How to Measure the Water Current of the Naryn River？

1. Where is the Naryn River

The Naryn River in Central Asia is an important watercourse. It is situated within Kyrgyzstan and is one of the main tributaries that feed the Syr Darya. The river originates from a source in the Tien Shan Mountains.

Further downstream, at the mountainous parts of Kyrgyzstan, it passes various beautiful valleys and alpine lands. The Naryn River is important in the local ecosystem, providing water for different flora and fauna. Surrounding areas support various types of wildlife, including fish species that are adapted to the cold, clear waters of the river. Along its banks, there are agricultural activities in some areas, where farmers use the river water for irrigation.

2. Flow Rate of the Naryn River

The flow rate in the Naryn River shows seasonal variation: during spring and early summer, because of snowmelt, the Tien Shan Mountains increase flow in the river. The water rises, and the current goes quite strong. This period is so important for transporting sediments and nutrients downstream that it provides enrichment to floodplains and adjacent ecosystems.

During the summer and fall, the flow rate stabilizes to some extent, depending on rainfall in the catchment area. In the winter, the flow rate may decrease, but it still maintains a flow due to groundwater contributions and the release of water stored in the upstream regions. Its value depends on various factors including snowfall in the upstream mountains, topography of the basin that decides how water will be collected and drained into the river, and also utilization by the local communities. It therefore always varies from time to time.

3. Methods to Measure the Water Current

Velocity Meter Method

The traditional approach is based on the usage of mechanical or electronic velocity meters. These are placed at fixed points in the water, which estimate the speed of the water that passes by them. To get an accurate view of the current, however, multiple placements are required at various locations and depths, which is a time-consuming process and might not provide a continuous profile of the current through the water column.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) method is a more advanced and efficient way to measure water current. It uses sound waves to measure the velocity of water at different depths simultaneously. By emitting acoustic signals and analyzing the Doppler shift of the reflected signals, it can create a detailed profile of the current from the surface to the riverbed. This provides for a more representative and precise measurement of the current of water across various river sections. Buoy method

In this method, buoys are set in the river, and their movements are continuously tracked. The displacing of the buoys with the water current gives an idea of the speed and direction of flow. There are drawbacks to this method also. It may not provide adequate velocity measurements at different depths and can be liable to external factors such as wind and waves, which affect the movement of the buoys.

Among these methods, the ADCP method is more advanced and handier for measuring the water current of the Naryn River.

4. Working Principle of ADCPs Using the Doppler Principle

ADCPs are based on the principle of the Doppler effect. An acoustic signal that is emitted from the transducer of an ADCP current meter into the water interacts with the moving particles in the water. Because the water is in flow, the frequency of the reflected sound waves coming back to the transducer is shifted, a phenomenon called a Doppler shift.

If the water is moving towards the transducer, then 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 flow meter is able to calculate the velocity of the water in different directions and at different levels within the water column. This enables it to provide a detailed profile of the water current, hence giving useful information about the speed and direction of flow from the surface to the riverbed.

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

The measuring equipment for high-quality measurement of the currents of the Naryn River should have the following characteristics.

The materials of its construction should be reliable because it will assure accuracy and consistencies in measurement. It should have a small size to make its deployment and retrieval at the river more effective, particularly on areas where accesses are poor. The equipment must be light to ease installation efforts and give less strain during 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 profiler, titanium alloy is an excellent choice. Titanium alloy has many advantages. It is highly resistant to corrosion, which is very important because the equipment is in contact with water that may contain various minerals, sediments, and pollutants. It has a good strength-to-weight ratio, enabling a durable yet lightweight casing. It also can resist mechanical stresses during deployment and operation in the flowing water of the Naryn River.

6.Selection of Appropriate Equipment for Current Measurement

There are two major factors that should be considered while choosing appropriate equipment for the measurement of current in the Naryn River.

According to the purpose of usage, during horizontal cross-section measurement, the Horizontal ADCP, or HADCP, is suitable. It is designed to measure with precision the flow velocities across a horizontal plane in the river, which is useful in understanding the lateral distribution of the current. For vertical cross-section measurement, the Vertical ADCP is more appropriate since it focuses on profiling from the surface to the bottom along a vertical line in the water column.

The second is that the use of different frequencies in ADCPs is suitable for various water depths. For example, an ADCP meter of frequency 600 kHz is suitable for a depth in water within 70 m, which can be accurate in current measurements at parts that are relatively shallow of the Naryn River. A higher-frequency ADCP with a 300 kHz setting could better measure currents in waters deeper to 110 m in such areas where the river possesses a greater depth.

There are well-known brands of ADCPs such as Teledyne RDI, Nortek, and Sontek. However, for those looking for a cost-effective option with good quality, the China Sonar ​PandaADCP is highly recommended. It is made of all-titanium alloy material and offers an incredible 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.