Watershed controls and tropical cyclone-induced changes in river hydraulic geometry in Puerto Rico

Study region: 24 stream gaging sites in Puerto Rico. Study focus: At-a-station hydraulic geometry (AHG), which describes how channel width, depth, and velocity vary with discharge at a river cross section, has long been used to study fluvial processes. Most prior AHG studies, however, focused on mid-latitude, temperate regions. Tropical zones, including those affected by tropical cyclones (TCs), have received less attention. This study analyzes spatial and temporal variability in AHG in Puerto Rico, and identified the characteristics that correlate with AHG parameters. These characteristics were then used to build regression models of these parameters. New hydrological insights for the region: Model performance suggests that AHG can be predicted at ungaged locations in Puerto Rico. The largest flood events, mostly caused by major TCs, were found to cause changes in all AHG parameters. Characteristics such as watershed land cover were found to be reliable predictors of AHG parameters. Reaches with steeper slopes were found to have limited lateral adjustability, which may reflect consolidated bank materials. Watersheds with high percentages of forested area showed larger changes in the AHG velocity relationship- related to changes in roughness-but less vertical adjustability than more developed watersheds. These results can help inform whether river channel properties in Puerto Rico and similar en-vironments are resistant to the forces of TC-induced flooding, and how these properties are affected by such floods.

Automated summary

This study analyzes the spatial and temporal variability of at-a-station hydraulic geometry (AHG) in Puerto Rico and builds regression models to predict AHG parameters. The study found that major tropical cyclones cause changes in all AHG parameters and that characteristics such as watershed land cover are reliable predictors. River reaches with steeper slopes and watersheds with a higher percentage of forested area show larger changes in AHG parameters.