ADCP's application in flood management of Slave River

1. Where is the Slave River?

The Slave River is located in the Northwest Territories of Canada. It is a main tributary of the Mackenzie River. The river has its source in Great Slave Lake and flows northward.

As it moves along its course, it cuts through a varied landscape comprising boreal forests and pieces of tundra. The Slave River provides a very vital transport corridor in the area and is a source of water for fishing and other domestic water supplies for small towns and communities in the area.

From the viewpoint of climate and water sources, the catchment area has a subarctic climate. It has long, cold winters with plenty of snowfall; during spring and summer, the snow melts, and there is rainfall. The snowmelt from the catchment area, along with rainfall and water from other tributaries, is the source of the river's water volume. This results in fluctuations in the water level and a risk of flooding in case of large-scale snow melting or heavy rainfall.

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

Snowmelt and Heavy Rainfall: The most important causes of floods in the Slave River are the rapid snowmelt in the spring period and heavy rainfall at the time of wet periods. Due to large amounts of water from melting snow in the catchment area, including additional rainwater, the volume can increase quickly. The topography in its vicinity near the source and tributaries can accelerate runoff, sending more water downstream.

Topography: The availability of floodplains and low-lying areas over the course of a river can easily accommodate spread water from the river and result in aggregation of water. These relatively flat areas slow down the speed of water, thus heightening the tendency of flooding. The confluence of other tributaries can also result in bringing more water during the high-flow periods and aggravate the flood situation.

Permafrost and Climate Change: Permafrost, in the higher latitudes through which the Slave River runs, is a serious consideration. Climate change-induced thawing of permafrost has implications for soil structure and drainage patterns. This can lead to the release of stored water and ground instability, potentially contributing to floods through processes like landslides.

Acoustic Doppler Current Profiler (ADCP) is a useful tool to understand and manage the flow of the Slave River during flood events.

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

ADCPs are based upon the principle of Doppler. The instrument sends out an acoustic signal into the water. In turn, as the water is in motion, it interacts with the moving particles of water. As the acoustic signal returns back to the ADCP profiler, the frequency of the reflected signal changes because of the Doppler effect.

The ADCP measures the differential frequency between the transmitted and received signal. From this frequency shift, it is able to compute the velocity of water at discrete depths. These instruments are commonly equipped with numerous transducers able to transmit and receive acoustic signals in various directions. This allows them to create a profile of the water velocity across a section of the river.

For instance, if the water is flowing towards the ADCP flow meter, then the reflected signal will have a higher frequency compared to that emitted. On the other hand, if the water is moving away from the ADCP current profiler, then the reflected signal will have a lower frequency. By precisely measuring these changes in frequency and using appropriate mathematical algorithms, the ADCP flow meter calculates the velocity of the water at various points within its measurement range.

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

Measurement of Velocity

For any flood events happening in the Slave River, Acoustic Doppler Current Profiler (ADCP) plays an important role in the correct measurement of the velocity of the water flow. By continuously monitoring the water velocity at different locations and depths, it provides real - time data on how fast the water is moving. This information is key to understanding the dynamics of the flood, such as predicting the direction and intensity of the movement of floodwaters.

Flow Measurement Application

In addition, ADCP flow meter can measure the flow rate of the Slave River. The code can combine the measured water velocities at several points across a section of the river using the known cross-sectional area of the river to calculate the total volume of water flowing through that section per unit time, that is, the flow rate. This information is crucial in the estimation of the general volume of the water in cases of flooding and making the right decisions when dealing with flood control or water resource management.

Application in Sediment Transport Research

Besides the measurement of flow and velocity, ADCP current profiler is helpful in sediment transport research along Slave River in the case of floods. While water flows, it transports sediments. The ADCP current meter can detect changes in the backscattered acoustic signal caused by the presence of sediments. From these changes, researchers can obtain an estimate of the quantity and movement of sediments-a critical fact for the study of the long-term evolution of the riverbed and the influence of flooding on the sedimentary environment within the river.

5. Data measured by ADCP can be used for flood warning and risk management of the Slave River in the following ways.

Flood Warning

Velocity and Flow Data Monitoring: In real time, the velocity and flow data obtained from ADCP profiler are continuously monitored. If the measured water velocity is more than a certain threshold or flow rate increases significantly, it might point toward the arrival of flood peaks or a flood situation that is imminent. This allows ample time for the relevant authorities to take precautionary measures, such as evacuation of people residing in low-lying areas or reinforcement of the flood defenses.

Water Level Prediction and Warning: By correlating the measured flow data with historical water level data and applying appropriate hydrological models, ADCP data can be used to predict future water levels. If the forecasted water level is predicted to exceed the flood warning level, warnings could be issued timely to the public for preparation for the flood.

Risk Management

Water Conservancy Project Scheduling Decision Support: The accurate flow and velocity data from ADCP current profiler can be helpful to assist decisions on the operation of water conservancy projects, such as dams and sluices. With the measured flow of water, for example, the release of water from a dam can be adjusted with the view to control the water level in the Slave River and alleviate the impact of floods.

Flood Disaster Assessment and Emergency Response: In the aftermath of a flood event, the data collected by ADCP current meter can be utilized to assess the extent of the flood disaster. It entails more information like the inundation extent, the velocity of flood flow, and the quantity of sediment deposition. It is quite useful for formulating emergency response plans and carrying out post-flood reconstruction and rehabilitation work.

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

In the measurement of the Slave River currents, some of the high-quality parameters that should be observed include the equipment used having reliable materials. Much attention should be paid to the casing of the ADCP flow meter, which is recommended to be made from titanium alloy. It has very high strength, enabling the equipment to bear the pressure and impact caused by the water that flows in the river. It is highly resistant against corrosion, too, which is extremely necessary considering the aquatic environment of Slave River that may have various corrosive substances in it.

Besides material reliability, its size and weight should be small and light, respectively. In this respect, it would be easy to install and operate the ADCP current meter  in any location along the river and particularly in those places which are inaccessible. Low power consumption is an essential factor because longer periods of continuous operation can be facilitated without changing the batteries or connecting with power sources. Besides, equipment cost should also be comparatively lower to make large-scale measurements feasible. A lower cost means that more ADCPs can be deployed along the Slave River, providing more comprehensive and detailed data for flood management.

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

In the selection of proper equipment for current measurement in Slave River, several factors should be considered. First, it has to consider what type of measurement the instrument will perform-if it is for horizontal cross-section measurement, then HADCP should be chosen; if for vertical cross-section measurement, then Vertical ADCP should be used.

Second, different frequencies are appropriate for different water depth levels. As an example, a 600 kHz ADCP will be suitable for water depths within 70 m. If the water depth in the Slave River is within this range and if the measurement requirements match, a 600 kHz ADCP can be considered. For deeper waters, like those exceeding 70 m up to 110 m, a 300 kHz ADCP is more appropriate, since it can provide more accurate measurements in such depths.

There are several famous brands for the ADCP current profiler in the market, like Teledyne RDI, Nortek, and Sontek. But these kinds of brands are more expensive; therefore, China Sonar ​PandaADCP is one of the good choices on cost-effective options. The all-titanium alloy material will guarantee that the machine is going to sustain many years in this water environment with great reliability. It also has an amazing cost-performance ratio. You can find more information about it on its official website: (​https://china-​sonar.com/).

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