MULTI-SCALAR MOUNTAIN HYDROGEOLOGY: FROM SMALL STREAMS TO MOUNTAIN RANGES

Groundwater is critical to the function and sustainability of mountain hydrologic systems at a variety of spatio-temporal scales. At the stream-reach scale, complex patterns of hyporeic exchange supply baseflow and create important micro-habitats. Regional groundwater flow redistributes water at the scale of mountain basins. At the scale of mountain ranges, water tables are controlled by complex interactions topography, climate and geology. Here we explore these three scales with field results, numerical modeling and data compilation, respectively. In a well-characterized, moderate-gradient mountain stream in the Sierra Nevada a concurrent SF⁶ tracer test and in situ radon analysis as well as temperature and conductivity measurements indicate a very low groundwater discharge rate, below the uncertainty of physical stream flow measurements. Numerical simulations are used to define the salient controls on regional groundwater flow in 3-D mountainous terrain by systematically varying topographic and hydrogeologic variables. Topography for idealized multiple-basin mountainous terrain is derived from geomatic data and literature values. Water table elevation, controlled by the ratio of recharge to hydraulic conductivity, largely controls the distribution of recharged water into local, regional, and perpendicular flow systems, perpendicular flow being perpendicular to the regional topographic gradient. Finally, range-scale water table type is explored using GIS data compilation, a new continental-scale permeability map and an analytical solution for water table type. Heterogeneous patterns of water table type are found in diverse mountain settings. Since groundwater is also a critical resource, especially in arid mountain areas, exploring the fundamental hydrogeologic processes at a variety of scales is critical to groundwater sustainability.