ADCP's Application in Flood Management of Songhua River

1. Where is Songhua River?

Songhua River is one of the major rivers in Northeast China. It is the largest tributary of the Heilongjiang River. The river has its source in the Changbai Mountains.

Geographically, it runs through a vast area covering mountainous regions and extending to the wide plains. It passes through important cities like Harbin. All these cities have their main water supply, transportation, and industrial use from the Songhua River. It is also an ecosystem that encompasses a number of living species. It nurtures the huge agricultural land in the plains, while different types of fish exist in the river itself.

From the perspective of rainfall, the Songhua River Basin enjoys a temperate monsoon climate: obvious wet and dry seasons. It normally rains from June to September during the wet season, when plenty of rain falls under the control of the monsoon. In addition to this rain, in spring, a lot of snow and ice melts from the mountains to form this important part of the water volume of the river.

2. What are the Reasons of Flooding in Songhua River?

Heavy Rainfall and Snowmelt: Heavy rainfall during the wet season is the main cause of the flood. The heavy catchment area of Songhua River results in enormous amount of water converging into it from different regions. In addition, the snow melting at its upper reaches in spring can lead to a great increase in the water volume. When the total inflow of water from rainfall and snowmelt increases over the carrying capacity, it causes flooding.

Topography: The course of the river contains areas with flat floodplains. In such cases, the flat land causes the water to run slowly, and this may eventually flood surrounding regions. There are also places where the channel itself may have natural constrictions that impede the normal flow of water and thus force backup and rising water levels.

Human-Induced Factors: Due to urbanization and different agricultural activities, the natural environment of this river has changed. Surface runoff increases because of pavement in cities, and also agricultural lands-with a deficient drainage system-can result in increased water coming into the river. Acoustic Doppler Current Profiler (ADCP) provides an advanced, easy measurement tool in an improved understanding and management of flood-related issues in comparison.

3. How do ADCPs Using the Doppler Principle Work?

ADCPs operate on the principle of the Doppler effect. They emit acoustic signals into the water. As these acoustic waves interact with moving particles in the water, such as sediment, debris, and water parcels of different velocities, the frequency of the reflected signals changes from the emitted signals because of the Doppler effect.

The ADCP measures these frequency shifts and, with the already known speed of sound in water and the angles of the emitted and received signals, calculates the velocity of the water at different depths. Multiple transducers in the ADCP current meter are arranged to measure the velocity components in different directions. By integrating these velocity measurements over different depths and cross-sectional areas of the river, the flow rate and other important hydrological parameters can be determined.

4. What are the Applications of ADCP in Floods of Songhua River?

Velocity Measurement: ADCP current profiler can give accurate velocity of the flow in water in the Songhua River for different locations and at varying depths. This becomes quite useful during flood events for knowing the dynamics of the flood. This helps in identifying where the flow is rapid, thus becoming hazardous to riverbanks, bridges, and other infrastructure, besides providing an opportunity to track variations in flow velocity over time during the progress of a flood.

Flow Rate Measurement Application: By combining the measured velocity data with the cross-sectional area of the river, ADCP flow meter can calculate the flow rate. This is important to predict the volume of water passing through different sections of the river during a flood. That helps in predicting the peak of the flood and its effect on the downstream areas, which plays an important role in strategies for flood management.

Sediment Transport Research: Flooding in the Songhua River can transport a lot of sediment. ADCP profiler is able to study the movement of sediment by detecting the echoes of acoustic signals, which are influenced by sediment particles. This gives very valuable information on how floods affect the evolution of the riverbed, sediment deposition, and erosion processes.

5. How can the Data Measured by ADCP be Utilized for Flood Warning and Risk Management of Songhua River?

Flood warning

Flow rate and velocity data: They should be monitored continuously using ADCP meter to detect abnormal increases of these parameters in advance. When these parameters reach critical levels or exceed them, the time at which this occurs serves as an early warning for flood peaks. In such events, timely warnings can be sent out to communities and emergency operations centres along the course of the river.

Water Level Prediction and Warning: By correlating the flow rate and velocity measured data with historical water level records, models can be developed for predicting future water level variations. This enables the issuance of advance warnings about the areas that might get inundated and how tall the floodwaters are likely to rise.

Risk Management

Water Conservancy Project Scheduling Decision Support: These ADCP data could contribute to decisions about the operations of water conservancy projects, including dams and reservoirs along the Songhua River, with respect to the best time and amount of water discharge from reservoirs to lessen the flood impact downstream.

Flood Disaster Assessment and Emergency Response: Following the occurrence of a flood, it is then possible to estimate the amount of its impacts, the extent of areas submerged, among other parameters such as its flow characteristic from ADCP-measured data. Such information offers guidance toward response strategies, involving the deployment of relief supplies or resources, the planning, and subsequent post-flood recovery.

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

In order to measure the current in the Songhua River, it is necessary that the equipment be made from reliable material. The casing must withstand the impact of floating debris, corrosion by water of different chemical composition, and extreme temperature fluctuations of the area.

The size of the equipment should be small enough to be installed and deployed easily at different locations in the river. A lightweight design is also beneficial for ease of transportation and installation. Low power consumption is necessary to ensure continuous operation over extended periods without the need for frequent battery replacements or high-energy power sources. Cost-effectiveness is another important factor to enable large-scale deployment for comprehensive monitoring.

The ADCP flow meter casing is preferably made from a titanium alloy. Titanium alloy enjoys several outstanding advantages: It has excellent corrosion resistance, crucial to the long-term exposure to the river water; it has a high strength-to-weight ratio, thus providing sufficient strength while keeping the equipment's weight at a reasonable level. This material's durability ensures stable performance under the diverse environmental conditions of the Songhua River Basin.

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

Based on Measurement Purpose

For horizontal cross-section measurement of the river, a Horizontal ADCP is suitable for the purpose, which will be able to provide flow velocity and other parameters very accurately in the horizontal direction across the river section. In the case of vertical cross-section measurement, a Vertical ADCP will be more appropriate to obtain the detailed velocity profile along the vertical axis of the river.

Based on Water Depth

Various frequencies of ADCP current meter are used for different water depths. In the case of water depth up to 70 meters, an ADCP with a frequency of 600 kHz can provide quite accurate measurement results. Whereas for deeper water up to 110 meters, an ADCP with a frequency of 300 kHz is more effective because it can penetrate deeper and give reliable data.

There are well-known ADCP brands like Teledyne RDI, Nortek, and Sontek. Additionally, a cost-effective Chinese brand, China Sonar PandaADCP, is worth considering. It is made of all-titanium alloy material, ensuring excellent performance and durability. You can find more information on its website: (https://china-sonar.com/)

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