How can we measure the coastal currents of Carballo?

1. Where is Carballo?

Carballo is a municipality located in the north-western part of Spain, in the province of A Coruña within the autonomous community of Galicia. It is located on the Atlantic coast-a region that boasts a ruggedly beautiful coastline.

Carballo is a town with a lot of history and culture. It has a very rich past, which can be traced from ancient times, and that reflects in the architecture of this place. The traditional Galician stone houses with thatched roofs dot the landscape of this place and give it a more rustic and appealing look. Locals are bound with the soil and sea, and their livelihood is closely related to the coastal environment.

Carballo borders several bodies of water, including very important ones: The Ría de Ares y Betanzos is the nearest major estuary. Such estuarine waters are considered to be of particular importance regarding local ecosystems since all kinds of fish, mollusks, birds, and many other sea creatures use it as a special place for reproduction. The estuary also acts as a natural nursery for many species, which is very important for the general health of the coastal environment. The Atlantic Ocean, with its open waters, continuously affects the climate, tides, and coastal processes of the area concerned.

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

The coastal currents near Carballo are influenced by a combination of factors. Tidal forces are a dominant factor. The tides are the fluctuations in sea level caused by the gravitational attraction of the moon and sun. During high tide, water is pouring into estuaries and along the coast, creating an in-going current. At low tide, the water will be going out to sea and creating an out-going current. The tidal range in this area can be quite large, which affects the speed and volume of the tidal currents.

However, wind is not the sole factor in the development of the currents of the coast. Prevailing winds from the Atlantic may push or drive the water towards and away from the shore. For example, the presence of westerly winds allows the surface water to converge toward the shore, thus resulting in a shore -parallel current. The intensity of the winds could vary by season; for instance, during winter months, stronger winds are experienced that might create more energetic currents along the coasts.

Another important factor would be the sea floor bathymetry off Carballo. The shape and depth of the seabed are able to deflect the flow of water. Submerged sandbars, rocky outcrops, and channels may do this, among others, to reroute or speed up the currents. For instance, a narrow channel between two land masses could funnel the water and increase the speed of the current, while a wide shallow area might cause the current to broaden out and slow down.

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

Surface Drift Buoy Method

This is a pretty simple, yet effective method for observing surface water flow. The drift buoys are deployed on the surface of the water and are conveyed by the currents of water. These buoys are normally fitted with GPS or any other tracking device that can transmit their position at periodic intervals. By following the movements of these buoys, a determination can be made by the researchers on the direction and velocity of the surface currents. This method is limited to the very top of the water and may not be entirely accurate as surface winds and waves could push the buoys off course of the true path of the current.

Moored Ship Method

In the moored ship method, a ship is anchored at some place in the coastal area. The water flow is measured by on-board instruments, which include current meters. The current meters work on different principles, such as the rotation of a propeller-like device by the passage of water through it. The speed of rotation is then translated into a measure of current velocity. However, this method provides accurate measurements only at one point and is highly limited in most aspects. The presence of the ship interferes with the flow of currents around its immediate area, and these measurements are confined to the vicinity of the anchored ship.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP current meter method has been one of the advanced and comprehensive measurement techniques for coastal currents. ADCPs measure the velocity at different levels in the water column by using the Doppler effect. They emit acoustic pulses into the water, which scatter off small particles in the water, such as plankton or sediment. The frequency shift of the reflected signals is analyzed to determine the velocity of the water at various depths. A backscatter profiling gives a rather detailed profile of the present structure from surface to subsurface currents. Besides, ADCPs can be mounted on different platforms, such as ships, buoys, or fixed moorings, which provides some flexibility in coastal current measurement.

4. Working Principle of the ADCPs Using the Doppler Principle

Doppler principle-based operation is possible for the ADCPs. When an ADCP current profiler sends an acoustic wave through the water, it travels through the water and encounters particles moving with the water current. As this wave strikes and bounces off these particles, the frequency of the reflected wave is different. If the particles, and hence the water, are moving towards the ADCP, the frequency of the reflected wave is higher than the original wave emitted. Whereas if the water is moving away from an ADCP, there is a reflected wave of a lower frequency than that of the transmitted pulse.

