ASSESSING THE ROLE OF DRAINAGE BASIN CHARACTERISTICS AND HYDROLOGY ON DISCHARGE RECORDS IN PUERTO RICO

As an isolated island in the Caribbean, Puerto Rico’s water supply is limited and largely (~70%) sourced from reservoirs. Sediment flux and transport in these basins, however, are filling these reservoirs faster than anticipated. To better predict present-day sediment movement, we first evaluate differences in the hydrologic basin response across multiple regions of Puerto Rico. We conducted a statistical analysis of 20-33 years of USGS hydrologic records from 9 watersheds located across Puerto Rico. We classified each watershed according to rock type (Volcaniclastic, Granodiorite, or an even mixture of the two), dominant land use/vegetation (upland forest, palm forest, pasture, and/or agriculture), and general region of Puerto Rico (central, southeast, and eastern). To characterize basin hydrologic response, we analyzed individual storm recession curves at each station using the discharge record to identify the number of days for each recession, the recession exponent or basin ‘flashiness’ (b), the area-normalized streamflow (q), and the characteristic response time (τ). Initial analysis reveals that most basins are typically defined by a recession that spans an average of 4-5 days. The recession exponent was significantly different across all analyzed regions, with basins in the more arid southeast region generally defined by the flashiest recession curves, and shorter recession durations. Basin comparison by bedrock suggests that basins underlain by Volcaniclastics are characterized by significantly shorter recession periods than those underlain by Granodiorite. In addition, basins underlain by Granodiorite are associated with higher discharge and flashier hydrographs than basins underlain by Volcaniclastics. Initial analysis of basins based on land use suggests significant differences, but specific trends remain ambiguous due to variability in land use and vegetation across the studied watersheds. Overall, this preliminary analysis provides initial insight into characterizing and predicting basin response in Puerto Rico across changes in climate, geology, and land use. A better understanding of basin response to storm events will enable more robust hydrologic and sediment transport modeling to predict future sediment movement into Puerto Rico’s drinking water reservoirs.