How can we measure the coastal currents of Huelva?

1. Where is Huelva?

Huelva is a city situated in the south - western part of Spain. It is on the Atlantic coast, in a region of great natural beauty and historic importance. The city is bounded by the Gulf of Cádiz, a body of water that is important in determining the local coastal environment.

From big marshes to estuaries, the variety of landscapes in Huelva is great: a home for numerous species of birds and other creatures. Feeding into the surrounding waters is the River Guadalquivir, bringing all sediments and nutrients that maintain a good productivity. The coastline is formed by sandy beaches and some rocky outcrops while having a gentle slope of the seabed down to deeper waters of the gulf.

Huelva is a city of great tradition and history. Having been a major port for many centuries, the sea and maritime trade have strongly marked the mentality of its inhabitants. The culture is deeply influenced by the sea, with the people very attached to the ocean. The architecture is very varied in the city, which reflects different periods, from the old fortifications to the modern industrial structures.

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

The coastal currents near Huelva are influenced by several factors. The tides in the Gulf of Cádiz have a great influence. Strong tidal currents can cause the water to go in and out of the estuaries and marshes, creating complex flow patterns. The outflow of the Guadalquivir River also influences the coastal currents. Freshwater from the river mixes with the saltwater of the gulf, causing changes in salinity and density that influence current flow.

The second factor involves wind patterns over the Atlantic Ocean. Prevailing winds, such as the westerlies, drive surface currents in a certain direction. General oceanic circulation patterns in the Atlantic also play their part. Large-scale ocean currents, such as the North Atlantic Current, are able to import different water masses and affect temperature and the general flow of the coastal waters around Huelva. The topography of the seabed, with sandbars and channels, may also divert and alter the currents.

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

The Surface Drift Buoy Method: These buoys are deployed at the surface of the water. These buoys are designed to move with the surface currents while their positions are determined by using satellite-based or other tracking systems. By analyzing the paths these buoys take over time, the direction and speed of the surface currents can be determined. However, this mainly provides information about the surface layer and does not give the complete picture about currents at different depths.

Anchored Ship Method: An anchored ship can be used as a platform for the measurement of current. Special instruments of measurement are attached on the ship to measure water flow around the ship. The measurement is also best taken at an exact position and has the only demerit of having interference from the same ship, affecting water flow.

Acoustic Doppler Current Profiler: ADCP current meter is a more modern and less labor-consuming way to perform current measurements along coastal areas. By means of ultrasound, the device counts the speed of water movements at several levels of depth. Giving out acoustic impulses, this ADCP current profiler counts a Doppler-displaced reflection that enables him to present the current profile from the surface down to the chosen depth in some detail. This will allow a better understanding of the coastal currents around Huelva compared to the rest of the methods.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They send acoustic signals, usually in short pulses, into the water. These signals, if intercepted by moving water particles, are reflected back with an altered frequency because of the Doppler effect. The change in frequency is proportional to the velocity of the water particles.

The ADCP flow meter has several transducers, which can emit and receive signals in various directions. This gives the ADCP profiler the different components of water velocities in both the horizontal and vertical directions based on the measurements of frequency shift in different directions. Since these acoustic pulses are sent regularly with intervals, it is possible at varied depth to build a profile of the current velocities along the column of water. This gives good information on the flow patterns, including the direction, speed, and any vertical shears in the currents.

5. What is necessary for high-quality measurement of the Huelva coastal currents?

For high-quality measurement of the coastal currents near Huelva, the equipment needs to be made from reliable materials. Considering seawater is corrosive and the general marine environment may be quite harsh, resistance to saltwater corrosion, pressure changes, and impacts is a big plus. A small size and lightweight are necessary for easy deployment either from a ship, buoy, or seabed. Low power consumption shall enable long-term operation without frequent battery replacements or any disruption in the power source. Cost-effectiveness is also in place to offer large-scale measurement processes.

In the casings of ADCPs, titanium alloy is a pretty good material. The corrosion resistance of the titanium alloy is very good, which is important for resisting the corrosive seawater in Huelva. Besides, it has a high strength-to-weight ratio, which can provide the required strength to protect the inner components without making the weight of the whole device too large. Therefore, it can be handled and installed easily.

6. How to Select the appropriate equipment to measure current?

Depending on Deployment Method

• Ship-borne ADCP: It can be deployed where you want to measure the currents while the ship is moving along the coast or at a specific location. The same offers flexibility in coverage and can provide continuous data with changes in position by the ship.
• Bottom-mounted ADCP: This is best for fixed-point measurements at the seabed. This could provide long-term, very accurate data on the current conditions at that particular point, which would be useful for the understanding of the local current patterns.
• Buoy-mounted ADCP: While fixed to a buoy that floats at the surface of the water, this could measure currents of the upper layer and could be telemetered wirelessly. The advantage will come in through ease in monitoring over long distances with wide coverage as influenced by the movement of a buoy.

The Frequency Basis

Various frequencies are ideal for different water depths. For instance, a 600 kHz ADCP is good to go for water depths of up to 70 meters, an ADCP with 300 kHz will handle up to 110 meters of depth, while that with 75 kHz is meant for very deep waters of as much as 1000 meters. It, therefore, enables you to choose the most suitable ADCP depending on the real conditions of water depth in the coastal area of Huelva.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also a great option. It is made of all-titanium alloy material, ensuring durability and offering an excellent cost-performance ratio. You can visit their website at https://china-sonar.com/ for more information.

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