How can we measure the coastal currents of Les Sables-d'Olonne?

1. Where is Les Sables-d'Olonne?

Les Sables-d'Olonne is a charming coastal town located in the Vendée department in the Pays de la Loire region of western France. Nestled along the Atlantic Ocean, it enjoys a prime coastal position.

Still a popular destination for tourists, it is also famous for its miles of sandy beaches with soft golden sands and crystal clear blue waters. The topography of the coastline is a perfect balance between sand shores, mild dunes, and rich coastal vegetation. The Gulf of Morbihan to the north and Bay of Biscay to the west have a dominant effect on its coastal waters. It has rather calm waters, as some spots face quite strong currents, due to the tide and the wind.

From a cultural point of view, Les Sables-d'Olonne is a city with a strong maritime tradition. Locals have their hearts with the sea, and fishing and sailing were important parts of the local economy and lifestyle for centuries. It is also one of the most popular tourist destinations, luring visitors from all over the world due to its mild climate, beautiful scenery, and all sorts of water sports.

2. What is the situation of the coastal currents near Les Sables-d'Olonne?

The currents along the coast off Les Sables-d'Olonne come about for several reasons: tides, first. Because of the regular tides in the Atlantic Ocean, water sometimes moves along the coast in one direction and sometimes in another, thus creating tidal currents. Depending on the moon phase and other conditions of an astronomical character, strength and direction may change.

Another important factor is wind. Dominant westerly and southwestern winds push against the surface waters creating wind-driven currents. During stormy weather strong and variable currents are greatly caused by strong winds.

The shape of the coastline and underwater topography also contribute to the process of changing the coastal currents. In this regard, bays and inlets on the Les Sables-d'Olonne coastline have the effect of either convergence or divergence of the currents. Offshore features like sandbars and reefs tend to break up the flow, developing complex current patterns.

3. How to Observe the Coastal Water Flow of Les Sables-d'Olonne?

Surface Drifting Buoy Method: This method of measurement is by releasing buoys on the water surface. As the buoys move due to currents, their movement can be followed with the help of satellites or radio signals. In this way, we can get an idea about the pattern of surface currents by following the path and speed of the buoys. The information obtained with this method is related to surface currents only, which may be interfered with by wind and waves.

Anchored Ship Method: The anchored ship, with a current meter and other instruments, could estimate the measurement of water flow in different directions in an anchored condition. During such situations, while the ship maintains her position, simultaneously, current meters record speed and current in multiple ways. But this again can only serve very little area, the stream itself getting distorted by their presence.

Acoustic Doppler Current Profiler (ADCP) Method: ADCP is an advanced and more convenient measurement technique. It makes use of the principle of the Doppler effect for the measurement of the velocity of water currents at different depths. The ADCPs can be deployed from ships, moored to the seabed, or attached to buoys, making the view of the coastal currents much wider and more accurate.

4. How do ADCPs apply the principle of the Doppler effect?

Basically, ADCPs apply the principle of the Doppler effect: they emit acoustic pulses in the water and reflect on the suspended particles or plankton while these move. Simultaneously with their reflection, these pulses exhibit a frequency shift which depends on the particles' speed. Correspondingly, an ADCP detects this change of frequency, making an approximation for the actual current speeds of water flow.

By emitting pulses at different angles and measuring the Doppler shifts in multiple directions, ADCPs can calculate the three-dimensional velocity of the water. They can give detailed profiles of current velocities at different depths, allowing for a more accurate understanding of the coastal current structure.

5. What's needed for high-quality measurement of Les Sables-d'Olonne coastal currents?

To obtain the suitable and proper measurements of the coastal currents at Les Sables-d'Olonne, different characteristics are necessary for measurement equipment.

• Reliability of Materials: The equipment has to be made of materials that can withstand the harsh marine environment, including corrosion from saltwater and the impact of waves and currents. Titanium alloy is an excellent choice for the casing of ADCPs. Titanium alloy has high strength, excellent corrosion resistance, and can maintain its structural integrity in the long term.
• Small and Light in Size: A smaller size and lighter weight make the equipment easier to deploy and handle. It can be attached more easily on buoys or installed on small boats without causing an impact on the measurement environment.
• Low Power Consumption: This is important, especially for devices that need to operate for long periods in the field. Low power consumption allows for longer battery life or reduces the need for large power supply systems.
• Low Cost: A lower cost makes it possible to use a larger number of devices for large-scale measurements, providing more comprehensive data.

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

Based on Usage Purpose:

Shipborne ADCP: It could be very ideal for large-scale surveys. This would better be used in obtaining detailed measurements along the moving path. Continuous data could be presented while the ship navigates through different areas.

Bottom-Mounted ADCP: Suitable for long-term measurement in one location. It is fixed to the seafloor and can record current data over a longer period without interference from surface conditions.

Buoyant ADCP: Can be used to measure surface and subsurface currents in areas where access by ship is difficult or when more flexible deployment is required.

Based on Water Depth:

600kHz ADCPs apply to water depth within 70m and provide high-resolution measurements in relatively shallow waters;

300kHz ADCPs apply to water depths up to approximately 110 meters, offering a good balance in range and resolution for measurement.

ADCPs of 75kHz are targeted for deeper waters, like up to 1000m, and will penetrate deeper into the open ocean or deep channels for current measurements.

These represent a few of the more recognizable names in commercially available ADCPs that are being commercially sold in today's markets; these are, respectively: Teledyne RDI, Nortek, Sontek, although for more restrictive financial allowances exists the Chinese firms making China Sonar ​PandaADCP: the instrument manufactured in all titan alloy is actually incredible about its cost performance-the product is classified economic type of ADCP, site internet reference ​https://china-sonar.com/.

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