DAM BREAK RISK IN COLOMBIAA Geospatial Assessment of Population Vulnerability from Flood Inundation

Eugene Derner, GEOG 594aSpring 2014

ANALYTIC QUESTION

What would be the flood impacts if either of these dams failed?

Two large dams with towns located very close, downstream.

COLOMBIA

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

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)

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

• 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

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

METHODOLOGY – MODEL #1• Dambreak Rules of Thumb• Only 2 parameters needed• Spreadsheet computes answer – flow and stage every mile

METHODOLOGY – MODEL #1• Dambreak Rules of Thumb• “Delineate” flood depth elevations as polygon

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

METHODOLOGY – MODEL #2• Run Simplified Dambreak • Input dam/reservoir data• Elevation cross section data

METHODOLOGY – MODEL #2• Run Simplified Dambreak • “Delineate” flood depth elevations as polygons

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)

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)

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?

THANK YOUQUESTIONS?