How to Measure Water Current of the Japurá river?

1. Where is the Japurá?

The Japurá River is a very special watercourse in South America. It constitutes one of the main affluents of the Amazon River, its course running through the heart of the Amazon rainforest. Originating in the Andes, it meanders through a wide, richly green expansiveness of the Amazon basin.

It is a natural wonder that carves its way through Colombia and Brazil. Along its path, small indigenous communities have settled, their lives thoroughly entwined in this river. These small communities are so rich in culture, having their own languages, traditions, ways of life passed from generation to generation.

The Japurá River forms part of the important transport route in almost a completely roadless region. Canoes and small boats travel across its water, moving people and goods between settlements that otherwise would be impossible to reach. The surrounding rainforest is home to an incredible variety of wildlife, from the spectrum of colorful macaws and toucans flying overhead through the canopy to the pink river dolphins swimming effortlessly in its waters, Japurá is a true hotbed of biodiversity. The fringe of the river is graced with dense growth consisting of giant trees, vines, and hosts of plant life forming part of the complex global web of ecosystems.

2. What is the Flow Rate of the Japurá River like?

The Japurá River is important both for the ecosystem in the Amazon and for all the communities that depend on it; it serves as an enormous channel for transporting water, nutrients, and sediments that maintain the great Amazon floodplain.

The discharge of the Japurá is quite irregular since the flow rate depends greatly on the complex hydrological cycle of the Amazon. In this rainy season, stretching between December and May, it is during this period that the river receives its above-average flow. Heavy rainfall within the catchment area makes the water level rise while the current becomes powerful. The river can swell to several widths of itself during the dry season, flooding expansive sections of the floodplain and creating a strange wetland ecosystem.

During the dry season, June to November, it decreases. The width of the river narrows while the level of the water goes down, though it still flows considerably due to base flow supplied by groundwater sources and minor tributaries. The average flow rate fluctuates according to the reach of the river. It has a larger gradient near its source in the Andes, thus the flow is considerably fast in the upper reaches. While coming near the Amazon River, it becomes slow when it enters into the flatter regions of floodplain.

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

There are some ways to measure water current of Japurá River.

Traditional Methods

Float method

A traditional and easy way to estimate the current of the water is to use a float. Some buoyant object-piece of wood or plastic bottle-is thrown into the river. If one can observe the time taken by the float to travel some known distance, an approximation of the surface current speed can be obtained. This does have some restrictions in this method. Wind, waves, and the float configuration can all lead to errors, and it gives information only on the surface current, not about the current at any given depth.

Current Meters

These may be either mechanical or electronic current meters. They measure the rate of flow of water at any particular point. The meters are dropped into the water at a particular depth and record the speed of water moving past them. The result can be more accurate than that from the float method at a single point in the water column. However, they are limited to this very local depth without giving any idea on the current profile at any other depth in the entire water column.

Advanced Method - Acoustic Doppler Current Profilers (ADCPs)

ADCPS are one of the advanced ways to measure the water current of the Japurá River.

3.1 How do ADCPs based on the principle of the Doppler work?

Acoustic Doppler Current Profiler(ADCP) utilize the principle of the Doppler effect. This instrument sends pulses of acoustic signals into the water. These pulses interact with particles suspended in the water and other substances such as sediment, plankton, and small debris. Due to the movement of water, the frequency of the reflected acoustic signals would change. This frequency shift is measured by the ADCP flow meter, and from this, using the Doppler formula, the estimate of the velocity of the water at various depths is extracted. An ADCP profile of the current of water throughout the water column is achieved through pulses emitted in several directions and at multiple frequencies. It provides far more substantial information of the river's current structure than the methods usually employed, which normally operate either from the surface or within a single point of the water column.

3.2 What is needed for high-quality measurement of the Japurá river currents?

To provide high-resolution measurements of the Japurá river currents, the equipment used needs to be highly reliable. Considering the Amazon rainforest environment, with its high humidity, heavy rainfall, and the hazards of floating debris that may cause possible damage, the measuring devices need to be resistant to these aspects. 

On the other hand, it should also be compact and light enough. That's important in the deployment process in special sites along the river that might only be reachable by canoeing or on foot via the rainforest. Besides, the low consumption allows equipment to operate without regular changes of batteries or external power sources. Other relevant aspects concern cost-effectiveness, mainly for large-scale or longtime measurement for monitoring the dynamics of the river. 

Another positive feature is related to the possibility of manufacturing the casing of ADCP current profiler with a titanium alloy. The principal property of this metal is that it provides very high resistance to corrosion; this is a very important factor when the environment, as in the case of the Japurá River, is full of water. The continuous attack of water, together with the other chemicals and sediments contained in it, serves as an agent of fast corrosion among other metals. The strength-to-weight ratio makes titanium alloy strong enough to resist the physical power of a river current and possible impact from logs or other floating objects. Its light weight gives more convenience for installation and transportation in general, and in particular, in those places where accessibility is poor.

3.3 How to Choose the right equipment for current measurement?

When choosing equipment for measuring the current of the Japurá River, one has to refer to the particularities of the measurement.

To make horizontal measurements

Horizontal measurements through a section can be made by using an HADCP. It provides a broad view of the current flow in a horizontal plane for an overall view of the flow pattern of the river. This becomes of critical relevance in assessing sediment and water movements across the river, the effects of currents on navigation, or the way currents distribute nutrients. 

Vertical ADCP

For vertical profile measurements, the current is better measured using a vertical ADCP. It also provides information about the detailed velocity of the water at different depths, important for studying the stratification and mixing of the water column. This aspect is very important when it comes to mapping out the oxygen distribution, temperature, and other properties of water, apart from providing insight into the behavior of aquatic organisms.

 Frequency Selection

Talking of frequency selection, for shallow stretches of the Japurá not exceeding 70 meters, a 600 kHz ADCP will be the best choice. In those much deeper stretches, reaching to about 110 meters, an ADCP of 300 kHz is what is required. The selection of frequency, therefore, is to be guided by how deep the water and what resolution of the current profile is desired.

There are well - known ADCP current meter 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 Japurá 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.