2026 CSDMS meeting-050
From CSDMS
(if you haven't already)
Log in (or create account for non-CSDMS members)
Forgot username? Search or email:CSDMSweb@colorado.edu
Browse abstracts
Geomorphic controls on suspended sediment dynamics in Puerto Rico
Sean Gallen,
(he/him),Colorado State University Fort Collins Colorado, United States. sean.gallen@colostate.edu
We analyzed USGS suspended sediment flux (Qs) and discharge (Qw) data from 61 Puerto Rican drainage basins (2-45 year records, 1967-2012) to identify controls on suspended sediment dynamics in mountain belts. Puerto Rico's central mountains span diverse crystalline rocks (granitic to ultramafic serpentine) and experience seasonal precipitation, with wet seasons when hurricanes and tropical low-pressure systems are common. Suspended sediment-derived erosion rates (0.61 ± 0.55 mm/yr) exceed longer timescale 10Be estimates by an order of magnitude, and show no clear relationship with topography, rock type, or mean annual precipitation. Despite topographic, geologic, and precipitation differences, normalized Qs statistics are similar across basins. Qs-Qw relationships show linear to weak clockwise hysteresis, but when considering runoff, they only exhibit linear to counterclockwise hysteresis, implying a system where sediment supply and transport are closely balanced. After major storms, most basins exhibit subtle clockwise hysteresis the following year. However, when accounting for runoff only, hysteresis is minimized, suggesting groundwater dilution and minimal storm-induced sediment loading. We identify a consistent runoff threshold (~0.2 mm/day) below which normalized Qs remains constant and above which it increases as a power function, representing rainfall needed to overcome threshold shear stress for sediment mobilization. This threshold explains why Qw probability distributions are light-tailed while Qs distributions are heavy-tailed. This phenomenon is attributed to a system where extreme events dominate suspended sediment transport, with>80% occurring during storms ≥10 times the mean discharge, and ~50% during storms ≥100 times the mean. Overall, Puerto Rico’s suspended sediment flux is weakly tied to landscape and climate variables but strongly governed by hydrologic extremes that control suspended sediment transport dynamics.
