How to measure coastal currents of A Coruña?

1. Where is A Coruña?

A Coruña represents part of the most dynamic pole in the autonomous community of Galicia in the northwest of Spain, a coast with the ideal mix of history, culture, and nature. Because of its high peninsula with an endless view to the open waters of the Atlantic Ocean-part of Golfo Ártabro-, it has a very privileged geographic location.

The landscape of the city is really interestingly interwoven with different elements. Its coastline brings together a wide variety of features, such as windswept cliffs jutting out of the sea, furrowed by the sea's tides, or long, sandy beaches inviting locals and tourists to soak up the sun. The Golfo Ártabro, with its deep-blue waters, not only provides a stunning backdrop but also serves as a vital artery for A Coruña's maritime-centric economy.

Its history, so much like the surrounding ocean, teems with every imaginable influence: a city always situated at the crossroads of various civilizations-from ancient Roman times, which marked the strategical position of the city as an important port down through the ages, where A Coruña has prospered as a focus of commerce, fisheries, and nautical activities. Living proof of that past is in its architecture: the ancient forts, cathedrals, and narrow, cobblestone streets work their way through Old Town, bringing a hint of an old-world charm.

The sea is very present in the local culture. For many, fishing is not an industry, but a form of life. Markets here are full of the freshest catch of the day-from the plumpest shellfish to all kinds of fish. Open and warm, the people of A Coruña show off their marine vocation in their festivals and traditions passed down for generations.

2. What is the situation of the coastal currents close to A Coruña?

Coastal currents in the area around A Coruña are determined by the complex interaction of different factors. Tidal forces-one of the basic driving elements-are due to the gravitational pull of the moon and the sun. The periodic rise and fall of the tides in the Golfo Ártabro give rise to a cyclic pattern of water motion. On high tide, water enters the gulf, thus creating an incoming current, while during low tide, the water recedes, creating an outgoing current.

Wind patterns also play a very important role. Prevailing winds from the Atlantic can be in the same or opposite direction to the tidal currents. Strong on-shore winds can push water toward the coast, adding to the incoming current, and affecting the distribution of heat, nutrients, and marine organisms. In contrast, off-shore winds will do the opposite and push the water away from the coast.

Another relevant factor could be the bottom topography of the sea floor off A Coruña. The general shape of the seabed would contain heights and depressions that might constrict or otherwise deflect the flow of water. Narrow channels or shallows will speed up the current, whereas deeper basins can slow it down or change direction. Besides, the input of freshwater from the local rivers pouring into the gulf may affect the density variation of the seawater, consequently generating the formation of the density-driven currents.

3. How to observe the coastal water flow of A Coruña?

Surface Drift Buoy Method

Surface drift buoy observation is a relatively simple method for its observation of the coastal water flow. These buoys float on the surface of the water and drift with the currents. They are fitted with tracking devices, such as GPS, capable of sending back their position at regular intervals. By tracking these buoys over time, their movements enable scientists to map the surface currents. This method has its limitations. It reflects information on the uppermost layer of the water column only, and usually extends just a few meters deep. The data reflect surface-level phenomena such as wind - driven waves, which may cause the buoys to veer off the pure current path.

Moored Ship Method

The moored ship method consists of keeping a ship stationed at a fixed location in the area of interest. Currents are measured using instruments onboard, such as mechanical current meters. Current meters are designed to measure current by a propeller-like device that rotates when water flows past it. The rotation speed is then converted into a measure of current velocity. Though this technique has the advantage of being able to give continuous data at one point, there are some disadvantages. The presence of the ship may interfere with the natural flow of the currents, especially in shallow waters. Also, the spatial coverage is limited to the immediate vicinity of the moored ship, making it difficult to obtain a comprehensive view of the large - scale current patterns.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP profiler method has emerged as a more advanced and versatile technique for measuring coastal currents. ADCPs are capable of measuring the velocity of water at different depths in the water column simultaneously. They emit acoustic signals into the water that are reflected by small particles suspended in the water, such as plankton, sediment, or air bubbles. The ADCP meter estimates the velocity of the water at various depths from the Doppler shift of the reflected signals. It offers high-resolution data across a comparatively big area. The method can be installed on several platforms, such as ships, buoys, or fixed moorings, making the instrument fit most of the measurement situations.

4. How do ADCPs using the Doppler principle work?

ADCPs operate on the basis of the well-known Doppler principle. The ADCP flow meter emits an acoustic wave into the water, which travels via the medium of the water. In this case, when such a wave encounters the small particles moving with the current of water, then the frequency that is reflected back from those particles differs from the emitted wave frequency. This frequency shift, which is known as the Doppler shift, is proportional to the velocity of the particles, and thus proportional to the velocity of the water.

