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Dillon Reservoir is a primary drinking-water reservoir for Denver, Colorado. Eutrophication of the reservoir is a concern, primarily due to phosphorus (P) loading. Because there are no agriculture operations in the watershed, many have attributed the P loading to onsite wastewater systems (OWS). This specific study focuses on the transport and fate of P. A watershed modeling effort using Soil and Water Assessment Tool (SWAT) was completed to understand the influence of various point and nonpoint sources of P in the Blue River watershed, which is the most developed of three primary watersheds that supply Dillon Reservoir. The watershed model was calibrated to measured streamflow, sediment, and P concentrations. The hydrologic model results are most sensitive to snowmelt parameters and orographic effects on precipitation and evapotranspiration. Sediment concentrations are most sensitive to the streamflow simulation, including the timing of spring snowmelt. However, uncertainties in chemical parameters prevent a rigorous assignment of relative contributions of P sources. However, the effort resulted in a better understanding of P chemical parameters required to simulate watershed-scale transport. The SWAT model is most sensitive to the P sorption coefficient, the P availability index, and the P enrichment ratio (a measure of P in runoff sediments compared to immobile sediments). Modeling results indicate that OWS are not significant sources of P to Dillon Reservoir.

Document Type: Research Article


Publication date: 2007-01-01

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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