Reservoir Infilling Following Hurricane María in Puerto Rico Relative to Background Rates of Deposition

Abstract:

Long term sediment gauging on rivers is expensive and few records exist in small watersheds. This is particularly true in the tropics where extreme precipitation from tropical cyclones often serve as the predominant mechanism for inducing landslides and other mass wasting events, yet the relative role of these extreme events in overall denudation and resulting reservoir infilling remains unclear. Hurricane Maria passed over Puerto Rico on September 20, 2017. Rainfall totals associated with the event exceeded 0.5 m, triggering over 40,000 landslides, and providing a rare opportunity to analyze resultant sedimentation within the island’s mountainous reservoirs. Here we present sediment core data from three reservoirs in Puerto Rico collected 2 years following the Maria event. Decadal rates of accumulation were calculated from shallow (<2m) sediment cores using short-lived radionuclides Cs-137 and Pb-210 and were combined with event stratigraphy developed using a combination of bulk density measurement, organic content, XRF-derived elemental composition and x-radiographic imagery. Present rates of decadal and event-induced accumulation are compared and contrasted with long-term annual sedimentation rates inferred from previous reservoir bathymetric surveys. Furthermore, we interpret hurricane María sedimentary characteristics in context of the sediment record to evaluate the relative magnitude of hurricanes induced sedimentation versus longer term erosion rates. Our findings provide insight on the role of hurricanes on denudation rates and resulting reservoir infilling over the past century in humid, mountainous, tropical settings.