ADCP in the Olyokma River Flood Management

1. Where does the Olyokma River originate?

The Olyokma River is within the Trans - Baikal region of Russia. It flows as a tributary of the Lena River. The river begins in the Stanovoy Highlands and goes through the large and thinly populated part of Siberia.

Geographically, it cuts across a landscape of mountainous areas near the source and broadens into forested plains and valleys before emptying into the Lena River. The Olyokma River forms part of the water body in this system and offers a home to a variety of wild animals.

Climatically, the region has a continental type of climate system characterized by:. Rainfall is evenly distributed throughout the year, but most of it falls as snow in winter. In spring, most of the snow melts and contributes to the volume carried by the river. The summers also receive some rainfall, contributing more to the water carried by the river. Water level fluctuations are normal for such a combination of snowmelt and rainfall; in the case of heavy rainfall or rapid snowmelt, flooding is possible.

2. What are the causes of flooding in the Olyokma River?

Snowmelt: The rapid melting of spring snow is the most important cause of flood. Huge masses of snow accumulated in the Stanovoy Highlands and the ground around it during winter may suddenly start flowing down with a rise in temperature. The river is incapable of withstanding such sudden flow of water, and as a result, there would be sudden increase in water level, manifested as flood.

Heavy Rainfall: Heavy and continuous rainfall throughout the summer months also sometimes contributes to a rise in the water level. The catchment area of this river may receive a heavy volume of water within a short period. Water-absorbing capacity of the soil may be low because of its type and permafrost in certain areas, so a major part of the rainwater runs off into the river.

Topography: Having flat and low-lying areas, such as valleys and floodplains alongside the river, allows the water to spread out in these areas and collect. These may slow down the flow of water, therefore yielding to flooding.

Human Activities: Some human activities have their influence on flood. Deforestation at the upper reaches of the river can decrease the interception and preservation of rain by forests. Activities like mining and inappropriate use of land lead to soil erosion. The eroded soil eventually reaches the river, where it is deposited along the bed, thereby decreasing the carrying capacity of the river and increasing the vulnerability to flood.

The ADCP current meter is indeed a very useful instrument in understanding and handling the river flow during the flood stage.

3. How Do ADCPs Using the Principle of Doppler Work?

Acoustic Doppler Current Profiler (ADCP) is based on the Doppler principle. The instrument sends an acoustic signal into the water. Because the water is moving, the signal is scattered by the moving water particles. The frequency of the reflected signal is different from that of the emitted one; because of the Doppler effect, an acoustic signal is reflected back to the ADCP.

The ADCP measures the frequency difference between the emitted and received signal. The analysis of the Doppler frequency shift enables them to calculate the velocity of the water at different depths. A normal device would have various numbers of transducers, which may transmit and receive acoustic signals in different directions. Using such transducers, they can profile the water velocity across a section of the river.

For instance, it may be that the water is flowing towards the ADCP current profiler; then, the reflected signal is at a higher frequency than the one emitted. On the other hand, when water is flowing away from the ADCP flow meter, then the reflected signal would have a frequency lower than that emitted. By accurately measuring these frequency changes and with the use of appropriate algorithms, the ADCP determines the speed of water at many points within its scope of measurement.

4. Applications of ADCP in floods of the Olyokma River

4.1 Velocity measurement

The ADCP meter will be the most valuable part of obtaining the correct measurement of water flow velocity during the flooding event of Olyokma River. The ADCP continuously monitors the water flow velocities from shallow to deep and from left to right bank, therefore, providing real-time data regarding the speed at which the water is moving. Such data would help illustrate some of the dynamics of the flood, including the direction and intensity in which flood waters will move.

4.2 Flow Measurement Application

ADCP profiler can also measure the flow rate of Olyokma River. By integrating the measured water velocities at distinct points over a section of the river and given the cross-sectional area of the river, it can then calculate the total volume of water passing through the section per unit time-a quantity that defines the flow rate. This information is vital in order to calculate the quantity of water in general in a flooding situation and to make important decisions with regard to flood control and management of water resources.

