How to measure coastal currents in Castellón de la Plana?

1. Where is the city of Castellón de la Plana?

Castellón de la Plana is an interesting city on the east coast of Spain. The name of this city is also known as only Castellón; it belongs to the Valencian Community, being situated at the shores of the Mediterranean Sea as part of a wonderful area named Costa del Azahar.

Geographically, the city is set on a coastal plain that slopes gently seawards. In the opposite direction, land rises northwards into the foothills of mountain ranges crossing the Iberian Peninsula, forming a handsome backdrop. The local climate is Mediterranean: hot, extensive summers and mild, wet winters. This sets ideal conditions for a rich biodiversity, including lush palm trees, stretches of citrus groves, and colorful, flower-filled gardens dotting the landscape.

In terms of culture, Castellón has a deep-rooted history. It has been shaped by various civilizations over the centuries, including the Iberians, Romans, and Moors. The old town is a UNESCO-recognized historical site, brimming with narrow, winding streets. These streets are lined with ancient buildings, such as the imposing Castellón Cathedral. Its architecture is an example of mixed Gothic and Baroque elements: elaborately sculptured frontages, imposing spires, and magnificent stained-glass windows. Most importantly, all kinds of festivals are celebrated in the city throughout the year. The biggest festival, Fiestas de San Vicente, shows vitality with its music, dancing, processions, and typical Valencian food.

The waters that are adjacent to Castellón de la Plana are from the Mediterranean Sea. There are nice beaches, though with fine-grained sand and pebbles, along the coastline. Shallow nearshore waters gradually get deeper when one goes further out, having several small coves and inlets. These are somewhat protected areas for boats and offer a home for a wide range of marine life.

2. What is the case of the coastal currents off Castellón de la Plana?

The coastal currents off Castellón de la Plana derive a number of influences. Tides, though relatively insignificant in the Mediterranean Sea compared to other seas, nonetheless account for a slow, rhythmic shift of water along the coast.

Wind patterns are a great determinant. These are the prevailing winds of the region, including the Mistral-like winds that can blow from the north-west, which may drive the surface currents. Indeed, strong winds can push the surface waters and create currents that flow parallel to the coast. During summer months, the sea-breeze effect also comes into play. It is observed that during the day, land heats up faster than the sea, causing air to rise over land, while cooler air from the sea rushes in, generating currents on a local scale.

The shape of the coastline and the bathymetry of the ocean floor can also influence the currents. The indented coastline with its bays and headlands may cause a shift in direction of the currents. Submarine topography, including reefs, sandbars, and submarine canyons, can also affect water flow at various depths. For instance, a reef may be able to divide the current or reduce the speed, creating areas with eddies and different current velocities.

It is the thermohaline circulation, although it affects more of the open ocean. But besides this, it is going to have some small impact on the coastal currents around Castellón, too. Density gradients may be induced by differences in water temperature and salinity and be capable of driving deep-water currents that could interact with surface and near-shore currents when the conditions are proper.

3. How to observe the coastal water flow of Castellón de la Plana?

Surface Drifting Buoy Method

This method involves placing in water a specially designed buoy that is fitted with a tracking device, either a GPS receiver or a radio transmitter. While the buoys are drifting with the surface currents, their positions are recorded at regular time intervals. From the trajectory described by the buoys over a period of time, the speed and direction of the surface currents can be computed. For instance, if a buoy travels some distance over a known length of time, the current velocity can be determined. The main advantage of this method is that it is rather simple and not very expensive. It can cover extensive areas of the ocean surface and therefore gives a wide view of the surface current patterns. However, it is highly affected by wind and waves. Strong winds can offset the buoys parallel to the actual current, and buoys provide the information about only the surface layer of the water column usually in the top few meters.

