Earth dam safety is important to because failure can result in devastating losses of human life and property. As Hurricane Maria crossed Puerto Rico, the dam spillway of Lago Guajataca in the northwest of the island suffered major damages, caused by overtopping due to extreme precipitation and other factors. After the hurricane, we initiated new surveying of the site with unmanned aerial vehicle (UAV) survey and structure-from-motion (SfM) analysis. The complete temporal analysis includes: SfM and airborne LiDAR datasets from 1930 until 2018. This analysis successfully captured the addition of volume associated with site improvements until the 1980s, approximately 31,000 m~3 of volume loss due to erosion triggered by Hurricane Maria, and the subsequent volume gain of about 17,000 m3 related to emergency repairs in the weeks and months after the atmospheric event. The methods used are remarkably effective to measure and monitor historical and ongoing site changes at earth dams.
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