How to Measure Water Current of Hongshui River?

1. Where is Hongshui River?

Hongshui River is an important river in south China. It is a big branch of Pearl River system.

It originates from the Yunnan-Guizhou Plateau and, through Guangxi, it flows into the sea. It passes en route through different kinds of scenery: mountain areas where it cuts its way in deep gorges, and the sides of the surrounding mountains are often covered with forests that play an important role in the ecosystem and water conservation.

Besides, the Hongshui River flows through a cultural heritage area. Indeed, most of its banks are inhabited by ethnic minorities. These people have their particular traditions and ways of life closely connected with the river. For instance, traditional fishing methods and water-related festivals are part of their cultural identity.

Besides, the river is an important transportation route in the region. It has been used for shipping goods and people for a long time. The fertile plains and valleys around the river support extensive agricultural activities, with crops like sugarcane and rice being grown, depending on the water from the river for irrigation.

2. What is the Flow Rate of the Hongshui River like?

The flow rate is of great ecological and self-sufficient importance in the Hongshui River and is due to many controlling factors.

One major factor is the seasonal rainfall. During the rainy season, often from April to September, there is a large rise in the upper reaches and the catchment area of this river due to heavy rains. Consequently, the current becomes fast, and its water level goes up. Heavy flow accompanies much sediment transport in this period, which might give great influence to the bed of a river and its channel morphology.

From October to March is the dry season, when the flow rate decreases. The river becomes shallower and its width may be reduced. However, it still has a base flow that is vital for the water needs of the local communities, irrigation for agriculture, and maintaining the ecological functions of the river. It is also impacted by the construction of dams and projects in the upper reaches with relation to water resources that alter the flow rate and distribution of the Hongshui River.

3. How to Measure Water Current of Hongshui River?

There are several methods for the measurement of the water current of the Hongshui River:

Velocity Meter Method: In this traditional method, the use of mechanical or electrical velocity meters is carried out. Mechanical velocity meters usually consist of a rotating element-a propeller-that turns with the flow of water. The speed of rotation is proportional to the water velocity. These meters are installed at discrete points in the river and are normally attached to fixed structures like bridges or piers. This method involves several installations at different locations and depths to achieve a proper concept of the general flow. It can be a rather labor-intensive process, especially given the length of the Hongshui River and the need to cover different sections.

Acoustic Doppler Current Profiler (ADCP) Method: ADCP is a more advanced and efficient way to measure water current. It uses acoustic waves to measure the velocity of water at multiple points within a water column simultaneously. It can give a very detailed profile of the water current from the surface to the riverbed by emitting sound pulses and analyzing the Doppler shift of the reflected signals. ADCPs can be mounted on boats or fixed structures along the river. This method allows a more accurate and comprehensive view of the flow patterns compared to the velocity meter method.

Buoy Method: Buoys equipped with sensors can be deployed on the surface of the Hongshui River. These buoys can measure the surface current while they themselves drift with the flow. The data collected includes the direction and speed of the surface movement. But this method mainly focuses on the surface layer and may not provide detailed information about the flow at deeper levels of the river.

Among these methods, the ADCP method is becoming more in vogue because it gives data that is fairly detailed and more extensive with relatively less effort and in a shorter length of time.

4. How Do ADCPs Using the Doppler Principle Work?

ADCPs work on the principle of the Doppler effect. When an ADCP is used in the measurement of the water current of the Hongshui River, it sends acoustic pulses into the water. These pulses interact with particles in the water, such as sediment particles, small aquatic organisms, or other suspended matter.

The Doppler effect makes the frequency of the reflected sound waves change when the particles are in motion. If the particles are moving towards the ADCP profiler, the frequency of the reflected waves is higher compared to the emitted frequency and vice versa. By measuring this shift in frequency with high precision and with the help of some advanced algorithms, the ADCP is able to calculate the velocity of the water at different points within its measurement range.

Besides velocity measurement, ADCPs can also determine the direction of the flow by analyzing phase differences of the reflected signals coming from different directions. In this way, detailed velocity profiles showing how the water is flowing at different depths and over different sections of the river are able to be created.

5. What's Needed for High-Quality Measurement of Hongshui River Currents?

To realize high-quality measurement of the currents in the Hongshui River, the equipment should possess the following characteristics:.

It will require that the materials of the equipment be reliable to hold out in adverse environmental conditions in the river. The Hongshui River has a great variation in water conditions: from highly turbulent flow with high sediment transport in the rainy season to relatively calm, limpid water in the dry season. Small size and lightweight will be advantageous for ease of deployment and retrieval, especially at potentially hard-to-reach sites.

Low power consumption is also very important. Due to the length of the river and the fact that equipment has to be placed at every other location, it is important to have equipment that can run for a long period with low power consumption for continuous and reliable data collection. Cost-effectiveness is another major factor: in order to carry out extensive measurements on the river, there is a need for affordable equipment without compromising on quality.

In the case of an ADCP meter casing, one could use titanium alloy as an excellent choice. Being highly resistant to corrosion, the importance of this cannot be stressed more, since the equipment would almost always be in contact with river water. Its strength-to-weight ratio is good, too, so a casing can be durable yet still keep the overall weight of the equipment relatively low. This helps protect the internal components and ensures ease of handling during deployment and retrieval.

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

In selecting appropriate equipment to measure current in the Hongshui River, the following two major factors shall be considered.

According to purpose of use, horizontal cross - section measurements can be performed by means of a horizontal ADCP flow meter. It gives the flow velocity across a horizontal plane and therefore is a very useful instrument in ascertaining how the water is behaving laterally within the river. In vertical cross-section measurements, the vertical ADCP would be more appropriate since it focuses on flow velocities from the surface to the riverbed along a vertical line, useful for understanding the flow characteristics in the vertical aspect.

Different frequencies are suitable for different water depths in terms of frequency. For instance, an ADCP current profiler with a frequency of 600 kHz is well-suited for water depths within 70 m. It can provide accurate measurements in the relatively shallower parts of the Hongshui River. In parallel, the ADCP at a frequency of 300 kHz will be suitable for water depths up to 110 m and could cope with deeper parts of the river where the flow patterns can be more complex.

There are well-known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. Additionally, a Chinese ADCP brand, China Sonar PandaADCP, is highly recommended. It has a casing made entirely of titanium alloy, which provides excellent durability and corrosion resistance. It also 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.