Anchored Ship Method

An anchored ship can serve as a fixed platform for the current measurement. Current meters can be suspended at different depths using cables from the ship. These current meters will be able to record the speed and direction of the water flow at each depth. A vertical profile of the current can be obtained by taking a series of measurements against the depth. For example, a ship would anchor near some point off the coast of Castellón and lower current meters every 10 meters from the surface to the bottom of the seabed. This technique gives good measurements but at a fixed location. It is very time-consuming and requires a lot of resources, such as the ship, crew, and equipment. The presence of the ship somewhat disturbs the natural flow of the currents, and the measurements are only around the vicinity of the ship.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler has become one of the preferred methods for measuring coastal currents near Castellón de la Plana. Basically, ADCPs work by using sound waves to measure the velocity of water at different depths. They can be deployed in several ways. A ship-borne ADCP can be used to measure currents while the ship is in motion along the coast; it will deliver a continuous profile of the currents over great areas. For measurement of current pattern over longer time spans at the same place, a bottom-mounted (sitbottom) ADCP can be moored on the seabed; and in order to perform the measurement over an area or, said differently, the currents in space (while floating around dynamically), the ADCP flow meter should be mounted on a buoy. An ADCP basically works by transmitting acoustic pulses into the water. When these sound waves contact small particles suspended in the water, such as sediment, plankton, or air bubbles, a portion of the sound energy is scattered back towards the ADCP. If the particles are moving with the water current, then the frequency of the scattered sound waves will be different from the frequency of the emitted waves-the Doppler effect. By measuring this frequency shift, the ADCP current profiler then calculates the velocity of the water at different depths. ADCPs provide high-resolution data across a large volume of water both horizontally and vertically and without significantly disturbing the natural flow of the currents.

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

ADCPs work by the principle of the Doppler effect. An ADCP current meter sends an acoustic signal-a sound wave-into the water; the signal travels through the water column. When this sound wave hits a particle in the water, such as a small piece of sediment or even a planktonic organism, some of that sound energy scatters back towards the ADCP.

In such a case, when the particle does not move regarding the ADCP, the scattered wave will be of a similar frequency as that of the emitted wave. On the other hand, when this particle moves along with the current of water, there is a shift in the frequency of the scattered sound wave, which is actually the Doppler shift. The magnitude of the Doppler shift is directly proportional to the velocity of the particle, and hence the water current, along the line of sight of the ADCP acoustic beam.

Most ADCPs have multiple, usually four or more, acoustic beams in a conical configuration. The ADCP meter can compute the three-dimensional velocity of the water by measuring the Doppler shift in each beam. For example, if one beam is sent upwards at a slight angle, another downwards, and two horizontally, then the ADCP profiler will be able to determine the current velocity in both vertical and horizontal components. Then, complex algorithms process data from the different beams. These algorithms take into consideration the geometry of the beam arrangement, the speed of sound in water-which may vary with temperature, salinity, and pressure-and the measured Doppler shifts. The result is a detailed profile of the current velocity and direction at different depths within the water column.

5. What's needed for high-quality measurement of Castellón de la Plana coastal currents?

Material Reliability

Any equipment used for measuring coastal currents around Castellón de la Plana must be made of materials able to resist the aggressiveness of the marine environment. The Mediterranean, with its saltwater, a high level of humidity, and strong storms sporadically, is corrosive and may be very damaging to test equipment. Titanium alloy is highly recommended for the casing of ADCPs. It is highly resistant to corrosion, with minimal degradation for long-term exposure in seawater. The material strength is also very high, and hence it resists mechanical stresses due to deployment, such as those from currents and waves. It has good fatigue resistance-an important attribute for equipment that may be subjected to repeated mechanical loading.

Small Size and Light Weight

Therefore, there is a pressing need for a small and lightweight ADCP. A smaller device is easier to maneuver around and to deploy in different settings. It can be more easily mounted on a small research vessel, on a buoy, or even moored to the seabed. For example, it would be much more effective to include a small-sized ADCP into the buoy-based measurement system since the space of the latter can be quite restricted. A lightweight device also minimizes interference with the natural flow of the currents. A heavy device could disturb the water flow even more and hence provide incorrect measurements. Besides, a light ADCP is easy to transport, which is also an advantage for fieldwork to be carried out in various locations along the coast of Castellón.

