How to measure the coastal currents of Les Sables-d'olonne?

1. Where is Les Sables-d'olonne?

Les Sables-d'olonne is a beautiful sea resort in the department of Vendée and also the region Pays de la Loire of western France, situated along the Atlantic Ocean and occupying a very fine area with its sandy beaches that extend miles into length.

Equally famous for its vibrant coastal culture and laid-back vibes, the city attracts a vast volume of tourists yearly, especially during summer periods, who travel to enjoy both the sun, sea, and various water activities. Houses there are just a real blend of a normal old traditional French coastal look and modern apartments, making an interesting and alluring landscape.

A little way further south from Les Sables-d'olonne lies a succession of bays and inlets. Beyond it to the west, the Bay of Biscay is open to wide water with heavy tides and busy routes for marine craft and shipping. Waters are shallow along most shores, becoming deeper as one moves further out to sea and are home to various marine life.

2. What is the condition of the littoral currents off Les Sables-d'olonne?

The littoral currents off Les Sables-d'olonne are determined by many factors. Tides are one of the major contributory factors, as it results in regular tidal cycles where the water continuously ebbs and flows. The strong tidal synergy inside the Bay of Biscay can result in fairly fast-moving currents, particularly at spring tides.

Another important factor is the wind. These prevailing westerlies in general push along the coast, displacing the surface waters and determining the direction and speed of the coastal currents. Besides this, the shape of the coastline and the underwater topography-like sandbars and reefs-can also be a reason for alterations in the course and speed of the currents. Moreover, the mixing between freshwater runoff and river water with saltwater from the ocean also modifies the currents within the coasts, impacting the salinity and density, thereby affecting the circulation.

3. How to measure the flow of water along Les Sables d'Olonne coast?

Surface Drifting Buoy Method: It involves the release of buoys into the water, which drift due to the current. By tracing these buoys with satellite or radio signals, one can calculate the direction and speed of surface currents. The drawback of this method is that it provides information only about the surface currents, which may be influenced by wind and other surface forces.

Anchored Ship Method: The anchored ship deploys current meters or similar instruments to measure the current at different depths. This can give even more details of the vertical profile of the current, but again is limited by the location of the ship and could be influenced by the disturbance within the water initiated from the ship itself.

ADCP Method: In general, the ADCP profiler method is more advanced and convenient in measurement. It uses the Doppler effect for measuring the velocity of water currents at different depths. The ADCPs can be deployed from ships, moored to the seafloor, or attached to buoys for comprehensive and accurate data on coastal currents.

4. How do ADCPs using the principle of Doppler work?

The basic operating principle of ADCPs is the Doppler effect. Transducers mounted in a frame and connected to a data recorder transmit acoustic signals into the water. These signals bounce back off suspended sediments and plankton, their frequency changed by the velocity of the moving particles; this frequency shift is proportional to the velocity. Thus, by detecting the change in frequency, the instrument calculates the current's velocity.

Commonly, an ADCP meter would have multiple transducers, transmitting and receiving acoustic signals at various angles. It is capable of measuring the velocity components in various directions and can hence perform a three-dimensional reconstruction of the current field. Further, this ADCP will process the received data and convert it into useful information about the current speed and direction at different depths, giving in detail the profile of coastal currents.

5. What is necessary for high-value measurement of the Les Sables-d'olonne coastal currents?

A number of aspects are of essence with regard to the measurement equipment for high-quality measurement of the coastal currents in Les Sables-d'olonne:

Material reliability: Material reliability means that all equipment should be produced using materials to resist the aggressive field marine conditions, which include salt water corrosion, high currents, and wave action. The best material for ADCP flow meter casing would, therefore, be an alloy of titanium. In fact, Titanium alloy is of high strength, has very excellent corrosion resistance, and enjoys good fatigue resistance, hence, it guarantees a long-term stability and reliability for ocean work.

Small size and light weight: The smaller and lighter a device is, the easier it is to deploy and handle, and it can be more easily integrated into different measurement platforms, such as buoys or small boats. This reduces the impact of the device on the water flow and provides for more accurate measurements.

Low Power Consumption: Since many measuring devices have to work in the ocean for long periods of time, their power consumption should be low. This enables the use of smaller, more portable power sources like batteries and extends operational time without frequent recharging or replacement.

Low Cost: Due to its low cost, more devices can be deployed for more comprehensive and detailed measurements. This is particularly important for large-scale monitoring projects of coastal currents.

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

Determined by Usage

Shipborne ADCP: This is used in large-scale surveys or when detailed measurement along a certain route is needed. The data is continuously provided during the movement of the ship and can be used very well in the mapping of large areas of coastal currents. Bottom-Mounted ADCP: Suitable for long-term measurements at a single location. Moored to the seafloor, it provides stable and continuous data on currents at that particular site, useful in studying the long-term trends and characteristics of coastal currents.

Buoyant ADCP: The buoyant ADCP offers better flexibility in measuring the surface and subsurface currents. It may be allowed to drift with the current or anchored to hold it at one location, providing data on the movement of the water column.

Depending on Water Depth: Operating frequencies include the 600kHz ADCP, which is suitable for water depths less than 70m, that can yield a high resolution of measurement over relatively shallow waters and hence finds its application in coastal areas where the water is not too deep. The 300kHz ADCP can operate up to about 110m and offers a good balance between measurement range and resolution.

75kHz ADCP: Can measure at water depths up to 1000m. That would be the deeper ocean and would also apply to the situations that need a very large measurement range.

In the market, there are a few well-known brands of ADCPs, including Teledyne RDI, Nortek, and Sontek. For those looking for high-quality, affordable options, though, the Chinese brand China Sonar PandaADCP is one to look at. Constructed from all-titanium alloy material, this produces an incredibly good cost performance. For more details, visit https://china-sonar.com/.

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