How to measure the Putumayo River water current?

1. Where does the Putumayo River come from?

The Putumayo River is a highly impressive water course through the heart of South America. Originating in the Andes Mountains of south Colombia, it then travels along a winding path through rain forests so fluffy and diversified in landscapes.

It forms, for quite a length, the natural border between Colombia and Peru as it flows southward, then penetrates Brazil, sharing in the rich tapestry of the Amazon River basin. On its banks are numerous small indigenous communities with a deeply traditional relationship to the river. These communities are dependent on the Putumayo River for daily livelihood through fishing, transport, and a source of water for drinking and other household purposes.

The river is equally a haven for an unbelievable array of biodiversity. Its waters range from carrying uncountable fish species, many being unique to the region, to carrying an immense variety of plant and animal life in the surrounding rainforests, nourished by its moisture. From colorful birds flitting among the trees to elusive mammals lurking in the undergrowth, the Putumayo River and its environs form a very important part of the Amazonian ecosystem.

Besides, the Putumayo River has participated in history and cultural interchange through the regions it travels. It has witnessed, during centuries, the transit of explorers, merchants, and distinct ethnicities and carries really rich stories and traditions.

2. How does the Flow Rate of the Putumayo River work?

The Putumayo River has significant features for the characteristic of its flow. Its flow rate is greatly controlled by the seasonal rainfall in the Amazon region.

In the wet season, the flow is high, and covers the period from December to May. Heavy rains in the Andes Mountains and over the large catchment area bring great volumes of water into the Putumayo River. This results in a very high flow rate wherein the river swells and at times even overflows its banks at lower-lying areas. Such increases in flow are crucial for recharging the volume of the river, maintaining further downstream ecosystems healthy, and transporting sediments that help in enriching the floodplains.

On the contrary, flow rates decrease during the dry season of the year, which begins from June to November. The flow rate is still sustainable enough to sustain many activities and organisms depending on the river. This averages from a few thousand cubic meters per second in the peak of the wet season to several hundred cubic meters per second during the drier months.

It is also the case that the volume of water carried by the Putumayo River affects navigation along the course of this river. During periods of high flow, larger boats can move with greater ease on the river and hence this eases trade and transportation of people and goods between communities and regions that the river connects.

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

The water current of the Putumayo River can be measured using a variety of methods: one method that involves the use of a velocity meter for measuring river current.

Velocity Meter Method

This traditional technique utilizes mechanical or electrical velocity meters. These are located at certain points of the stream to directly measure the velocity of water at those points. This, however requires great caution in placement and also several measurements at various depths and positions to make an estimation of the overall current of water. Given the length and, in most cases, scarcely accessible position the Putumayo River traverses, this technique is generally cumbersome and tedious to cover a significant percentage of the river.

Acoustic Doppler Velocity Profiler Method

The Acoustic Doppler Current Profiler (ADCP) is a more advanced and user-friendly instrument utilized in the measurement of water currents, where sound waves are transmitted to measure water particle movement. It can measure water velocity simultaneously at numerous depths by transmitting an acoustic signal and determining the Doppler shift in the reflected signals. This gives an extremely detailed profile of the water current, allowing a more accurate determination of the flow conditions along the river. The ADCP instruments could be mounted on boats traveling down the river and taking the measurements. They can also be deployed on bridges or attached to buoys for continuous monitoring.

Buoy Method 

In the buoy method, buoys are placed into the river that would carry sensors measuring the movement of the water around them. Floating on the surface of the water, buoys can give an indication about the current at the surface, although generally they are less likely to capture in detail the complexity of the water current compared to other methods, at least in relation to the variations of velocity at greater depth.

Of all the available means, however, acoustic doppler flow meter stands out as a more advanced and efficient one in carrying out measurements of water current in the Putumayo River.

4. How do ADCPs Based on the Doppler Principle Work?

The ADCP current profiler work on the Doppler principle. When an ADCP current meter sends out an acoustic signal into the water, the sound waves travel through the water and interact with the moving particles of water. Since the water particles are in motion, due to the Doppler effect, there is a shift in frequency of the reflected sound waves.

If the water particles are moving towards the ADCP flow meter, the reflected wave frequency is higher than the emitted one. In contrast, if the water particles are moving away from the ADCP profiler, the reflected wave frequency is lower. Precisely measuring this shift in frequency allows the ADCP to measure the velocity of the water particles at different depths.

Then, it integrates these discrete velocity measurements at different depths into a continuous profile of the water current. It will be hugely crucial for describing in fine detail the actual flow of the water and not just on the surface along the vertical section of the river.

5. What is Required for Quality Measurement of the Putumayo River Currents?

A number of factors regarding the equipment are fundamental for high-quality measurement of the currents of the Putumayo River.

It shall possess high material reliability first, which should be resistant to the aggressive conditions of a fluvial environment, since it will constantly be exposed to water, sediment, and temperature changes. The Putumayo River has a very high and very low level of water; during rainy seasons, much debris flows with it, compromising the durability of the measuring equipment.

Desired system characteristics in this respect are a small size, light weight, and low power consumption. A compact and lightweight piece of equipment is easier to manipulate and deploy both on a boat and buoy. Low power consumption means that the equipment can work for really long time without frequent battery replacements or reaching a continuous source of power, which may be important in the far areas along the river.

Another important criterion is cost. The cheaper the measurement device, the wider the range it can be put on for monitoring the river, and the more area it can cover.

Concerning the casing of the ADCP meter, the incorporation of the titanium alloy is an excellent choice. Titanium alloy carries many advantages. The material will be highly resistant to corrosion, an important factor when working with water bodies such as that of the Putumayo River, where equipment will always be in contact with water and probably corrosive agents. It shall also be heavy, durable, and resistant to physical impacts and changes in pressure that may take place during its deployment and operation. Additionally, titanium alloy has relatively low density, and that would help keep the overall equipment light.

6. How to Choose the Right Equipment for Current Measurement?

Various factors have to be considered while choosing the appropriate equipment for measuring the current of the Putumayo River.

Based on Use Purpose

When the intention is to measure the horizontal cross-section of the river current, one should use a horizontal ADCP or HADCP. For HADCPs, designs are intended for the accurate measurement of the flow of water in the horizontal plane, useful for deducing the overall movement of water across a certain section of the river.

If the purpose is to measure the vertical cross-section of the river current, then a vertical ADCP is what should be utilized. A vertical ADCP will provide a very accurate measurement of water velocity at different depths and hence will give a very detailed profile of how water flows vertically in the river.

Based on the Frequency

The choice of frequency also depends on the depth of water in the Putumayo River. Up to 70 meters of water depth, a 600 kHz ADCP is usually an option that would be suitable. A frequency of 600 kHz provides good resolution and accuracy within the water current in relatively shallower waters.

For deeper waters, for instance, above 70 meters up to about 110 meters, a 300 kHz. ADCP would be more suitable. The frequency travels deeper into the water with a lower speed of 300 kHz while still yielding reliable measurement results about the water current.

The brands known in the market for an ADCP are few. Some of these are Teledyne RDI, Nortek, and Sontek. However, with price consideration but not compromising quality, a better option would be the China Sonar PandaADCP. The all-titanium alloy material could guarantee good durability and reliability. Its great cost-performance ratio may offer an excellent alternative in water current measurement for the Putumayo River. You can get more details from its official website: https://china-sonar.com/.

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