How to Measure Water Current of Nanpan River?

1. Where is Nanpan River?

The Nanpan River is an important watercourse in China. It lies in the southwest of the country and is one of the upper reaches main tributaries of the Pearl River.

It winds through the Yunnan-Guizhou Plateau, a region of outstanding karst landscapes. Its banks are also home to a variety of ethnic minority communities. They have a deep attachment with the river and belong to a rich cultural heritage that is often associated with water. For example, fishing and water-related festivals form an important part of their traditions.

It passes through other lands that are important agriculturally. Fertile plains and valleys allow rice and corn, amongst others, to grow, with the river playing an important part as a water resource to aid in the irrigation required in these lands.

2. What is the Nanpan River Flow Like?

The flow rate of the Nanpan River is an ecologically and human-activity-wise important issue, which is influenced by multiple factors.

Seasonal rainfall has a very big effect. During the rainy season, from May to October, the amount of rainfall increases tremendously in the catchment area of the river. The flow rate is higher. The river is fuller and the current stronger. During this high-flow period, there is transportation of more sediment, which can have an impact on the riverbed and the shape of the river channel.

During the dry season, which is between November and April, it decreases. The river would be shallow and its width may be reduced. Nevertheless, it still has a base flow that is necessary to satisfy water needs in local communities as well as for the ecologic functioning of the river. Besides, projects dealing with water resources, such as dams or reservoirs in the upper reaches of the Nanpan River, can also affect the flow rate.

3. How to Measure Water Current of Nanpan River?

There are several ways to measure the water current of the Nanpan River:

Velocity Meter Method: This is the traditional method that employs mechanical or electrical velocity meters. Mechanical velocity meters often have a propeller-like component that rotates during the flow of water. The speed of rotation is related to the water velocity. These meters are placed at specific points in the river, usually attached to bridges, piers, or other fixed structures. However, this method requires multiple installations at different locations and depths to get a comprehensive understanding of the overall flow. It can be labor-intensive, especially given the length of the Nanpan River and the need to cover different sections.

The Method of ADCP: ADCP is a more advanced, rapid technique to measure water current. By using acoustic waves, this method measures the velocity in every layer in a water column at almost the same time. Just by emitting sound pulses, after analyzing the Doppler shift of the reflected signals, it can provide a close profile of the water current, from the surface to the bottom of the riverbed. ADCPs can be mounted either on boats or fixed across the river. This means that this method gives a more accurate and comprehensive representation of the flow patterns than probably the velocity meter method.

Buoy Method: Buoys with sensors attached can be set up on the surface of the Nanpan River. The buoys, as they move with the flow, measure the surface current. Data gathered by the buoys would involve the direction and speed of the surface movement. However, this method primarily deals with the surface layer and may not be very informative for the flow in other, deeper levels of the river.

Out of these, the ADCP method is becoming more popular due to its ability to provide extensive and detailed data with relatively less effort in a shorter time frame.

4. How do ADCPs using the Doppler Principle Work?

The ADCPs work on the principle of the Doppler effect. An ADCP while measuring the water current of the Nanpan River 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.

Since these particles are in motion, due to the Doppler effect, there is a shift in frequency of the reflected sound waves. If the particles move toward the ADCP profiler, the frequency of the reflected waves is higher than the frequency emitted by the transmitter; if they are moving away, it will be lower. The precise measurement of this frequency shift allows the ADCP, by means of sophisticated algorithms, to compute the velocity of water at different points within its measurement range.

In addition to the velocity measurement, ADCPs are also capable of determining the direction of flow by analyzing the phase differences of the reflected signals from different directions. This provides a very accurate velocity profile that shows how the water is flowing at different depths and across different sections of the river.

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

For high-quality measurement of the Nanpan River currents, the equipment should possess certain characteristics.

The materials of the equipment need to be reliable to withstand the harsh environmental conditions of the river. The Nanpan River has a wide range of water conditions, from high - flow periods with a lot of sediment to relatively calm and clear water in the dry season. A small size and light weight are beneficial, especially for ease of deployment and retrieval, especially in areas that may be difficult to access.

Another important issue is low power consumption. Since the length of the river requires the placement of equipment in many places, it is vital to have the ability to have equipment operate for long times with low power requirements. Cost-effectiveness is also a major concern. For comprehensive measurement across the river, reasonable equipment at low cost but without sacrificing quality should be adopted.

For the casing of the ADCP meter, a very good material is titanium alloy. Its corrosion-resistance property is excellent, which is absolutely necessary as the equipment would almost always come into contact with the water of the river. Its strength-to-weight ratio is also pretty good, making it durable in such a case while maintaining relatively low weight for the entire equipment. This helps in protecting the internal components and facilitates ease of handling during both deployment and retrieval.

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

In choosing what kind of equipment to undertake a current measurement of Nanpan River, two cardinal points must be considered.

On account of the purpose meant, horizontal cross-section, and measurements, the horizontal ADCP or HADCP must, therefore, be suitable. It measures the flow velocity across a horizontal plane and provides valuable information on how the water is laterally moving within the river. In the case of vertical cross-section measurements, the vertical ADCP flow meter would be more appropriate since it focuses on the flow velocity from the surface to the riverbed along a vertical line, useful for understanding the vertical flow characteristics.

Different frequencies are suitable in terms of frequency for different water depths. For instance, an ADCP current profiler operating at a frequency of 600 kHz is well-suited for water depths within 70 m. It could give good measurements in those relatively shallow parts of the Nanpan River. Meanwhile, the ADCP of 300 kHz frequency will be better for water depth up to 110 m and should be used across those deeper sections of the river where flow patterns could be more complicated.

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.