How to Measure the Water Current of the Saint Marys River

1. Where is the Saint Marys River

The Saint Marys River is a significant watercourse in North America. This river lies between Lake Superior and Lake Huron and connects these two Great Lakes. The river forms part of the border between the United States, specifically Michigan, and Canada, particularly Ontario.

The Saint Marys River area is a location of historical and economic importance. The river has long served as a vital transportation route for ships carrying cargo, including iron ore, grain, and other commodities. It also provides habitat for an array of living organisms. There are fish species that migrate through the river, while the wetlands and riverbanks around it serve as a home to several species of birds, mammals, and other wildlife.

2. Discharge of the Saint Marys River

The discharge of the Saint Marys River depends on many factors. The water levels of Lake Superior and Lake Huron have a great impact. In general, the river is uniform because of the linkage with the two large lakes.

If Lake Superior has a high water level, the discharge in the Saint Marys River may increase. While at times of low water upstream, flow rate may be reduced. There is also the influence of seasons. For instance, at times when snow melts in spring, there can be a higher flow rate. The average flow rate is also affected by the balance between the inflow from Lake Superior and the outflow to Lake Huron, as well as any water management activities such as diversions for power generation or other uses.

3. Measuring the Water Current of the Saint Marys River

Velocity Meter Method

This is a traditional approach that depends on the use of mechanical or electronic velocity meters. In this case, meters are placed at key points in the water to provide a reading of the passing water speed. However, such placements have to be at various locations and depths of water for a comprehensive understanding of the current. This can indeed be time-consuming and hardly offers a continuous profile in the water column.

ADCP Method

It is the more advanced and efficient way to measure water current. Using reflected sound waves, it simultaneously measures the velocity of water at different depths. By sending out acoustic signals and processing the Doppler shift of the reflected signals, it builds up a profile of the current right from the surface to the bed of the river. This allows a more accurate and comprehensive measurement of the water current across different sections of the river.

Buoy Method

In this method, the buoys are installed on the stream and their movements monitored for time. The displacement caused by these buoys because of the water flow indicates their speed and the direction where the flow has to head. However, there exist limitations in regard to such a method of flow discharge measurement. It will not present the accurate velocity at varied depths nor will it be out of various environmental factors like the wind, which can affect the buoy motions.

Among these methods, the ADCP current meter method is more advanced and convenient for measuring the water current of the Saint Marys River.

4. How ADCPs Using the Doppler Principle Work

The operation of ADCPs is based on the Doppler effect. An acoustic signal emitted from the ADCP flow meter transducer into the water interacts with the moving water particles. Due to the flow of water, the frequency of the reflected sound waves back to the transducer shifts, a phenomenon known as the Doppler shift.

If the water is moving toward 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, then the frequency will be lower. By precisely measuring this frequency shift at multiple angles and depths, the ADCP meter can 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, providing valuable information about the speed and direction of the flow from the surface to the riverbed.

5. Requirements for High-Quality Measurement of Saint Marys River Currents

For high-quality measurement of the Saint Marys River currents, the measuring equipment should have certain characteristics.

The materials used for its construction should be of good quality to ensure good, precise, and consistent measurements. Small size is advantageous to ensure that deployment and retrieval in the river are done easily, especially in areas that have difficult access.

It should also be of less weight to make the installation easy and to reduce the energy needed in handling.

Low power consumption: this is important to allow for long measurement periods without a need for frequent replacement of batteries or a complicated supply of power.

Cost-effectiveness: it would allow more widespread use and larger-scale measurement campaigns.

When it comes to the casing of the ADCP profiler, titanium alloy is a good choice. Titanium alloy has many advantages. It is highly resistant to corrosion, which is highly needed in the sense that the equipment is always in contact with water, which may be of any mineral composition and contain various sediments and pollutants. It also has good strength to weight ratio to enable it to have strong but lightweight casing. It could also support the mechanical stresses during its deployment and operation in the flowing water of the Saint Marys River.

6. How to Select Appropriate Equipment to Measure Current

While selecting proper equipment to measure the current of the Saint Marys River, two important factors need to be considered.

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

Different frequencies of the ADCP are suitable for different water depth ranges. For example, in the case of ADCPs of 600 kHz frequency, the water should not exceed 70-m depth; thus, current measurements across relatively shallow sections of Saint Marys can be attained with higher accuracies from this type of device. Still, an ADCP can have as low as 300 kHz with deeper waters of around 110 m, which in turn becomes useful for places where depth in general is greater there.

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.