How to Measure Water Current of Selenga River?

1. Where is the Selenga River?

The Selenga River is an attractive stream winding its course through the limitless lands of Mongolia and Russia. Starting in mountainous areas in the country of Mongolia, it gains its strength in different terrains, which involve beautiful steppes, rolling hills, and thick forests.

This river is a life-giving artery for many communities along its banks. Through Mongolia, it passes through expanses of land where nomadic herders have thrived for centuries; their livestock depend on these waters for drinking. Such a river also plays an immense role in the local ecosystem, providing a habitat to a rich variety of fish species, waterbirds, and many other forms of wildlife.

As it crosses into Russia, it continues to be an essential part of the region's fabric. It flows near towns and cities where it supplies water for domestic use, supports local industries, and offers opportunities for recreational activities like fishing and boating. The Selenga River is also culturally significant, with many local traditions and stories being intertwined with its waters. It has seen the passage of time, the growth of communities, and the change of seasons, thus turning it into part of the common heritage for both nations.

2. What is the flow rate of the Selenga river like?

The Selenga is important in the regions it passes through due to its great contribution to Mongolian and Russian water systems; hence, it plays a significant role in maintaining the ecological balance.

The flow rate in the Selenga River is seasonal. During spring, snowmelt from surrounding mountains raises its flow by as high as many times. The water level rises, and the current gets quite powerful, full of sediments and nutrients carried by it to enrich the downstream areas. This is an important period for the river's ecosystem since it rejuvenates the habitats along its banks and replenishes the water bodies it feeds into.

In summer the flow rate stabilizes somewhat yet it still continues to deliver a steady supply of water for all needs of the local communities and natural environment. The flow in this river is maintained by rains in the catchment and groundwater discharging into it. During the fall and winter seasons, the flow rate begins to taper off. However, it never completely dries up due to the large volume of water stored in its basin and the contributions from tributaries. The average flow rate varies depending on the amount of rainfall in the upstream regions, topography of the river basin that determines how water is collected and drained, and the local communities' pattern of usage.

3. How to measure water current of Selenga River?

There are several methods to measure the water current of the Selenga River:

Velocity Meter Method

This traditional method utilizes mechanical or electronic velocity meters. These meters are placed at selected points in the water to measure the speed of the water passing by. With many sets placed at different locations and depths, however, a good realization can be attained. The process is slow since the meters have to be placed with care at appropriate spots. It may also fail to provide a continuous profile of the current through the water column, since complete coverage is impossible. Sometimes gaps would exist between our realizations in how the water is flowing at each depth.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is an advanced and efficient way of measuring the current in water. It works by sending out sound waves to measure water velocity at several depths all at once. It will send out acoustic signals, using the Doppler shift in the reflected signals, to develop a very detailed profile of the current from the surface to the riverbed. The aim is to provide an estimate of the water current at any instance over more sections of the river with higher accuracy and, in detail, for a complete pattern of flow.

Buoy Method

Buys are set in the stream and followed over a length of time. The displacement of buoys due to the water current gives an indication of speed and direction. Nevertheless, the technique also has some limitations. The approach may not be effective in providing appropriate measures of the velocity at different levels of depth because the buoy movements might be interfered with by the surrounding forces such as wind and waves. These other forces interfere with the exact depiction of the effect caused by the water current on the buoys.

Among these, the ADCP current meter method is more advanced and convenient for measuring the water current of the Selenga River, since it can provide detailed and precise data across different depths and sections.

4. How do ADCPs using the Doppler principle work?

ADCPs operate based on the Doppler effect. When an acoustic signal is emitted from the ADCP flow meter transducer into the water, the sound waves interact with the moving water particles. As the water is flowing, the frequency of the reflected sound waves that return to the transducer undergoes a change, which is known as the Doppler shift.

If the water is moving towards the transducer, then the frequency of the reflected waves will be higher than the emitted frequency. On the other hand, if the water is moving away from the transducer, the frequency of the reflected waves will be lower. By precisely measuring this frequency shift at multiple angles and depths, the ADCP profiler is able to calculate the velocity of the water in different directions and at different levels within the water column. This enables it to create a detailed profile of the water current, thus providing valuable information on the speed and direction of the flow from the surface to the riverbed.

5. What is needed for high-quality measurement of Selenga river currents?

For high-quality measurement of the current of the Selenga River, the measuring equipment should have a specific character. The materials used in its construction must be reliable to give true and invariable measurements of the phenomenon. Any disadvantage or instability in the materials could affect the data obtained on the river's current.

A small size is beneficial for the equipment as it allows for easier deployment and retrieval in the river, especially in areas that might be difficult to access. Besides, being lightweight simplifies the installation process and reduces the effort required for handling the equipment.

Low power consumption is necessary. It ensures that the equipment can operate for extended periods without needing to replace the batteries or having a complex power supply arrangement. This is quite significant in the case of the Selenga River, which flows through relatively remote areas where it may be inconvenient to access the equipment for maintenance purposes.

Cost-effectiveness is also a very important aspect: good performance at reasonable costs is enabling wider use and more extended measurement campaigns, which is essential to constitute the knowledge of the current from space and time sections of interest for the river in particular.

The casing of an ADCP flow meter can be made using several kinds of materials; a suitable choice is a Titanium alloy. The advantages of this are as follows. It is highly resistant to corrosion, which is very important because the equipment is always in contact with water that could contain a number of minerals, sediments, and pollutants. The resistance will make the device last longer and be durable, hence protecting the internal parts from damage caused by the aquatic environment. Besides, titanium alloy has a good strength-to-weight ratio, which allows for a durable yet lightweight casing. This enables the casing to sustain mechanical stresses that will arise from the deployment and operation in flowing water of the Selenga River without overloading the equipment with excess weight.

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

In determining what kind of equipment will suit best in measuring the Selenga River current, there are mainly two aspects to consider.

Different types of ADCPs fit different measurement requirements and thus are suitable for different purposes of usage. For horizontal cross-section measurements, the Horizontal ADCP will be the appropriate choice. This is designed to very accurately measure the flow velocities across a horizontal plane in the river, which is useful to know the lateral distribution of the current.

The Vertical ADCP is better suited for vertical cross-section measurement. This type of ADCP current profiler will focus on profiling the current from the surface to the bottom along a vertical line in the water column, providing details about how flow velocity varies with depth and its impact on the riverbed and aquatic life.

Secondly, different frequencies of ADCPs are suitable for different water depths. For example, an ADCP with a frequency of 600 kHz is suitable for water depths within 70 m. It can provide accurate current measurements in relatively shallower parts of the Selenga River. An ADCP flow meter with a frequency of 300 kHz is more appropriate for deeper waters up to 110 m, which can be useful for areas where the river has greater depth.

There are well-known brands of ADCPs, including Teledyne RDI, Nortek, and Sontek. However, for those who need an economical solution with good quality, the China Sonar PandaADCP is highly recommended. It is made of 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.