How can we measure the coastal currents of Alicante?

1. Where is Alicante?

Alicante is a very beautiful coastal city in the Valencian Community of Spain. It lies on the southeastern coast of the Iberian Peninsula, facing the Mediterranean Sea. The city has long, sandy beaches and mild weather, drawing tourists from different parts of the world.

This whole region of Alicante is a juxtaposition of nature's beauty combined with historical quaintness. It dominates by the imposing Castle of Santa Bárbara that crowns one of the heights overlooking the sea and the city, while the littoral has characteristic features formed by coves and inlets besides great expanses of sandy beaches. The depth in open water is gradually reached by easy slopes.

In Alicante, the marine environment is very rich. There is huge variability in species that could be found within Mediterranean waters: from different species of fish, crustaceans, to other species. The port is a hub of immense importance with respect to maritime activities in this region. Besides, local fishing is an important sub-economic sector of this region. In Alicante, a Mediterranean climate usually predominates; winters are soft, while summers become very hot and dry. It conditions the coastal water temperature and salinity variations and hence the general tendency of coastal currents.

2. What is the situation of the coastal currents in the vicinity of Alicante?

The general circulation patterns of the Mediterranean Sea have a major influence on the coastal currents in the vicinity of Alicante. In the Western Mediterranean, there is a broad anti - clockwise circulation which affects the flow of water in the Alicante area. Tides also play their role, but the tidal range in the Mediterranean is relatively small as compared to other seas. The tidal currents can circulate the water in and out, though the force is lesser when compared to more tidally active regions.

The local winds play a decisive role. The prevailing winds such as the easterly and westerly winds drive the surface currents. Of particular significance, the sea breeze of the summer months alone can produce marked variations in surface water circulation. The bottom contours, including any submerged ridges and valleys, will also bend and divert the currents. Freshwater discharge from rivers and streams will increase the volume, decrease the salinity, and lessen the density of the adjacent body of water and modify the current movements.

3. How to observe the Coastal Water Flow of Alicante?

Surface Drift Buoy Method: The surface drift buoys are set on the surface of the water. Carried by the surface currents, their motion is followed by satellite-based or other tracking systems. From the trajectory of such buoys over time, the direction and speed of the surface currents can be deduced. However, this approach provides information pertaining mainly to the surface layer and may not present a complete picture of currents at different depths.

Anchored Ship Method: This method relies on the possibility of using an anchored ship itself as a sort of platform in current measurement. The ship is installed with instruments for measurements of water flow. It allows more precise readings at one and the same location, but it is limited just to the site around the anchored ship and, besides, such a method faces interference created by this very ship due to the natural water flow.

Acoustic Doppler Current Profiler Method: ADCP current meter is more advanced and quite efficient in measuring coastal currents. It applies a series of sound waves to measure water velocity at several depths simultaneously. This technique works by emitting acoustic pulses along with analyzing the Doppler-shifted reflections to deliver the current profile from the surface down to a certain depth. Thus, more specific information about the coastal currents close to Alicante can be provided than with any other technique.

4. Operating Principles for ADCPs based on the Doppler Principle

The nominal operating principle of ADCPs depends on the Doppler effect. They emit acoustic signals, usually in the form of short pulses, into the water. As those signals encounter moving water particles, because of the Doppler effect, the frequency of the reflected signal changes; the change is proportional to the velocity of the water particles.

Multiple transducers fitted with an ADCP current profiler can transmit and receive in different directions. The frequency shifts in the different directions result in the ADCP profiler being able to calculate the velocity components of water in the horizontal and vertical directions. Because the acoustic pulses are outputted at regular intervals in addition to multiple depths, a profile of the current velocities throughout the entire water column can be constructed. This will give meaningful information on the flow patterns, such as direction, speed, and any vertical shears in the currents.

5. What is required for high-quality measurement of the Alicante coastal currents?

For high-quality measurement of the coastal currents around Alicante, the equipment has to be made from reliable materials. Given the corrosive nature of seawater and the sometimes harsh marine environment, the materials should be able to resist saltwater corrosion, pressure changes, and potential impacts. A small size and light weight are desirable for easy deployment, whether on a ship, a buoy, or at the seabed. Low power consumption is required for long-term operation without frequent battery replacements or disruption in the power source. And naturally, cost-effectiveness to enable large-scale measurements is also important.

For the construction of ADCP meter casings, titanium alloy stands out as being an excellent candidate. Titanium alloys possess very good corrosion resistance, which would be essential when subjected to the marine waters off Alicante for prolonged periods of time. Therefore, it has a high enough strength-to-weight ratio to stabilize the internal equipment with minimal mass. This serves to make the product easier to transport and deploy into position.

6. How to Choose proper equipment for present measurement?

Based on Deployment Method

• Ship-borne ADCP: This will be helpful when one wants to measure the currents of the ship while it is moving along the coast or staying at a particular location. It provides flexibility in covering different areas and can give continuous data as the ship changes position.
• Bottom-mounted ADCP: suited for fixed-point measurements on the seabed. It can give long-term and quite accurate data about the current conditions at that very place, which is useful to understand the local current patterns.
• Buoy-mounted ADCP: When buoy-mounted on water, it gives the currents in the top layers and communicates wirelessly by transmitting the currents. This serves the purpose where remote monitoring at a place is easy and can survey a wide area depending upon the buoy travel.

Based on the Frequency

Different frequencies are applicable for different water depths. For example, a 600 kHz ADCP is suitable for water depths up to 70 meters. An ADCP of 300 kHz can go up to 110 meters, and a 75 kHz ADCP can go as deep as 1000 meters. This will enable you to choose the most appropriate ADCP based on the actual water depth conditions in the coastal area of Alicante.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also a great option. It is made of all-titanium alloy material, ensuring durability and offering an excellent cost - performance ratio. You can visit their website at https://china-sonar.com/ for more information.

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