ADCP in The Tambo River Flood Management

1. Location and Course

Tambo River flows in the South American continent, with most of its part running across Peru. High in altitude when it flows from its source, it gradually reaches more level plains as it journeys downstream.

It originates from the Andes Mountains, winds through valleys, and covers plateaus. Further into its course, it passes through topographically and highly dissected elevation areas. The river course could also be influenced by the local geology and soil types, which in turn could alter the flow of the river and the bank formation process.

2. Climate and Rainfall

The broad range of elevations around the Tambo River creates a varied climate, cooler in the upper areas closer to the Andes, with more pronounced wet and dry seasons. Most of the rain that feeds the volume of the river falls during the wet season.

The climate there may be more arid or semi-arid in the lower-lying areas, but it nonetheless often receives water from the upper parts of the river. In general, the pattern of rainfall and snowmelt in the higher elevations dictates the flow in the river. Changing rain and temperature can alter the water level. Flooding can occur during very heavy rainfall or when snow melts at a faster rate.

Causes of Flooding

Heavy Rainfall and Snowmelt: Heavy rainfall in the upper catchments during the wet season and the resultant rapid melting of snow may introduce volumes of water that are inordinately large into the river. This can be more than what Tambo River is designed for, with resultant flooding further downstream. The mountainous nature of the terrain accelerates runoff to funnel water quickly into the river channel. 

Topography: Low-lying areas and floodplains along the course of the river allow water to spill over and collect. Generally flat plains reduce the speed of the water, which increases the possibility of flooding. Also, at higher flows, the tributaries entering into the Tambo River can introduce extra water, adding to the flood problem.

Human - Induced Changes: Deforestation in the catchment area may reduce the capacity of a forest to intercept and retain rainwater. It leads to soil erosion and the eroded soil is then deposited in the river, hence reducing its carrying capacity. In this respect, agriculture and urban development are two human-induced changes which disrupt the natural drainage and water flow and thus further increase the flood risk.

4. Role of ADCP (Acoustic Doppler Current Profiler)

Yet, they should be considered key devices to understand and manage the Tambo River flow during the flooding stage.

How ADCPs Work

The operational principle of Acoustic Doppler Current Profilers (ADCPs) is based on the Doppler principle. There is transmission of an acoustic signal into the water. Because of the flow of water, the signal experiences moving water particles. The reflected acoustic signal, after interaction with the moving particles, is received with a frequency change according to the Doppler effect back at the ADCP doppler.

The ADCP flow meter detects a Doppler shift between the frequency of the emitted signal and that of the received signal. By analyzing this frequency shift, it can deduce the velocity of water at each depth. Typically, the devices carry several transducers that can emit and receive acoustic signals in many directions. From these, they are able to profile the water velocity over a cross-section of a river.

For instance, if the water is moving towards the ADCP profiler, then the returning signal frequency is higher than that of the emitted one. This, in turn, would mean that when the water is moving away from the ADCP current profiler, it returns a signal with a frequency lower than the one that had been emitted. By precisely measuring such frequency changes and with appropriate mathematical algorithms, the ADCP doppler can deduce the velocity of the water at various points of its measurement range with great accuracy.

Applications of the ADCP in the Tambo River

Velocity Measurement: During the event, which is the flood, of the Tambo River, the velocity should be measured with the best possible proximity to accuracy. ADCPs can continuously observe the water flow at various depths and locations, hence providing real current-time data concerning the speed at which the water moves. This then becomes quite vital in understanding the nature of the flood, like the direction and intensity of the movement of floodwaters.

Flow measurement: ADCPs are also capable of carrying out the flow rate measurement of the Tambo River. With a known cross-sectional area of the river, it will be able to compute the total volume of water passing through the section per unit time by collating the measured water velocities across different points in the section. This is vital information for the understanding of a flood's volume and making effective decisions on the control of the flood and management of water resources.

Sediment Transport Research: Aside from flow and velocity measurement, ADCPs are helpful in sediment transport research during floods. Simultaneous with the flowing of water, it carries sediments. These sediments alter the backscattered acoustic signal in the ADCP flow meter. By using these changes, the quantity and motion of the sediments can be estimated by the researcher, something very important for understanding the long-term evolution of the bed, and the effect of the flood on the river's sedimentary environment.

5. Use of ADCP Data for the Purpose of Flood Warning and Risk Management

Flood Warning

Velocity and Flow Data Monitoring: The real-time data of velocity and flow derived from ADCPs is continuously monitored. When the water velocity measured exceeds a threshold value or the flow rate increases considerably, it may indicate the arrival of flood peak or possibility of flood. This allows the necessary authorities to take early measures to evacuate people in low-lying areas or increase the flood defenses.

Water Level Forecasting: Measured flow data is correlated with historical data on water levels, and appropriate hydrological models can be used on ADCP data to predict future water levels. In case the predicted water level is above the flood warning level, timely warnings can be issued to the public to get ready for the flood.

Risk Management

Water Conservancy Project Decisions: The accurate flow and velocity data provided by ADCPs enable decisions to be made regarding the operation of the water conservancy projects such as dams and sluice gates. For example, in terms of the measured water flow, a decision could be taken on how much more or less water should be released from the dam in order to control the Tambo River's water level and minimize the impact of flood.

Assessment of Flood Disaster: ADCPs collect data on the severity of the flood after an event. This would cover information such as the extent of the inundation, the velocity of floodwaters, and the quantum of sediment deposition. This type of information is crucial to formulate emergency response plans and undertake post-flood reconstruction and rehabilitation work.

6. Requirements for High - Quality Current Measurement

Reliable Equipment Materials: The materials for equipment, especially the ADCP meter casing, must be of superior material to ensure high measurement quality of the Tambo River currents. Given the quality of the water and possible debris inside the river, durable and corrosion-resistant material such as a titanium alloy is preferred. Titanium alloy has high strength to resist the high pressure and impact from the water flow.

Appropriate Size and Weight: Size and weight of the equipment small and light to facilitate easy installation and operation of the ADCP flow meter at various sites along the river, where site inaccessibility may pose a problem. LOW POWER CONSUMPTION: This has the advantage of longer continuous operation without needing frequent replacements of batteries or connections to a power source.

Affordability: It should be affordable enough to permit extensive measurements. The lesser the cost, the more ADCPs will be installed along the Tambo River and hence provide more comprehensive and detailed data for flood management.

7. Selecting Appropriate Equipment for Current Measurement

Horizontal ADCP or Vertical ADCP: Type of Measurement: When the type of measurement required is horizontal cross-section, HADCP needs to be chosen. When the measurement of vertical cross-section is required, Vertical ADCP will result in an appropriate choice.

Consideration of Water Depth: Different frequencies suit different water depths. A 600 kHz ADCP is suitable for water depths within 70 m. If the Tambo River has water to this depth, and if the measurement requirements are in line with the requirement, one can consider a 600 kHz ADCP. In deeper waters, say over 70 m up to 110 m, a 300 kHz ADCP is best for the betterment of measurement accuracy.

Some of the well-recognized ADCP doppler brands in the market are Teledyne RDI, Nortek, and Sontek. Those who might be on the lookout for an even affordable alternative will find China Sonar PandaADCP ideal. The material used in its build-up is an all-titanium alloy that guarantees its strength and dependability in the aquatic environment. Most importantly, it offers an incredibly good value for the price. You can learn more about it on its website: (https://china-sonar.com/).

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