Watershed Controls and Tropical Cyclone-Induced Changes in River
Hydraulic Geometry in Puerto Rico
Abstract
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. For example,
identification of landscape and river reach drivers of hydraulic
geometry can help to predict channel properties at ungaged sites and to
understand channel responses to major floods. Most prior AHG studies
have focused on mid-latitude, temperate regions. Tropical
zones-including those affected by tropical cyclones (TCs)-have received
less attention. This study analyzed spatial and temporal variability in
hydraulic geometry at 24 stream gaging sites in Puerto Rico, and
identified the watershed and river reach characteristics that correlate
with each hydraulic geometry parameter. These characteristics were then
used to build regression models of AHG parameters, with relatively high
predictive power. The largest flood events from each site were found to
cause systematic changes to AHG parameters; most of these floods were
caused by major TCs. Upstream drainage area, average watershed
elevation, watershed land cover and other characteristics were found to
be significant predictors of AHG parameters. Reaches with steeper slopes
were found to have limited lateral adjustability, which may reflect
consolidated bank materials and valley confinement. Watersheds with high
percentages of forested area showed greater changes in roughness but
less vertical adjustability than more developed watersheds. These
correlation results help inform whether river channel properties in
Puerto Rico and similar environments are resistant to the forces of
TC-induced flooding, and how these properties are affected by major
floods.