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Dam Breach AnalysisLarge and Small
June 3, 2015
Matt Scott, Water Resources EngineerLisa Brink, Water Resources Engineer
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Introduction
• Discussion of Dam BreachTechnical Analysis for a Large and Small Dam
• Dam Safety – Emergency Action Plans• Considerations for Floodplain
Administrators
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Teton Dam Failure - Courtesy geol.ucsb.edu/
Dam Breach Introduction
Dam Break Introduction
Large Versus Small Dams
Lessons Learned
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Dam Breach Parameters
• Breach parameter determination fundamental to breach analysis• Dam breach parameters define the development of a dam breach,
and include:– Breach height, hb
– Breach width, B– Breach side slopes, m– Time to full breach
formation, tfm
B
hb
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Dam Breach Parameters – Breach Height
hb
hb
Dam in Profile ViewDownstream Face
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Dam Breach Parameters – Breach Width
B
Dam in Profile ViewDownstream Face
BB
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Dam Breach Parameters – Time to Failure
Dam in Profile ViewDownstream Face
tf
• Directly related to peak flow• Related to volume of water stored and depth of water stored
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Mode of Failure
• Overtopping – uncontrolled flow over the dam• Piping – seepage through the dam erodes soil, creating a
flow path through the embankment
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Teton Dam Failure - Courtesy geol.ucsb.edu/
West Point Dam (Large) versus John Creighton Boulevard Dam (Small)
Dam Break Introduction
Large Versus Small Dams
Lessons Learned
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Project Introduction
• West Point Dam, Georgia– Map dam breach inundation– Inform USACE Emergency
Action Plan• John Creighton Boulevard
(JCB), Omaha, NE– Map dam breach inundation– Inform City’s Emergency
Action Plan
Courtesy wikimedia.org
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High Hazard
West Point Dam, Georgia JCB, NE
Dam BreachLarge and Small
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PurposeWest Point West Point
– Power Generation– Recreation– Flood Control– Fish and Wildlife– Area
Redevelopment– Navigation
Courtesy fws.gov
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PurposeJCB
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West Point Dam Size
• At summer normal pool elevation:– Area of 25,900 acres – Storage of 604,527 acre-feet
• West Point Dam located on the Chattahoochee River
Courtesy usace.gov
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JCB Dam Size
• Maximum Capacity:– Area of 14 acres– Storage of 90 acre-feet (top of dam)
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Input Data - Topographic
West Point Omaha
Dam BreachLarge and Small
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Input Data – OperationalWest Point Dam
Courtesy lrn.usace.army.milCourtesy lrn.usace.army.mil
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Input Data – OperationalJCB
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Breach ParametersPrediction of Embankment Dam Breach Parameters
JCB
Dam BreachLarge and Small
Time to breach (hours) 0.71
Final breach width (ft), B 40
Final breach height (ft), hb 8
West Point
Time to breach (hours) 3.8
Final breach width (ft), B 380
Final breach height (ft), hb 96
m
B
hb
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Modeling Approach
West Point JCB• Unsteady HEC-RAS
– Overtopping Failure
Dam BreachLarge and Small
• Unsteady HEC-RAS– Sunny Day Analysis versus
Spillway Design Storm– Piping Failure– Downstream limit: 2-foot
difference in water surface elevations (Dam breach versus 100-year)
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Modeling Approach – FEMA FIS DataWest Point
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Modeling Approach - Incremental Hazard Analysis JCB
• Request by Nebraska DNR
• Dam volume small compared to possible hydrologic events
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Downstream CharacterizationWest Point
Rural
Small Towns
Downstream Modeled Extent
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Downstream CharacterizationJCB
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Teton Dam Failure - Courtesy geol.ucsb.edu/
Lessons Learned
Dam Break Introduction
Large Versus Small Dams
Lessons Learned
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Lessons Learned
• Dam Breach analyses help describe total flood risk in a community– Potential for dams to increase hazard
• EAPs may be helpful in developing local floodplain ordinances• Dam breach hazards not intuitive or straightforward
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Dam Safety Information
http://www.damsafety.org/map/
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Questions?
Credit: https://susannesartandlife.wordpress.com/tag/shark/