ADCP's application in flood management of Selenga river

1. Where is the Selenga River?

The Selenga River is located in Central Asia. It's a big trans-boundary river, passing through Mongolia and Russia.

It originates in the Khangai Mountains of Mongolia. Further downstream, the river changes character many times as it flows through a variety of landscapes, from mountainous, to steppe-like open spaces, and wetlands. This waterway gives life to many agricultural and pastoral activities on both sides of its course in Mongolia. It flows into Russia, ending in Lake Baikal.

The catchment areas of the Selenga River fall within the continental climate, with cold winters with snow and relatively warm summers. Snow melt in spring and summer rainfall significantly mark the volume of water in the river. This can create extreme fluctuations due to snowmelt from the mountains, along with the rainfall. Heavy rains or quick snowmelting can make the river break its edges and therefore flood the nearby territories.

2. What is the cause of flooding in the Selenga River?

Snowmelt and Heavy Rainfall: A combination of rapid snowmelt in spring and heavy rainfall during the wet season is considered the main reasons for flood occurrences. Suddenly, huge amounts of water from snow melting in the mountains and additional rainwater can fill the river. The mountainous terrain close to its source quickens the runoff process, sending a great volume of water downstream.

Topography: The coming of floodplains and low-lying areas along the course of the river allows water to spread out and accumulate. Relatively flat areas slow down the flow of water, making floods more likely to occur. The meeting of tributaries adds extra water at times of high flow and aggravates the flood situation.

and Use Changes: Human activities such as deforestation and the expansion of agriculture affect the flood pattern in a river. Deforestation decreases the interceptive and retention capacity of the forest over rainwater. Soil erosion caused by agricultural activities deposits eroded soil in the river and consequently diminishes its carrying capacity.

The ADCP current meter is a useful tool in understanding the flow of the Selenga River and how to manage the discharge during floods.

3. How do ADCPs using the Doppler principle work?

ADCPs are based on the principle of Doppler. The instrument sends an acoustic signal into the water. Due to its flow, the signal is scattered by the moving particles in the water. When the acoustic signal is reflected back to the ADCP current profiler, the frequency of the reflected signal shifts due to the Doppler effect.

ADCP measures the difference between the frequency of the emitted signal and that which is returned. By analyzing this frequency shift, it can calculate the velocity of the water at different depths. Most ADCPs are multitransducer instruments that send and receive acoustic signals in several different directions. This provides a profile of the water velocity across the section.

For instance, if the water is flowing towards the ADCP flow meter, the reflected signal would have a higher frequency than the emitted one. If the water was flowing away from the ADCP meter, the reflected signal frequency would be lower. By measuring these changes in frequency with great precision and using the appropriate mathematical algorithms, the ADCP can determine the actual speed of the water at several points within the measurement area.

4. Application of ADCP in the floods of the Selenga River

Velocity Measurement

Measuring the velocity of water flow during flood events of the Selenga River, ADCP profiler is indispensable. It monitors continuously at various depths and different locations to obtain real-time data on how fast the water is flowing. This will help engineers understand important dynamics such as the direction and the movement intensity of floodwaters.

Flow Measurement Application

ADCP is also capable of providing the flow rate of the Selenga River. By integrating the measured water velocities at various points across a section of the river with the known cross-sectional area of the river, the instrument can calculate the total volume of water flowing through the section per unit time, that is, the flow rate. All this information is important for evaluating the general water volume in the case of a flood and for decision-making with respect to flood control and water resource management.

Application in Sediment Transport Research

Other than flow and velocity measurement, ADCP is applicable in the sediment transport studies along Selenga River during floods. While the water is in flow, there is sediment transport. The ADCP can detect changes in the backscattered acoustic signal caused by the presence of sediments. Such changes are thus analyzed to obtain an estimation of the quantity and mobility of sediments, useful for the study of the long-term evolution of the riverbed and in assessments of the effects that flooding events may have on the sedimentary environment of the river.

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

Flood Warning

Velocity and Flow Data Monitoring: In this regard, real-time velocity and flow data from ADCP are monitored constantly. If the measured water velocity is more than the threshold value or the flow rate increases considerably, that may indicate that a flood peak is approaching or a potential flooding situation might occur. This allows for an early warning to the relevant authorities to take necessary steps like the evacuation of people from low-lying areas or strengthening their flood defenses.

Water Level Prediction and Warning: Measured flow data correlated with historical data on water level using appropriate hydrological models allows ADCP data to predict future water levels. In case the predicted water level is going to exceed the flood warning level, timely warnings can be issued to the public, enabling them to prepare for the flood.

Risk Management

Water Conservancy Project Scheduling Decision Support: The accurate flow and velocity data from ADCP meter can help make decisions on the operation of water conservancy projects such as dams and sluices. Based on the measured water flow, for instance, water release from a dam can be regulated to control the water level in the Selenga River and hence reduce the impact caused by floods.

Flood Disaster Assessment and Emergency Response: The ADCP data can be used in assessing the severity of a flood after the event has occurred. It involves information like the inundation extent, velocity of the floodwaters, and sediment deposition quantity. All such information is vital for formulating emergency response plans and for carrying out post-flood reconstruction and rehabilitation works.

6. What is necessary for high-quality measurement of currents of the Selenga River?

The following aspects should be taken into consideration for high-quality measurement of the Selenga River currents. Reliable materials are used in the equipment. In particular, much attention is paid to casing ADCP profiler. The casing is recommended to be made from the alloy of titanium. It has very high strength that can resist the pressure and impact from the water flow in the river. Besides, it has a very high corrosion resistance, which is also very important since the surrounding environment-water in the Selenga River-might contain different corrosive components.

Besides material reliability, the size and weight of the equipment should be as small and light as possible. This makes it easy to install and operate the ADCP current profiler in different locations along the river, especially in those areas that are difficult to access. Low power consumption is also important because longer continuous operations can be performed without changing batteries or connecting to a power source frequently. Besides, the cost of the equipment should be relatively low to realize large-scale measurement. The lower the cost of these ADCPs, the more that can be deployed along the Selenga River to provide more comprehensive data for flood management.

7. How to Choose the Right Equipment for Current Measurement?

In regard to the selection of the proper equipment for current measurement in the Selenga River, a number of aspects should be considered, first of all, based on the type of measurement required, if it is for horizontal cross-section measurement, an HADCP must be selected; or if the measurement is for a vertical cross-section, a Vertical ADCP current meter is to be used.

The second one is that different frequencies are applicable to different water depths. For instance, a 600 kHz ADCP works for water depths within 70 m. If the water depth in the Selenga River is within this range and the measurement requirements match, a 600 kHz ADCP can be used. In deeper waters, such as over 70 m up to 110 m, it is more appropriate to use a 300 kHz ADCP since it will give more accurate measurements in that depth.

There are famous brands for ADCPs existing in the market, like Teledyne RDI, Nortek, and Sontek. However, for those who have the aim of saving money, China Sonar PandaADCP is a good option. It is made of all-titanium alloy material, which allows it to be durable and reliable in the water environment. Besides, it realizes an incredible 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.