145-3 Reduced water storage capacity after multiple tropical cyclones: Assessing Sediment Accumulation in Caonillas & Dos Bocas Reservoirs after Hurricanes María (2017) and Fiona (2022)

Session: Dynamics of Natural and Built Environments (Posters)

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Abstract:

Fresh-water reservoirs are vital to ensure reliable water supply, facilitating hydropower, regulating floods, and supporting recreation. However, these installments are increasingly vulnerable to the adverse effects of sedimentation that diminishes reservoir storage, increases flood vulnerability, and degrades infrastructure. Climate change and potential increased frequency of extreme weather events can exacerbate sedimentation rates, notably tropical cyclone events.

In Puerto Rico, recent tropical cyclone events–including Hurricane María in 2017 and Hurricane Fiona in 2022–have accelerated the rate of reservoir sedimentation, especially by triggering tens of thousands shallow, predominantly debris flow landslides in the rugged mountainous interior of the island. In this study, we investigated sediment accumulation in Lago Caonillas (catchment area = 125 km²) and Lago Dos Bocas (catchment area = 615 km²) following the impacts of Hurricanes María and Fiona. Bathymetric data were collected using a GPS-integrated sonar system, processed in GIS, and compared to previous surveys. We determined excess sedimentation by comparing the total storage capacity observed in our results to projected storage capacity using the 21st century background sedimentation rates determined by previous bathymetric survey data (0.27 Mm³/yr for Caonillas and 0.12 Mm³/yr for Dos Bocas). 

Our results include over 7,000 depth sounding points for Caonillas, and over 3,500 for Dos Bocas, which were vertically corrected based on each lake’s standard operational level, and then interpolated throughout the reservoir using triangulated irregular network (TIN). The storage capacity of Lago Caonillas is interpreted to be 35.2 Mm³ in 2025, which is 63% of the original 55.7 Mm³ capacity in 1948. Excess sedimentation attributed to María and Fiona in Lago Caonillas is 1.43 Mm³ which represents 6 years worth of background sediment delivery. The storage capacity of Lago Dos Bocas is interpreted to be 11.6 Mm³ in 2025, which is 31% of its original 37.5 Mm³ capacity in 1942. Excess sedimentation attributed to María and Fiona in Lago Dos Bocas is 3.4 Mm³ which represents 29 years of annual sediment delivery.

These results underscore the critical role of extreme weather events and shallow mass wasting in sediment dynamics. This study offers significant insights into storm-driven sedimentation processes, thereby informing the long-term management of reservoirs and the mitigation of associated hazards to society.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9263

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