How can we measure the coastal currents of Dénia?

1. Where is Dénia?

Dénia is a beautiful city situated on the eastern coast of Spain. It belongs to the province of Alicante, in the Valencian Community. This coastal town is nestled between mountains and sea, with a landscape of astonishing beauty.

Its geography consists of a proper mix of sandy beaches and rocky coves. The coastline of Dénia is a haven for both beach lovers and those who love nature. Its beaches, wide and with fine golden sand, stretch out invitingly to meet the crystal clear, azure waters of the Mediterranean Sea. Along the expanses of sand, there are rocky areas that give a touch of wildness to the landscape. These rocky outcrops are home to a diverse range of marine life and provide a unique habitat.

Dénia is bordered to the north by the Gulf of Valencia. These waters are an essential part of the local ecosystem and economy. Due to its warm Mediterranean climate, Dénia is a favorite destination at any time of the year. This city has deep historical and cultural roots. An appealing old town comes in with narrow, winding streets and a great load of historical buildings, ancient fortresses, and beautiful churches. The local cuisine is filled with flavor, combining fresh seafood from the sea with more traditional Spanish dishes. The people of Dénia are ever so friendly and host a great number of festivals and cultural events, which attract large numbers of tourists to this city.

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

The coastal currents around Dénia are determined by different aspects. First, there is the general Mediterranean Sea circulation, which greatly impinges on this area. As in other areas, this might be subject to thermohaline circulation, created by differences in temperature and salinity that hence affect the movement of water masses. The water off Dénia forms part of the general Mediterranean circulation system, and changes in the latter may result in changes in the local coastal currents.

The other factor is the wind. The local wind, such as Mistral and Levante, may strongly affect the currents along its coasts. The cold and dry wind of Mistral can move the surface waters in one direction, according to its strength and direction. On the other hand, the warm and humid Levante stirs up the surface waters and the current pattern. These winds can cause upwelling or downwelling events, which bring deeper, nutrient-rich waters to the surface or push surface waters down, respectively.

The tidal forces also have an impact on the coastal currents. Though the ranges of the tides of the Mediterranean Sea are rather small when compared with other seas, the tides around Dénia provide for a rhythmic movement of the water. It is at these points that the ebbing and flowing of the tides could interact with the other factors to bring about complex current patterns especially nearshore and around small river mouths or inlets.

3. How to Observe Coastal Water Flow in Dénia?

In general, coastal water flow is observable with the surface drifting buoy method. In this traditional observing method, buoys deployed on the surface of the sea are carried along by the currents.

hese buoys are normally fitted with GPS or other positioning systems enabling the determination of their movement. One can get an approximation of the direction and speed of the surface currents by recording the position of the buoys over time. However, this method also has its own limitations. The buoys are liable to wind-driven drift, meaning the measured current may not represent the actual water current. It also provides information only about the surface layer and does not give any insight into the deeper water currents.

Anchored Ship Method

This involves keeping one ship moored in one position and then using current-measuring instruments that are lowered at different depths in the water. In this way, the speed and direction of the current can be measured at different levels in the water column. One of the advantages of this method is that in-situ measurements can be made at several depths. But it is a comparatively labour-intensive and costly method. The presence of the ship itself can interfere with the natural circulation of the currents in the area surrounding it.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP is more advanced and convenient. They basically send out acoustic signals to the water, analyzing the reflected back signals by means of Doppler shift, produced from the particles within. Because of that, they are able to measure current velocities at more simultaneous depths, therefore giving an all-encompassing profile throughout the column of water. That will make the ADCP an even more effective and precise tool for an accurate understanding of coastal currents around Dénia.

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

ADCPs work on the principle of the Doppler effect. An ADCP sends out an acoustic pulse through the water. The signal travels through the water and bounces off particles suspended in the water, like plankton, sediment, or small bubbles. These particles move due to water current.