Low Power Consumption

Since many ADCP deployments may be in remote locations or on battery-powered systems, it is essential that power consumption is kept at a minimum. The device with low power implication would give longer usage without much battery replacement and recharging, thus enabling long-term, autonomous measurements. As an example, a bottom-mounted ADCP deployed at or near the sea floor for many months at a time has to operate at a very low power to minimize failure and ensure the acquisition of continuous data sets. Low power consumption also allows for smaller, less costly power sources such as solar panels or small-capacity batteries.

Low Cost

The cost-effectiveness will be especially important when large-scale measurements have to be performed. Several ADCPs at different locations and different depths could be necessary in order to acquire an appropriate insight into the coastal currents near Castellón de la Plana. If the price is lower, then more devices could be purchased and installed; in this way, a higher resolution, both in time and space, could be obtained from the measured series. This will help obtain a more correct and detailed cognition of the intricate patterns of currents. Besides, the cheaper variant is more within the reach of research institutions and organizations that have limited funds.

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

Based on Usage

• Ship-borne ADCP: This type of ADCP suits large-scale surveys of the coastal currents. It enables the ship-borne ADCP to continuously measure currents while the ship cruises along the coast, therefore giving a broad-scale view of the current patterns over a large area. For example, if researchers want to map the general flow of currents along the entire coastline of Castellón, a ship-borne ADCP would be the best choice. It travels a very long distance while generating an average profile of the present velocity and direction within discrete points down its path;
• Sit-bottom ADCP: The bottom sits, is meant for measurements taken on fixed or point stations in a lengthy process. A sit - bottom ADCP may be moored to the bottom in the location a scientist is interested in studying for the long - term trends and variations in current velocity and direction, such as near a particular port entrance or a known upwelling zone. It will provide continuous data over an extended time interval, which is needed for the study of the long - term behavior of coastal currents. For example, monitoring currents off a fishing port for several years can help in understanding how the currents affect fish migration patterns and fishing activities.
• Buoy-mounted ADCP: Buoy-mounted ADCPs are well-suited for monitoring currents in areas where access by ship may be difficult or for studying the interaction between the surface currents and the atmosphere. These buoys can be put in very remote areas, those areas where the sea is very rough, or wherever the currents are expected to be highly variable. They can also be useful in the measurement of short-term fluctuations in surface currents. For example, in locations where the sea-breeze effect could be a factor that can make the surface currents change really fast, a buoy-mounted ADCP can pick up those changes in real-time.

Based on Frequency

• 600kHz ADCP: This operates best in water as deep as about 70m in order to measure currents. In the quite shallow coastal waters, for instance, around Castellón de la Plana, like in bays and nearshore areas, the 600 kHz ADCP could give high-resolution data. Its higher frequency thus provides more detailed current velocity and direction measurements of the upper layers of the water column. It can measure, for example, the small-scale variations in current speed and direction near the beach with a high degree of accuracy, which is important for understanding processes such as beach erosion and sediment transport.
• 300kHz ADCP: With a slightly lower frequency, the 300kHz ADCP has greater penetration through the water column. It is suitable for water depths of approximately 110m. This frequency can be used in areas where the water is a bit deeper but still within the coastal zone near Castellón. It provides a good balance between depth penetration and data resolution. Such a 300kHz ADCP could be used, for example, where the seabed slopes down gradually, to measure currents from the surface to mid-water.
• 75kHz ADCP: In deeper waters, up to 1000m, the 75kHz ADCP is the one for the job. In the outer parts of the Mediterranean Sea off Castellón, where the water can get very deep, the lower frequency of the 75kHz ADCP allows the sound waves to travel further and measure current with accuracy at greater depths. This further serves in the study of deep-water currents, which can have a consequential effect on the general coastal circulation patterns.

Some of the well-known brands in the market are Teledyne RDI, Nortek, and Sontek. However, for cost-effectiveness with no compromise on quality, a Chinese brand, China Sonar PandaADCP, should be considered. Made entirely of titanium alloy, it offers excellent durability and corrosion resistance. Its price-performance ratio is highly competitive, making it an attractive option for both small-scale research projects and large-scale oceanographic surveys near Castellón de la Plana. 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.