ADCP in Yangtze River Flood Management

1. Where is the Yangtze River?

The Yangtze River is the longest river in Asia and the third-longest in the world. It rises from the Tanggula Mountains in Qinghai-Tibet Plateau, China.

Geographically, it cuts across a wide range of topography. At its headwaters, it passes through high-altitude areas, mountain gorges such as the famous Three Gorges. It flows downwards, reaching the plains, meandering through agricultural areas and some of the most populous urban areas, such as Wuhan, Nanjing, and Shanghai. Besides, the Yangtze River is also an important transportation artery for travels and shipment of goods upwards and downwards along the river. Moreover, it supplies water to a very large number of industries, agriculture, and domestic usage.

The Yangtze cuts through areas with a subtropical monsoon climate in the middle and lower reaches in terms of climate and rainfall. Distinct wet and dry seasons occur. During the wet season, normally from June to September, much rain falls due to the influence of the monsoon. In the headwaters, the climate is more composite due to the combination of cold alpine climate and the impact of the westerlies. Also, it is fed by the snowmelt off mountains. This can easily combine rain with snowmelt to huge ups and downs in levels, and there is a chance of flood during the wet season.

2. What are the causes of Yangtze River flooding?

Monsoon Rainfall: Heavy and sustained rainfall owing to the wet season is perhaps one of the great causes of flooding. The mighty volume of water, falling in a limited time span, can go into filling the river and all its tributaries almost instantly. The plain lands within its middle and lower courses diminish the speed of the current so that the water can spread and overflow into the surrounding areas.

Snowmelt-in case of a sudden rise of temperature in the catchment area, sudden snowmelting can result. The sudden inflow of water into the river causes it to swell and flood the lower regions. This factor, coupled with heavy monsoon rains, would aggravate the flood situation.

Topography: The great lengths of floodplains and low-lying areas along the entire course of the river allow water to spread out and accumulate. Furthermore, most of the tributaries to this river contribute more water when the river is at high flows and therefore have further deteriorated the flood situation.

Human Activities: The massive growth of urbanization and industrialization along the Yangtze River has drastically affected its flooding. Construction of buildings, roads, and other infrastructure in flood-prone areas has reduced its natural floodplains and the river's ability to absorb excess water. Agricultural activities, such as poor irrigation and soil erosion, also contribute to increased surface runoff and flooding.

ADCP doppler thus acts as a useful tool in the understanding of the Yangtze River flow regime and handling during flooding.

3. How are ADCPs using the Doppler principle applied?

Acoustic Doppler Current Profilers (ADCPs) operate using the principle of the Doppler effect. The device sends out an acoustic signal into the flow of water. Because of water flow, the signals run into the moving water particles. As the acoustic signal bounces back to the ADCP flow meter, the frequency of the reflected signal is different due to the Doppler effect.

Its operating principle involves the measurement of frequency difference between the emitted and received signals. With this shift in frequency, the ADCP meter calculates water velocity at different levels. It normally contains a number of transducers, each capable of emitting and receiving acoustic signals along different directions from it, thereby allowing one to obtain a profile in the form of the water velocity across a section of the stream.

For instance, if the water is moving towards the ADCP current profiler, then the frequency of the reflected signal will be higher than that of the emitted one, and vice versa, in the event that the water is flowing away. Precise frequency changes, combined with applying the appropriate mathematical algorithms, will allow the ADCP doppler to accurately deduce the velocity of the water at various points within its measurement range.

4. What are the applications of ADCP in Yangtze River floods?

Velocity Measurement

As such, Acoustic Doppler Current Profiler (ADCP) will be very significant in the measurement of the velocity of water flow during the flood events in the Yangtze River. It continuously monitors the water velocity at various locations and depths to generate real-time data over speed at which the water is moving. This information is crucial in the dynamics of understanding the flood; one can use it to predict the direction and intensity of movement that the floodwaters might take.

