ADCP in Mantaro River Flood Management

1. Location of Mantaro River

The Mantaro River is located in Peru and also flows through the central part of the country. The source of the river is in the Andes Mountains, from where it passes through various kinds of topography.

It passes through the high altitude of the Andes mountain range; its course, for the most part, lies in mountainous valleys and gorges. As it moves further downstream, it pours into most beautiful wide plains and valleys. As such, it serves several cities and towns along its route, giving a clear supply of water for domestic use, irrigation, and industrial activities in these areas.

The areas of Mantaro River present an intricate climate regarding weather and rain due to the changes in elevation. The upper reaches are much colder since it lies in the Andes, where precipitation takes the form of snow during winter months. In spring and summer, there is much contribution to the water volume through the melting of snow. In the lower areas, the climate can be considered more temperate; there is a differentiated wet and dry season, with high rainfall during the former, usually from November to March. As a result of the snowmelt and rainfall, the variation in the level of water in the river often produces a predisposition to flooding, either by too much rain or from rapid melting of snow.

2. Por qu é causa inundaciones el río Mantaro?

Heavy Rainfall and Snowmelt: Heavy rainfall throughout the wet season and intense snowmelting in the upper catchments of Andes are the main factors causing the floods. These two sources release heavy volumes of water, rapidly raising the volume of the river. Runoff in this mountainous upper part is quick, quickly concentrating a huge amount of water downstream in a very short time.

Relief: There are floodplains and low-level areas along the course of the river, which are able to accommodate water to spread and collect. The generally flat plains slow down the movement of water, hence increasing the possibility of flooding. Secondly, junctions where other tributaries join may add more water when experiencing high flow, aggravating the flood situation.

Human activities include: Deforestation in the catchment area reduces the interception and retention capability of the forest cover. Increased soil erosion due to deforestation results in the deposition of eroded soil, besides other sediments, in the river that reduced its carrying capacity. Agricultural and urban expansion alteration of the natural flow and drainage pattern of water, hence increasing the flood risks.

In this regard, ADCP doppler has proved more advanced and handy in measurement for understanding and managing the flow of the river during these flood events.

3. How do Doppler principle-based ADCPs work?

Principle of Doppler is the basis on which ADCPs work. The device sends an acoustic signal out into the water. Since water is flowing, this signal interacts with the moving particles of water. As the acoustic signal is reflected back to the ADCP current profiler, because of the Doppler effect, the frequency of the reflected signal changes.

The ADCP measures the frequency difference between the emitted signal and the received one. With this frequency shift, it calculates the water velocity at different depths by means of analysis. These devices normally have a variable number of transducers, capable of emitting and receiving acoustic signals in different directions. By doing so, they can provide a profile of the water velocity across a section of the river.

For example, in the case when water is moving towards the ADCP flow meter, the frequency of the reflected signal back will be higher than that of the emitted one. In contrast, when the water moves away from the ADCP, the reflected signal frequency is lower. Precise measurement of such frequency changes and further processing by using the appropriate mathematical algorithms enables the ADCP current profiler to correctly determine the velocity of water at different points in its measurement range.

4. What are the Mantaro River flood applications of ADCP?

The speed measurement

During flood events in the Mantaro River, Acoustic Doppler Current Profiler (ADCP)  is crucial for accurately measuring the velocity of the water flow. By continuously monitoring the water velocity at different depths and locations, it provides real-time data on how fast the water is moving. This information is essential for understanding the dynamics of the flood, such as predicting the direction and intensity of the floodwaters' movement.

Flow Measurement Application

It can also measure the flow rate of Mantaro River. Measured water velocities across a section combined with the known cross-sectional area of the river allow ADCP meter to calculate the total volume of water flowing through the section per unit time, by which it arrives at the flow rate. This information is crucial to estimate the general volume of water in the case of flooding, besides creating flood control or regulating decisions about water resources.

