ADCP's Application in Flood Management of the Guaviare River

1. Where is the Guaviare River?

In Colombia, the lengthiness of this river makes its ranking significant in the class category among all the rivers throughout the Amazon Basin. Passing along the huge and nearly natural region of the forest cover it follows a course that can result from rainstorms within the Colombian forest area.

It passes through some small indigenous communities and settlements. The Guaviare River basin, in terms of rainfall, is of a tropical climate that is characterized by high levels of rainfall throughout the year. The wet season especially sees heavy downpours that contribute to the river's high water volume. The river is an important source of water for the local communities in fishing, transportation, and also plays an important role in maintaining the ecological balance of the surrounding rainforest.

2. Why does the Guaviare River flood?

The main cause of the flooding in the Guaviare River is the heavy and unending rainfall from the tropical climate prevailing over its basin. When this reaches beyond the normal carrying capacity of the river, the water level immediately starts to rise.

The generally flat topography of the floodplain of the river is another cause for the flooding. The water can spread out easily over these low-lying areas. In addition, the deforestation in the upper reaches of the river basin, though efforts are being made to control it, may also have a part to play. It decreases the ability of the land to absorb water, increasing surface runoff and hence giving rise to higher volumes of water entering the river. Considering the complexity of these flood-causing factors and the management of the river's behavior during such events, Acoustic Doppler Current Profiler (ADCP) offers a more advanced and efficient means of measuring and understanding the flow of the river.

3. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They send acoustic signals into the water. Due to the interaction of these acoustic waves with the moving water particles, the frequency of the reflected waves changes because of the Doppler effect.

Multiple transducers are installed on an ADCP current meter, capable of sending and receiving acoustic signals in various directions. The velocity of the water flow at different depths and across different sections of the river cross-section can be determined by precisely measuring the frequency shift between the emitted and received signals. For instance, it is able to record flow velocities from the riverbed all the way up to the water surface, across different widths of the river in the Guaviare River, offering an all-inclusive understanding of the water movements within the river.

4. What are the uses of ADCP in floods of the Guaviare River?

Flow Velocity Measurement: With the ADCP profiler, there is the ability to get correct flow velocity of the Guaviare River in times of flood. This is essential in determining the speed at which water is moving through various parts of the river. Through good monitoring of flow velocity, one is able to identify those areas where the flow of water is increasing or decreasing, which may provide information on the development and possible consequences of the flooding. For example, changes in flow velocity can be closely monitored near the riverbanks or in the main channel.

Flow-rate Measurement Application: The flow rate can be determined by multiplying the measured flow velocity by the cross-sectional area of the river. For instance, in the case of flooding in the Guaviare River, this would be highly important in estimating the total amount of water passing through any particular section per unit of time. This helps in predicting the general magnitude of flood and its downstream effects, which is quite important for flood forecasting and preparedness.

Sediment-transport Research: Guaviare River carries an appreciable volume of sediment during a flood event. It is possible for ADCP meter to capture this motion of sediment particles based on the backscattered analysis of acoustic signals, and thus it enables one to study the sediment transport process that occurs in the flooding. This has implications regarding understanding of long-term changes to be expected on the bed, for the good health of the fluvial ecosystem.

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

Flood Warning Aspect

• Flow-Velocity and Flow-Rate Data Monitoring: The ADCP current profiler will, through continuous flow velocity and flow rate data, serve to trigger abnormal changes in flow patterns. If the flow velocity exceeds a given threshold value or the flow rate rises suddenly, then it should trigger an early flood warning. This can be provided to local government authorities, rapid action groups, and nearby communities along the riverbank.
• Water Level Prediction and Warning: The flow data acquired from ADCP can be integrated with other hydrological models for water level change prediction. More precise flood warnings could be given, especially in areas at risk of flooding along the Guaviare River, by analyzing the relation of flow rate and water level.

Risk Management Aspect

• Water Conservancy Project Dispatching Decision Support: The accurate flow data provided by ADCP is very important for the operation and decision-making in water conservancy projects such as dams and reservoirs on the Guaviare River. Decisions about water release or storage can be made more effectively to mitigate flood risks downstream.
• Flood-disaster Assessment and Emergency Response: After a flood occurs, the ADCP - measured data can be used to assess the extent and impact of the flood. This helps in formulating appropriate emergency response strategies, such as organizing rescue operations and conducting damage assessment surveys.

6. What’s needed for high-quality measurement of Guaviare River currents?

For high-quality measurement of the Guaviare River currents, several aspects regarding the measuring equipment are crucial. Firstly, the material of the equipment should be reliable. It needs to withstand the harsh aquatic environment of the Guaviare River, including potential corrosion from the water, impacts from floating debris, and the abrasive effects of sediment.

Smaller size and lighter weight are preferable since these features will make the installation and deployment of the equipment at many places along the river easier. The power consumption should be low to allow for continuous operations, especially in areas that may have limited or fluctuating power supplies. Economical viability is also paramount, given that large-scale deployment may be required to provide full coverage of the current monitoring in the river.

The casing of ADCP flow meter is made preferably of Titanium alloy. Titanium alloy shows excellent resistance to corrosion, which is essential for a long time, under the chemical and physical action of the Guaviare River water. It also features a good strength-to-weight ratio; hence, equipment is more durable and easily manipulated during installation and maintenance.

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

The equipment selection for current measurement at Guaviare River depends on the purpose of measurement. For horizontal cross-section measurement, a Horizontal ADCP is suitable to present the flow velocity in great detail across the width of a river. For vertical cross-section measurement, a Vertical ADCP is more suitable for the accurate measurement of the flow velocity distribution from the riverbed to the water surface.

According to the ADCP frequency, a 600kHz ADCP could work well in relatively shallow areas-for example, less than 70 meters-of water depth of the Guaviare River, while for the deepest parts of the river (approximately 110 meters), a 300kHz ADCP would be appropriate.

There are various ADCP brands available in the market, such as Teledyne RDI, Nortek, and Sontek. However, it is worth highlighting a recommended Chinese ADCP brand-China Sonar PandaADCP. It is made of all-titanium alloy material and provides excellent performance while offering an impressive cost-effectiveness ratio. You can visit its website (https://china-sonar.com/) for more information.

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