How to Measure the Water Current of the Milk River

1. Where is the Milk River?

The Milk River is one of the major streams in the United States and Canada. Its source is in Glacier National Park, Montana, USA, from where it flows north to form part of the international boundary between the two countries before its discharge into the Missouri River.

It cuts across a vast array of lands: from grasslands to prairies and even semi-arid areas. The river happens to be an important ecosystem for the regional fauna, serving as a water source for different animal species, including deer, antelope, and many bird species. It has cultural and historical significance to the native inhabitants and early settlers in this region. In addition, it serves as a water source for some agricultural activities along its course, though its flow and availability can be somewhat variable given the climate of the region.

2. What is the flow rate of the Milk River like?

Seasonal and climatic variations cause huge changes in flow rates of the Milk River. During spring, snowmelting from surrounding mountains and at higher elevations increases the flow rate of the river. The melting of snow and ice sends a relatively large volume of water downstream, and thus the river experiences a higher-flow period.

During the summer and autumn, the flow rate slowly decreases due to the reduced influence of snowmelt in those months, as well as higher evaporation rates. During winter, this flow might be further reduced, while in colder periods or stretches, parts of the river may partially freeze over. The average flow rate may vary from only a few cubic meters per second during the low-flow winter or dry periods to several hundred cubic meters per second during the peak of the spring snowmelt.

3. How to measure water current of the Milk River?

Velocity Meter Method

Traditional monitoring involves the use of mechanical or electronic velocity meters. These instruments are used to measure water current velocities directly at selected points along the river. To obtain a thorough record of the general current of water, several readings are required at various points over different parts of the stream. Considering the length and altered stages of flow in the Milk River, this particular method of measurement can be time-consuming and requires more manpower.

ADCP Method

ADCP current meter represents a more sophisticated and handy method for the measurement of water current. It depends on the use of sound waves for the detection of water particles' movements. By emitting acoustic signals and analyzing the Doppler shift of the reflected signals, it can measure the velocity of water at multiple depths simultaneously. This gives a very thorough profile of the water current and thus provides a better estimation of the flow conditions within the river. ADCPs are available for mounting on boats where the river is navigable, on bridges if available, or on buoys for continuous monitoring.

Buoy Method

The buoy method consists of setting buoys in the river, which will have sensors that measure the movement of water around them. The buoys float on the surface and can give some indication about the surface current. However, it might not be as captive of all the complexities regarding the water current, especially when trying to comprehend the variations of velocity in greater depths compared to the other methods.

Of these methods, the ADCP current profiler is the more advanced and suitable one for measuring the water current of the Milk River.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the basis of the Doppler principle: an ADCP flow meter sends out an acoustic signal into the water; the sound waves travel in water and collide with moving particles of water. Because the water particles are moving, the frequency changes in reflected sound waves, according to the Doppler effect.

If the water particles are moving towards the ADCP meter, then the reflected wave will be of higher frequency compared to the emitted frequency. On the other hand, if the particles are moving away from the ADCP, then the reflected wave will have a lower frequency. The precise measurement of this change in frequency will enable the ADCP to calculate the velocity of the water particles at different depths.

The ADCP profiler then combines these individual velocity measurements at various depths to create a complete profile of the water current. This therefore allows detailed insight into how the water is flowing, not only at the surface but also throughout the vertical section of the river.

5. What's needed for high-quality measurement of the Milk river currents?

For high-quality measurement of the Milk River currents, the equipment needs to have certain characteristics.

The equipment should have high material reliability. It must be able to withstand the harsh conditions of the river environment, including exposure to water, sediment, and varying temperatures. The Milk River's variable flow and the presence of debris during high-flow periods require durable equipment.

It is also desirable that it has a small size, lightweight, and low power consumption. A compact and lightweight device is easier to handle and deploy on a boat or attached to a buoy. Low power consumption ensures that the equipment can run for longer periods without frequent battery replacements or access to a continuous power source.

The cost-effectiveness of that solution is a plus. Cheaper means there will be more ADCP meter devices put around, offering full coverage to monitor the river.

However, for the casing of an ADCP flow meter, titanium alloy should be one of the best choices. If dealing with water bodies like the Milk River, where the equipment would be constantly in contact with water or other possibly corrosive substances, this alloy is highly resistant to corrosion. The material is also strong and durable to withstand physical impacts, as well as changes in pressure that might occur during deployment and operation. Besides, titanium alloy has a relatively low density that helps in general with keeping the equipment lightweight.

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

While choosing the right equipment for measuring the current of the Milk River, various factors need to be considered.

Based on the Purpose of Use

In the case of the intention to measure the horizontal cross-section of the river current, then a horizontal ADCP current profiler is the appropriate choice. HADCPs are suitable devices meant for real measurement of water flow across the horizontal plane, and such a measurement will present the overall movement across this section of the river.

If one is interested in measuring the vertical cross-section of the river current, a vertical ADCP current meter will do the work. These instruments can measure the velocity of the water at various depths, thereby providing a detailed profile of how the water is flowing vertically within the river.

Based on the Frequency

The frequency again depends on the depth of water in Milk River. A 600 kHz ADCP would normally suffice for water depths up to 70 meters. A 600 kHz frequency provides a good resolution and is usually quite accurate for measuring the current of water in relatively shallow waters.

For deeper waters, say over 70 meters up to about 110 meters, a 300 kHz ADCP would be more appropriate. Lower frequency of 300 kHz can go deeper in water and still get reliable measurement of the water current.

Well-known brands include Teledyne RDI, Nortek, and Sontek. In recent years, for those who need an economical option while having very good quality, China Sonar PandaADCP can be one of the options. It is fabricated from all-titanium alloy material, hence guaranteeing strength and ensured reliability. Its cost-performance ratio is exceptional, therefore it would be a good alternative to measure the water current of the Milk River. More details about it can be obtained from its official website: https://china-sonar.com/.

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