ADCP's Application in Flood Management of the Nelson River

1. Where is the Nelson River?

The Nelson River is a major river in Canada. It is located in the central part of the country and is an important part of the Hudson Bay drainage basin. The river's source is in Lake Winnipeg and it flows north - eastward for about 640 kilometers (398 miles) before emptying into Hudson Bay.

It passes through regions with a subarctic climate. Consequently, it has long and cold winters and relatively short cool summers. The volume of the river water is influenced by snow melting in its surroundings during spring and early summer. In addition, precipitation within the warmer months also helps keep its flow.

2. What are the reasons for floods in the Nelson River?

The flooding in the Nelson River can be contributed to by several factors, including snowmelt. During spring, with the snowpack built up over the long winter months melting at a very fast rate, there is an enormous amount of water released into the river. If the rate of snowmelt becomes too high and the river's capacity to carry this water downstream is not enough, it results in flooding.

Heavy rainfall during the summer months can also be one of the causes of floods. Intense and long-lasting rainstorms can raise the level of the river quickly. The flat topography of the regions through which the river flows can exacerbate the flood situation. The floodplains have limited natural drainage, and when the water level rises, it can spread over a wide area.

Another factor is the presence of ice jams. During the spring thaws, the ice can be broken up and jam in the river. These ice jams block the typical flow of water, backing it up and flooding the surroundings.

In this context, an Acoustic Doppler Current Profiler (ADCP) offers a more technically advanced and efficient measurement methodology than traditional techniques, important for effective flood management.

3. How do ADCPs using the principle of the Doppler work?

The ADCPs make use of the Doppler effect. They send out acoustic pulses into the water. The pulses interact with moving particles in the water, like sediment grains, small aquatic organisms, and other suspended matter. When the acoustic waves bounce back after hitting these moving objects, a frequency shift occurs.

The magnitude of this frequency shift is directly related to the velocity of the moving objects and, consequently, the velocity of the water. For example, if an ADCP flow meter is placed in the Nelson River, perhaps on a floating platform or a fixed structure near the riverbank, it sends out sound waves that penetrate the water column. While the waves are reflected back by the flowing water and its constituents, the ADCP current meter analyzes the received signals to calculate the speed and direction of the water flow at different depths.

4. What are the applications of ADCP in floods of the Nelson River?

Flow velocity measurement: ADCP profiler is able to determine the water flow velocity in the Nelson River with high accuracy. During flooding, this is critical data that show the speed at which floodwaters are traveling. It helps in the prediction of the development of a flood-for instance, the speed at which water will arrive in downstream locations and which places have a greater chance of receiving damage from high-velocity flows.

Flow rate measurement: The measured velocities are combined with the cross-sectional area of the river, which is also obtainable with ADCP meter, to give the flow rate of the river. In a flood, it becomes necessary to know how much volume of water is passing through a given section, thus predicting the overall impact on downstream regions.

Sediment transport studies: ADCP current profiler is able to detect the movement of sediment particles with the flow of water. This is very helpful during flooding, which allows the researchers to have a proper view of the amount of sediment carried by the river. Sediment transport study provides the necessary knowledge on variations that would be expected in the riverbed, like areas where deposition or erosion could be taking place, thus leading to the instability of riverbanks and other infrastructures.

5. How can the data measured by ADCP be used in the flood warning and risk management of the Nelson River?

Flood warning

Flow velocity and flow rate data monitoring: Continuous monitoring of flow velocities and flow rates by means of ADCP current meter can facilitate early detection of changes that may indicate an impending flood. For instance, if the velocities or flow rates start to increase beyond normal levels, it can trigger an alert system. This enables the authorities to issue timely warnings to communities along the riverbanks.

Water level prediction and warning: By analyzing the relationship between flow rates, velocities, and water levels using historical data and ADCP measurements, future water levels can be predicted. This helps in providing accurate warnings to residents to take appropriate preventive measures such as evacuation or flood - proofing.

Risk management

Water Conservancy Project Scheduling Decision-Support: ADCP data is useful in the operation decision-making process concerning the different dams, reservoirs, and other water conservancy projects along Nelson River. For instance, when predicting a flood, it might be necessary to adjust the releases of water from the reservoir to avoid flooding downstream with a view to keeping structures safe through the ADCP-measured data.

Flood disaster assessment and emergency response: In the aftermath of a flood event, for example, ADCP data allows assessing the extent of the damage, such as the degree of erosion, changes in the riverbed, and effects on infrastructure. This will guide the emergency response efforts and help formulate future flood mitigation strategies.

6. What's needed for high-quality measurement of the Nelson River currents?

The equipment for the high-quality measurement of the Nelson River currents should be made from materials that are reliable. Of importance, the size and weight should be small to allow easy deployment along the river at various locations like on boats or at bridges, among others. It is good to have low power consumptions for long-term monitoring, especially in places that have limited power supply. Cost-effectiveness is of essence to ensure wide deployment for monitoring comprehensively.

The casing of ADCP flow meter is preferably made of titanium alloy. Titanium alloy has very good corrosion resistance, which is an important aspect, especially considering that the water in the Nelson River may contain many different minerals and salts. Also, it has a good strength-to-weight ratio, keeping the equipment durable yet still fairly easy to handle and install.

7. How to choose the right equipment for current measurement?

The following should be considered when selecting equipment to measure current in the Nelson River: A Horizontal ADCP (HADCP) is suitable for horizontal cross-section measurements. It measures the flow velocities across a horizontal plane, hence giving a good understanding of the overall flow pattern in a particular reach of the river. The Vertical ADCP will be more suitable for vertical cross-section measurements, as it profiles the velocities from the water surface to the riverbed along a vertical line.

An ADCP current meter with a frequency of 600 kHz is adequate for water depths up to approximately 70m. For deeper reaches, frequencies of 300 kHz are more suitable for water depths up to approximately 110m.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option, the China Sonar ​PandaADCP ​is recommended. It is made of all-titanium alloy materials and offers a good cost-performance ratio. You can find more information at (​https://china-sonar.com/​).

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