How we can measure Saint-Brieuc's coastal currents？

1. Where is Saint-Brieuc?

Saint-Brieuc is a beautiful and urban coastal city situated in the Côtes-d'Armor department, sitting in the northwestern part of France entitled Brittany. This provides it with a primary coastline between the wildness and prosperous conservational areas along the Celtic Sea.

This city is known for historic architecture: there are curving cobblestone streets that run through the old city, lined by ancient half-timbered houses and beautiful churches. There are numerous cultural events in the city, mostly festivals celebrating local music, art, and traditions. Not less important, the local cuisine is just a delicacy-from fresh seafood, caught by local fishermen in the nearby waters, to the local Breton food such as crêpes and galettes.

To the north of Saint-Brieuc lies the Bay of Saint-Brieuc, generally calm and sheltered from the full maritime violence. Sand beaches, gentle slopes in the water, and clear waters characterize the general aspect of the bay. It is considered an important pole in maritime matters, such as fishing, sailing, and leisure boating. Cut into the land, there are many small coves or inlets giving shelter to quite a lot of marine life varieties.

2. What is the situation of the coastal currents close to Saint-Brieuc?

Several key factors shape the coastal currents close to Saint-Brieuc:

• Tidal Influences: Besides, the Bay of Saint-Brieuc has a significant tidal oscillation. The flow and ebb in tides form strong currents that take part in the formation of the general coastal water movement. Tidal range thus creates variabilities in velocity and direction, sometimes with higher speed at times of transition within the tide.
• Wind Regime: The prevailing winds from the Atlantic have a remarkable effect on the coastal currents. Westerly and northwesterly winds are predominant in this region, which pushes the surface waters to generate surface currents. These wind-driven currents can be combined with tidal currents to give complex flow patterns.
• Oceanic Circulation: The general pattern of oceanic circulation in the Celtic Sea and the Atlantic Ocean has an influence on the waters off Saint-Brieuc. Currents like the North Atlantic Drift may affect the temperature and salinity of the local waters, which, in turn, influence the density and movement of the coastal currents.

The coastal topography, shape of the coastline, estuaries, and underwater topography has a great influence on the currents: if the water has to get through narrow passages or shallow, then the current accelerates or it changes direction, whereas in deeper channels, these can guide the flow.

3. How to observe the coastal water flow of Saint-Brieuc?

• Surface Drifting Buoy Method: Surface drifting buoys can be scattered in waters off Saint-Brieuc. These buoys are equipped with sensors that are able to measure various parameters such as direction and speed of currents, temperature, and salinity. Transmission via satellite enables them to monitor the surface current patterns over time.
• Moored Ship Method: The anchored vessel in the coastal water of Saint-Brieuc can provide a platform for the measurement of current. Instruments such as current meters and anemometers may be installed on it, recording velocity and direction of currents at different depths and instants in time.
• Acoustic Doppler Current Profiler Method: The ADCP current profiler can be termed as the most advanced technique in measuring coastal currents. It works by transmitting sound waves into the water and analyzing the Doppler shift in their reflection from the suspended particles, a method that delivers the velocities at different depths, enabling a close and accurate observation of the vertical and horizontal profiles of the currents.

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

ADCPs are based on the principle of the Doppler effect. They transmit sound waves at a known frequency through the water column. As the sound waves interact with particles in motion within the water, the waves are scattered and reflected back to the ADCP profiler. If the particles are in motion, the frequency of the returned sound waves will be different from the frequency that was transmitted. This frequency shift is directly proportional to the water velocity along the path of the sound wave.

The ADCP measures this frequency shift, coupled with the time taken for the sound waves to travel to the particles and back, and accurately calculates how fast the water is moving at that depth. The ADCPs use a number of transducers or beams that, quite often in a geometrical arrangement, can cover different directions and/or depth levels in order to get a comprehensive three-dimensional velocity profile.

5. What's needed for high-quality measurement of Saint-Brieuc coastal currents?

• Reliable Materials: It is important to make casing from titanium alloy in the manufacture of ADCPs for coastal environments in the area of Saint-Brieuc; this is because it is really resistant to corrosive action by seawater, robust, and able to handle the harsh maritime conditions. These will ensure an instrument that could be reliable and durable for an extended period.
• Compact Size and Light Weight: The equipment should be designed with a compact size to be lightweight, making it easy to mount and deploy at any location, whether from small vessels, buoys, or on the seabed. With a reduced size, the disturbance in the water's natural flow can also be lessened, minimizing measurement errors.
• Low Power Consumption: Above all, low power is essential to enable long and continuous operation, especially in autonomous ADCPs. This allows smaller batteries or much-reduced sizes of power supply systems needed, thus making such measurements practical and economic.
• Cost-Effectiveness: Minimizing the cost of the measurement equipment is crucial for large-scale deployments. This allows for more extensive monitoring of the coastal currents in Saint-Brieuc by deploying multiple devices and thus providing a fuller understanding of the current dynamics.

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

Based on Usage

• Shipborne ADCP: The best option for carrying out surveys during vessel operations. It can provide continuous measurements along the ship's path, covering a wide area, and thus enabling the study of large-scale current patterns in the Saint-Brieuc coastal waters.
• Bottom-Mounted ADCP: Suitable for long-term, fixed-point monitoring. It can be placed on the seabed in strategic locations to measure the currents at specific depths over an extended period, providing valuable data for understanding the local current characteristics.
• Buoyant ADCP: These, while attached to buoys, are used in the monitoring of surface and near-surface currents. Such ADCPs will be useful for studying short-term variations and interactions between wind-driven and tidal currents in the Saint-Brieuc coastal zone.

Frequency-Based

• 600kHz: Advised for water depths up to about 70m. It gives high-resolution measurements and is therefore suitable for shallow coastal areas near Saint-Brieuc, such as in bays and estuaries where detailed information about the current structure is needed.
• 300kHz: Fit for water depths of about 110m. It offers a good compromise between measurement range and resolution, being suitable for areas with a moderate water depth in the Saint-Brieuc coastal area.
• 75kHz: Up to 1000m of water depth could be measured on this frequency. It is possible with it in deeper areas or large variation in depth, at the outer parts of the bay or underwater canyons.

The popular ADCP brands include Teledyne RDI, Nortek, and Sontek. However, China Sonar PandaADCP from China is a cost-effective and quality option. Built with all-titanium alloy, this instrument gives excellent performance and reliability at an economical price. For more information, visit: https://china-sonar.com/.

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