DAM BREAK RISK IN COLOMBIA A Geospatial Assessment of Population Vulnerability from Flood Inundation Eugene Derner, GEOG 594a Spring 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 MODEL Geospatial 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

RESULTS LA 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)

RESULTS SALVAJINA 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 YOU QUESTIONS?