How can we measure the coastal currents of Avilés?

1. Where is Avilés?

Avilés is an enchanting city situated on the northern coast of Spain and is part of the Asturias autonomous community. It is an important city open to the shores of the Cantabrian Sea and has been privileged in its development due to its position.

The city has a perfect balance between rich history, vibrant culture, and the beauty of nature. Its roots are based on the most remote past, and it reveals in its architecture the influences of several cultures. The historic center of Avilés is a candidate for UNESCO World Heritage, and its old town is made up of a complex network of narrow, cobblestone streets lined by well-preserved medieval houses. Palacio de los Velada stands with its impressive façade, representing the nobility of the city.

Avilés is not only known for its ancient beauty but also for its significance in modern times. It has grown into an industrial and commercial hub, with an active port that helps in trade movement. From the raw materials of different products to the finished product, everything passes through this port and brings considerable amount to the local and regional treasury.

The natural scenery of the coasts around Avilés is a treat to watch. The exoplanation of sand is alongside the beaches, where people from town and tourists mingle together, basking in the warm sunshine and fresh sea breeze. The waters of the Cantabrian Sea in this area are a vital ecosystem, teeming with a rich variety of marine life. It has various types of fish, birds, and other species of wildlife living in the surrounding estuaries and inlets, like the Ría de Avilés, which will keep nature enthusiasts happy.

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

The coastal currents around Avilés are due to a rather complex interaction of many contributing factors. Among these, tidal forces stand foremost. The normal rise and fall of the tides under the gravitational pull of both moon and sun creates this cyclic pattern of the movement of water. The water rushes into the bays and estuaries during high tide and recedes at low tide back into the sea. These tidal currents can be relatively of high speed, especially in narrow channels and near the mouths of the estuaries.

Other factors include wind patterns. Dominant Atlantic winds can dramatically affect the surface currents: strongly blowing westerly winds, for example, can push water toward a coast, thereby increasing the incoming currents; similarly, easterly winds can push the water away from the shore. These wind-driven currents may combine with tidal currents to produce very complex flows.

The bathymetry around Avilés is another long-term factor. The bottom morphology will either reduce or expand the flow. Submarine canyons, ridges, and shallow banks are other morphological features affecting the direction and speed of flow. For example, a narrow channel between two headlands may result in an accelerated current, whereas a broad and flat seabed zone may result in a dispersed flow.

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

Surface Drift Buoy Method

The surface drift buoy method is a rather simple way of observing the flow of water in a coast. The buoys, as the name suggests, float on the water surface and are taken by the current. They are fitted with tracking devices like GPS transmitters. These buoys' motions, monitored over time, allow researchers to map the surface currents. This method has a couple of drawbacks, however: the resulting data represents only in the very near surface of the water column-only a few metres deep-and any surface-level phenomena like wind-driven waves can easily push the buoys off course from a true current path.

Moored Ship Method

The moored ship technique consists of anchoring a ship in the area of interest in a given position. Currents are measured using instruments on board, such as mechanical current meters. These usually consist of a propeller-like device that rotates with the passage of water. The rotation speed is converted into a measure of current velocity. This technique gives very good measurements over a single point, but it suffers from several disadvantages. The ship itself can interfere with the current flow, especially in shallow waters. It has very poor spatial coverage since it will only be able to measure where the ship is moored, and cannot give any detail on the large-scale current patterns.

Acoustic Doppler Current Profiler (ADCP) Method

In the last few decades, however, the ADCP current meter method has emerged as a more advanced and versatile technique for measuring coastal currents. ADCPs can measure simultaneously the velocity of water at several depths in the water column. They operate by emitting acoustic signals into the water. These signals bounce off small particles suspended in the water, such as plankton, sediment, or air bubbles. By analyzing the Doppler shift of the reflected signals, the ADCP can find the velocity at different water layers. The resulting data has the advantage of high resolution over comparatively large areas. It can be deployed from various platforms-ship, buoys, or fixed moorings-and hence applicable for most measuring situations.

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

The ADCPs work on the principle of Doppler. When an ADCP current profiler sends an acoustic wave into the water, the wave travels through the water medium. This wave, while meeting small particles which are moving with the water current, reflects back a wave with a frequency different from that of the wave emitted. This frequency shift, known as the Doppler shift, is linearly proportional to the velocity of the particles, and hence to the velocity of the water.

