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DAM BREAK RISK IN COLOMBIAA Geospatial Assessment of Population Vulnerability from Flood Inundation
Eugene Derner, GEOG 594aSpring 2014
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ANALYTIC QUESTION
What would be the flood impacts if either of these dams failed?
Two large dams with towns located very close, downstream.
COLOMBIA
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ASSESSMENT OF TWO DAMS• La Esmeralda and Salvajina Dams
• Characteristics• Large reservoirs: >500k acre-ft storage• Tall Dams: >=500 ft • Embankment style construction: not
likely to fail unless over filled
• Why these two dams?• Nearby population!• Small town < 2 miles downstream
La Esmeralda
Salvajina
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LA ESMERALDA• Characteristics• 778 ft (237 m) tall• Reservoir capacity over 550k acre-ft
• Population at risk• Santa Maria 3 miles downstream
• Mountainous canyon terrain
• Elevation drop from dam to town 1500 feet (500 ft/mile)
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SALVINA DAM• Characteristics• 486 ft (148 m) tall• Reservoir capacity over 560k acre-ft
• Population at risk• Suarez 1 mile downstream
• Foothills – small mountain terrain
• Elevation drop from dam to town 165 feet
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• Reservoirs are full. Dams in danger of being overtopped. • Worst case scenario• Condition consistent with the failure of embankment construction dam.
• Reservoir capacity is at maximum
• Dam failure due to overtopping and erosion of dam from top to bottom.
ASSUMPTIONS
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DATA – INPUTS TO DAMBREAK MODELGeospatial• DEM
• Hydrosheds – 3 arc second (90 meter) best source• Derive inputs for dambreak model
• Cross-section elevation slices• River channel slope
• Distance to points of interest• Terrain – Mountainous, foothill or plains
Hydrologic• Type of dam• Water elevation behind dam• Volume of water OR surface area of reservoir• Channel bottom elevation at foot of dam
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METHODOLOGY – MODEL #1• Dambreak Rules of Thumb• Only 2 parameters needed• Spreadsheet computes answer – flow and stage every mile
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METHODOLOGY – MODEL #1• Dambreak Rules of Thumb• “Delineate” flood depth elevations as polygon
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METHODOLOGY – MODEL #2• Derive elevation cross section data from DEM• One at midpoint between dam and town• Two at upstream and downstream sides of town
Cross sections
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METHODOLOGY – MODEL #2• Run Simplified Dambreak • Input dam/reservoir data• Elevation cross section data
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METHODOLOGY – MODEL #2• Run Simplified Dambreak • “Delineate” flood depth elevations as polygons
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RESULTSLA ESMERALDA
• Certain inundation of ENTIRE town of Santa Maria and highway leading from Dam to town • Rules of Thumb shows higher flood
(typical)• Max water depth 248 ft!• Time to flood less than 10 minutes!• Population 4,498 (2005)
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RESULTSSALVAJINA
• Certain inundation for MOST of Suarez• Rules of Thumb shows higher flood
(typical)• Max water depth 188 ft!• Time to flood less than 15 minutes!• Population 4519 (2005)
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CONCLUSIONS• Dam failure, although highly unlikely, would be catastrophic
• Very little time for warning• 15 minutes or less
• HydroSHEDS DEM resolution ~90 meters• Too coarse? • Does it matter for a flood of this magnitude?
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THANK YOUQUESTIONS?