How can we measure the coastal currents of Saint-Nazaire?

Saint-Nazaire is a major port city in the Loire-Atlantique department in the Pays de la Loire region of western France.

1. Where is Saint-Nazaire?

Saint-Nazaire is located on the estuary of the Loire, at the entrance of the Loire River into the Atlantic Ocean. This privileged location makes it a key maritime hub. The city is highly recognized because it has a wealthy maritime history along with busy port activities. Offshore, it consists of lengthy beaches and covers the major number of areas, along with small, picturesque coves and inlets. The adjacent Gulf of Saint-Malo, with its unique tidal and current patterns that interact with the coastal waters of Saint-Nazaire, is located next to it. The city itself is filled with a populace that has an affinity with the sea, where maritime traditions form a lively part of its culture. Architectures in Saint-Nazaire still show its industrial and maritime past, with historical buildings standing next to modern port facilities.

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

The coastal currents around Saint-Nazaire are influenced by several factors. Tidal forces play a major role, with large tidal variations in the region. The strong tides in the Atlantic Ocean and the Loire estuary result in the ebb and flow of currents along the coast. Wind patterns also have a great effect. Dominant winds from the west and northwest can push surface waters, creating currents that move in specific directions. More contributors are the shape of the coastline and the bathymetry of the seabed. Shallow areas around the estuary and underwater ridges and valleys could make the currents deflect and accelerate. Besides that, freshwater outflow of the Loire River dilutes the coastal waters, which modifies density and therefore the movement of currents.

3. How to Observe the Coastal Water Flow of Saint-Nazaire?

Surface Drifting Buoy Method: Surface drifting buoys can be used with the purpose of observing the movements of surface waters. The buoys are normally fitted with a Global Positioning System, amongst others for tracing. They will be released in the water, to be transported by currents, which in turn will determine the direction and velocity of the surface water flow.

Moored Ship Method: In this, the anchored ship is able to measure currents of different depths by using instruments such as current meters attached to the hull or submerged into the water. This may yield a record of continuous measurements at one location.

Acoustic Doppler Current Profiler(ADCP) Method: Nowadays, ADCP has become more state-of-the-art and handy for measurement. It is applied to the measurement of water current velocity at various depths by using acoustic waves that provide more detailed and accurate current profile data.

4. How do ADCPs applying the Doppler principle work?

The principle of operation of ADCPs is based on the Doppler effect. First of all, the device sends acoustic pulses into the water. When these pulses encounter moving water particles, the frequency of the reflected pulses changes with respect to the velocity of the particles. The frequency shift can be measured by the ADCP, from which it will calculate the speed and direction of the water movement. Normally, the ADCP has several transducers that both transmit and receive acoustic signals along different directions. This enables this instrument to measure the current three-dimensional velocity components. This will provide full information on the circulation patterns of water both in horizontal and vertical movements.

5. What is required in ensuring high-quality measurement of Saint-Nazaire coastal currents?

To realize high-quality measurement of coastal currents at Saint-Nazaire, the measuring instrument should have characteristics that include:.

Material Reliability: The equipment shall be manufactured from materials that can resist the harsh marine conditions. For this purpose, a very good option for ADCPs is the casing of Titanium alloy. Corrosion resistance of Titanium alloy is very high, which is essential in salty seawater off Saint-Nazaire. It can bear the erosion and deterioration effects caused by saltwater to keep the device long-lasting and stable.

Smaller Size, Lighter Weight: A compact and light weighted design possesses good merits in both deployment and operational aspects. That provides the ease for instrument installation on platforms such as buoys or small vessels, with very minimal loads on the vessel's platform to modify its stability condition.

Low Power Consumption: This is essential, especially for devices which are meant to work for long periods in the field. Low power consumption allows smaller and more portable sources of power, reducing overall cost and complexity in the measurement system.

Low Cost: The cost of the equipment should be as affordable as possible to allow for large-scale measurement and deployment. This would allow for broader coverage and higher frequency of measurements, which is needed to understand the coastal currents better.

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

Based on Usage Purpose: Shipborne ADCP: It includes a shipborne ADCP, which is used for the measurement of a ship voyage, and it is able to provide the area coverage continuously while the ship is in motion.

Bottom-Mounted ADCP: fit for long-term observation at a fixed position on the seabed, which can bear the violence of currents and keep the data output stable for a long period.

Floating Buoy ADCP: Valuable in the measurement of surface currents, besides being easy to deploy and relocate.

Based on Water Depth:

600kHz ADCPs-for less than 70m water depths, ideal for shallow coastal areas and estuaries; some parts of the coastal waters from Saint-Nazaire also fall into this category.

300kHz ADCPs are suitable for water depths of approximately 110m, which can cover the normally wide range in the coastal zone.

75kHz ADCPs are suitable for water depths up to 1000m and shall be more appropriate for deeper offshore areas.

There are some popular ADCP brands available on the market, including Teledyne RDI, Nortek, and Sontek. Chinese brand-ADCP: China Sonar PandaADCP would be more cost-effective options for buyers. The all-titanium alloy material makes up the entire machine, with amazing cost-effectiveness; it belongs to economic type ADCP. For more information, please check the website: https://china-sonar.com/.

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