Hydrogeology Of Lake Tahoe Basin

Author : Wes Christensen
Publisher :
ISBN 13 : 9781303442322
Total Pages : pages
Book Rating : 4.4/5 (423 download)

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Download or read book Hydrologic Characterization and Modeling of a Montane Peatland, Lake Tahoe Basin, California written by Wes Christensen and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Perennial wetlands in montane environments are often supported at least in part by groundwater input. Groundwater is especially important for wetlands in areas with a snow melt dominated precipitation regime and high summer evapotranspiration rates. Understanding of the groundwater hydrology that supports wetlands in montane environments is often complicated by steep topography, inadequate characterization of the subsurface material, and sparse data. This study examines the groundwater system supporting Grass Lake, the largest peatland in the Sierra Nevada Mountains, located south of Lake Tahoe, California. Field measurements are used to quantify important aspects of the hydrologic system supporting Grass Lake. Late-season groundwater flows into the peatland are estimated using surface water measurements and water budget. Groundwater contributions are approximately 2 to 10 times higher than surface water contributions after July, depending on the water year. Measurements of hydraulic gradients reveal areas of groundwater recharge and discharge. In general, there is more groundwater discharge along the southern portion of the peatland. Measurements of groundwater level relative to the peat surface indicate areas that may be more susceptible to drying and subsequent decomposition of peat. Indirect inversion of numerical models is used to estimate the value of important parameters governing groundwater flow in the peatland. Thermal and hydrologic parameters of the peat are estimated using piezometer scale (~1m) models of heat transport. Atmospheric heat exchange and inclusion of the thermal properties of a metal piezometer improve the fit between the model and the field data. Four sets of random parameters are used to generate synthetic data. The parameter estimation process is tested by attempting to recover the original parameters used to generate the data. Including the entropy of the temperature time series as an observation improves the recovery of the original parameter values.A watershed scale hydrogeologic model is used to evaluate the potential response of the peatland to predicted changes in climate. Watershed geology was mapped at a scale of 1:5000 and used to define hydrogeologic units in the model. Field data from 2010 and 2011 were used to calibrate the hydraulic conductivity of the various geologic units in the model. Parameter estimates from the calibration process are consistent between years for all but the most sensitive parameters. Consideration of unsaturated properties of the subsurface material is shown to improve the fit between the measured and simulated heads in the peatland. The predicted change from a snow dominated to rain dominated precipitation regime results in a significant decrease in simulated late-season pressure head and saturation over approximately half of the peatland. The decrease in saturation is most significant on the east and west ends of the peatland and around the edges.