THE INFLUENCE OF PERMEABILITY ON GROUNDWATER FLOW PATHS IN CENTRAL OREGON

Large differences in permeability between different volcanic terranes in central Oregon result in systematic differences in groundwater flow path lengths and depths, even where boundary conditions are similar. In general, lower permeability conditions result in more groundwater flow restricted to the shallow subsurface where near-surface deposits and local topography have a large influence. Higher-permeability conditions, in contrast, are more conducive to deeper, longer flow paths where regional geology and topography dominate. Such variation in flow path geometry can influence the distribution and density of springs, the spatial distribution of groundwater discharge to streams, and the aquifer response to climate inputs. For example, the low permeability of deposits in the upper Crooked River basin results in a higher density of springs, lack of large-discharge springs, and more seasonally variable surface-water flow compared to adjacent parts of the Deschutes Basin in which it resides. This talk presents a simple numerical analysis of the influence of permeability on flow path geometry and compares the resulting insights with field data, discusses some possible implications with respect to climate change, and provides suggestions for further research and data collection.