ADCP Application in the Oka River Flood Management

1. Where is the Oka River?

The Oka River is a major river in Russia. It is one of the biggest tributaries of the Volga River, which is located in central Russia. It flows through diverse landscapes-from plains and forests to some urban areas.

It flows through cities such as Nizhny Novgorod. The Oka River basin enjoys a climate with a continental pattern of clear seasonal patterns in rainfall. Precipitation is unevenly distributed, with spring and summer relatively wet in the form of rainfall and as a result of snow in the surrounding areas that ultimately melts into the river. The river is a considerable supply of water for domestic use and agriculture, and in relation to industry, transportation also, and is a component of a rich aquatic life in the area.

2. What causes Oka River flooding?

Oka River flooding may be due to numerous causes. Intense rainfall during wet seasons, especially in spring and summer, is one of the primary causes. When heavy rain falls over a short period or if the accumulated rainfall in time is beyond the usual capability of the river to take water, the water level might shoot up in no time.

Snowmelt from the upstream catchments also contributes to flood events. The melting snow during spring adds a lot of water to the river. Again, the relatively flat floodplains found in some reaches allow the water to spread out easily if there is a flood. Land use changes, like basin urbanization and deforestation, reduce the natural infiltration and drainage capability of the ground, increasing the surface runoff and thereby aggravating the flood situation. With such complex causation factors for floods, Acoustic Doppler Current Profiler (ADCP) offers a more advanced and efficient way to measure and manage the flow of the river during flood periods.

3. How do ADCPs using the Doppler principle work?

The principle of operation of ADCPs is based on the Doppler effect. A device emits acoustic signals into the water. The moving water particles interact with these signals. When acoustic waves bounce back after hitting the moving particles, due to the Doppler effect, the frequency of the reflected waves changes.

The ADCP has multiple transducers, which can transmit and receive acoustic signals in different directions. Precise measurement of the frequency shift of the reflected signals provides the velocity of the water flow at different depths and across different sections of the river cross-section. For instance, in the Oka River, it can measure the flow velocity from the riverbed to the water surface and across different widths of the river.

4. What does the application of ADCP entail in floods of the Oka River?

Flow Velocity Measurement: ADCP current meter can carry out very accurate flow velocity measurements of the Oka River in cases of flood. This forms a very important basis of knowing the speed of movement of water through different parts of the river. The flow velocity may be used to detect points where the water is moving fast, probably from a surge in a flood, or even changing its behavior in some way. For example, flow velocity variations can be detected with high accuracy near riverbanks or in the main channel.

Flow-rate Measurement Application: It is possible to determine the flow rate by combining the flow velocity measured and the cross-sectional area of the river. In the context of the Oka River floods, this information will be useful in estimating the total volume of water passing through a particular section per unit time, which helps in flood forecasting and understanding the overall magnitude of the flood.

Sediment-transport Research: In a flood, a huge quantity of sediment is moved along the Oka River. ADCP current profiler will be able to detect moving sediment particles by analyzing the backscattered acoustic signals, thus enabling the study of sediment-transport patterns during floods, which is necessary for understanding the long-term evolution of the riverbed and its impact on the river hydrological characteristics.

5. How can the data measured by ADCP be utilized in the aspect of flood warning and risk management of the Oka River?

Flood Warning Aspect

• Flow-velocity and Flow-rate Data Monitoring: ADCP flow meter continuously monitors the flow velocity and flow rate to detect abnormal changes. If the flow velocity is above a certain threshold or if the flow rate suddenly increases, it can trigger an early flood warning. The information can be passed on to local authorities and communities nearby the river.
• Water - level Prediction and Warning: The flow data obtained from ADCP profiler can be used in conjunction with other hydrological models to predict water - level changes. By analyzing the relationship between flow-rate and water-level, more accurate flood warnings can be issued, especially in the flood-prone areas of the Oka River.

Risk Management Aspect

• Water-Conservancy Project Dispatching Decision Support: The precise flow data from ADCP meter contributes to the operation of water-conservancy projects like dams and canals along the Oka River. Decisions on water release or storage can be taken more effectively in order to reduce flood risks downstream.
• Flood-disaster Assessment and Emergency Response: In the aftermath of a flood event, the ADCP-measured data can be used to assess the extent and impact of the flood. This helps in formulating appropriate emergency-response strategies, including rescue operations and damage-assessment surveys.

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

For high-quality current measurement of the Oka River, this equipment should be made with reliable materials that can bear the harsh conditions of the aquatic environment in water corrosion and possible impacts of floating debris and sediment. The small size and lightweight will ensure easy installation and deployment at different sites along the river.

It is also required to have low power consumption in order to keep the units operating continuously, particularly in locations that are quite far-flung and where the power supply is very limited. Cost-effectiveness is another factor since extensive deployment may be required for detailed river-current monitoring. The casing is preferably made of titanium alloy. The resistance to corrosion is very high, which is very necessary due to the corrosive effect of the Oka River water with time. It also offers good strength-to-weight ratio for durability and ease of equipment manipulation.

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

The measurement purpose should be regarded as the first step when choosing equipment for current measurement in the Oka River. In Horizontal cross-section measurement, HADCP would become a suitable option since it gave a detailed flow-velocity information throughout the width of the river. In Vertical cross-section measurement, a Vertical ADCP is more appropriate for vertical measurement of the flow velocity distribution from the bed of the river to the water surface.

Regarding the frequency of ADCP, for relatively shallower parts of the Oka River, for example, less than 70m of water depth, a 600kHz ADCP can be used for valid measurement. For relatively deeper areas, say about 110m, a 300kHz ADCP is more suitable. There are several ADCP brands, including but not limited to well-known brands: Teledyne RDI, Nortek, and Sontek. The Chinese ADCP brand is China Sonar PandaADCP. It is made of all-titanium alloy material and offers excellent performance and cost - effectiveness. 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.