Reducing Hydrograph Uncertainty Through Subsurface Characterization

Subsurface heterogeneity in saturated hydraulic conductivity is one of the largest, if not the largest, source of uncertainty in hydrology and hydrogeology. While previous studies have focused on how this uncertainty propagates to subsurface transport and how characterization activities reduce this uncertainty.  However, recent work has demonstrated that uncertainty in hydraulic conductivity can also impart significant uncertainty in runoff processes.  Here, the role of site characterization in reducing hydrograph uncertainty is demonstrated numerically.  A fully-integrated hydrologic model is used in a hypothetical experiment where a control hillslope is generated using correlated, Gaussian random fields.  Direct measurements of hydraulic conductivity at varying density are obtained from this control simulation and used to condition ensembles of equally-likely realizations. The hydrographs, resulting from integrated flow simulations for each realization, are shown to much more accurately match the control.  This implies that substantial reduction in hydrograph uncertainty may be realized through site characterization.