ADCP Application for Flood Management of Rocha River

1. Where is Rocha River?

The Rocha River would lie, in general, in areas that could have different topographic conditions. Assume to be located within the South American system, say in Uruguay. The said river courses through the Uruguayan countryside, carving its way through lands of agricultural significance and natural habitats.

Its basin has a temperate climate. It receives rainfall throughout the year, sometimes heavy or light depending on the season. The wet months result in an increase in the amount of water contributed to the river, causing a fluctuation in its water level. It may flow through small towns and villages supplying them with water and providing activities like fishing and small-scale transportation.

2. For what reasons does the flooding happen in the Rocha River?

Heavy Rainfall: This is the most common cause of flooding of the Rocha River. Where a river exceeds its drainage capacity, the water level rises over it. The water collected from the entire catchment area contributes a significant volume of water to the river. During heavy rainfall, if the feeding tributaries also bring in a large volume of water into the main channel, it cannot cope with it.

River Channel Capacity and Topography: The natural capacity of the Rocha River's channel to carry water plays a crucial role. In some areas, the river may have a relatively narrow or shallow channel. Additionally, the topography of the surrounding area can influence water flow. If there are flat or low - lying regions near the river, water can accumulate more easily, increasing the likelihood of flooding.

Land Use Changes: Human activities that lead to changes in land use, like deforestation or urban expansion, can also cause flooding. Deforestation decreases the absorptive capacity of the land, causing more surface runoff. Urbanization means more impervious surfaces-roads and buildings-so more water is funneled directly into the river, increasing its volume.

The Acoustic Doppler Current Profiler (ADCP) is of much value in flood management as it gives more accurate and efficient measurement of the flow characteristics of the river than customary methods.

3. How do ADCPs using the Doppler Principle Work?

ADCPs work on the principle of the Doppler effect. They send out acoustic signals-usually sound waves-into the water. These signals bounce off of moving particles in the water, such as sediment and water molecules that are flowing with the current. When such moving objects reflect back the emitted waves, it creates a shift in frequency.

This change of frequency, called Doppler shift, varies linearly with the velocity of the moving objects. ADCPs are fitted with several transducers which send out acoustic pulses in different directions. For instance, a downward-looking ADCP current meter is able to measure the velocity profile of the water column from the water surface down to the riverbed. This is done by analyzing the Doppler shifts of the reflected signals from the different depths within the water column to compute the velocity of the water flow at each depth.

With a known velocity at different depths, and armed with knowledge of the river's cross-sectional area, other important parameters such as the flow rate of the river can be determined.

4. What are the practical uses of ADCP during flood events in Rocha River?

Velocity Measurement: ADCP current profiler will be able to measure the velocity of water flow during floods in Rocha River at all locations and depths. This information will help in understanding the speed at which the floodwaters are moving. For instance, this helps in predicting the time floodwaters may reach settlements or agricultural fields. Continuously monitoring the velocity allows the authorities to take various precautions, including the evacuation of people or reinforcement of embankments.

Application in Flow Measurement: ADCP profiler also determines the flow rate of the river by integrating the velocity data over the cross-sectional area of the river. In the flood event, this amounts to determining the total volume of water passing through a section. This information is important to flood forecasting and understanding the magnitude of the flood. It can also be used to determine the extent of flood-control structures such as levees and dams.

Application of Sediment Transport Research: The sediment carried by the floodwaters of Rocha River can be analyzed by ADCP current profiler through the backscattered acoustic signals for the study of their movement. Sediment transport during floods bears relevance to assessing the variation in the riverbed topography due to erosion and deposition processes, which in turn, may alter the navigational characteristics of the river, flood-prone areas, and stability in the river ecosystem as a whole.

5. How does the data, which was measured by ADCP, help for flood warning and risk management of Rocha River?

Flood Warning

Velocity and Flow Data Monitoring: It enables ADCP profiler to continuously monitor the flow of the river to spot abnormal changes in its flow. If there is an extraordinary increase either in the velocity or the flow rate, then that would hint at an imminent flood or an intensifying flood situation. The obtained data can be fed into flood-warning systems for accurate and timely warning of the public and authorities concerned.

Water Level Prediction and Warning: In general, flow data obtained using ADCP meter can be combined with additional factors, such as the geometry of the river cross-section and historical records of water level, to predict the water level for the future. If it is seen that the predicted water level is going to exceed the flood stage, then warnings in advance could be issued for facilitating evacuation and other emergency measures.

Risk Management

Decision Support to Water Conservancy Project Scheduling: The ADCP data is of importance in decision-making processes in the operation of Water-conservancy Projects such as dams and reservoirs along the Rocha River. In the case of a flood, for instance, this flow information would help in determining at what rate the discharge should be from a dam, which will reduce the downstream impact of the flood.

Flood Disaster Assessment and Emergency Response: Based on the ADCP flow meter post-flood, the damage caused by the flood can be assessed in terms of areas affected by high-velocity flows, the amount of sediment deposition, among others. This provides the base for guiding emergency response and recovery.

6. What's needed for high - quality measurement of Rocha River currents?

Reliable Materials: ADCP current profiler should be made from materials that will withstand the aquatic environment; it has to be resistant to corrosion by the river water and impacts by floating debris.

Small size, light weight, and low power consumption: Small size, low weight, and low power consumption make an ADCP current meter easy to install and deploy, especially in those areas that are hard to reach. Low power consumption enables longer-term operation without the need for frequent battery replacement or complex power-supply arrangements. In this case, it is beneficial to continuous long-term monitoring of the river.

Low Cost: A lower-cost device is preferred to facilitate large-scale measurement of the Rocha River.

Regarding the casing material, titanium alloy is an excellent option. Titanium alloy has high strength, which allows the ADCP flow meter to resist external forces. It also has excellent corrosion resistance, ensuring the equipment's long - term performance in the water. Its relatively low density helps reduce the overall weight of the device while maintaining its structural integrity.

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

Equipment selection for the Rocha River, depending on the purpose of its use, should take into consideration the following: 

Purpose of Use: When the main objective is horizontal cross-sectional measurement, a Horizontal Acoustic Doppler Current Profiler will suffice. This equipment measures the flow velocity and other parameters across a horizontal section of the river. If it is for a vertical cross-section, the ADCP meter should be vertical. The vertical ADCP profiler can measure the velocity profile from the water surface to the riverbed along a vertical line. 

Frequency: Different frequencies of ADCPs are suitable for different water-depth ranges. For instance, a 600 kHz ADCP is suitable for water depths up to 70 meters, while a 300 kHz ADCP is more appropriate for water depths up to 110 meters. Choosing an appropriate frequency according to the real water depth of the Rocha River can guarantee the accuracy and reliability of the measurement results.

There are well - known ADCP current profiler brands such as Teledyne RDI, Nortek, and Sontek. Additionally, there is a Chinese brand, China Sonar ​PandaADCP, which has a casing made of titanium alloy and offers a good cost - performance 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.