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Bathymetric survey and sedimentation analysis of Lago Patillas, Puerto Rico, August 2019

April 27, 2021

In August 2019, the U.S. Geological Survey, in cooperation with the Puerto Rico Electric Power Authority, conducted a bathymetric survey of Lago Patillas to update stage-volume data in order to determine the sediment infill rates and to generate a bathymetry map. Water-depth data were collected along predefined lines using single-beam depth sounder and Differential Global Positioning System technology. The study also included delineating a new reservoir shoreline based on 2016–17 light detection and ranging data and the establishment of a new official vertical datum at the reservoir referenced to the Puerto Rico Vertical Datum of 2002 (PRVD02). Survey results indicated that the storage capacity was 12.96 million cubic meters in 2019 at an elevation of 67.55 meters above PRVD02. The mean annual loss of capacity from 1961 to 2019 is 0.08 million cubic meters per year. The point of zero remaining storage of Lago Patillas is projected to be 161 years, ending in 2180.

The new vertical datum referenced to PRVD02 was established at Lago Patillas by conducting a Global Navigation Satellite System static observation in March 2019, which indicated that the spillway elevation is 67.55 meters. The new spillway elevation datum supersedes the previous datum (mean sea level) used on the island of Puerto Rico.