Measuring Great Lakes flows helps forecast water levels

Posted on December 2, 2021

DETROIT- Monitoring the amount of water moving through the Great Lakes system is important to help forecast Great Lakes water levels and support international monitoring efforts.

U.S. Army Corps of Engineers officials physically measure discharge, or flow, in the connecting channels using acoustic technology. Monthly flow in the connecting channels is the largest contributing factor to the level of each Great Lake and is a critical piece in forecasting Great Lakes water levels.

Detroit District Hydraulic Engineer, Matt McClerren demonstrates flow measurement on the Detroit River and how the Corps of Engineers estimates monthly flows the fifth ‘On the Level’ video, available on the district’s website at https://go.usa.gov/xFEWx.

“The measurement of flow is made using an Acoustic Doppler Current Profiler (ADCP) attached to a manned boat,” said McClerren. “While traversing the river, the ADCP sends sound waves into the water column which returns the speed of water while simultaneously measuring the shape of the river channel. The speed multiplied by a measured area results in the total flow of the channel.”

Flow is the amount of water passing a given point in the river at a specific time. On the connecting channels, a relationship develops between the boat measured flow, water level and water velocity.

Water flows between the Great Lakes via connecting channels, which includes the St. Marys, St. Clair, Detroit, Niagara, and St. Lawrence Rivers. Flow is measured multiple times each year. The Detroit District is the only Great Lakes district that measures flow.

“When we most recently measured in October, there was about 7,000 cubic meters per second of water flowing down the Detroit River, which equates to almost three Olympic swimming pools worth of water passing by every second,” according to McClerren.

The first recorded discharge measurements in the connecting channels were in 1841 on the Niagara River. Prior to the development of acoustic technology, a price current meter measured the speed of water. This was time consuming and required a significant amount of manpower. Acoustic technology allows a small crew to measure flow very rapidly and more accurately than conventional technology.

The mission of the Hydraulics and Hydrology Branch is to monitor all water that flows in and out of the Great Lakes. Monitoring the levels and flows are critical to support international outflow management activities at key locations where flows are managed.

‘On the Level’ videos are available on the District’s website and YouTube page at:
https://go.usa.gov/xFEWx and https://youtube.com/playlist?list=PLqtbMFyAaYYNkKS2wxdyBsDYSBQXP3HLq.

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