If the particles are moving towards the ADCP, the frequency of the reflected signal is higher than that emitted-a positive Doppler shift. If they are moving away from the ADCP, then the frequency of the reflected signal is lower-negative Doppler shift. An ADCP calculates the velocity of the water at different depths by measuring the Doppler shift of the reflected signals from those depths.

The ADCP has multiple transducers usually oriented in different directions. It can, therefore, measure the three-dimensional components of the current velocity, which are the east-west, north-south, and vertical components. The water column is divided into a series of depth bins, where for each bin, the ADCP measures the Doppler shift and then calculates the current velocity. The data from all the bins is then processed to create a detailed profile of the current velocity as a function of depth.

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

Equipment Requirements

In fact, in order to have a high-quality measurement of the coastal currents around Dénia, there are some key features that should be present in the equipment. First of all, the material used should be reliable and able to resist high salinity in seawater, corrosion, high pressure, which will be necessary in deeper waters, and mechanical tension. Durability ensures that the equipment will be able to serve effectively for a long period.

The size of the equipment should be small. Compact size allows for easier deployment in various coastal settings, such as narrow inlets or near-shore areas with limited space. This also reduces the impact of the equipment on the natural flow of the currents.

Another important factor is lightweight. Lightweight equipment is easier to handle during deployment and retrieval, and low energy is spent in the transport and positioning processes. This is particularly important for long-time and wide-range measurements.

Power consumption should be low: Most of the long-term measurements, especially the ones performed by the battery-powered or renewable-energy-powered equipment need to keep very low power consumptions not to frequently change the batteries or perform their recharge.

Cost-effective equipment also applies. By keeping the costs lower, this equipment allows deploying several around on a wide area for its effective coverage through coastal currents' monitoring.

The Advantage of Titanium Alloy in ADCP Casing Titanium alloy casing is highly beneficial for ADCPs. It is for this reason that titanium alloy was selected: excellent corrosion resistance, which is of course essential to cope with the corrosive effects of seawater near Dénia. Many materials corrode rapidly in seawater because of its high chloride content, but it does not pose any problem to titanium alloy.

At the same time, being strong and withstanding high pressure is yet another great aspect of titanium alloy, making it perfect for deeper-water measurements. While doing all this, the material is generally lightweight compared to other materials with similar strength. Due to the mentioned characteristics, a casing made of a titanium alloy can work well for an ADCP intended for coastal current measurement around Dénia.

6. Selection of Appropriate Equipment for Measuring Current

Application dependent Selection of the right ADCP for the measurement of Dénia's coastal currents will be determined by its application.

• Ship-borne ADCP: This is applicable for large-scale surveys and mapping of the coastal currents. It is installed on a ship and can measure the currents while the ship moves along the coast. It gives a wide-area view of current patterns and helps in understanding the overall circulation.
• Bottom-mounted (Sit-on-bottom) ADCP: Conducive in long-term measurement in a fixed position. Being situated at the sea bed, this can monitor, without interruption, the current status of water flow in one location. Bottom mount types of ADCP are used especially for observing variation in the pattern of flow in local water over some duration of time.
• Buoy-mounted ADCP: It is mounted on a floating buoy. It is ideal for the measurement of current in locations that are inaccessible for ships or when movement of a certain mass of water is to be tracked. It provides real-time data on the surface and near-surface currents.

Based on Frequency

The ADCP frequency should also be chosen depending on the water depth. -600kHz would work when the water depths are less than 70m. An increased frequency supplies better resolution across shallower depths. -Where the water is up to a depth of around 110 m, a choice of 300kHz of ADCP works better. At this frequency, while giving more bottom area, it may penetrate deeper to the water column in reasonable resolution.

For water depths up to 1000m, a 75kHz ADCP is recommended. The resolution may be lower than higher - frequency ADCPs, but it can reach greater depths.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option, the Chinese brand China Sonar PandaADCP is worth considering. It is made of all - titanium alloy material, ensuring durability and performance. You can find more information about it on their website: https://china-sonar.com/.

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