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Document: A Bayesian belief network approach to explore alternative decisions for sediment control and water storage capacity at Lago Lucchetti, Puerto Rico (Doc-336)

336
Authors
Bousquin, J., W.S. Fisher, J. Carriger, and E. Huertas
Year
2014
Title
A Bayesian belief network approach to explore alternative decisions for sediment control and water storage capacity at Lago Lucchetti, Puerto Rico
Document Type
Report
Report Number
EPA/600/R-14/296
Place Published
Ofice of Research & Development,
Publisher
EPA
Abstract
A Bayesian belief network (BBN) was developed to characterize the effects of sediment accumulation on the water storage capacity of Lago Lucchetti (located in southwest Puerto Rico) and to forecast the life expectancy (usefulness) of the reservoir under different management scenarios. The conceptual approach included water and sediment delivery from two sources, from the Lucchetti watershed and from a tunnel linking Lago Lucchetti to three upstream reservoirs. Variables in the model included precipitation and erosion factors (soil type, landscape slope, and land use) applied to the Lucchetti watershed and to watersheds of the upstream reservoirs. The lack of available data for water and sediment flows in the watershed and through tunnels connecting the reservoirs led to several unique methods for network data acquisition. Status quo model runs demonstrated that sediment trapping has continuously declined in all four reservoirs since their construction and that every year a greater proportion of sediment is moving downstream through tunnels or spillways. The model compared favorably with incidental measured data in the region. Sensitivity analysis demonstrated that current sediment accumulation in Lago Lucchetti can be attributed in large part to sediment erosion from the Lucchetti watershed with only minor influence (~8%) from upstream reservoirs. Two decision scenarios were explored by including additional nodes for (1) partial and full conversion of sungrown land use to shadegrown coffee cultivation in the Lucchetti watershed and (2) partial or complete dredging the reservoir. Both management actions were examined singly and in combination for effects on reservoir life expectancy (beyond the year 2000) with varying water capacity targets. Using 50% water storage capacity as a target, model runs for status quo (no decision implemented) resulted in a probability range that averaged 5.57 years (or 50% water storage capacity in the year 2005). Partial and full conversion of land from sungrown to shadegrown coffee cultivation raised the life expectancy to 5.89 and 6.57 years, respectively. Partial and complete dredging of the reservoir resulted in a life expectancy of 37.3 and 40.7 years, and full implementation of both management options resulted in a life expectancy of 44.4 years.
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