How can we measure the coastal currents of Bilbao?

1. Where is Bilbao?

Bilbao, the largest city in the Basque Country of northern Spain, is strategically located at the mouth of the Nervión River, where it meets the Cantabrian Sea. This location has been instrumental in the development of the city over centuries as a major port city.

The city is a mix of rich history and modern innovation. Its historical roots trace back to the Middle Ages, with the Old Town, known as "Casco Viejo," a UNESCO World Heritage site. Narrow, curving streets such as the famous "Siete Calles" (Seven Streets) make up the Casco Viejo, lined with charming medieval buildings, bustling markets, and traditional Basque taverns. These areas are a real testament to how long the city and its cultural heritage have stood the test of time in terms of architecture.

Probably, the modern face of Bilbao finds its most striking representation in the Guggenheim Museum Bilbao. This masterpiece by Frank Gehry grew to become not only an icon for the city but also played an important role in making Bilbao one of the important cultural and tourist cities. Its singular curvilinear shape in titanium, glass, and limestone stands in contrast with the urban landscape and invites people from every part of the world.

The major economic center and cultural and historical attractions of Bilbao make this city a vibrant place. In fact, its port is the busiest in all of Spain; it receives diverse goods, including raw materials and highly technological products. Its economy flourishes with financial, technological, and service-related industries. It's a beautiful and ever-changing landscape of sandy beaches, rocky cliffs, and the open Cantabrian Sea, teeming with life.

2. What is the situation regarding coastal currents near Bilbao?

The situation of coastal currents around Bilbao depends on a complex set of influential factors. Amongst the most important driving factors are tidal forces. The moon and sun gravitational attraction produces regular tides rising and falling in the Cantabrian Sea. A lot of water enters the estuary formed by the Nervión River during high tide, where strong incoming currents are developed; they may be very strong in the narrow channels, near the mouth, where the water is funneled in. During low tide, it pulls back, which develops the outgoing current carrying the sediment and nutrients back to sea.

Another very important influence involves the prevailing wind pattern. Generally speaking, strong winds blowing inshore from the Atlantic Ocean may be greatly responsible for surface currents. Westerly winds, common in this area, could push water toward the shore, further strengthening the incoming currents. They also tend to cause upwelling in some regions, in which cold deep-ocean water that is rich in nutrients rises to the surface. The consequences of such an upwelling on the marine ecosystem are phenomenal, where quite diverse phytoplanktons throng to bloom at the base of the food web. Easterly winds, by contrast, might produce a movement of water away from the shore that also influences both direction and velocity of coastal currents.

The morphology of the coastline and sea bed bathymetry around the coastline of Bilbao are factors involved. A close estuary confluence given by the River Nervión together with the shoreline topology, such as headlands and bays, can constrict and distribute the flux. Topography of the sea floor with the uneven depths and underwater features such as ridges and canyons may deflect the currents. For example, submarine canyon might act as a conduit for deep -water currents while a shallow bank can force the current to slacken its speed and also change its course in a different direction.

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

Surface Drift Buoy Method

The surface drift buoy method is the relatively simple way of observing the flow of the water in the coastal area. Drift buoys are deployed on the surface of the water. These buoys are fitted with tracking devices, such as GPS, for the continuous monitoring of position. Since these buoys will be carried by the currents, the data derived from their movement can map the surface current. However, this technique has its disadvantages. It provides information on the top layer of the water column, which is usually a few meters deep. The buoys are also influenced by surface winds and waves, which may make them deviate from the pure current path. This may result in an inaccurate representation of the actual current direction and speed, especially in areas with strong wind-wave interactions.

Moored Ship Method

The moored ship method requires anchoring a ship at a selected location in the coastal waters off Bilbao. The water flow is measured by instruments carried on board, such as mechanical current meters. These current meters usually operate on the principle of rotation of a propeller-like device by the passage of water, and the speed of rotation is converted into a measure of current velocity. While this method could give quite accurate measurements at a point, it has loads of disadvantages. The presence of the ship itself may disturb the natural flow of the currents, especially in shallow waters. The turbulence from the ship's hull and anchor could affect the accuracy of the measurements. Other than that, spatial coverage is limited to the vicinity of the moored ship in which features at large scale of the current can hardly be acquired.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP current meter method is one of the modern advanced and versatile methods for the determination of coastal currents. In this technique, the ADCPs measure velocity of water at various levels within the water column by employing the Doppler effect. They send acoustic pulses into the water, which are reflected back by small particles suspended in the water, such as plankton, sediment, or air bubbles. From the frequency shift of the reflected signals, the ADCP can calculate the velocity of the water at different depths. This method offers high-resolution data over a relatively large area. It can be deployed on different platforms, such as ships, buoys, or fixed moorings. ADCPs are capable of providing an accurate vertical profile of the current structure so as to facilitate a better understanding of the complex interactions between surface and subsurface currents. They measure the three-dimensional velocity of the water flow, which is required for the proper characterization of coastal current dynamics.

4. How do ADCPs using the Doppler principle work?

It works on the principle of Doppler. When an acoustic wave is emitted by an ADCP current profiler into the water, the wave has to travel through the water medium. This wave, when it meets small particles moving with the water current, reflects back from those particles with a frequency different from that of the wave emitted. The result, called a Doppler shift, depends linearly on the particle velocity (hence directly on water velocity).

Most ADCPs feature several (four or even more) acoustic beams with nonzero angles between each of the beams. Such a multidirection Doppler shift gives one the ability for calculation of the real three-dimensional water flow velocity using the Doppler effect:. For instance, one beam might be pointing vertically downwards to measure the vertical component of the current, while other beams pointed at an angle can measure the horizontal components. With all the data coming from the various beams that form a unit with the ADCP, it can without a doubt determine magnitude and direction in three-dimensional space. This constitutes a great advantage of ADCPs, as they are able to measure the full vector of the current velocity and thus give a more complete insight into the complex flow dynamics in coastal waters.

