the probable maximum flood (pmf) is an event calculated by ferc to occur once every 10,000 years by...
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![Page 1: The Probable Maximum Flood (PMF) is an event calculated by FERC to occur once every 10,000 years By comparison, the flood of September, 1986 was a 100-year](https://reader038.vdocuments.mx/reader038/viewer/2022102900/5519bd3455034660578b4a33/html5/thumbnails/1.jpg)
The Probable Maximum Flood (PMF) is an event calculated by FERC to occur once every 10,000 years ◦ By comparison, the flood of September, 1986 was a
100-year flood event The FERC requires all “high hazard” dams to
be able to safely pass the 10,000-year flood without failing (overtopping)◦ FERC considers Edenville to be a “high hazard” dam
because its failure would likely result in loss of life and property at Sanford Lake and downstream
What is the “PMF”?
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Six spillways will be reconstructed to double their capacity to pass flood water◦ There are 3 spillways at the Tobacco River side of
the dam and 3 spillways adjacent to the Edenville powerhouse on the Tittabawassee River side
The total capacity of the six spillways is currently 32,000 cubic feet per second (cfs) (or 14,400,000 gallons per minute)
To comply with FERC’s mandate, the capacity of the six spillways will have to be increased to 64,000 cfs (or 28,800,000 gpm)
What needs to be done?
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Spillway ComparisonCurrent configuration of spillways
Tittabawassee side adjacent to powerhouse shown; Tobacco spillway is similar
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Spillway comparison
FERC-Mandated alteration of spillways
Tittabawassee side adjacent to powerhouse shown; Tobacco spillway is similar
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3-Dimensional ViewsExisting spillway construction
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3-Dimensional ViewsFirst concrete pour inside spillway (summer 2013)
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3-Dimensional ViewsNew concrete pier extensions (summer 2014)
This work takes place “in the dry” behind a sheet pile cofferdam
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3-Dimensional ViewsStoplogs are placed between piers & rest on new concrete sills
Once stoplogs are in place water levels can be returned to normal
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3-Dimensional ViewsConstruction work taking place between 2015 and 2016
More concrete is
poured in the base of the
spillway
Existing gate and bridge are
removed
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3-Dimensional ViewsConstruction work taking place between 2015 and 2016
Concrete rollaway slabs and most of upstream barrel arches are removed
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3-Dimensional ViewsConstruction work taking place between 2015 and 2016
New concrete crest is poured
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3-Dimensional ViewsConstruction work taking place between 2015 and 2016
Concrete overlay is placed over entire pier structure
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3-Dimensional ViewsConstruction work taking place between 2015 and 2016
New bridge is constructed
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3-Dimensional ViewsTobacco Spillway to be completed in 2016
New gate is installed and stoplogs are removed
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3-Dimensional Comparison
Existing spillway Modified spillway