ADCP Applied to the Japurá River (Caquetá) - Flood Management

1. Where is the Japurá (Caquetá) River?

The Japurá, in the Amazon rainforest area of South America, belongs to the biggest tributary rivers of the Amazon River. The source of this river originates in the Andes mountain range in Colombia.

It flows through a vast area of dense rainforest, through parts of Colombia and Brazil. The climate is tropical, with high humidity and abundant rainfall throughout the year. The continuous rainfall and runoff from the surrounding forest and its tributaries sustain the water level of this river.

2. Why does the flooding take place in the Japurá (Caquetá) River?

In fact, there are several factors contributing to flooding in the Japurá (Caquetá) River. Among them, the most dominant is the heavy and sustained rainfall. With its tropical climate, heavy rainstorms are expected in this region. In addition to that, large catchments and numerous tributaries bring a colossal amount of water during the rainfall events.

Another factor is the flat topography of the Amazon basin. The river runs over areas that have a very gentle slope. This easily spreads when the volume of water increases. The presence of extensive wetlands and floodplains along the river also contributes to the inundation during high - water periods.

Deforestation in the catchment of the river can also fuel flooding. With the takedown of trees, less water can be absorbed in the soil. This brings more runoff on the surface with an increased amount of water, thus possibly causing more flood incidents in the river.

In this regard, the Acoustic Doppler Current Profiler (ADCP) offers a more sophisticated and efficient measurement technique than traditional methods, which is crucial for effective flood management.

3. How do ADCPs using the Doppler principle work?

ADCPs operate based on the Doppler effect. They emit acoustic pulses into the water. These pulses interact with moving particles in the water, such as sediment, plankton, and other small organisms. When the acoustic waves bounce back after hitting these moving entities, a frequency shift occurs.

This frequency shift is directly related to the velocity of the moving objects and, by extension, the velocity of the water. For instance, an ADCP current meter placed in the Japurá (Caquetá) River, perhaps on a boat or a fixed structure near the riverbank, sends out sound waves that penetrate the water column. While the waves are reflected back by the flowing water and its constituents, the ADCP flow meter analyzes the received signals to calculate the speed and direction of the water flow at different depths.

4. What are the uses of ADCP in floods of the Japurá (Caquetá) River?

Flow velocity measurement: The ADCP profiler will be able to measure the velocity of water flow in the Japurá (Caquetá) River with great accuracy. During flood events, this is highly valuable information as it shows how fast the floodwaters are moving. It helps in predicting the spread of the flood and identification of areas where high-velocity flows may cause erosion or other damage.

Flow rate measurement: Flow rates can be calculated using the measured velocities in combination with the cross-sectional area of the river, which also can be determined by using an ADCP flow meter. In terms of a flood, for example, knowing the flow rate is important in quantifying the amount of water that is passing through that particular section and what is predicted to happen downstream.

Sediment transport research: ADCP current meter is able to detect the movement of sediment particles with the flow of water. In cases of flooding, this gives important information on the amount of sediment carried by the river. Understanding sediment transport helps in predicting changes in the riverbed, such as areas of sediment deposition or erosion, which can affect the stability of the river and its infrastructure.

5. How can the data measured by ADCP be utilized for flood warning and risk management of the Japurá (Caquetá) River?

Flood warning

Flow velocity and flow rate data monitoring: With the ADCP current profiler, continuous monitoring of flow velocities and flow rates allows for early detection of abnormal changes that may signal an imminent flood. If the velocities or flow rates increase beyond normal levels, an alert can be triggered to allow timely warnings to the communities along the riverbanks.

Water level prediction and warning: By understanding the relationship between flow rates, velocities, and water levels from historical data and ADCP measurements, future water levels can be predicted. This information is crucial in giving correct warnings to residents to take necessary precautions such as evacuation or flood proofing.

Risk management

Water Conservancy Project Scheduling Decision-Support: ADCP data is useful in making decisions on the operation of dams, reservoirs, and other water conservancy projects along the Japurá (Caquetá) River. For example, in the event of a predicted flood, the releasing of water from reservoirs can be adjusted according to the ADCP-measured data to mitigate downstream flooding and maintain the safety of the structures.

Flood disaster assessment and emergency response: Immediately after a flood event, ADCP data can be used to assess the extent of damage, including erosion, changes in the riverbed, and the impact on infrastructure. This information guides emergency response efforts and helps in formulating future flood mitigation strategies.

6. What's needed for high-quality measurement of the Japurá (Caquetá) River currents?

The equipment for high-quality measurement of currents in the Japurá (Caquetá) River should be made with reliable materials. Compact size and light weight are advantageous for easy deployment at any location in the river, on boats, or bridges. Low power consumption is necessary for long-term monitoring, especially in areas where power supply is limited. Cost-effectiveness is also important to enable extensive deployment for comprehensive monitoring.

The casing of ADCP flow meter will be made of titanium alloy preferably. Titanium alloy has excellent resistance to corrosion, which may be required for the waters of the Japurá (Caquetá) River, laced with various minerals and salts. The strength-to-weight ratio of this material is also quite good, which provides strength to this equipment and makes it moderately easy to handle and install.

7. How to choose the right equipment for current measurement?

When choosing equipment for current measurement in the Japurá (Caquetá) River, consider the following. For horizontal cross-section measurements, a Horizontal ADCP (HADCP) is suitable. It measures the flow velocities across a horizontal plane, providing a clear understanding of the overall flow pattern in a particular reach of the river. A Vertical ADCP shall be the one of choice, as it profiles the velocities along a vertical line from the water surface to the riverbed for vertical cross-section measurements.

For frequencies, the 600 kHz frequency suits water with a depth of around 70m. And for sections of deeper reaches, 300 kHz would be an appropriate option to cover around 110 m depth of water.

There are well-known ADCP profiler brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option, the China Sonar PandaADCP is recommended. It is made of all - titanium alloy materials and offers a good cost - performance ratio. You can find more information at (https://china-sonar.com/).

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