Application in Flow Measurement

It can also measure the flow rate of the Yangtze River. The latter can be calculated by integrating the water velocities measured across a section of the river into the known cross-sectional area of the river to arrive at the total amount of water that will flow through the section in every unit time, or what it is more commonly referred to as flow rate. This is crucial data for any assessment of the total volume of water in the case of a flood and also for decisions relating to flood control or water resource management.

Application in Sediment Transport Studies

Besides flow and velocity measurements, ADCP current profiler can be applied to sediment transport studies along the Yangtze River during flooding. When water flows, it carries sediments. Changes in the backscattered acoustic signal, due to the presence of sediments, can be detected by the ADCP flow meter. From this variation, it is possible to estimate quantity and motion, which is of great importance for studying the long-term evolution of the riverbed, and the action of floods on the sedimentary environment of this river.

5. How can the data measured by ADCP help in making flood warnings and managing the risks of Yangtze River?

Flood Warning

Velocity and Flow Data Monitoring: Consistent monitoring of real-time velocity and flow data from ADCP meter is considered. When the water velocity, as measured, exceeds a higher threshold or manifests a sudden surge in the flow rate, that could be indicative of the arrival of a flood peak or a prospective flood situation. Thus, early warning can be issued to the relevant authority to take precautionary measures for evacuation or strengthening flood defenses in the low-lying areas.

Water Level Prediction and Warning: Measured flow data correlated with the historical water level data and appropriate hydrological model can present ADCP data for prediction of future water levels. If the predicted water level is well over the flood warning level, timely warnings can be issued to the public, making preparation for the flood.

Risk Management

Support for Water Conservancy Project Scheduling Decisions: The accurate flow and velocity data from ADCP flow meter will help the decision-making process on operation of water conservancy projects. For instance, the measured water flow can be used to regulate release of water from a dam to control the water level in the Yangtze River during serious flood seasons.

Flood Disaster Assessment and Emergency Response: Data from ADCP current meter could contribute to the assessment of the flood disaster after it, like the area of flooding, average velocity of floodwater flow, and deposits. It will be very useful in the formulation of emergency response plans for executing post-flood reconstruction and rehabilitation works.

6. What is needed for high-quality measurement of the Yangtze River currents?

High-quality measurement of the Yangtze River currents will require many things. The first factor is that the materials of the equipment should be reliable. This pertains to the casing of the ADCP doppler. For this reason, the casing is recommended to be made from titanium alloy. There are numerous advantages present in titanium alloy. It has high strength that can enable the equipment to sustain the pressure and impact caused by the flowing water of the river. Besides, it is highly corrosion-resistant because there may be some corrosive substances in the water environment of the Yangtze River.

Besides material reliability, the size and weight of the equipment should be small and light. Thus, installation of the ADCP profiler would be easy at the various sites along the river, including those that may not be easily accessible. It should be a low-power-consuming type so it can operate for more extended periods without increasing the frequency of battery replacement or a connection to a power source. Besides, the cost of equipment should be reasonably low to facilitate large-scale measurement. A low cost will entail the deployment of more ADCPs along the Yangtze for more comprehensive and detailed information on flood management.

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

When choosing the right equipment for the current measurement in the Yangtze River, several aspects need to be taken into account. According to the kind of measurement that needs to be done, whether horizontal cross-section measurement or vertical cross-section measurement, an appropriate one should be chosen. The former would be the Horizontal ADCP (HADCP), while the latter is a Vertical ADCP.

Second, different frequencies are applied to different water depth, for instance, within 70 m, the frequency of 600 kHz is suitable. If the water depth in the Yangtze River is in this range and it meets the requirements of the measurement, an ADCP flow meter with 600 kHz can be considered. For the deeper waters, for example, over 70 to 110 meters, the 300 kHz ADCP would be more suitable as it is able to give better results for such a depth.

There are also quite a number of renowned ADCP profiler brands out there, including Teledyne RDI, Nortek, and Sontek. However, the China Sonar PandaADCP would be quite budget-friendly. It is made of all - titanium alloy material, which ensures its durability and reliability in the water environment. Moreover, it offers an incredible cost - performance ratio. You can find more information about it on its official website: (https://china-sonar.com/).

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