Application and analysis of a coupled surface and groundwater model

Abstract

A model which couples two-dimensional transient saturated subsurface flow (Boussinesq equation) and one-dimensional gradually-varied unsteady open-channel flow (Saint-Venant equations) is developed and applied to the Truckee River system in northern Nevada. The coupled model involves simultaneous numerical solution of the surface and subsurface flow equations using the Galerkin finite-element method. This paper attempts to address questions regarding the application of such a model to both real and hypothetical hydrologic systems in terms of analysis of parameter sensitivity, predictive uncertainty and uniqueness of model solution. Investigation of parameter sensitivity provides information regarding the relative accuracy with which individual system parameters should be measured in order to insure successful model operation. Model predictive uncertainty is evaluated based on comparison of model output and field observations obtained over a two-year period from the Truckee River study area in northern Nevada. Results indicate fair to good prediction of both high and low river stage and groundwater table elevations with predictive accuracy decreasing with distance away from river channel. A procedure for quantifying uniqueness of model solution is developed to provide insight into the reliability associated with extrapolation of model output beyond the limits of observed field measurements. Based on results for the Truckee River system, such extrapolation appears to be justified.