Dam Failure Analysis for the Lago El Guineo Dam, Puerto Rico

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The USGS Scientific Investigations Report 2016-5070 describing a hydrologic and hydraulic study to assess the potential hazard to human life and property associated with the hypothetical failure of the Lago El Guineo Dam was completed by the USGS in cooperation with the Puerto Rico Electric Power Authority. 

The Lago El Guineo Dam is within the headwaters of the Río Grande de Manatí and impounds a drainage area of about 4.25 square kilometers. The National Dam Safety Program and the Puerto Rico Inspection and Regulation of Dams and Reservoirs Program require each dam owner to prepare an Emergency Action Plan (EAP). The EAP must be prepared, maintained, and executed when needed to minimize property damage, injury, or loss of life in the event of an emergency-flooding situation caused by dam failure. The EAP requires hydrologic and hydraulic analyses of the dam to assess the potential downstream hazard to human life and property.

Location of Lago El Guineo and the dam in the Rio Grande de Manatí hydrographic basin, Puerto Rico.

Location of Lago El Guineo and the dam in the Rio Grande de Manatí hydrographic basin, Puerto Rico.

Above the Lago El Guineo Dam, the simulated inflow peak discharges from HEC–HMS resulted in about 550 and 414 cubic meters per second for the 6- and 24-hour probable maximum precipitation events, respectively. The 24-hour, 100-year recurrence storm simulation resulted in a peak discharge of about 216 cubic meters per second. For the hydrologic analysis, no dam failure conditions are considered within the model. The results of the hydrologic simulations indicated that for all hydrologic conditions scenarios, the Lago El Guineo Dam would not experience overtopping. For the dam breach hydraulic analysis, failure by piping was the selected hypothetical failure mode for the Lago El Guineo Dam.

Results from the simulated dam failure of the Lago El Guineo Dam using the HEC–RAS model for the 6- and 24-hour probable maximum precipitation events indicated peak discharges below the dam of about 1,340 and 1,430 cubic meters per second, respectively. Dam failure during the 24-hour, 100-year recurrence rainfall event resulted in a peak discharge directly downstream from Lago El Guineo Dam of about 1,180 cubic meters per second. Dam failure during sunny-day conditions (no precipitation) produced a peak discharge at Lago El Guineo Dam of about 1,015 cubic meters per second assuming the initial water-surface elevation was at the morning-glory spillway invert elevation.

Aerial photograph of the Lago El Guineo Reservoir facing upstream.

Aerial photograph of the Lago El Guineo Reservoir facing upstream. Photograph courtesy of the Puerto Rico Electric Power Authority

The results of the hydraulic analysis indicate that the flood would extend to many inhabited areas along the stream banks from the Lago El Guineo Dam to the mouth of the Río Grande as a result of the simulated failure of the Lago El Guineo Dam. Low-lying regions in the vicinity of Ciales, Manatí, and Barceloneta are among the regions that would be most affected by failure of the Lago El Guineo Dam. Effects of the flood control (levee) structure constructed in 2000 to provide protection to the low-lying populated areas of Barceloneta, were considered in the hydraulic analysis of dam failure. The results indicate that overtopping can be expected in the aforementioned levee during 6- and 24-hour probable maximum precipitation events. The levee was not overtopped during dam failure scenarios under the 24-hour, 100-year recurrence rainfall event or sunny-day conditions.