ADCP's Application in Flood Management of the Alazeya River

1. Where is the Alazeya River?

The Alazeya River is situated in the Russian Far East. It is a major watercourse in the area. The river meanders across a large and sparsely inhabited area, with its course controlled by the peculiar topography of the Siberian tundra and taiga regions.

It crosses some small indigenous villages. From the point of view of rainfall, the basin of Alazeya River has a cold climate with relatively small precipitations. However, during the spring, snowmelt contributes significantly to the replenishment of the water volume of this river. The river forms part of the local ecosystem, serving for the water needs of the local wildlife and as a means of transportation in some areas.

2. What are the causes of the flood in the Alazeya River?

Flooding in the Alazeya River is generally brought about by rapid snow melting. During the spring break-up, a lot of snow that has been accumulating over the winter melts rapidly, and the water rushes into the river, bringing about a sudden rise in water volume.

The river's generally flat floodplain and the occurrence of permafrost in the area also contribute to the flooding. The permafrost limits the infiltration of water, so the surplus water from snowmelt or heavy rainfall (less common) tends to remain on the surface and enter the river, causing over - bank flow. In addition, ice jams can form during the break-up of river ice in spring, impeding the normal downstream flow of water and forcing water to back up and flood. For the measurement of such flood-related parameters, the traditional methods have their own limitations in such a harsh and remote environment. Hence, Acoustic Doppler Current Profiler (ADCP) provides an accurate and efficient alternative in this regard.

3. How do ADCPs using the Doppler principle work?

ADCPs are based on the principle of the Doppler effect. The instrument sends acoustic pulses into the water. The moving particles of water scatter the pulses. When the acoustic waves reflected back after striking the moving particles, the frequency of the reflected waves shifts due to the Doppler effect.

The ADCP current meter is fitted with multiple transducers that are capable of transmitting and receiving acoustic signals in different directions. By accurately measuring the frequency shift of the reflected signals, the velocity of the water flow at different depths and across different sections of the river cross-section can be determined. For example, in the Alazeya River, it can measure the flow velocity from the riverbed to the water surface and across different widths of the river.

4. What does ADCP apply in floods of the Alazeya River?

Flow Velocity: ADCP measures the flow velocity of the Alazeya River during flood seasons with much good accuracy. This also becomes important in understanding the speed at which water is moving within different parts of the river. This can be achieved by monitoring the flow velocity, which will highlight regions of fast-moving water that could indicate a surge in the flood or a change in the behavior of the flood. For example, flow velocity changes near the riverbanks or in the main channel can be closely monitored.

Flow-rate Measurement Application: Measured flow velocity is combined with the cross-sectional area of the river to compute the flow rate. In this context, with respect to the Alazeya River floods, this information is crucial for the estimation of the total volume of water passing through a particular section per unit time. It helps in flood forecasting and in understanding the overall magnitude of the flood.

Sediment-transport Research: During floods, a significant amount of sediment is transported along the Alazeya River. ADCP current profiler can detect the movement of sediment particles through the analysis of backscattered acoustic signals. This enables researchers to study the sediment - transport patterns during floods, which is important for understanding the long - term evolution of the riverbed and the impact on the river's hydrological characteristics.

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

Flood Warning Aspect

• Flow-velocity and Flow-rate Data Monitoring: The ADCP flow meter enables continuous monitoring of flow velocity and flow-rate to detect abnormal changes in them. If the flow velocity is higher than the threshold or the flow-rate increases suddenly, it could trigger an early flood warning. The information can then be conveyed to the local communities and other relevant authorities in the remote areas near the river.
• Water-level Prediction and Warning: Flow data from ADCP meter can be integrated with other hydrological models to predict changes in water level. By studying the relation between flow rate and water level, more accurate warnings of floods can be issued, especially in the flood-prone areas of the Alazeya River.

Risk Management Aspect

• Water-Conservancy Project Dispatching Decision Support: The accurate flow data from ADCP provides valuable input in the operation of water-conservancy projects such as small dams or flood-control structures along the Alazeya River. Decisions on water release or storage can be made more effectively to mitigate flood risks downstream.
• Flood-disaster Assessment and Emergency Response: In the aftermath of a flood event, the ADCP-measured data can be used to make assessments of the flood extent and flood impact. This helps formulate appropriate emergency-response strategies, including rescue operations and damage-assessment surveys.

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

For high-quality current measurements of the Alazeya River, the equipment has to be manufactured from reliable materials. The equipment should sustain the impacts of the aquatic medium, such as corrosion by water and probable impacts of floating debris and sediment. It is also preferred if the equipment is compact and lightweight because it enables easy installation and re-deployment at any selected location of the river.

This, in turn, means that it should have low power consumption to enable continuous operation, especially in remote areas where the power supply may be limited. Cost-effectiveness is also another factor since large-scale deployment may be required for comprehensive river-current monitoring. The casing of ADCP profiler is preferably made from Titanium alloy. Resistance to corrosion in the titanium alloy is excellent and thus required due to the degrading forces from the water of Alazeya over a prolonged time period. Moreover, a very good strength-to-weight ratio would contribute much to maintaining durability as well as to the management of the equipment.

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

First of all, measurement equipment is selected on the basis of measurement purposes. For horizontal cross - section measurements, a Horizontal ADCP may work for the purpose of measurement due to the fact that it produces highly detailed flow-velocity information over the width of the river. The Vertical ADCP shall be more appropriate for measuring flow-velocity distribution from the riverbed to the water surface during vertical cross-section measurements.

For the frequency of ADCP, in the relatively shallow parts of the Alazeya River, such as the water depth less than 70m, a 600kHz ADCP can be able to provide accurate measurements. For the place with around 110m water depth, a 300kHz is more suitable. There are some brands of ADCPs in the market, such as well-known brands like Teledyne RDI, Nortek, and Sontek. And there is one Chinese ADCP brand recommended here-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.