Assessing the uncertainty associated with regional groundwater model development for the Fernley/Wadsworth hydrographic basins, Nevada

Modeling of groundwater flow is fraught with many uncertainties such as errors in conceptual deficiencies, numerical errors, and inadequate parameter estimation. This study assesses the uncertainty in a predictive groundwater model due to input parameters uncertainty. Three parameters, hydraulic conductivity, irrigation recharge and evapotranspiration (ET) rates were identified as uncertain. A preliminary sensitivity analysis was conducted to establish acceptable range for each parameter. Parametric uncertainty analysis was performed in a stochastic framework (Monte Carlo analysis) that allows for assessing the effects of the parameter distributions on the drawdown in wells expected from Wadsworth area and net change in flow of Truckee River.; Analysis suggests the uncertainty in predictive model (drawdown) was sensitive to uncertainties in hydraulic conductivity and irrigation recharge. The variation in ET rate shows insignificant change in the model's predictive capabilities. However, the model's predictions in terms of net change in flow of Truckee River are insensitive to all three parameters.