Sediment and water in motion: Hydrological insights and policy recommendations for the Guánica Bay, Río Loco Watershed.

Abstract

The Guánica Bay/Río Loco Watershed (GBRLW), located in southwestern Puerto Rico, represents a unique system influenced by extensive hydrological modifications, land-use changes, and sediment transport challenges. Historically, the watershed was reshaped by the Southwest Project (Lajas Valley Project), which expanded its drainage area and introduced interbasin water transfers to support agricultural irrigation. These modifications, combined with urban expansion and deforestation, have amplified sediment fluxes into coastal waters, threatening marine ecosystems, particularly coral reefs. This research integrates hydrological and sedimentary analyses with Geographic Information Systems (GIS) to examine the interplay between land use, water management, and sediment transport in the GBRLW from 2013 to 2017. During the study, data collected from six monitoring stations provided insights into sediment behavior under varying hydrological conditions, including extreme drought events in 2015-2016. Key findings highlight that sediment sources are linked to agricultural practices, and infrastructure management, with the Lajas Valley agricultural lands being significant contributors. The Yauco 2 hydroelectric system emerged as a critical water source during droughts, underscoring the reliance on interbasin transfers for maintaining water levels in Lago Loco. The study also evaluated public policies, including the Puerto Rico Water Law and Climate Change Adaptation Plan, identifying gaps in watershed management. Recommendations emphasize adopting Best Management Practices (BMPs), such as slope stabilization, sediment traps, and improved agricultural practices, to mitigate sedimentation impacts and enhance water use efficiency. By providing a comprehensive assessment of hydrological and sedimentary dynamics, this study informs sustainable management strategies for the GBRLW. The findings underscore the need for an integrated approach to address climate change impacts, sediment management, and water allocation conflicts. Ultimately, the research contributes to protecting coastal ecosystems and offers a replicable framework for watershed management in similar contexts globally.