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What is the “PMF”?

What is the “PMF”?. 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

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What is the “PMF”?

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  1. What is the “PMF”? • 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

  2. What needs to be done? • 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)

  3. Spillway Comparison Current configuration of spillways Tittabawassee side adjacent to powerhouse shown; Tobacco spillway is similar

  4. Spillway comparison FERC-Mandated alteration of spillways Tittabawassee side adjacent to powerhouse shown; Tobacco spillway is similar

  5. 3-Dimensional Views Existing spillway construction

  6. 3-Dimensional Views First concrete pour inside spillway (summer 2013)

  7. 3-Dimensional Views New concrete pier extensions (summer 2014) This work takes place “in the dry” behind a sheet pile cofferdam

  8. 3-Dimensional Views Stoplogs are placed between piers & rest on new concrete sills Once stoplogs are in place water levels can be returned to normal

  9. 3-Dimensional Views Construction work taking place between 2015 and 2016 Existing gate and bridge are removed More concrete is poured in the base of the spillway

  10. 3-Dimensional Views Construction work taking place between 2015 and 2016 Concrete rollaway slabs and most of upstream barrel arches are removed

  11. 3-Dimensional Views Construction work taking place between 2015 and 2016 New concrete crest is poured

  12. 3-Dimensional Views Construction work taking place between 2015 and 2016 Concrete overlay is placed over entire pier structure

  13. 3-Dimensional Views Construction work taking place between 2015 and 2016 New bridge is constructed

  14. 3-Dimensional Views Tobacco Spillway to be completed in 2016 New gate is installed and stoplogs are removed

  15. 3-Dimensional Comparison Existing spillway Modified spillway

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