How can we measure the coastal currents of Gandia?

1. Where is Gandia?

Gandia is one of the most beautiful coastal cities and belongs to the Valencian Community, Eastern Spain. It faces the shores of the Mediterranean Sea and offers a blend of natural beauty with rich cultural heritage.

The city has been endowed with a very beautiful coastline, stretching over miles with its sandy beaches, inviting and picturesque. The soft, golden sand meets the clear, blue waters of the Mediterranean, creating a postcard-perfect setting. In addition, the coastal area is dotted with rocky outcrops along certain sections, further adding to the visual diversity of the shoreline.

Geographically, Gandia is enclosed by the Gulf of Valencia to the north. This gulf forms one part of the western Mediterranean Sea. These waters are a haven not only for the local marine life but also serve to further other key economic activities for the area, such as fishing and tourism.

Gandia has an incredibly rich history that stretches over several centuries. This is an important settlement that has lived through various periods in history, as attested to by its architecture. The old part of Gandia is a candidate to become a UNESCO World Heritage Site due to its well-preserved medieval buildings, which include the impressive Palace of the Dukes of Gandia. This city also boasts a very vibrant modern culture, replete with festivals, local markets, and traditional cuisines that appeal to tourists from all parts of the world.

2. What is the situation of the coastal currents near Gandia?

Several elements drive the coastal currents in this area around Gandia. First of all, large-scale circulation of the Mediterranean Sea is relevant. The general circulation in the western Mediterranean, established by thermal-salinity differences, might be important in the local development of currents in the area near Gandia. For instance, the thermohaline circulation, though slow but powerful, can move the water masses in one direction and thereby dictate the coastal currents.

The second factor involves wind. The prevailing winds of the region may push the surface waters along the coast or create upwelling and downwelling phenomena. In Gandia, sea-breeze circulation is rather frequent: during daytime, the land is heated more than the sea, causing the air over the land to rise and drawing in cooler air from the sea. This sea-breeze can push the surface waters to start the movement, generating coastal currents. In this respect, during the night, while the land cools rapidly, the direction of wind might get reversed, leading the current in a reversed direction.

Tidal forces also come into play, although the tides are rather small in the Mediterranean Sea compared with some other large bodies of water. This relatively low tidal range might be able to induce small-scale fluctuations in coastal currents near Gandia because of the interaction of incoming and outgoing tides, which could give rise to intricate patterns of flow in estuarine and near-shore regions.

3. How to Observe the Coastal Water Flow of Gandia?

Surface Drifting Buoy Method

One of the traditional ways of observation has been the use of surface drifting buoys in studying the flow of water along coasts. They float on the surface of the water, their movements depending on currents. Therein, besides being driven by water movement, buoys have attached sensors to them to detect changes in various parameters including position; generally using GPS. By tracking the progress of these buoys over a period of time, researchers can obtain the direction and speed of the surface currents. This method, however gives information about the surface layer of the water column alone and is also subjected to wind-induced drift, which sometimes provides unreliable results.

Anchored Ship Method

Another technique is the anchored ship method. A ship moors at a fixed location in the water, and current-measuring instruments are lowered into the water to a variety of depths. Instruments like these may be capable of determining the velocity and direction of currents at numerous levels in the water column. This is a better methodology as it is an in situ measurement at different levels of depth. However, this is relatively time-consuming and expensive, since it requires a ship and a crew. Besides, the presence of the ship at times interferes with the natural flow of the currents around it.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP has been an advanced and more convenient device or method in measuring coastal currents. They work by sending acoustic signals through the water and analyzing the Doppler shift of those signals reflected back by the suspended particles in the water to measure simultaneous current velocities at more than one depth. This will provide a detailed profile of the current velocity over a range of depths and therefore a better understanding of the coastal currents near Gandia compared to the other two methods mentioned above.

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

The basic working of ADCPs depends on the principle of the Doppler. In the working process of ADCP, a transmitted acoustic signal travels into the water from ADCP, through the water column, bouncing off small particles, moving with water currents.

The frequency of the reflected signal is different from the frequency of the emitted signal due to the Doppler effect. If the particles are moving towards the ADCP, the frequency of the reflected signal will be higher-a positive Doppler shift-and if they are moving away from the ADCP, the frequency will be lower, a negative Doppler shift.

