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This paper presents the results of a computational fluid dynamics (CFD) model study of the hydraulics of groundwater flow and porous pipe underdrains. The study was conducted using a three-dimensional CFD model built in ANSYS Fluent. The model was validated by replicating previous experimental results of saturated subsurface flow (water surface level above the aggregate) for a 10.2-cm perforated pipe shrouded in loose laid aggregate. The CFD model consistently overpredicted the flow rate for a given head and aggregate depth by an average of 11%. After considering the effect of pipe perforation blockage due to aggregate, the average overprediction decreased to only 6%. The discharge coefficient for the perforated pipe computed using the CFD model was 0.54 compared with 0.49 from experiments. It was also found that the discharge was quite small at the upstream end of the pipe, with the bulk of the water entering the pipe in the vicinity of the outlet. Finally, the computational results showed that, for saturated flow conditions, the flow was predominantly in the vertical direction within the aggregate whereas it was mainly horizontal when the water surface level was below the top of the aggregate level (unsaturated condition). The losses associated with the two flow scenarios were explored. The results obtained have practical applications in the design and analysis of porous pipe underdrains. [ABSTRACT FROM AUTHOR]

The preponderance of evidence in the scientific community supports the premise that global climate is changing. The precise impacts of climate change on natural and man-made systems remain less certain. Municipal water supplies, particularly those that rely on summer snowmelt to augment storage capacity, may experience significant changes in their flow regimes in the future. This paper presents an evaluation of climate change impacts on a water resource system using a three-stage modeling approach: General circulation models (GCMs) to simulate global climate, basin scale hydrology models, and water resource system simulation models. This approach is applied to two river basins in the Puget Sound Region of the Pacific Northwest: The Cedar and South Fork Tolt Rivers, which are the principal sources of water for the Seattle metropolitan region. The greatest source of uncertainty associated with climate change impacts arises from the range of future scenarios produced by GCMs. This uncertainty is addressed by incorporating multiple climate models at every stage of the process and using the values produced to generate an ensemble average that quantifies the most likely impact. The ensemble average is characterized by an envelope of uncertainty based on the range and spread of the individual GCM ensemble members. Hydrologic impacts of climate change such as alteration of historic streamflow patterns and snow accumulation are explored, as well as impacts to the water supply system’s yield. [ABSTRACT FROM AUTHOR]