Several ADCPs are normally equipped with three or more acoustic beams oriented in different directions. Since the measurable Doppler shifts in each of the beams are obtainable, it is possible to calculate the three-dimensional velocity. For example, one beam may be oriented vertically downwards to measure the vertical component of the current and other beams oriented at an angle to measure horizontal components. With that, the ADCP can give a complete view of the three-dimensional velocity vector of the current-magnitude and direction.

5. What is needed for good measurement of the Carballo coastal currents?

Equipment Reliability

It will be important for the equipment used to measure Carballo's coastal currents to be very reliable. It is a really harsh coastal environment: saltwater, waves, and weather continuously change. To that end, ADCPs, as well as all other measurement devices, should be made from noncorrosive material. The internal electronics should be well-guarded against possible water ingress in order to maintain performance with a high degree of accuracy for an extended period.

Size, Weight, and Power Consumption

Equipment size: The equipment must be of a size that can be easily deployed in most of the coastal environments. For example, a compact ADCP flow meter might be deployed in considerably shallower waters than could a large device, or deployed in very constricted areas where space is a premium. Another important aspect of the equipment is weight. This is critical when equipment must be deployed on floating platforms or small vessels. A lighter device minimizes the load, therefore making it much easier to install and recover.

Long-term measurements require low power consumption. Most often, equipment may be powered by batteries or solar panels. Low power devices will keep working for longer, since it would not be necessary to replace or recharge batteries too frequently for continuous data collection.

Cost-effectiveness

Cost-effectiveness is a priority, considering it may be used for large-scale measurements. Possibly, more than one device needs to be set up in order to acquire full understanding of the coastal currents around Carballo. So, the reasonable cost of such equipment is critical for being able to deploy a number sufficient for measurements.

Titanium Alloy for ADCP Casing

The casing of the ADCP meter should preferably be of a titanium alloy. The corrosion resistance of titanium alloy is excellent, which is very important for equipment used in the salt-water environment of Carballo's coast. It also possesses a high strength-to-weight ratio, which means that it can support the mechanical stresses exerted by the marine environment, such as wave impacts and water pressure, and still remain light. Besides, the biocompatibility of the titanium alloy is a great advantage for the marine ecosystem surrounding it since there will be less chemical interaction that could be harmful.

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

Based on Usage

• Ship-borne ADCP: This applies to the measurements from a moving ship. In this way, one can continuously measure the coastal currents over a big area while the ship is on its journey. This type of ADCP will be useful in mapping the large-scale pattern of currents and thereby understanding the overall circulation in the coastal waters off Carballo.
• Bottom-mounted ADCP: These are placed on the seafloor and are suited for long-term, fixed-location measurements. It can provide a detailed understanding of the local current conditions at a specific site, including how the currents interact with the seabed and the benthic ecosystem.
• Floating-buoy ADCP: This is an ADCP that is mounted on a buoy and, while the buoy is anchored or drifting, makes current measurements from the surface down to several hundred meters. These are used for monitoring the transportation of water masses, interaction of surface and subsurface currents, and real-time current data over a specific area.

Based on Frequency

The ADCP profiler frequency will depend on water depth. A 600kHz ADCP is a good choice for water depths up to about 70m. The higher frequency provides high-resolution measurements of the current velocity, which is beneficial for shallow-water areas such as near-shore regions and estuaries. For water depths up to about 110m, a 300kHz ADCP offers a balance between depth penetration and vertical resolution. For deeper waters, up to 1000m, a 75kHz ADCP is more suitable as it can penetrate deeper into the water column, although it may have a lower vertical resolution compared to higher-frequency ADCPs.

There are well-known ADCP brands in the market, such as Teledyne RDI, Nortek, and Sontek. However, for a cost-effective option with high-quality performance, the China Sonar ​PandaADCP is worth considering. It is made of all-titanium alloy, which provides excellent durability. You can find more information about it at (​https://china-sonar.com/). This brand offers a good balance between quality and cost, making it a viable choice for measuring the coastal currents of Carballo.

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