Flood- inundation maps for Río Grande De Loíza in and near Caguas, Puerto Rico, 2026

Digital flood- inundation maps for a 2.7- mile reach of Río Grande De Loíza in Caguas, Puerto Rico, were created by the U.S. Geological Survey. Water- surface profiles were computed for the stream reach by using a one- dimensional, steady- state, step- backwater model. The model was calibrated to the current (2025) stage- streamflow relation (rating curve) for the U.S. Geological Survey streamgage 50055000, Río Grande De Loíza, Puerto Rico. The resulting hydraulic model was then used to compute 16 water- surface profiles for water levels (flood stages) ranging from 19.00 to 34.00 feet at the streamgage; these flood stages range from “moderate flood stage” to above “major flood stage” as defined by the National Weather Service. The 34.00- foot stage exceeds the historical maximum peak stage of 33.20 feet, recorded at the streamgage in 1945. The simulated water- surface profiles were used in combination with a digital elevation model derived from light detection and ranging (lidar) data to map the inundated areas associated with each flood profile.

The flood- inundation maps and the supporting hydraulic model produced by this study can be used by emergency managers and local officials to assess flood- mitigation strategies and to define flood- hazard areas to help protect life and property, to coordinate flood- response activities such as evacuations and road closures, and to aid post- flood recovery efforts.