Most ADCPs utilize multiple acoustic beams-four or more-commonly oriented in different directions. The ADCP current profiler can determine the three-dimensional velocity of the water flow from measurements of the Doppler shift in each of these beams. These velocity vertical and horizontal components can, on the one hand, be determined very precisely using data combined from a few beams directed slightly downwards and upwards, horizontally. In general, measuring the complete vector of the current velocity, a huge plus with ADCPs, aids in reaching higher grounds of advanced understanding of complicated flow dynamics at coastal waters.

5. What is needed to obtain high-quality A Coruña coastal currents measurement?

Equipment Reliability

To measure the coastal currents of A Coruña with high quality, equipment reliability is very vital. The marine environment is so aggressive because it has high salinity, strong waves, and variable meteorological conditions. ADCPs will have to be made of materials capable of resisting these adversities. The metals used should be rust-resistant, and the electronics well-sealed against water ingress. This goes a long way in ensuring reliability-a reliable ADCP can guarantee that the data collected will be accurate and consistent over a long deployment period.

Size, Weight, and Power Consumption

The ADCP should have a compact size. A compact device is relatively easy to deploy in numerous locations, including shallow waters and places that may have very limited access. It also has a lesser impact on the natural flow of currents. The ADCP should have lightweight, mainly for applications whereby it is supposed to be deployed on floating platforms or small vessels. This helps reduce the load on the platform and facilitates ease of installation and retrieval.

Another important consideration is low power consumption. Most ADCPs are designed to be powered either by batteries or renewable sources such as solar panels. If a device is set with low power requirements, then the time spent running without the need for recharging or refueling will result in longer continuous data collection.

Cost-effectiveness

This is particularly essential in applications when large-scale measurement is required. To perform recordings of coastal currents around, for example A Coruña, various ADCPs would be deployed in different locations. An affordable ADCP thus enables someone to carry out such large-scale studies without having an excessively high costs.

Titanium Alloy for ADCP Casing

The housing of ADCP current meter shall preferably be in Titanium alloy. It has a number of advantages; it is perfectly resistant to corrosion, which means long-term use in A Coruña's coastal waters and their salinity. In applications, this represents a high strength-to-weight ratio for the mechanical stresses exerted by wave impacts and water pressure that it will face while situated under these circumstances in a marine environment-and without any tacking of additional weight onto the casing. Besides, there is biocompatibility of titanium alloy; it has minimal effects on the ecosystem of the ocean-a very serious aspect with which one can trust in most sensitively coastal area like A Coruña.

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

Based on Usage

• Ship-borne ADCP: This type of ADCP is installed on a moving ship. It is ideal for large - scale surveys of coastal currents over a wide area. As the ship traverses different regions, the ADCP can continuously measure the currents along the ship's path. This gives the broad-scale view of the present distribution that is useful for the understanding of large-scale oceanographic processes and applications, such as in the planning of shipping routes.
• Bottom-mounted ADCP: It is also known as a moored or bottom-tripod ADCP, placed on the sea floor. It is ideal for long-term measurement at fixed locations. Because it stays fixed on the bottom of the ocean, it is able to deliver regular information on currents at that one spot, thereby allowing research on local current patterns, their fluctuations over time, and the consequences on the benthic ecosystem.
• Floating-buoy ADCP: These are ADCPs mounted on a floating buoy. They can be either stationary buoys that are anchored in place or buoys that drift with currents. Floating-buoy ADCPs are good for monitoring the movement of water masses, studying the interaction between surface and subsurface currents, and for real-time current conditions in an area.

Based on Frequency

The type of frequency of an ADCP applied is determined by the depth the water is to be measured at.

• A 600kHz ADCP is well-suited for up to approximately 70m of water depth. Due to this higher frequency, the current velocity is well resolved at high resolution in shallow waters of estuaries and nearshore and in the shallower parts of the Golfo Ártabro.
• A 300kHz ADCP is suitable for waters of about 110m water depth. It is an excellent compromise between depth of penetration and vertical resolution and is therefore quite universally applicable in coastal areas with intermediate water depth.
• In deeper waters, say up to 1000m, the more suitable instrument will be the 75kHz ADCP. The low frequency can reach a little bit deeper in the water column, while probably not offering the vertical resolution as compared with the higher-frequency models.
• There are several well-known ADCP brands on the market, including Teledyne RDI, Nortek, and Sontek. However, for anyone seeking a cheap but high-quality solution, the China Sonar PandaADCP is worth considering. Manufactured from pure titanium alloy, it represents an excellent blend of durability and 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 not only provides reliable equipment but also contributes to making high-quality current measurement more accessible and affordable for the scientific community and those involved in coastal management around A Coruña.

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