How to Measure Water Current of Yalong River?

1. Where is Yalong River?

The Yalong River is a major river in China. It lies mostly in the southwestern part of the country, running through the mountainous regions of Sichuan and Yunnan provinces. Originating from the Bayan Har Mountains, it traverses through diverse terrains that include deep gorges, high plateaus, and lush valleys.

Along its course, there are many small towns and villages whose people have a close relationship with the river. The river has long been a vital source of water for drinking, irrigation, and domestic use for these communities. In addition, it plays an important role in hydropower generation. Many large hydropower stations have been built along the Yalong River, utilizing its mighty flow to generate electricity, with significant contribution to the regional energy supply.

Around this spot are plenty of natural beauties and biodiversity. The varieties of flora thrive along both banks, while the fish population in the waters comprises many species. The Yalong River originates from the Tibetan Plateau with a rich deposit of cultures by the local ethnic groups, who have their own stories associated with the river. Quite often, the river reflects in their folk dances and songs, especially during festivals signifying life and prosperity.

2. What is the flow rate of the Yalong river?

The flow rate of the Yalong River has a marked seasonal variation. In this area, the rainy season is generally from May to September; heavy rainfall in the upper mountainous regions makes the flow greatly increase. The water volume swells rapidly, and the current becomes quite strong, with a relatively high velocity. This is also the period when, due to abundant water availability, more electricity can be generated by the hydropower stations along the river.

During the dry period, from October to April, the rate of flow decreases. The river still keeps a certain flow that can sustain the ecological environment and meet the basic water requirement of the local communities as well as the areas further downstream. The average flow rate is affected by the amount of precipitation in its catchment area, the topography of the river basin which governs water convergence and diversion, and the operation of hydropower projects that may partly regulate the flow.

3. How to measure water current of Yalong River?

Following are some of the methods to calculate the water current of Yalong River:

Velocity Meter Method: This involves the use of mechanical or electronic velocity meters. These meters are placed at certain points in water to measure the speed at which water passes by them. This method requires multiple placements at different locations and depths to get an overall understanding of the current. It can be quite time-consuming and may not provide a continuous profile of the current throughout the water column.

Acoustic Doppler Current Profiler (ADCP) Technique: The ADCP technique is somewhat more sophisticated and effective than the former. It measures simultaneous water velocity at different depths utilizing sound waves. By emitting the acoustic signal and then analyzing the reflected signal with the Doppler frequency shift, it gives a very fair profile of the current right from the surface to the bed of the river. This allows for better and more precise measurement of the water current across various sections of the river.

Buoy Method: In this technique, buoys are dropped in the river and their displacements are observed over time. The shifting of buoys by water current shows the speed and direction of flow. However, this method also has certain drawbacks. It may not give accurate velocity measurements at different depths and is susceptible to external factors like wind and waves, which can influence the movement of the buoys.

Among these methods, ADCP is a more advanced and convenient method for measuring the water current of the Yalong River.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. An acoustic signal emitted from the ADCP transducer into the water interacts with the moving water particles. Because the water is in flow, the frequency of the reflected sound waves back to the transducer shifts; this is called the Doppler shift.

If the water is moving towards the transducer, the frequency of the reflected waves will be higher than the emitted frequency. If the water is moving away from the transducer, the frequency will be lower. By precisely measuring this frequency shift at multiple angles and depths, the ADCP can calculate the velocity of the water in different directions and at different levels within the water column. With it, it records a clear profile of water current from its speed to its flow in a direction from its surface right into the bed of the river.

5. What is to be prepared in measuring high-value Yalong River Currents?

For high-quality measurement of the Yalong River currents, the equipment should possess some key characteristics. The materials used in its construction need to be reliable so that accurate and consistent measurements can be taken. The small size is beneficial for ease in deployment and retrieval within the river, especially in areas with difficult access. It should also be lightweight, allowing for easy installation and a reduced amount of effort in its handling.

Low power consumption is essential to ensure that the equipment can operate for extended periods without the need for frequent battery replacements or a complex power supply setup. Cost-effectiveness is another important factor as it enables more widespread use and larger-scale measurement campaigns.

When it comes to the casing of the ADCP, titanium alloy is an excellent choice. Titanium alloy has many advantages. It is highly resistant to corrosion, which is important, since the equipment is in constant contact with water that might contain minerals, sediment, and other pollutants. Besides, it has a great strength-to-weight ratio, and thus is durable yet lightweight in casing. Also, the material would withstand the mechanical stresses during its deployment and in operation against the flowing water of Yalong River.

6. How to Choose right equipment for current measurement?

When choosing the right equipment to measure the current of Yalong River, two aspects need to be considered:

According to the purpose of use, if for horizontal cross-section measurement, Horizontal ADCP-HADCP would be suitable. It is designed to measure the flow velocities over a horizontal plane in the river with accuracy for the lateral distribution of the current. The Vertical ADCP would be more appropriate in regard to vertical cross-section measurement, because this will profile the current from surface to bottom along a vertical line in the water column.

Frequency tolerance by various ADCPs is suitable for different water depths. For example, a frequency of 600 kHz is quite suitable for water depths within 70 m. That could allow it to measure the current correctly in the shallower parts of Yalong River. A frequency of 300 kHz, however, can be more suitable for waters as deep as 110 m, thus useful when the river part gets greater in depth.

Well-known brands include Teledyne RDI, Nortek, and Sontek. However, for those who are in search of an economical one with good quality, it is highly recommended to check the China Sonar ​PandaADCP. It is made from all-titanium alloy material and enjoys an incredibly good price-performance ratio. You can find out more about it on its website: ​https://china-sonar.com/.

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