Application in Sediment Transport Research

Besides flow and velocity measurement, ADCP flow meter may also be useful for sediment transport research on Mantaro River during flooding. When the water flows, it carries sediments. The ADCP meter can detect changes in the backscattered acoustic signal due to the presence of sediments. From these changes, an estimate of the amount and movement of sediment can be obtained by researchers. This is important within the framework of long-term evolution of the river bed and what changes floods have upon this river's sedimentary environment.

5. How is the data measured by the ADCP to be used for the implementation of flood warning and risk management of Mantaro River?

Flood Warning

Velocity and Flow Data Monitoring: The real-time velocity and flow data obtained by ADCP profiler are monitored. When the water velocity that is measured is more than the limiting value, or the flow rate increases obviously, this situation can be regarded as a harbinger of flood peaks or flooding. Thus, an early warning can be issued to enable the relevant departments to prepare accordingly, including the evacuation of people in low-lying areas and the reinforcing of flood defenses.

Water Level Prediction and Warning: Measured flow data correlated with historical data of water level and appropriate hydrological models can serve to predict future water levels. If the forecasted predicted water level is to rise above the flood warning level, timely warnings can be issued to the public in order to get ready for the flood.

Risk Management

Water Conservancy Project Scheduling Decision Support: Precise flow and velocity data from ADCP current profiler can support decisions related to the operation of water conservancy projects like dams and sluices. For example, based on the measured water flow, the release of water in a dam can be adjusted with the aim of regulating the level of water in the Mantaro River, therefore delaying the effect of flooding.

Flood Disaster Assessment and Emergency Response: The ADCP data after the flood will come in handy for assessment of the magnitude of flood regarding the extent of inundation, the velocity generated by the floodwaters, and the quantity of sediment deposition. This information is very valuable for formulating emergency response plans and undertaking post-flood reconstruction and rehabilitation work.

6. What does high-quality measurement of Mantaro River currents require?

Several things are required to carry out high-quality measurements of Mantaro River currents. First, the equipment should have good materials. First is the casing of the ADCP flow meter. It should be made from a titanium alloy. For the purpose of this work, several advantages have been identified with the use of a titanium alloy. It has high strength, enabling the equipment to resist pressure and impact in water flow in a river. The material applied is highly resistant to corrosion, which is important due to the water environment of Mantaro River that may contain various corrosive materials.

As well as the material's reliability, the size and weight of the equipment should be as small and light as possible. This allows for easier installation and operation of the ADCP profiler in various locations along the river, even in more inaccessible regions. Low power consumption is also important to realize longer operation without battery exchange or frequent connections to a power source. Furthermore, the equipment cost should not be too high to enable large-scale measurement. A lower cost will allow more ADCPs to be installed along Mantaro River with less expenditure and provide more comprehensive and detailed data related to flood management.

7. How to choose the right equipment when measuring currents?

In the process of selecting appropriate equipment for current measurement in the Mantaro River, various aspects should be put into consideration. First, if the type of measurement required is horizontal cross-section measurement, then a Horizontal ADCP (HADCP) should be selected, and for vertical cross-section measurement, a Vertical ADCP will be appropriate.

Second, different frequencies are suitable for different water depths. For example, a 600 kHz ADCP shall be appropriate in water depths within 70 m. If the Mantaro River depth in the area of measurement is within this range and in case of a match with the requirements, then a 600 kHz ADCP will be considered. For deeper waters, exceeding 70 m up to 110 m, a 300 kHz ADCP shall be more appropriate to provide an exact measurement for such depths.

A few of the renowned brands for ADCP flow meter on the market are Teledyne RDI, Nortek, and Sontek. However, at an effective cost, the China Sonar PandaADCP will serve the purpose. The all-titanium alloy material ensures its strength and reliability in a watery environment. Besides, it has an extraordinary cost-to-performance ratio. You may find more information about it on its website at : (https://china-sonar.com/).

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