How to Measure Water Current of Slave River?

1. Where is Slave River?

Slave River is one of the major rivers of Canada's Northwest Territories. Geographically, it falls in the northern part of the country. The river is one of the major tributaries of the Mackenzie River system. Its origin is from the Great Slave Lake.

It flows through the boreal forests and tundra regions of the immense and rugged Canadian landscape. Large mammals such as moose and wolves, and many species of waterfowl, are part of the wildlife that populates these areas. The river forms a very important habitat and source of water for these animals and the vegetation that grows around it. Small communities and indigenous people have settled along its banks. The Aboriginals have a long-standing attachment with the Slave River, for fishing, conveyance, and as a source of water for domestic and customary use.

Culturally, the river holds great importance for the indigenous communities. It is an integral part of their history, traditions, and stories that have been passed down through generations. The river is often a site for traditional ceremonies and is a symbol of their connection to the land and water.

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

The Slave River forms a crucial part of the regional water systems and ecosystems. The flow rate depends on seasonal and other factors.

In spring, as well as at the beginning of summer, there is significant flow in the river due to the release of ice along the Great Slave Lake and from snowmelt originating within the area. The water level rapidly increases, with a correspondingly strong current. This would, therefore, be the right season for sediment and nutrient transportation that would be responsible for the enrichment both downstream and into the floodplains.

During the late summer and fall, the flow rate stabilizes to some extent. However, it still provides a consistent water supply for the needs of the local communities and the wildlife. Its flow is also affected by rainfall in the catchment area. During winter, flow rate decreases, and a part of the river gets frozen. The average flow rate depends upon the amount of snow falling and ice forming in the catchment areas, the nature of topography of the drainage basin regarding catchment and discharge, and the utilization pattern of water by the people of that area.

3. How to measure water current of Slave River?

There are several ways for measuring the water current of Slave River:

Velocity Meter Method

The traditional method employs mechanical or electronic velocity meters. In this method, these meters are placed at points in the water where one wants to measure the speeds of the water passing through. However, to obtain a more comprehensive understanding of the current, multiple placements at different locations and depths are required. This can often be a time-consuming operation and may not give a continuous profile of the current throughout the water column.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP is a much more advanced and efficient method of measurement of water current. It uses sound waves for measuring the velocity of water at various 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 allows for a more accurate and comprehensive measurement of the water current across different sections of the river.

Buoy Method

It consists of merely placing buoys in a river and following their motion as a function of time. The speed and direction of flow will be proportional to the magnitude of displacement of buoys that the water current creates in these buoys. In this method, certain assumptions were taken for granted. It will also not provide very correct measures of velocities at different depths, because wind and waves will certainly make the buoys also move due to factors other than water flow.

Among these, the ADCP method is more advanced and convenient for measuring the water current of the Slave River.

4. How do ADCPs using the Doppler principle work?

ADCPs are based on the principle of the Doppler effect. An acoustic signal is transmitted from the ADCP transducer into the water, where the sound waves are scattered by the moving water particles. Due to the flow of water, the frequency of the reflected sound waves back to the transducer shifts; this is what is called a Doppler shift.

That means, depending on whether the water moves towards or away from the transducer, reflected waves will occur either with a higher or a lower frequency than in emission. By precisely measuring the exact value of this frequency shift for numerous different angles and probe lengths, the ADCP computes independently, one from another, velocities within successive layers of the flow profile of different directions. 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's needed for high - quality measurement of Slave river currents?

The measuring equipment for high-quality measurement of the Slave River currents should have the following characteristics: the materials used in its construction should be reliable for accurate and consistent measurements; a small size is appropriate as it enhances deployment and retrieval in the river, especially in areas that are difficult to access; the equipment should also be lightweight to simplify the installation process and reduce the effort required for handling.

This will help the equipment to operate for long hours without the need for frequent battery replacements or complicated power supply setup. Cost-effectiveness allows the possibility of more extensive use and larger-scale measurement campaigns.

Titanium alloy is one of the best materials that can be used for casing in an ADCP. It has a lot of advantages. It is very resistant to corrosion, which is very important since it is always in contact with water, which may be carrying any minerals, sediments, and impurities. Additionally, it has a great strength-to-weight ratio; it provides an impact-resistant but lightweight casing. It is also able to withstand mechanical stresses upon deployment and in operation within the moving water of the Slave River.

6. Choosing the right equipment for measuring current

While choosing the right equipment for measurement of the Slave River Current, two major factors will be considered.

Depending on the usage purpose, for horizontal cross - section measurement, the Horizontal ADCP is suitable to go for. It is designed to correctly measure the flow velocities across a horizontal plane in the river, which is useful in understanding the lateral distribution of the current. In the case of vertical cross-section measurement, the Vertical ADCP would be more appropriate since it is designed for profiling the current from surface to bottom along a vertical line in the water column.

Different frequencies of ADCPs are suitable for different water depths. For instance, an ADCP at 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 Slave River. For deeper waters up to 110 m, an ADCP with a frequency of 300 kHz is more appropriate, which can be useful in areas where the river has 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.