How to Measure the Water Current of the Tagus River

 1. Location of the Tagus River

The Tagus River, in Portuguese known as Rio Tejo, is one of the most important rivers in the Iberian Peninsula. Originating in the Sierra de Albarracín in eastern Spain, it flows west across Spain and into Portugal, discharging its waters into the Atlantic Ocean near Lisbon.

It is a very important river for those regions in which it courses through, because of the agricultural supply or the irrigation of vineyards, olive groves, and other crops. Giving domestic water and other industrial uses in many cities and towns that line its course-such as Madrid and Lisbon-albeit via canals and water transfer systems, is based on it. It is also important to note that the Tagus River has its own substantial history of shipping and trade along the ports and harbors lining its banks.

The river in itself is of a varied nature. Various kinds of fish-carp, catfish, and shad-inhabit it. Various species of birds and reptiles, along with small mammals, have their nests along its banks. The flood­plains and wetlands along the river play a crucial role in maintaining the ecological balance in the region and are normally breeding and feeding areas for a large number of species.

2. Tagus River Flow Rate Characteristics

Flow in the Tagus River is seasonal and climatic. During its wet season, normally during the winter months in the Iberian Peninsula due to prevailing Atlantic weather systems, the flow rate of the river increases. This results from an increased amount of rainfall within its catchment area, sending more water downstream.

This flow rate is reduced during the dry season, usually during summer. However, it still maintains its base flow, essential for the existence of its fishes and other aquatic life forms, which helps the activities concerned that rely on water, such as irrigation and domestic water supplies. Its average flow can be as low as a few hundred cubic meters per second during the dry season to several thousand cubic meters per second at the peak of the wet season.

Besides, the volume of water carried by the Tagus River affects navigation. During its high-flow period, larger ships can navigate it, while during the low-flow period of the year, navigation may be restricted, especially to those vessels that have a deeper draft.

3. Methods to Measure the Water Current of the Tagus River

Velocity Meter Method

This is a traditional approach where mechanical or electronic velocity meters are employed. These instruments are set at certain points across the river to measure directly the current flow at those exact points. However, for a complete picture of the general current, many measurements would be needed at different depths and parts of the river. The Tagus River is pretty long, and its conditions range from one extreme to another; therefore, this is quite a labor-and time-consuming way of measurement.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP is a more advanced and much handier method of measuring water currents. It basically detects the motion of particles in water with the help of sound waves. By emitting acoustic signals, it receives the reflected signals with a Doppler shift, which helps in measuring the velocity of water at more than one depth simultaneously. This gives a very thorough profile of the water current, enabling a far more accurate assessment of flow conditions right across the river. The ADCPs could be mounted on boats, bridges, or even deployed on buoys for continuous monitoring.

Buoy Method

The buoy method involves placing buoys in the river with sensors that measure the movement of water around them. The buoys are floating on the surface and can give some indication of the surface current. They may not perceive the complexity of water current with as much clarity as the other methods, especially when the variation in velocity across different depths is considered.

Of these, the ADCP current profiler is considered a more advanced and efficient means of measuring the water current of the Tagus River.

4. How ADCPs Using the Doppler Principle Work

ADCPs are based on the principle of the Doppler effect. A signal, when emitted by an ADCP profiler into the water, travels with the sound waves through water until it collides with the moving water particles. Since the latter is in motion, due to the Doppler effect, there is a shift in the frequency of the reflected sound waves.

If the water particles are moving towards the ADCP flow meter, the reflected wave frequency will be higher than the emitted frequency. Conversely, if the water particles are moving away from the ADCP, the reflected wave frequency will be lower. By precisely measuring this change in frequency, the ADCP can calculate the velocity of the water particles at different depths.

These individual velocity measurements are then combined by the ADCP current meter to form a complete profile of the water current. This forms a detailed understanding of how the water flows, not just at the surface, but throughout the vertical section of the river.

5. Requirements for High - Quality Measurement of the Tagus River Currents

In addition, the measuring equipment has to possess some features for quality measurement of the Tagus River currents. The equipment should be made of highly reliable materials. It must be able to bear the water and sediment resistance of the bad river environment, as well as temperature resistances. Variable flow of the Tagus River and debris-laden water flow in high flows require durable equipment.

Other desirables are small size, light weight, and low power consumption. The smaller and lighter a device is, the easier it would be to handle and deploy, whether on a boat or attached to a buoy. Low power consumption means that for long periods, the equipment is operable without frequent battery replacements or access to a continuous power source.

Cost is a big factor: the lesser it costs, the more the measurement equipment can be applied to monitor the wider coverage of the river.

Titanium alloy, in addition, is one of the best options for casing the ADCP. It is highly resistant to corrosion, which is an important factor when dealing with water bodies like the Tagus River, where the equipment will be in close contact with water and probably corrosive substances all the time. The material will also be strong enough and durable to resist possible physical impacts and changes of pressure that might happen during deployment and operation. In addition, the density of titanium alloy is relatively low; hence, it contributes to the overall aim of lightweight equipment.

6. Selection of Appropriate Equipment for Current Measurement

There are various factors that need consideration in choosing the appropriate equipment for measuring current in the Tagus River.

According to the Intended Use

If the intention is to measure the horizontal cross-section of the river current, one should use a horizontal ADCP. The HADCPs are so designed that they provide better results in water flow within the plane, which helps determine the overall movement of water across a given section of the river.

If the focus is to measure the vertical cross-section of the river current, then a vertical ADCP would be the best choice. In the measuring capability of the vertical ADCPs, the velocity of the water at different depths is included with accuracy that clearly shows the profile of how water is flowing vertically within the river.

Based on Frequency

The choice of frequency is basically dependent on the water depth along the Tagus River. With the selection of a 600 kHz ADCP, it is expected that water depths up to 70 meters will normally suffice. This 600 kHz is a good frequency since it serves with good resolution in the measurement of currents for relatively shallow waters.

For deeper waters, say above 70 meters and to around 110 meters, the more applicable one is the 300 kHz ADCP. The 300 kHz lower frequency can delve deeper into the water and still yield good water current measurements.

Some of the well-known brands of ADCP are Teledyne RDI, Nortek, and Sontek. However, for those seeking a cost - effective option with excellent quality, the China Sonar PandaADCP is worth considering. It is made of all - titanium alloy material, ensuring durability and reliability. With its remarkable cost - performance ratio, it provides a great alternative for measuring the water current of the Tagus River. You can find more information about it on its official website: https://china-sonar.com/.

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