ADCP in Saint Marys River Flood Management

1. Where is Saint Marys River?

The Saint Marys River is a major river in North America. It drains Lake Superior into Lake Huron and forms part of the border between the United States (Michigan) and Canada (Ontario).

The length of this river is about 120 km. During its passage, it traverses varied topography. It has areas of outstanding natural beauty with forests and wetlands and areas of human-influenced development, with the cities of Sault Ste. Marie in the United States and Canada respectively using the river for shipping, fishing, and tourism among other economic activities. The Saint Marys River forms an important transportation link in the movement of goods between the upper and lower Great Lakes.

The Saint Marys River basin has a climate typical of the northern mid-latitudes, with four quite pronounced seasons. Winters are cold and snowy, and summers are mostly mild to warm. The snow melt in spring and the rain throughout the year ensure volumetric flow in the river. The most essential parts that keep up the river's water levels and flow are the flow from Lake Superior and the input from tributaries.

2. Why do floods occur in Saint Marys River?

Snowmelt and Heavy Rainfall: Most floods in the Saint Marys River are contributed to by snowmelt, coupled with heavy rainfall. During spring, heavy masses of snow, which have been accumulating through the winter season in this basin where the river is located, start melting. If there is also heavy rainfall at this time, a large amount of water enters the river system. The various tributaries that feed into the Saint Marys River add more water, and when the total volume of water becomes more than the natural carrying capacity of the river, then flooding can take place along its banks, particularly in low-lying areas.

Ice Jams: During winter, the river freezes over. When the ice starts breaking up in spring, jams can occur. These may impede the usual river flow and force water to back upstream, flooding over its banks. The backed-up water may be powerful in force and cause destruction to the infrastructure such as docks, levees, and bridges.

Upstream Water Management and Dam Releases: The Saint Marys River is also influenced by the operation of dams and other water management structures upstream. Sudden or unexpected large-volume releases from upstream reservoirs or dams can surge the water level in this river very quickly and cause flooding further downstream.

In the context of flood management, Acoustic Doppler Current Profiler (ADCP) offers a more modern and efficient way of measuring the flow of the river compared to the traditional methods.

3. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They send acoustic signals, or simply sound waves, into the water. These signals interact with moving particles in the water, like sediment particles and water molecules that are in flow with the current. When the emitted waves are reflected back by these moving objects, a change in frequency takes place.

This frequency shift, or Doppler shift, is linearly proportional to the velocity of the moving objects. Most ADCPs are fitted with multiple transducers that transmit acoustic pulses in several directions. For instance, a downward-looking ADCP current profiler can determine the velocity profile of the water column from the water surface down to the riverbed. By analyzing the Doppler shifts of the reflected signals from different depths within the water column, the ADCP current meter can calculate the velocity of the water flow at each depth.

Once the velocity at different depths is known, together with knowledge of the river's cross-sectional area, which can be measured or estimated, it becomes possible to calculate other important parameters such as the flow rate of the river.

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

Velocity Measurement: During flood events on the Saint Marys River, ADCP current profiler can precisely record the velocity of water flow at various locations and depths. This information is necessary in understanding how fast the flood waters are moving. This may allow anticipation of when flood waters would reach susceptible places like communities living along riversides, industrial areas, and facilities such as bridges and electric plants. By observing velocity continuously, authorities could therefore initiate necessary actions like evacuating the area or reinforcing the flood protection structure.

Flow Measurement Application: The velocity data of ADCP flow meter works out the flow rate of the river by integration over the cross-sectional area of the river. During flooding, it helps to give an idea about the total amount of water that passes across the section concerned. This will serve as basic information necessary in forecasting floods, and knowing what actually took place concerning the flood magnitude. It can also serve in determining the capability of such flood-control structures as levees and dams.

Sediment Transport Research Application: ADCP meter can study the backscattered acoustic signals as sediment is carried by the floodwaters of the Saint Marys River to understand the sediment movements. Sediment transport in flood conditions is important to know the alteration of the riverbed topography. Sediment deposition and erosion might alter the depth, width, and stability of the river, which impacts the occurrence of floods in the future and the general health of the river ecosystem.

5. How can data measured by the ADCP be utilized in the aspects of flood warning and the risk management of Saint Mary's River?

Warning about the Flood

Velocity and Flow Data Monitoring: In using the ADCP profiler to continuously monitor the velocity and flow data, an abnormal change within the river can easily be ascertained more in advance than before. A sudden increase in velocity or a significant change in flow rate can indicate an approaching flood or a worsening flood situation. This data can be integrated into flood-warning systems to provide timely alerts to local communities, emergency responders, and relevant authorities.

Water Level Prediction and Warning: ADCP-measured flow data is combined with other factors, like the geometry of the river's cross-section and historical records of water levels, to provide predictions of water levels that will be reached in the future. If the predicted water level is to rise above the flood-level mark, early warnings are issued for people to evacuate or take appropriate precautions.

Risk Management

Water Conservancy Project Scheduling Decision Support: The ADCP data provides valuable input for decision-making with regard to the operation of water-conservancy projects such as dams, reservoirs, and diversion channels along the Saint Marys River. For instance, during a flood, the flow data will help in determining the rate of release from a dam to mitigate the impact of the flood downstream.

Flood Disaster Assessment and Emergency Response: In the aftermath of a flood, ADCP data can be employed to assess the damage caused by the flood.

This will involve assessing the areas covered by high-velocity flow, the quantity of deposition carried out, among other factors. This information is useful for guiding emergency response and recovery efforts, such as search and rescue operations and post-flood rehabilitation of infrastructure and ecosystems.

6. What's needed for high-quality measurement of Saint Marys River currents?

For high-quality measurement of the Saint Marys River currents, several aspects need to be considered.

Durable Equipment Materials: The ADCP flow meter shall be manufactured from materials able to resist the harsh conditions in the Saint Marys River environment: resistant to corrosion by river water, impacts of floating debris such as branches, logs, and ice in colder months, and abrasion caused by sediment particles.

Small Size, Light Weight, and Low Power Consumption: A smaller and lighter ADCP meter is easier to install and deploy, especially in those areas that are difficult to access along the river. Low power consumption allows for longer-term operation without frequent battery replacement or complex power-supply arrangements, which is advantageous for continuous and long-term monitoring.

Low Cost: A lower-cost ADCP is preferred to facilitate large - scale deployment for comprehensive monitoring of the river.

As for the casing material, titanium alloy is an excellent choice. It has high strength that allows the ADCP profiler to bear the strong external forces, excellent corrosion resistance that guarantees the equipment's long-term performance in the water, and it is of relatively low density, which can help reduce the overall weight of the device while maintaining its structural integrity.

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

When selecting equipment to measure current in the Saint Marys River, consider:

Purpose of Use: If the focus is to measure horizontal cross-sectional flow, then HADCP shall be used. It measures flow velocity and other parameters across a horizontal section of the river. If the measurement is for a vertical cross-section, then a vertical ADCP is more appropriate as it can measure the velocity profile from the water surface to the riverbed along a vertical line.

Frequency Selection: With respect to the ADCP's various frequencies, different devices operate optimally over different ranges of water depth. Generally, an ADCP current profiler frequency of 600 kHz could suit water within 70 meters, while for a larger range-like water depths up to 110 meters, one should adopt 300 kHz. Hence, based on the real water depth of the Saint Marys River, an appropriate frequency is required to determine measurement accuracy and dependability.

There are well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. Additionally, there is a Chinese brand, China Sonar PandaADCP, which features a casing made of titanium alloy and offers a good cost - performance ratio. You can visit its website (https://china-sonar.com/) for more information.

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