Flood-Induced Geomorphic Change of Floodplain Extent and Depth: A Case Study of Hurricane Maria in Puerto Rico

Rainfall from tropical cyclones (TCs) in Puerto Rico and similar environments can cause extreme riverine flooding accompanied by substantial scour, transport, and sediment deposition. These processes can alter channel and floodplain properties that, in turn, influence the susceptibility to future flooding. The potential of these geomorphic impacts of major floods to influence floodplains (e.g., 100-year flood extent and depth) has received relatively little research attention. Using high-resolution LiDAR topography collected shortly before and shortly after Hurricane Maria in Puerto Rico, this study examines how 10- and 100-year flood extent and flood depth changed in thirteen river reaches in response to Hurricane Maria, a devastating TC that struck Puerto Rico in September 2017. These findings were contextualized by comparing them against floodplain extent and depth changes resulting from peak flow quantile estimates created with and without Hurricane Maria streamflow observations. Changes in the flood extent (depth) associated with geomorphic responses to Hurricane Maria were up to 7% (16%) for 10-year floods. Somewhat smaller changes of up to 4% (8%) were found for 100-year flood extents (depths). On average, these changes were smaller than the peak flow quantile effects for the 100-year flood but greater for 10-year events. These results suggest that, at least in tropical areas affected by TCs, geomorphic changes wrought by major storms should be added to the list of considerations in floodplain mapping and updating. This issue may become more important as climate change continues to intensify TC-induced rainfall and flooding. (C) 2022 American Society of Civil Engineers.