How to Measure Water Current of the Pilcomayo river?

1. Where is the Pilcomayo?

The River Pilcomayo is a significant course of water in South America, with its origin in the highlands of Bolivia, then running its course through Paraguay and Argentina.

In Bolivia, the river begins its course from the Andes Mountain, then cuts through mountainous and alpine meadows. In Paraguay, it passes through arid and semi-arid areas. Here, in the involved ecosystems, it forms part of the essential water source for human needs and agriculture.

It passes through small country villages faithful to it along its course. The inhabitants use the Pilcomayo River for fishing and irrigation. In Argentina, it continues its course on a bed of heterogeneous materials, which defines a natural environment and influences local ecosystems by participating in the regional water balance. From dry to more moderate, the vegetation growth along its river banks depends on areas with much or little regular water supply; hence, from arid-resistant shrubs in arid parts to more lush plants where the water supply is more stable.

It is a symbol of much more than its water volume: it carries the history and the traditions of indigenous peoples, the settlers, too, where the flow carries stories and legends within its movement, which represents a trade route and a transportation means for centuries.

2. What is the Flow Rate of the Pilcomayo like?

The Pilcomayo exhibits a very seasonal flow variation, with surges in river discharge during the rainy season, typically during that time of the year when there is rain in the Andean highlands. This is due to the augmentation of melting snow on the mountainous areas and simultaneous rainfall, which collectively increase the volume of water in the river. It is at this stage that the current is quite strong, accompanied by much higher water volume.

Its flow rate is normally less during the dry season. It can become decidedly shallower and narrower in some places. This reduced flow is because of lesser precipitation and higher rates of evaporation in arid and semi-arid regions through which it passes. Even the average rate of flow differs along its length. In the upper reaches, closer to its mountain origin, it can be relatively faster on account of the greater slope. As it moves into much flatter plains, the flow becomes considerably slower.

The most common human activities with the river have been water abstraction for agricultural purposes and the building of smaller dams that eventually altered the average river flow. This condition has changed natural flow variations and has wider implications for its ecological potential and the communities depending upon it.

3. How to Measure Water Current of the Pilcomayo?

There are various methods by which the water current of the Pilcomayo can be measured.

Traditional Approaches

Float Method

The easiest way to have a rough estimation of the water current is done using a float. Any floating object, such as a small piece of wood or plastic bottle, is let free in the river. It is possible to approximate this by measuring the time taken for a float to travel a known distance. This technique is rather coarse; due to wind, the shape of the float, among other factors, it will be indicative only for the surface current. 

Current Meters

Mechanical or electronic devices moored in the water at a specific depth to gather information about the speed of the passage of water around them. They can present single-point measurements of the water column with better accuracy than floats. They also suffer from the limitation that measurements are taken only to a particular depth and not for current throughout the water column.

Advanced Method - Acoustic Doppler Current Profilers (ADCPs) This is a more advanced and efficient way to measure the water current of the Pilcomayo.

3.1 How do ADCPs using the principle of the Doppler work?

In principle, an ADCP profiler works through the Doppler effect: An ADCP meter emits acoustic pulses out into the water. The pulses interact with the suspended particles in the water, or more specifically, the sediment and other small life forms in the flow change the frequency of the reflected acoustic signals. 

It is this frequency shift that is measured by the ADCP flow meter , using the Doppler formula to arrive at the water velocity at different depths. With the capability of transmitting pulses in multiple directions and at different frequencies, the ADCP doppler is able to generate a very detailed profile of the water current across the entire water column. This gives a far more complete picture of the current structure in the river than can be achieved with traditional methods.

3.2 What is necessary to make good quality measurements of Pilcomayo currents?

In fact, high-quality measurement of the Pilcomayo currents requires that the equipment be sound and reliable. Since the Pilcomayo River flows under strong currents during the rainy season, with a high sediment load and in arid regions where temperatures can be extremely high, the measuring devices will have to be robust enough to withhold such forces. 

The equipment should be compact and lightweight for ease of deployment, especially from remote areas along the river or from boats. Similarly, a low power consumption is crucial for ensuring that the equipment operates for long without necessarily changing batteries or depending on an external source of power. Cost-effectiveness is also vital, as the measurement on a large scale can be needed for full comprehension of dynamics in a river. 

Using titanium alloy for the casing manufacture of ADCP current profileris convenient. Its high resistance to corrosion is very important for an environment rich in water, like Pilcomayo; it is also strong and resistant to the physical forces brought by the river current and any possible impacts. Its light weight makes it even more convenient to install and transport.

3.3 How to select appropriate equipment for current measurement?

While choosing equipment for measuring the current of the Pilcomayo, attention must be given to special demands that are made by the measurement.

For Horizontal Measurements

This will involve the horizontal measurement across a section of the river. To this end, the appropriate device is the horizontal ADCP current meter, otherwise known as the HADCP. It gives an overall view of the current flow in a horizontal plane, which comes in useful in ascertaining general flow patterns that occur within the river. 

For Vertical Profile Measurements

The latter is much better for the vertical profile measurements of the current. It may give detailed information about the velocity of the water at different depths, which is the most important issue in studying stratification and mixing of the water column. 

Frequency Selection

In the case of frequency selection, a 600 kHz ADCP might be good to go for frequencies in those relatively shallower parts of the Pilcomayo, say, up to around 70 meters. In the case of deeper parts of up to about 110 meters, a better option would be a 300 kHz ADCP.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option with good quality, the China Sonar PandaADCP is a great choice. It is made of all - titanium alloy, providing durability and resistance to the Pilcomayo's environment. It also offers an excellent price - performance ratio. You can visit https://china-sonar.com/ for more information.

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