The city of Ann Arbor has announced that starting the morning of Thursday, July 26, 2012, the Argo Cascades (the bypass around Argo Dam) will be shut down temporarily in order to keep the flow of water over the dam itself at the levels required by federal and state agencies. The Huron River has shown decreased flow for the past few weeks due to the lack of rain this summer.
At the city council’s July 16, 2012 meeting, public services area administrator Craig Hupy briefed the council on the fact that the city’s two hydroelectric dams (Barton and Geddes) were not generating electricity, due to the diminished river flow.
From the emailed communication sent by community services area administrator Sumedh Bahl to city councilmembers, the city administrator and other staff late Wednesday afternoon: “To comply with the Federal Energy Regulatory Commission and the MDNR [Michigan Dept. of Natural Resources] minimum flow requirements across Barton and Argo dams, the low flow in the river has necessitated closing Argo Cascades. Presently it is planned to stop the flow through Cascades tomorrow [July 26] morning. Staff will continue to monitor river flows and the flow will be restored to the Cascades when flow in the river improves.”
Added at 7:30 p.m. July 25 after initial publication: The key statistic is discharge rate, measured in cubic feet per second. The dam should ideally have at least 100 cfs of flow. Since July 16, the mean daily discharge rate has been between 60 and 80 cfs. Data on discharge rates is available from the USGS website. [.jpg of chart showing decreasing mean discharge rate over the last several months] [link to dynamic Google chart with daily discharge data back to 1980]
In city staff memory 1988 was a year with particularly low flow. That year in June and July, the river went several days with discharge rates in the range of 20-40 cfs. [.jpg of chart showing 1988 flow rates]
Update July 26 10:30 a.m. Cheryl Saam, who manages the city of Ann Arbor canoe liveries, confirmed in a telephone interview that the Argo Cascades flow was partially cut off this morning by inserting a stop log (a metal plate). Flow to the cascades was reduced by half, which will keep some flow through the cascades bypass, but is also expected to counter the dropping level of Argo Pond behind the dam. With some rain expected through the day, Saam hoped that the stop log could be removed soon. The designed flow rate for the cascades is 60 cfs.
Boat rentals for river trips from Argo to Gallup are suspended while the cascades have the stop log in place, Saam said. The low water levels had already led to modifications in the livery’s rental practice. For the last few weeks the Argo livery has been renting only single-person kayaks for those trips (not any canoes), because of the overall low flow in the river – as there are places where the river level is so low that the boats must be picked up and carried.
Update: Aug. 3. The city has announced that flow to the Cascades has been restored and the amenity is open for recreation again.