Tietê River Water Current Measurement

1. Where is the Tietê River?

The Tietê River is one of the most important watercourses in Brazil. Its source is in the Serra do Mar, passing through the states of São Paulo and Minas Gerais.

It passes through very different landscapes: mountainous with lush vegetation and waterfalls, valleys, and plains in its upper course; and lower down, it widens into broad valleys and plains, the sites of large urban and industrial complexes. The Tietê River plays an essential role in the water supply and infrastructure of the region. It supplies water for domestic consumption, agriculture, and industry.

However, it also suffers badly from environmental damage because of its high levels of pollution from industrial and domestic wastes. Despite all this, the river still hosts a number of diverse aquatic species. It has many species of fish, such as piaucu and traíra. Its riverbanks are nests for waterbirds like herons and ducks. The floodplains and wetlands along the river contribute vitally to ecological balance: they serve as areas of reproduction and feeding for many species.

2. What is the flow rate in the Tietê River?

The flow rate of the Tietê River has seasonal and climatic variations. During the rainy seasons-roughly from October to March-the catchment area around the river usually receives considerable rainfall. This automatically increases the flow rate of the river significantly. The river can become quite powerful during this period, with a high volume of water flowing downstream.

The flow rate diminishes during the dry season, which is between April and September. At the same time, it retains the base flow important for the continuance of life in water and for sustaining community activities dependent on it. The average flow rate can thus oscillate from several hundreds of cubic meters per second during the dry season up to several thousands during the height of the rainy season.

3. How to measure water current of the Tietê River?

Velocity Meter Method

This traditional method is done using mechanical or electronic velocity meters. Such devices are installed at various specific points in the river to measure directly the speed of water flow at those particular locations. Nevertheless, complete knowledge of the general water current calls for several measurements with variable depths and across different sections of the river. As the Tietê River is very extensive and its conditions vary significantly, this procedure can be highly labour and time-consuming.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP current profiler offers an advanced, convenient way of measurement. The technique detects the movement of water particles by using sound waves. By emitting acoustic signals and analyzing the Doppler shift of the reflected signals, it can measure the velocity of water at a number of depths simultaneously. This gives a very thorough profile of the water current and hence allows for an even more precise evaluation of the flow conditions along the entire river. The ADCPs can be mounted on boats, bridges, or even deployed on buoys for continuous monitoring.

Buoy Method

In the buoy method, buoys with sensors are put into the river to measure the movement of water around them. The buoys float on the surface and can give an indication about the surface current; they cannot fully represent the complexity of water current like the other methods, especially when trying to understand the variation in velocity at different depths.

Among these methods, the ADCP flow meter stands out as a more sophisticated and efficient option for measuring the water current of the Tietê River.

4. How do ADCPs using the Doppler principle work?

The ADCPs operate based on the principle of the Doppler effect. Whenever an ADCP sends out an acoustic signal into the water, sound waves will travel through the water and engage with the moving particles of water. Due to the movement of water particles, the frequency of the reflected sound waves changes with the Doppler effect.

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

Accordingly, the ADCP profiler then combines these individual velocity measurements at various depths to create a complete profile of the water current. This enables detailed understanding of how the water is flowing not only at the surface but also throughout the vertical section of the river.

5. What is needed for high-quality measurement of Tietê river currents?

The equipment would have to possess certain characteristics for high-quality measurement of the Tietê River currents.

The material reliability of this equipment should be high. It should be resistant to the adversities of the aquatic environment, such as being in contact with water and sediments, and temperature fluctuations. The Tietê River presents a flow that can vary, besides debris carried in periods of high flow. It demands resistant equipment.

Also, small size, low weight, and low power consumption are preferred. A compact and lightweight gadget is more convenient for manipulation and placing either on a boat or attached to a buoy. Low power consumption means equipment is capable of working for long periods without needing frequent replacements of batteries or access to a continuous power source.

Cost - effectiveness is an important factor. A lower - cost option enables more widespread use of the measurement equipment, allowing for more comprehensive monitoring of the river.

When it comes to the casing of the ADCP, titanium alloy is an excellent choice. Titanium alloy is highly resistant to corrosion, which is essential when dealing with water bodies like the Tietê River where the equipment will be constantly in contact with water and potentially corrosive substances. It is also strong and durable, able to withstand physical impacts and the pressure changes that may occur during deployment and operation. Besides, the density of titanium alloy is relatively small, which contributes to reaching the general purpose of equipping with lightweight equipment.

6. Selection of Appropriate Equipment for Current Measurement

Selection of appropriate equipment for measuring Tietê River current requires consideration of a number of variables.

According to the Intended Use

When the intention is toward measuring the horizontal cross-section of the river current, an HADCP should be used. HADCPs are designed to measure the flow of water in the horizontal plane with a high degree of accuracy, which helps in ascertaining the overall movement of water across any particular section of the river.

In case of measurements related to the vertical cross-section of the river current, one should select the vertical ADCP. A vertical ADCP gives one the correct value that shows the velocity of the water at different depths, giving a detailed profile of how the water flows vertically within the river.

Based on Frequency

The frequency of operation depends on the depth of the Tietê River water; for instance, a 600 kHz ADCP would be good to go in waters with a depth of up to 70 meters. A frequency of 600 kHz provides good resolution and accuracy in measuring the water current in relatively shallow waters.

For deeper waters, say above 70 meters and to about 110 meters, a 300 kHz ADCP would be more suitable. The lower frequency of 300 kHz can go deeper in the water while still providing adequate measurements of the water current.

There are renowned brands of ADCPs that have secured a niche for themselves in the industry; these 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 Tietê 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.