ADCP's application in flood management of Mackenzie River

1. Where is the Mackenzie River?

The Mackenzie River is in the Northwest Territories of Canada. It is the longest river system in Canada and originates from Great Slave Lake.

It flows northward through a broad, diverse landscape of boreal forests, tundra, and extensive floodplains. The river is highly important for transportation infrastructure in these remote northern regions and provides water for fishing, domestic water supplies in many local communities, and is also an important component of hydroelectric power generation in some places.

The climate of the region is subarctic, according to climate and water resources. The winters are long and extremely cold with ample snowfall; springs and summers receive snowmelt and rainfall. The resultant snowmelt from the huge catchment area, apart from the rainfall and the water from the tributaries, forms a significant contributor to the water volume of the river. When all these factors combine together, the volume of water changes very significantly and may cause flooding, which would be quite real during heavy snow melting or during intense rainfall.

2. What causes floods in the Mackenzie River?

Snowmelt and Heavy Rainfall: The main causes of flooding in the Mackenzie River are rapid snowmelting during spring and heavy rainfall during the wet season. All water from the melting of snow in the catchment area, along with the additional rainwater, can surge the volume of the river all of a sudden. Mountainous and hilly terrains around some of its tributaries accelerate the runoff process, hence channeling a large quantity of water into the main channel.

Topography: The river's course has large floodplains and low-lying areas that provide water to spread out and collect. Generally flat plains slow down the water, which can create a lot of flooding. Where many tributaries come together, during the high-flow period, the added amount of water could turn out to be adverse conditions for flooding.

Permafrost/Soil Conditions: The ground conditions of northern regions through which the Mackenzie River passes are highly influenced by permafrost. It is possible that such permafrost could thaw due to climate change and alter the soil structure and drainage pattern. This released water from it can make the ground less stable and prone to sliding or any other event leading to flooding.

The Acoustic Doppler Current Profiler (ADCP) is the most viable tool for comprehension and management of the Mackenzie River flow during the flood events.

3. How do ADCPs using the Doppler principle work?

The working principle of ADCPs is based on the Doppler effect. First, the device sends an acoustic signal into the water. Since the water is in flow, the signal interacts with moving water particles. When the acoustic signal is reflected back to the ADCP current meter, due to the Doppler effect, the frequency of the reflected signal is changed.

That is the difference in frequency between the emitted signal and the received one. Processing this frequency shift, it calculates the velocity of the water at different depths. Most of them have a few transducers, which send and receive acoustic signals in multiple directions. This gives them a profile of the water velocity across a section of the river.

For instance, in the case of water flowing towards the ADCP current profiler, the frequency of the reflected signal would be higher compared to the emitted one, while when the water is flowing away from the ADCP profiler, the reflected signal will be one with a lower frequency. Precise measurements of these frequency shifts and appropriate algorithms allow the ADCP meter to correctly calculate the velocity of the water at different places inside its measurement range.

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

Velocity Measurement

ADCP flow meter becomes important during flood events in the Mackenzie River as it gives the real and accurate velocity of water flow. It continuously monitors the water velocity at various depths and locations with a view to supplying real - time data regarding the speed at which water moves. This becomes important in understanding the dynamics behind a flood, including in the determination of the direction and intensity of the floodwaters movement.

Flow Measurement

Application ADCP current profiler is also capable of flow rate measurement. It takes the known cross-sectional area of the river and adds to it the measured water velocities across a section in the river. It uses these two pieces of information together to calculate the total volume of water passing through the section per unit time-the flow rate. This becomes vital information in analyzing the general volume of water during a flood and making informed decisions on flood control and management of water resources.

Application in Sediment Transport Study

Besides flow and velocity measurement, ADCP flow meter is useful in sediment transport study along Mackenzie River during flooding. While water flows, it carries sediments. The ADCP profiler is able to detect the variation in the backscattered acoustic signal produced by the presence of sediments. From this variation, it is possible to estimate the quantity and movement of sediments, a very important factor in long-term evolution understanding both in the riverbed and the action of floods on the sedimentary environment of this river.

5. How can the data measured by ADCP be utilized to develop flood warning and in risk management of the Mackenzie River?

Flood Warning

Velocity and Flow Data Monitoring: In real time, the ADCP current profiler obtains velocity and flow data that is continuously monitored. If the water velocity is above the critical threshold or if there is a considerable rise in the flow rate, this may be a signal of the approaching flood peak or a potential flood situation. The possibility of issuing an early warning enables various authorities to take necessary precautions, such as evacuation of people in low-lying areas or fortification of flood defenses.

Water Level Prediction and Warning: Measured flow data correlated with historical data of water level and appropriate hydrological models can be used for the prediction of future water levels using ADCP data. In case the predicted water level is foreseen to exceed the warning level of flood, timely warnings can be issued to the public, enabling them to prepare for the flood.

Risk Management

Water Conservancy Project Scheduling Decision Support: Accurate flow and velocity data provided by ADCP flow meter will be useful in decision-making for the operational aspects of water conservancy projects like dams and sluices. For example, according to the measured water flow, it is possible to regulate the release of water from the dam to control the water level of the Mackenzie River and reduce the impact brought about by flooding.

Flood Disaster Assessment and Emergency Response: In case of a flood, ADCP data can be utilized to ascertain the magnitude of the flood. It would contain information on inundation extent, flow velocity, and sediment deposition. This information is very beneficial to devise immediate responses for such situations and in conducting post-flood reconstruction and rehabilitation work.

6. What is required for high - quality measurement of the Mackenzie River currents?

In order to carry out a high-quality measurement of the Mackenzie River currents, several factors should be considered, above all, the equipment used in the measurement shall contain reliable materials. First and foremost, much attention shall be paid to casing ADCP current profiler. The casing is recommended to be made of titanium alloy. The strength of the titanium alloy is very high, meaning the equipment will be able to resist the pressure and impingement caused by water flow in the river. Moreover, it is highly resistant to corrosion, taking into account the possible content of a variety of corrosive substances in the water of the Mackenzie River.

Besides material reliability, size and weight of the equipment should be as small and lightweight as possible. This makes it easier to install and operate the ADCP current meter in different locations along the river, particularly those that are difficult to access. The power consumption should also be low to make the ADCP flow meter work for as long a period of time without changing batteries or hooking it to a power source every now and then. Besides, the cost of equipment should be fairly low so large-scale measurement is possible. A lower cost will allow the deployment of more ADCPs along the Mackenzie River for more comprehensive and detailed data in flood management.

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

The following aspects should be kept in mind when choosing the right equipment to carry out current measurement in the Mackenzie River. First of all, according to the type of measurement it will be used for, if the measurement is to be taken for a horizontal cross - section, then an HADCP should be chosen. If the measurement is to be used for a vertical cross - section, then a Vertical ADCP shall be used.

Secondly, for different water depths, different frequencies shall be applied. The 600 kHz ADCP, for example, can work only in water to a depth of up to 70 m. If the water of the Mackenzie River falls within this range, a 600 kHz can be considered if the measurement requirements match. If the water is deeper than 70 m up to 110 m, a 300 kHz will be more appropriate since it would give more accurate measurements at such depth.

Some of the well-recognized ADCP profiler brands in the market include Teledyne RDI, Nortek, and Sontek. However, those seeking to make a lower price investment could consider the China Sonar ​PandaADCP model. It is all made of titanium alloy material for strength and assurance of a steady life span in water. It also offers an incredible cost-to-performance ratio. You can find more about it on its official website: (​https://china-​sonar.com/).

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