This frequency shift-the Doppler shift-is measured for signals reflected from different depths in the water column, enabling the ADCP to calculate the velocity of the water at those depths. An ADCP generally has several transducers oriented in different directions. It measures the three-dimensional components of the current velocity: east-west, north-south, and vertical.

The ADCP segregates the water column into a series of depth bins. It independently measures the Doppler shift for each bin and then computes the current velocity. The data processed thereafter may be utilized to provide an informed profile of the current velocity as a function of depth.

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

Equipment Requirements

High measurement quality of the currents in the Gandia coastline will demand several characteristics for the measurement equipment. First among them is the material reliability of the equipment. As it will serve in a harsh marine environment, its constitution should provide resistance to corrosion and to high pressure-most especially for deeper measurements-and also be withstood to mechanical stress.

The size of the equipment must be small. Small size is suitable for deployment at most locations, especially at those locations where little room is available for it, like near-shore regions or inside estuaries. A smaller size can minimize interference with natural flow in currents.

The weight of the equipment must be light; this is very advantageous for deployment and retrieval. An operator or small team can handle lightweight equipment more easily. It also minimizes the amount of energy lost during movement by the equipment itself during deployment.

Another important requirement is low power consumption. This is very important for long-term measurements, especially when the equipment is powered by batteries or renewable energy sources such as solar panels. Low power consumption ensures that the equipment can operate continuously for extended periods without frequent battery replacements or recharging.

The cost of equipment should be as low as possible, so that the measurement devices can be deployed on a large scale-a necessary thing while obtaining comprehensive measurements of coastal currents over a wide area.

The Advantage of Titanium Alloy in ADCP Casing

The casing in ADCPs is best made of titanium alloy. Titanium alloy has a number of advantages: very resistant to corrosion, especially for longtime exposure in the saltwater environment in the Mediterranean Sea near Gandia. This material would have the capacity to withstand seawater, particularly chloride ions dissolved in water, over a very long period of action without deteriorations that can be assumed as relevant.

The strength of the titanium alloy is fairly high, too, which provides structural integrity under the high-pressure condition, especially when the ADCP is used in deeper water. At the same time, it is lightweight compared with some other high-strength materials, and this meets the requirement of having a light-weight device. These properties make the titanium alloy the correct choice of material in making ADCP casing employed in measuring the coastal currents close to Gandia.

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

Based on Usage

Selection of appropriate ADCP to carry out current measurements for the currents flowing in proximity to Gandia coast rests upon its exact usage.

Ship-borne ADCP: This one would be sufficient in wide-area large-scale surveys. It will be installed in a moving ship; while it sails, it will be continuously able to make current measurements along the track of that particular ship. The Ship-borne ADCPs are habitually used for mapping in the open sea or along large-scale current patterns off the coast.

Bottom-mounted (Sit-on-bottom) ADCP: It is deployed on the ocean floor. It provides the best performance in terms of current measurement and is suited for longterm, fixed-point measurements. While sitting on the bottom, it has been designed to monitor current conditions continuously from a specific location, with valuable data on local current variations throughout time.

Buoy-mounted ADCP: As the name suggests, it is mounted on a buoy floating in the water. This type is helpful for current measurement in areas difficult to reach by ship or when following the movement of a particular water mass. It can provide real-time data on the surface and near-surface currents while being mobile.

Based on Frequency

Frequency of ADCP should be seriously selected according to the water depth: Within 70 m, the frequency of 600 kHz is acceptable for an ADCP. Because of the frequency, higher frequency ADCPs will have a short wavelength and thus provide better resolution in the current-velocity at relatively shallow depths.

Up to 110m in water depth, a good choice will be the 300kHz ADCP. This can provide better depth penetration into the water column and give a good resolution at the same time.

An ADCP frequency of 75kHz will be necessary to make measurements up to water depths of 1000 m. This will enable a view to be taken to a greater depth although there might be some compromise with the resolution in contrast to the high-.

There are some well-known ADCP brands in the market, such as Teledyne RDI, Nortek, and Sontek. However, for those who want high-quality and cost-effective options, the Chinese brand China Sonar ​PandaADCP is highly recommended. It is made of all-titanium alloy material, which ensures excellent durability and performance. Considering the very reasonable price it costs, the value it delivers on the measurement of coastal currents near Gandia is of immense quality. You can find more about this product on their website: ​https://china-sonar.com/.

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