5. What's required for high-quality measurement of Bilbao coastal currents?

Equipment Reliability

Equipment reliability is the first thing needed for high-quality measurement of Bilbao's coastal currents. The marine environment off Bilbao is very rough due to high salinity, strong waves, and variable meteorological conditions. ADCPs and other instruments are required to be manufactured using materials that are resistant to corrosion. Electronics inside the instrument should be well-protected against water ingress for delivering very accurate and consistent readings over an extended period of time. The slightest malfunction or inaccuracy of the equipment will produce flawed data that will misinterpret the pattern of coastal currents and its implication for the local ecosystem, shipping, and other human activities.

Size, Weight, and Power Consumption

The size of the equipment must be small. A compact ADCP flow meter is easier to deploy in various locations, especially in the shallow waters near the river mouth and in the narrow channels of the estuary. It also has less impact on the natural flow of the currents. The weight of the equipment is also crucial, particularly for applications where it is to be deployed on floating platforms or small vessels. A lightweight device reduces the load on the platform and makes installation and retrieval more convenient. Low power consumption is important when long-term measurements are required. In most cases, this equipment can be powered by a battery or even renewable sources, such as solar panels. A low-power device enables longer operating times without replacing or recharging batteries frequently for continuous data recording.

Cost-effectiveness

The cost of the instrument is an important factor, especially when measurements over a large area need to be made. In order to obtain a good overview of the coastal currents around Bilbao, for instance, several ADCPs would have to be deployed at different locations. Only an economical ADCP will make such large-scale investigations economically viable. High equipment costs might mean only a limited number of devices can be deployed, and hence incomplete data. The cost and performance have to balance for the accurate measurement of the coastal currents.

ADCP Casing-Titanium Alloy

The casing of the ADCP meter is preferably to be made of a titanium alloy. Titanium alloy offers quite a few advantages. It also has very good resistance to corrosion, which is absolutely essential for the structures that would eventually serve in a saltwater environment like Bilbao for extended service. A high strength-to-weight ratio will further enable the casings to support mechanical stresses-especially wave impact and water pressure - in the marine environment with minimal addition of weight. Besides, titanium alloy is biocompatible, that means it has little effect on the marine ecosystem. This is because there are several species found in the Bilbao coastal waters, and no used material in the measuring equipment should cause any harm to the environment.

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

Based on Usage

• Ship-borne ADCP: This type of ADCP profiler is installed on a moving ship. It is suitable for large-scale surveys of coastal currents over a wide area. While the ship moves along the coast near Bilbao, the ADCP can continuously measure the currents, thus providing a broad-scale view of the current distribution. This will be useful for the understanding of large-scale oceanographic processes, such as the overall circulation patterns in the Cantabrian Sea around Bilbao, and applications like shipping route planning. Ship-borne ADCPs can cover large distances in relatively short times, enabling the mapping of extensive current patterns in a relatively short time.
• Bottom-mounted ADCP: It is also referred to as a moored or bottom-tripod ADCP, mounted on the seafloor. The bottom-mounted configuration is appropriate for measurement over long durations at one location. Since it stays in one place on the ocean floor, it can give consecutive data on the currents of a certain site. This is helpful in studying local current patterns, temporal variations, and the response of the benthic-sea floor-dwelling ecosystem. Bottom-mounted ADCPs provide insight into how currents interact with the seabed-an interaction that may have important implications for sediment transport and the distribution of benthic organisms.
• Floating-buoy ADCP: The ADCPs are attached to a floating buoy. They can either be stationary buoys anchored in place or floating buoys that drift with the currents. Floating buoy ADCPs are useful in monitoring the movement of water masses, the interaction between surface and subsurface currents, and for giving real-time current conditions of a particular area. They can be used in places where ship-based or bottom-mounted measurements are not possible, for example, in shallow lagoons or places with high tidal current velocities.

Based on Frequency

The selection of the ADCP frequency depends on the water depth to be measured.

• 600kHz ADCP will be good for water depth up to about 70m. This higher frequency allows for high-resolution measurements of the current velocity in shallow waters, such as in the estuary near Bilbao, near-shore areas, and the shallower parts of the Cantabrian Sea. The detailed information provided by the 600kHz ADCP can help in these areas to understand the complex flow patterns influenced by the river-sea interaction, coastline, and local bathymetry.
• A 300kHz ADCP will be adequate for water depths of about 110m with an excellent balance in the penetration of depth and vertical resolution, making it favorable for a great number of coastal applications, which also extends to areas of intermediate water depth off Bilbao. It has a frequency that can give useful data on the structure of currents within areas where neither the depth of water is too shallow nor too deep.
• For bigger depths up to 1000m, it performs better with 75kHz; the lower the frequency, the deeper the signals can travel into the water column, and while this potentially reduces the vertical resolution compared with higher frequency instruments, in areas of greater depth in the Cantabrian Sea west of Bilbao, for example, such regions could obtain higher currents from the 75kHz ADCP-a measurement very relevant for the estimate of total circulation of that part of the sea.
• Several other prominent ADCP brands include Teledyne RDI, Nortek, and Sontek.

In any case, China Sonar PandaADCP is of high recommendation in your hunt for such an affordable yet quality unit. The instrument's titanium alloy body of the highest degree provides super quality while being moderately priced. 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/). Besides its sturdy machinery, this brand contributes much to making the present measurement at high quality and rather cheaply available both for the scientific world and for persons related to Coastal Management of Bilbao.

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