devices.

Size, Weight and Power Consumption

The size of the equipment should be small and the weight light, especially when the ADCP profiler is deployed from a buoy or a small vessel. A smaller and lighter device is easier to handle and install. The power consumption of the ADCP should be low. In this way, longer-term deployment is possible, especially in remote areas where access to a continuous power source is limited.

Cost-effectiveness

Cost is also an important consideration, especially in the case of big measurement projects. Cost-effective ADCP can make them deploy in more places, thereby achieve a deeper understanding of the coastal current system.

Titanium Alloy Casing for ADCP

The casing of the ADCP current profiler is preferably of titanium alloy. The advantages of the titanium alloy are as follows. This is absolutely resistant to corrosion, which is imperative in the salty water of the coastal waters at Concarneau. Severe corrosion can badly damage internal components of the ADCP, possibly leading to devices that either give wrong measurement or completely fail in their operation. Titanium alloy belongs to the high strength-to-weight ratio and is strong enough to bear forces due to water currents and waves with relatively lighter weight. This combination of properties makes titanium alloy an ideal material for the ADCP meter casing, ensuring the long-term reliability and performance of the device.

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

Based on Usage

Ship-borne ADCP: This type of ADCP flow meter is installed on a moving ship. It provides suitability for large-scale surveys of wide areas of coastal currents. While the ship is in motion, the ADCP can make continuous measurements at different locations; it can hence give a wide view of the scale of current patterns.

Bottom-mounted ADCP: It is otherwise called a moored or seabed-deployed ADCP, fixed onto the seafloor. This type is useful for long-term, continuous monitoring of currents in one location. It may deliver quite detailed data on the temporal variations of the currents at that site.

Buoy-mounted ADCP: These ADCPs are attached to floating buoys. These are very well suited for applications in which measurements at different depths are sought along with high mobility, but specifically for measuring surface-layer currents.

Based on Operating Frequency

ADC frequency varies with the water depth at which measurement will take place. A 600kHz ADCP is suitable for water depths of up to about 70m. The higher frequency provides more detailed measurements in shallower waters. For depths up to about 110m, a 300kHz ADCP is a better choice. And for measuring currents in deeper waters, up to 1000m, a 75kHz ADCP is recommended. With the lower frequency, there is greater penetration through the water column, although resolution may be somewhat reduced compared to higher-frequency ADCPs.

There are a few well-known ADCP brands in the market, such as Teledyne RDI, Nortek, and Sontek. But for those in search of cost-effectiveness yet high quality, the Chinese brand China Sonar PandaADCP should be considered. Made of absolutely titanium alloy, this has excellent corrosion resistance and durability. Its price-performance is in a relatively high position, especially for coastal current measurement projects. You can contact them or find more information about China Sonar PandaADCP at their website: https://china-sonar.com/.

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