ADCP's Application in Flood Management of Tarim River

1. Where is Tarim River?

The Tarim River is located in the Xinjiang Uygur Autonomous Region of China. It is the longest inland river in China. It goes through a vast arid region, mainly in the Tarim Basin.

Course it gets in the desert area, where the geographical setting assumes a unique ecological system. Surrounding the river are the oases, which happen to be important for the local agriculture and human settlement. There are cities and towns lining its banks, among which is Aksu and Korla. These areas take a water supply from this very river through an extensive irrigation system that supports cotton and other crops.

The Tarim River Basin enjoys a continental arid climate where the amount of precipitation is scanty. The river's water comes principally from the melting of snow and ice in the mountain surroundings, such as those provided by the Tianshan Mountains. However, it has been observed that heavy rainfall in mountainous areas and snowmelt in abnormal periods make the water volume in the Tarim River surge suddenly.

2. What are the Reasons for Floods in Tarim River?

Abnormal Snowmelt and Rainfall: The main reasons for floods in the Tarim River involve abnormal water volume increases-very fast snowmelting up in the mountains or heavy rain in the upper reaches. Then, the water in these streams flows into the river, which, if the inflow is above the normal carrying ability of this river, then the result is a rise in water levels to cause flooding.

Geographical Features: The topography is not so uneven along various reaches of the course taken up by the Tarim River. A relatively smooth landscape flattens the stream's water flow to much slower rates; hence, accumulation is more feasible and resulting in spillover flood in surrounding areas. Its channel could also have certain bent sites that would reflect the back flow of water with flooded banks and spillovers, respectively.

Human-Induced Factors: Man-made activities also include the over-exploitation of the water resource and changes in the irrigation system, which can affect the balance of the Tarim River. For instance, improper water diversion can cause a sudden increase in the water volume of the certain section and thus increase the flood risk. In this regard, the Acoustic Doppler Current Profiler (ADCP) has a more advanced and efficient means of measurement for data related to floods compared to the other methods available.

3. How Do Doppler Principle ADCPs Work?

ADCPs work on the principle of the Doppler effect. They emit acoustic signals into the water. When those acoustic waves encounter moving particles in the water, such as sediment, small debris, or simply water parcels with different velocities, the frequency of the reflected signals compared to the emitted signals changes due to the Doppler effect.

The ADCP measures these frequency shifts and, with the velocity of sound in water and angles of the emitted and received signals known, calculates the speed of the water at various water depths. Multiple transducers on the ADCP current meter are arranged in such a way that the resultant velocity components are measured in various directions. By integrating these velocity measurements over different depths and various cross-sectional areas of the river, the flow rate and other hydrological parameters of interest are determined.

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

Velocity Measurement: ADCP flow meter is able to measure the velocity of water flow in the Tarim River with high accuracy at different locations and depths. During flood events, this information is crucial for understanding the dynamics of the flood. It helps identify areas where the flow is rapid and could endanger riverbanks, bridges, and other infrastructure.

Flow Rate Measurement Application: By combining the measured velocity data with the cross-sectional area of the river, ADCP profiler can calculate the flow rate. This is vital for the prediction of the volume of water passing through different sections of the river during a flood. It enables anticipation of the flood peak and its impact downstream, which is important for flood management strategies.

Sediment Transport Research: The Tarim River can carry a large amount of sediment during floods. ADCP meter is able to analyze the sediment movements by detecting the echoes of acoustic signals affected by sediment particles. This helps in understanding 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 Tarim River?

Flood Warning

Monitoring of Velocity and Flow Rate Data: Through ADCP, velocity and flow rate data can be continuously monitored to quickly detect abnormal increases. As these parameters approach or exceed the critical values, this may serve as an early warning of an impending flood peak. This allows for timely warnings to be issued to communities and emergency management agencies along the river.

Water Level Prediction and Warning: By correlating the measured flow rate and velocity data with historical water level records, models can be developed to predict future water level changes. This helps in providing advance warnings about the areas that may get inundated and the height of the floodwaters.

Risk Management

Water Conservancy Project Scheduling Decision Support: The ADCP data can be used to support decisions in the operation of water conservancy projects like dams and reservoirs along the Tarim River. For instance, it will determine the appropriate time and amount of water to be released from the reservoirs to reduce the impact of floods downstream.

Flood Disaster Assessment and Emergency Response: After the flood, the measured data can be used in assessing the disaster caused by the flood in terms of inundated area extent and flood flow characteristics. Such information helps in emergency response by including planning for the allocation of relief resources and the post-flood recovery work.

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

To perform high-quality measurements of the currents in the Tarim River, the equipment should be made from reliable materials. The casing should resist impacts that might be caused by floating debris, corrosion in water with different chemical compositions, and extreme temperature differences characteristic of the arid zone.

Small equipment size, which can easily be installed and deployed at various points along the river, is appropriate. Light in weight: light equipment design is good because the equipment would be easy to transport and install. Power consumption: low power use in equipment is crucial for its possible continuous operations over a considerable amount of time without the use of heavy batteries or sources with high energy. Cost-effective: so that it allows large-scale deployment for dense coverage of monitoring.

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

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

Based on Measurement Purpose: Horizontal ADCP (HADCP) will be used for the horizontal cross-section measurement of the river, as it will give accurate flow velocity and other parameter measurement in the horizontal direction across the river section. Vertical ADCP is better for the vertical cross-section measurement to obtain the detailed velocity profile along the vertical axis of the river.

Based on Water Depth: ADCPs of different frequencies are used depending on the depth of water. Up to 70 meters of water depth, an ADCP with a frequency of 600 kHz can show very accurate measurement results. An ADCP with a frequency of 300 kHz works better in deeper water of up to 110 meters since it can give more penetrating and 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.