ADCP in Bow River Flood Management

1. Location and General Features

The Bow River is a river in the Canadian province of Alberta. It is part of the South Saskatchewan River's major tributary. The source of this river is located in the Canadian Rockies, particularly around Bow Lake and other glacial fed lakes.

It then passes through the city of Calgary and other smaller communities. Its alpine origin and the nature of prairies that it flows to regulate the climate in the Bow River basin. This area has a cold alpine climate in the mountains where snowfall is heavy throughout winter. Moving into the prairies, it turns into a continental kind of climate, cold in winters but warm in summers. It is also fed by the Rockies through snowmelt during spring and early summer, adding a lot to its volume of water. Rainfall also adds to its flow, especially during the summer months.

2. Reasons for Floods

**Snowmelt：**Snowmelt contributes to a huge increase in the volume of water in the Bow River. This can be quite rapid and extensive if there is a heavy snowpack in the Rockies. If the rate of snowmelt is too intense and exceeds the river's capacity to carry this water downstream, it causes flooding. The high-water period driven by snowmelt usually occurs from late spring to early summer.

Heavy Rainfall: Heavy rainfalls are common in the river basin, especially during the summer months. Intense and long-lasting rainstorms can swell the river very fast. When heavy rainfall coincides with the already high water levels from snowmelt, it further aggravates the flood risk.

Topography and Land Use: The city of Calgary and other urban areas along the river can alter the landscape through human-induced means, affecting the flow of the river. For instance, urbanization can decrease natural infiltration and increase surface runoff. Also, the river's path through the prairies and its relatively flat areas means that when water levels rise, it can spread out over the floodplains more easily.

3. How ADCPs Using the Doppler Principle Work

The working principle of ADCPs, or Acoustic Doppler Current Profilers, is based on the Doppler effect. They emit acoustic pulses into the water. These 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, by extension, the velocity of the water. For example, an ADCP current meter could be deployed in the Bow River by mounting it on a boat or fixed structure near the riverbank; it sends out sound waves that penetrate the water column. The ADCP flow meter analyzes the received signals reflected back by the flowing water and its constituents to calculate the speed and direction of the water flow at different depths.

4. Applications of ADCP in Floods

Flow Velocity Measurement: It is possible to determine with great accuracy the flow velocity of water in the Bow River using ADCP meter. This is highly valuable information in the case of flooding. By knowing how fast the floodwaters are moving, it becomes possible to predict the spread of the flood and to identify areas where high-velocity flows may cause erosion or other damage to riverbanks and infrastructure.

Flow Rate Measurement: Combining the measured velocities with the cross-sectional area of the river, also determinable using ADCP meter, enables the flow rate calculation. In the context of a flood, knowing the flow rate is essential for assessing the volume of water passing through a particular section of the river; this helps in predicting the overall impact downstream.

Sediment Transport Research: ADCP current meter is able to detect the movement of sediment particles along with the flow of water. In events of flooding, this gives some insight into the amount of sediment carried by the river. Understanding sediment transport gives insight into changes in the riverbed, such as deposition and erosion areas. These changes are important for the stability of the river and its structures.

5. Application to Flood Warning and Risk Management Using ADCP Data

Early Flood Warning

Flow Velocity and Flow Rate Data Monitoring: It monitors continuous flow velocities and flow rates from ADCP current profiler to allow for quick recognition of changes that can lead to a flood. In other words, if there are unexpected increases in flow velocity or flow rate over a specified normal value, alerts are triggered, which authorities may quickly issue to communities along riverbanks.

Water Level Prediction and Warning: By studying the relationship between flow rates, velocities, and water levels using historical data and the ADCP measurements, the forecast of future water levels could be done. The resultant information is vital in ensuring that correct warnings are made to the residents to take necessary action like evacuation or flood-proofing.

Risk Management

Water Conservancy Project Scheduling Decision Support: The data from the ADCP current meter is very useful to make decisions on the operation of dams and reservoirs or other kinds of water conservancy projects located along the Bow River. For instance, if it is forecast that a flood is going to occur, the release of water from such reservoirs can be modified based on the ADCP-measured information to reduce downstream flooding with a view to safety of these structures.

Flood Disaster Assessment and Emergency Response: The ADCP data could also be employed post-flood to analyze the damage caused-for example, the extent of erosion, the variation in bed levels, and the destruction to infrastructure. This informs emergency response activities and the planning for future flood mitigation activities.

6. Requirements for High-Quality Current Measurement

Equipment to accurately record the currents of the Bow River should be made with more reliable materials. Smaller in size and light in weight, it should not be a problem to place them at any instance across the river, whether in boats or bridges.

The low power consumption is critical in enabling long-term monitoring, which has limited power supply. Cost-effectiveness is also important to enable widespread deployment for comprehensive monitoring. The casing of ADCP profiler is preferably made of titanium alloy. Titanium alloy provides excellent corrosion resistance, which is necessary when dealing with the Bow River's water that may contain various minerals and salts. It also has a good strength-to-weight ratio, making the equipment durable and relatively easy to handle and install.

7. Selection of Equipment for Current Measurement

In selecting equipment for current measurement along the Bow River, the following should be considered.

In horizontal cross-section measurements, the HADCP is suitable because it measures the flow velocities across a horizontal plane and gives a clear understanding of the general flow pattern in a particular reach of the river.

In the case of vertical cross-section measurements, a Vertical ADCP is ideal since it profiles the velocities from the water surface to the riverbed along a vertical line.

Concerning frequencies, an ADCP flow meter with a frequency of 600 kHz shall be suitable for water depths up to approximately 70m. In sections with deeper waters, frequencies of 300 kHz are more appropriate for water depths up to about 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.