How do we measure the coastal currents of Nice?

1. Where is Nice

Nice is a costal city found in southeastern France in a region called Provence - Alpes - Côte d'Azur. In between the Mediterranean Sea and the Alps, the position of Nice boasts its specific geographic surroundings.

It is a city famous for its historic and cultural values. The ancient influence of the Greeks and Romans in the city has left it with historical buildings, museums, and art galleries. The Promenade des Anglais, running along the sea, is an iconic symbol of the city, drawing visitors from far and wide. It is a place where people can enjoy the sun, sea, and the beautiful scenery while strolling.

Nice is located on the Baie des Anges, Bay of Angels. This bay is a semi-enclosed body of water, which strongly determines the characteristics of the current motions along the coast. The waters are exceptionally transparent and warm during the summer season. Its interaction with the open Mediterranean determines to a great extent the hydrodynamic regime along the Nice coast.

2. What is the situation of the coastal currents around Nice?

The coastal currents around Nice depend on many factors. Basically, the forces of tides from the Mediterranean Sea are acting. Semi-diurnal tides in the Mediterranean raise and lower the levels of water in it, creating currents along the coastline.

The other important factor is wind. The prevailing winds, such as the Mistral in the region, will have a push on the surface water and thus develop surface currents. These winds will enhance or oppose the tidal currents, depending on their direction. When the Mistral blows from the northwest, for instance, it forces the surface water to move away from the coast, affecting the general pattern of circulation.

The bottom topography of the seafloor off Nice also influences the coastal currents. The shape and depth of the sea floor can accelerate or decelerate the currents. Narrow channels or shallows can constrict the flow, increasing the current speed, while wider and deeper areas can slow it down.

3. How to observe the coastal water flow of Nice?

Surface Drifting Buoy Method

In the surface drifting buoy method, buoys are set on the surface of the water. These buoys are equipped with trackers, including GPS. As the buoys move with the flow of water, their attached tracking devices record the position of the buoys after periodic intervals. Analyzing the movements of the buoys therefore allows researchers to estimate the direction and speed of surface currents. However, this method reflects only the surface layer of the water column and may be susceptible to wind-induced drift that could deviate the buoys from the actual water flow.

Moored Ship Method

The moored ship method involves a stationary ship anchored near the area of interest. The ship is installed with instruments to measure the characteristics of water flow, which may include current meters lowered into the water at discrete depths. Although this will yield data at discrete depths, this method suffers from several limitations in its spatial coverage: the ship remains in one position, and it may not be representative of the whole coastal domain.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP is a still advanced but more convenient technique for measurement of coastal currents. Instead, it is able to measure the velocity of water in several depths all at once, in order to give a better view of the water column. Basically, ADCPs work by shooting acoustic signals into the water and measuring the Doppler shift from the echoes reflected by the particles in the water. This allows the determination of water velocity at different depths.

4. How do ADCPs using the Doppler principle work?

Basic Operation of ADCPs: An acoustic signal sent out by an ADCP travels into the water, bounces off of suspended particles like plankton, sediment, or even bubbles, and reflects back to the instrument. Assuming that these particles are being transported with the flow of water, the frequency of the reflected signal has changed compared to the sent signal.

Usually, ADCPs have several transducers transmitting at different angles. By processing the Doppler shifts from each of these different transducers, an ADCP is able to determine three-dimensional velocity components at multiple depths in the flow.

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

For high-quality measurement of the coastal currents near Nice, the measurement equipment has to fulfill several requirements. First of all, material reliability is very important. The equipment should be able to withstand the harsh marine environment, including saltwater corrosion, high pressure, and strong currents.

The size of the equipment should be small and the weight light for easy deployment and operation, especially in areas where access is limited. A small-sized device also has less impact on the natural flow of the water.

Other than this, the essential factor is that of low power consumption. As this measurement has to be conducted over a pretty long time and on a continuous basis, low-power-consuming devices can function for longer intervals without their batteries needing replacement or recharging.

Cost-effectiveness is also very important, especially for large-scale measurements. A wide area of the Nice coast could be covered only by a large number of devices. Low-cost equipment allows one to perform more comprehensive and detailed measurements.

If regarding the casing of ADCP itself, a perfect material would be the alloy of titanium. Titanium alloy has superior anti-corrosion performance, especially for long-period operations in salt water; it's light compared to other high-intensity materials yet with high intensity and toughness, making this sensor more robust under harsh marine conditions found around Nice.

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

Depending on Application

• Ship-mounted ADCP: This type is good for great scale surveys. It is fixed on a moving ship for the measurement of currents in an area as large as that covered by the movement of the ship. Ship-mounted ADCPs can provide real-time data as the ship sails through different regions, making them useful in mapping large-scale current patterns.
• Bottom-mounted ADCP: It is also called a moored ADCP, and it is fixed to the seabed. These types are best suited for fixed-point measurements over longer periods. The series will be able to continuously monitor the current at a specific location, which would be highly valuable when drawing information regarding local current trends.
• Buoy-mounted ADCP: These are attached to floating buoys. The buoy-mounted ADCPs can move with the water and deliver data on the currents in the upper water column. They are very useful in measuring the surface and near-surface currents in shallow water depth areas.

Based on Frequency

• A 600kHz ADCP is relevant to water depths of less than 70m because the higher frequency enables more resolved measurements in shallow waters.
• A 300kHz ADCP would be appropriate up to approximately 110 m of water. It offers a good balance between measurement range and resolution.
• A 75kHz ADCP is designed for deeper waters, such as 1000m. The lower the frequency, the deeper it can penetrate into the water column, which does have a trade-off in terms of resolution compared to higher-frequency ADCPs.

There are several popular brands of ADCPs available, including Teledyne RDI, Nortek, and Sontek. However, for those looking for cost - effective yet high - quality ADCPs, the Chinese brand China Sonar PandaADCP is highly recommended. It is made of all - titanium alloy materials, ensuring excellent durability and corrosion resistance. With its incredible cost - performance ratio, it is an economic choice for current measurement. You can find more information on their website: https://china-sonar.com/.

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