COUPLED HYDROECOLOGIC MODELING OF GROUNDWATER FLOW AND VEGETATION PATTERNING IN MOUNTAIN MEADOWS

As is common around the world, the hydroecology of riparian areas of the Last Chance Watershed in the northern Sierra Nevada, California, are being drastically affected by stream incision that has been caused by logging, over-grazing, and road/railroad construction. Stream incision causes drainage of groundwater from the riparian meadow sediments that encourages a succession from the native wet meadow vegetation to sagebrush and dryland grasses. The purpose of this work is to better understand the hydroecology of these meadow systems in order to help inform restoration efforts that have been initiated to reestablish the ecosystem function of the riparian meadows. We collected aerial, near-infrared imagery to document the distribution of these vegetation communities and collected supporting field data including stream stage records, water table hydrographs, sediment hydraulic properties, and topographic transects to characterize the hydrologic function of the meadow. The hydrologic response was simulated with a finite element model of variably saturated groundwater flow that was coupled to an empirical, time-dependent, vegetation threshold relationship between vegetation type and depth to the water table. Simulations of the hydrology and vegetation patterning were performed for pristine, degraded (incised), and restored conditions. The modeling results capture the salient features of the observed vegetation patterning.