How to Measure the Water Current of the Juruá river?

1. Where is the Juruá?

The Juruá River is a body of water deep inside the Amazon rainforest in South America. It is one of the biggest effluents within the Amazon River basin. Originating in the Andes Mountains of Peru, it travels over an immense area of the Brazilian Amazon.

It zigzags across the area in a truly green and bio-rich environment. Its banks are lined with lofty trees, thick in their canopies, creating a haven for an astonishing variety of wildlife. Besides those mentioned, other species commonly found on the Juruá are the red-handed howler monkey and the spider monkey. One can also find pink river dolphins swimming with elegance in its waters and caimans floating in subaquatic silence. The exuberance of the surrounding rainforest is filled with a cacophony of birds, from vibrant macaws to even the tiny hummingbirds.

On its margins, small indigenous communities lived in a very close relationship with the Juruá: fishing, transportation, and daily water come from the river, as does their traditional culture, which was in full accordance with the rhythms of the river. The Juruá is an important artery of trade and communication between these communities in one of the most remote regions.

2. What is the Flow of Juruá River?

The discharge is very irregular, controlled by the complex hydrological cycle of the Amazon. The discharge rises considerably during the rainy period from December to May. Heavy rainfall in the Andean headwaters and in its extensive catchment area makes the water level rise considerably. Powerful currents and swelling of the river during this time, often to several widths of the river during the dry season.

During the dry period, which is between June and November, the flow rate reduces. The width of the river reduces like the level in depth. However, it still sustains a reasonable flow because of the base flow from the groundwater sources and smaller tributaries. The flow rate also varies based on the average at every point along the river. In the reaches near the source, in the Andes, it can be relatively fast because of the higher gradient, but approaching the Amazon River and entering the flatter regions of the floodplain, it slows its flow.

3. How to Measure Water Current of the Juruá River?

There are more ways to measure the water current of the Juruá River.

Traditional Methods

Float Method: One of the traditional ways to approximate water current is by using floats. A buoyant object-a block of wood or a plastic bottle-is dropped into the river. Based on the time taken while the float travels the known distance, an approximation of the surface current speed is derived. This way of determining current speed doubtless has its drawbacks. Wind, waves, and the float shape all can introduce errors, and it gives information only about the surface current and not the current at different depths of the ocean. 

Current Meters: Mechanical or electronic current meters can be used to measure the speed of the water at a given point. These current meters are placed at certain depths under water and record the speed of the water that flows through them. They are more accurate at that one point in the water column than is the float method but are restricted to just that one depth and do not provide a true picture of the current profile throughout the water column.

Advanced Method - Acoustic Doppler Current Profiler (ADCP),The ADCPs are more advanced and efficient in measuring the water current of the Juruá River.

3.1 How Do ADCPs Using the Doppler Principle Work?

ADCP current meter is based on the principle known as the Doppler effect. A device emits an acoustic pulse into the water. The pulses interact with the suspended particles and other substances in the water, like sediment, plankton, and small debris. Because the water is in motion, the frequency of the reflected acoustic signals begins to shift. This frequency shift is measured by the ADCP doppler and processed with the Doppler formula to compute the velocity of water at various depths. The ADCP flow meter can create an extremely detailed profile of the current throughout the water column by transmitting pulses in more than one direction and at several different frequencies. This provides a much more complete view of the current structure of the river than traditional methods that measure at only the surface or a single point in the water column.

3.2 What is required for high -quality measurement of currents of Juruá river?

The equipment has to be very reliable; only then can the measurement of the currents of the Juruá river be of good quality. There is high humidity, large rainfall events, and possibly floating debris, since it is an area within the Amazon rainforest. The measuring devices installed will have to maintain their performance accordingly. 

It should also be compact and lightweight. That would be important to ensure ease of deployment, especially for the remote areas along the river that are accessible only by boat or on foot through the rainforest. Low power consumption is desirable to ensure equipment can operate for an extended period without the frequent change of batteries or other external power sources. Other essential aspects are cost-effective, particularly with large-scale or long-term measurements that are usually necessary to monitor the river dynamics. 

The casing of the ADCP meter is made from titanium alloy, which has a great advantage. The corrosion effect is quite minimal in the case of this titanium alloy, which is so essential in an area like the Juruá River, where water content is high. Other kinds of material will quickly be corroded by the water exposure, along with other different chemicals and sediments. The strength and toughness of the titanium alloy resist the physical forces exerted by the river current and possible impacts from floating logs or other debris. Because of its light weight, installation and transportation are easier, especially in places where access is poor.

3.3 How to Choose the Appropriate Equipment for Current Measurement? 

While selecting the equipment to measure current for Juruá River, certain specifics have to be kept in mind related to the measurement.

For Horizontal Measurements: Horizontal ADCP or HADCP is quite adequate for horizontal measurement across a section of the river. It can provide the current flow in a horizontal plane with a wide view, hence useful in understanding the general flow pattern of the river. This is of particular importance when studying water and sediment movement across the stream and the effects of current on navigation and nutrient distribution. 

For Vertical Profile Measurements: Vertical profile measurements of the current would be better with a vertical ADCP because it could provide more detailed information in respect of the velocity at each different depth of the water. This is important regarding the stratification and mixing of the water column, which in turn is important for understanding the distribution of oxygen, temperature, and other properties in the water and the behavior of aquatic organisms. 

Frequency Selection: For the relatively shallow reaches of the Juruá River, reaching up to approximately 70 meters, an ADCP profiler of 600 kHz can be used. The recommended depth, if it is greater and reaches about 110 meters, calls for a 300 kHz ADCP. That means the depth of the water profile and resolution required determine the frequency that will be selected.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option with good quality, the ChinaSonar PandaADCP is a great choice. It is made of all - titanium alloy, providing durability and resistance to the Juruá River'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.