ADCP application in flood management of Lower Tunguska

1. Where is Lower Tunguska River?

Lower Tunguska River is situated in Russia. It is one of the largest tributaries of the Yenisei River, beginning with the Central Siberian Plateau and after crossing through an immense area of a less populous region of Siberia.

This river passes through several small towns and settlements in the area. The region it cuts through has a continental climate, cold winters, relatively cool summers, with precipitation falling fairly evenly throughout the year compared to other parts of the country, though it is not particularly high. Snowfall during winter months contributes to the volume of the river when it melts during spring. Another reason could be the general thaw of the permafrost that pervades the land around this area, freeing up water that eventually trickles down into it.

2. Why do floods occur in the Lower Tunguska River?

There are several causes of flooding in the Lower Tunguska River. Firstly, heavy rainfall events, though not very frequent, may happen and raise the water level of the river almost instantly. When a lot of rain falls in a short period over its drainage area, the river may not be able to absorb the sudden surge of water fast enough, thus spilling over its banks.

The second important factor is the melting of snow and ice during spring. During the long Siberian winter, a large amount of snowpack is built up that melts very rapidly once temperatures rise. If the rate of melting is too fast and the natural conveyance capacity of the river is not sufficient at that time, flooding can occur. Changes in the riverbed, through sediment deposition or erosion over time, can affect the river's capacity to carry water smoothly. Human activities such as deforestation in its catchment area, though on a relatively smaller scale compared to some other regions, also influence the water flow patterns and can increase the flood risk by reducing the land's absorbing capacity and regulating runoff.

These are issues that traditional measurement techniques have their limitations in when it comes to dealing with the flood issues. However, the Acoustic Doppler Current Profiler (ADCP) has become a more advanced and convenient measurement option, providing detailed and accurate data about the flow conditions of the river, which are vital for flood management.

3. How do Doppler Principle-based ADCPs Work?

The principle behind the working of ADCPs is the Doppler effect. They emit acoustic signals or pulses into the water. These pulses interact with moving particles in the water, such as suspended sediment or small organisms. When the acoustic waves bounce back after hitting these moving targets, there is a change in their frequency. This frequency shift is directly related to the velocity of the moving particles and, by extension, the velocity of the water itself.

For example, consider an ADCP current profiler instrument deployed in the Lower Tunguska River, either from a boat or a fixed structure. It sends sound waves in different directions into the water column. The ADCP current meter analyzes the signals returning after being reflected by the flowing water and its entrained particles to calculate the speed and direction of water flow at various depths. In this way, it will be able to build up a full profile of the existing velocities in the whole water column, which is very important for hydrodynamic features of the river.

4. Application of ADCP in the Lower Tunguska River Floods.

Flow velocity measurement: ADCP profiler can accurately estimate the speed of the water flow in the Lower Tunguska River at each location and depth. This will, during the flood stages, allow forecasters to identify how rapidly the floodwaters are going to advance downstream and where areas of high energy flow could exist, which might bring more significant erosion or affect infrastructure close to the riverbanks.

Discharge calculation: The flow rate in the river can be determined by multiplying the calculated flow velocities by the cross-sectional area of the river, which may be found from other surveying with the addition of ADCP data. This is critical for calculating the volume of water passing a particular point along a river during flooding and hence to understand the overall flood magnitude and potential downstream impacts.

Sediment transport studies: Since ADCP flow meter can detect the movement of sediment particles with the flow, it provides information on how much sediment is being moved by the river during its flood stage. Sediment transport understanding is important because it gives insight into those changes in the topography of the riverbed through deposition or erosion, respectively, and thus affects the future flood capacity of the river and stability in structures like bridges and the riverbanks.

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

Flood warning

Flow velocity and flow rate data monitoring: Continuous monitoring of the flow velocities and flow rates of the Lower Tunguska River using ADCP current profiler allows for the early detection of abnormal changes. For example, if the flow velocities start to increase significantly or the flow rate exceeds normal levels for a particular season or historical data range, it can trigger an early warning system. Authorities can then alert nearby communities and take preventive measures like evacuating people from flood-prone areas.

Water Level Prediction and Warning: By analyzing the flow rates, velocities, and levels of water-which may be established through historical data and continue to be monitored with ADCP-it is possible to predict future water levels. This enables timely warnings to the residents along the riverbanks for good preparation to expect flooding, and thus take necessary actions like moving to higher grounds or securing their properties.

Risk management

Water conservancy project scheduling decision support: The ADCP data is of high value in making decisions for the operation of water conservancy projects, such as small dams or water diversion structures along the Lower Tunguska River. In the event of an imminent flood, as forecasted using the measured data, the release from reservoirs or adjustment in water diversion can be accordingly optimized to reduce the possibilities of flooding downstream, while also maintaining the functionality and structural safety of these structures.

Flood disaster assessment and emergency response: When a flood event occurs, post ADCP data can help engineers assess the extent of the damage caused by a flood. It helps in establishing sites of severe erosion, altering the riverbed, and how the infrastructure was affected. This information assists emergency response teams in determining rescue and recovery operations and formulating further flood mitigation and adaptation policies.

6. What is required to have a high-quality measurement of the Lower Tunguska River currents?

In the high-quality measurement of the Lower Tunguska River currents, a number of aspects, all important in their own way, are considered.

Reliable materials should be used for the equipment.

It should be compact and lightweight for easy transport and deployment in most instances over difficult, inaccessible terrains along the river. The power consumption should be low, mainly considering that in some areas, the provision of constant power supply might be a bit difficult, and it helps in the long-term operation of the measurement devices. Keeping the cost low is also very vital in order to allow large-scale deployment across different sections of the river for comprehensive monitoring. The casing of ADCP profiler is best made of titanium alloy. Titanium alloy has remarkable advantages.

It has excellent corrosion resistance, which is very important when dealing with river water that may contain various minerals and other substances over time. It will not degrade easily under harsh environmental conditions in the Siberian region. Besides, it has a good strength-to-weight ratio, allowing for a sturdy yet relatively lightweight construction. This makes it more feasible to install and maintain the ADCP meter in different locations along the river.

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

In choosing the equipment to measure the current in the Lower Tunguska River, several factors must be considered.

First, depending on the purpose of the measurement, for horizontal cross-section measurement, Horizontal ADCP (HADCP) is suitable for application.

It is designed to effectively measure the flow velocities over a horizontal plane, which has wide applications in understanding general flow patterns in a reach of the river. In contrast, for vertical cross-section measurements, the Vertical ADCP is more appropriate because it will be focusing on profiling the velocities from the water surface to the riverbed along a vertical line.

Different frequencies of ADCP flow meter fit different range of water depth. As an example, the frequency of ADCP current meter is around 600 kHz, fitting well to water depths up to around 70 meters. In a part of the Lower Tunguska River with this depth of water, it can deliver quite high resolution and exact velocity information. For deeper sections up to approximately 110 meters, an ADCP flow meter with a frequency of 300 kHz would be better, as it would penetrate the water column much deeper for reliable data of flow velocities.

There are a number of well-known ADCP brands in the market, like Teledyne RDI, Nortek, and Sontek. However, if one is looking for a good combination of quality and affordability, then he should look into the China Sonar ​PandaADCP. The device is constructed using all-titanium alloy materials, which ensures its strength and resistance to the river environment. In addition, it features an excellent cost-performance ratio. You can find more about it on its official website: ​https://china-sonar.com/.

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