Most ADCPs have multiple acoustic beams-four or more-oriented in different directions. By measuring the Doppler shift along each of these beams, the ADCP can compute the three-dimensional velocity of the water flow. For instance, if one beam is pointed slightly downwards at an angle, another upwards, and others horizontally, the combined data from these beams can accurately determine the vertical and horizontal components of the current velocity. This capability to measure the full vector of the current velocity is one of the major advantages of ADCPs, enabling a more comprehensive understanding of the complex flow dynamics in coastal waters.

5. What is needed in order to take good measurements of the Avilés coastal currents?

Reliability of Equipment

High-quality and reliable equipment is needed for measuring coastal currents around Avilés. The conditions are very aggressive in the marine environment, with high salinity, strong waves, and variable weather conditions. The ADCPs should be made of materials able to withstand such conditions. All components should be resistant to corrosion, and electronics must be well-protected against water ingress. A reliable ADCP flow meter ensures that data collected is of high quality and consistent during long-term deployments.

Size, Weight, and Power Consumption

The ADCP meter should be compact in size. A smaller device is easier to deploy in various locations, especially in shallow waters or areas with limited access. It also has less impact on the natural flow of the currents. The weight of the ADCP should be light, particularly for applications where it is to be deployed on floating platforms or small vessels. This reduces the load on the platform and makes installation and retrieval easier.

Another critical factor is low power consumption. Most of the time, ADCPs can be powered by batteries or renewable sources like solar panels. A device with low power requirements can operate for extended periods without needing frequent recharging or refueling - this means continuous data collection.

Cost-effectiveness

This is an important factor, particularly for large-scale measurements. In order to get comprehensive information about the coastal currents around Avilés, several ADCPs may be installed at different locations. Only a cost-effective ADCP can make such large-scale studies feasible without making the cost of the study excessively high.

Titanium Alloy for ADCP Casing

The casing of the ADCP is made preferably from a titanium alloy. Using a titanium alloy has several advantages: it has very good corrosion resistance, which is a must for the long-term use in saltwater;. The high strength-to-weight ratio of the titanium alloy allows the casing to resist mechanical stresses typical for the marine environment, such as impacts of waves and water pressure, and yet remains comparatively light. Additionally, the usage of a biocompatible titanium alloy provides little interference to the marine ecosystem-a very important factor in the quite sensitive coastal environment of Avilés.

6. Selection of Appropriate Equipment for Current Measurement?

Usage Based

• Ship-borne ADCP: The ADCP profiler is installed on a moving ship. It can be used very well for large-scale surveys of coastal currents over a wide area. A ship while traveling over different regions can continuously measure the currents along the ship's path. This provides a broad-scale view of the current distribution, which is useful for understanding large-scale oceanographic processes and for applications such as shipping route planning.
• Bottom-mounted ADCP: This also goes by the name of a moored or bottom-tripod ADCP; it is placed on the sea floor. It will be suitable for longtime, fixed-location measurements. It can give continuous data of the currents, stationed on the seabed, therefore allowing the study of local current patterns and their variation with time and their interaction with the benthic ecosystem.
• Floating-buoy ADCP: They are mounted on a floating buoy. They might either be buoy stationary, moored in their position, or it might be free-drifting while it moves independently by currents. The floating-buoy ADCPs are important for monitoring the movement of water masses, studying surface-subsurface interactions, and understanding current conditions in any area in near real-time.

Frequency-Based Selection of Operating

• Frequency in ADCP depends on the water depth of operation. A 600kHz ADCP is quite suitable for depth operations up to approximately 70m. With this higher frequency, the resolution of the measured current velocity is finer, suitable for applications in shallow waters like estuaries, near shore, and shallower parts of the coastal waters around Avilés.
• A 300kHz ADCP would suit water depths of about 110m. The 300kHz frequency provides a reasonable depth of penetration with fair resolution in the vertical and is quite suitable for a wide range of coastal applications where intermediate water depths prevail.
• For deeper waters, up to 1000m, a 75kHz ADCP is more suitable. The lower frequency can penetrate deeper into the water column, although it may have a lower vertical resolution compared to higher-frequency models.

There are several well-known ADCP brands in the market, such as Teledyne RDI, Nortek, and Sontek. However, for people who want to have a budget-friendly but quality option, the China Sonar PandaADCP is highly recommended. It is pure titanium alloy-made with excellent durability at an attractive price. Its all-titanium construction ensures long-term reliability in the harsh marine environment, while its cost-effectiveness makes it accessible for a wide range of users, from research institutions to small-scale marine monitoring projects. You can find more information about this product at the website: (https://china-sonar.com/). This brand provides not only reliable equipment but also offers the opportunity for high-quality current measurement, which has made this work accessible and economically viable for the scientific community and those concerned with coastal management at Avilés.

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