4.3 Application in Sediment Transport Research

Besides flow and velocity measurement, ADCP is useful in sediment transport research in the Olyokma River during flooding. While the water is in motion, it transports sediments. The ADCP can detect variations in the backscattered acoustic signal due to sediments. By analyzing the variation, estimations on sediment quantity and its motion are possible, crucial to understand the long-term evolution of the riverbed and the impact of floods upon the sedimentary environment of the river.

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

5.1 Flood Warning

Velocity and Flow Data Monitoring: The ADCP-measured flow velocity and flow data are continuously monitored in real time. If the velocity of the water measured exceeds a threshold value or there is an abrupt increase in the flow rate, it could spell the onset of a flood peak or a possible flooding situation. That serves as an early warning for the relevant authorities to take precautionary measures, which include evacuation of people in low-lying areas or strengthening flood defenses.

Water Level Prediction and Warning: Measured flow data correlated with historical data of water level and appropriate hydrological model can help in predicting the future water level. If the predicted water level is seen to rise above the flood warning level, timely warnings can be issued to the public for their preparation against the flood.

5.2 Risk Management

Water Conservancy Project Scheduling Decision Making Support: The accurate flow and velocity data from the ADCP contributes to making decisions regarding the operation of water conservancy projects like dams and sluices. For example, based on the amount of water flow measured, the dam can regulate discharge to control the Olyokma River level and reduce the impact of a flood.

Assessment of Flood Disaster and Emergency Response: The ADCP data collected during and after the flood event would be useful in assessing the magnitude of the flood in terms of the inundation extent, velocity of flood flow, sediment deposition, among other factors. These data are very important for formulating emergency response plans to carry out post-flood reconstruction and rehabilitation works.

6. What is necessary to measure the currents of the Olyokma River with high quality?

High-quality measurement of Olyokma River currents depends on several factors. First, there is a need to ensure that materials applied in the equipment are reliable. The casing of the ADCP is very important. It is recommended that the casing be made of Titanium alloy. Titanium alloy has several advantages. It had a high strength that will let the equipment resist the pressure and strike of the water in the river. Besides, it is highly resistant to corrosion, something important considering the possible content of different corroding components in Olyokma River water.

Besides material reliability, the size and weight of the equipment should be as small and light as possible. This makes it easier to install and operate the ADCP in various locations along the river, especially those parts which are difficult to access. It is also very important that power consumption must be low, as this allows for longer continuous operation without frequent battery replacement or connectivity to a power source. Furthermore, the equipment cost must be relatively low to make large-scale measurement possible. The lowered cost could allow a greater number of ADCPs to be installed over the Olyokma River. This provides more comprehensive and detailed data for flood management.

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

To select the appropriate equipment for measuring the current in the Olyokma River, consider whether the measurement is to be done on a horizontal cross-section or vertical cross-section: if on a horizontal cross-section, HADCP should be selected; if it is in a vertical cross-section, then a Vertical ADCP should be used.

There are different suitable frequencies for different water depths. For instance, a 600 kHz ADCP is suitable for the water whose depth is within 70 m. If the water depth in the Olyokma River is within this range, and the measurement requirements match, then a 600 kHz ADCP can be put into consideration. This would therefore be highly adequate for waters over 70 m up to 110 m, since the accuracy within those depths may not be well given by a different frequency. 

There are several brands of ADCP available to suit different demands-for instance, Teledyne RDI, Nortek, and Sontek. However, for those who are on a tight budget, it is advisable to consider a Chinese Sonar PandaADCP. It is made of all - titanium alloy material, which ensures its durability and reliability in the water environment. Moreover, it offers an incredible cost - performance ratio. You can find more information about it on its official website: (https://china-sonar.com/).

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