Analyzing the effects of geological and parameter uncertainty on prediction of groundwater head and travel time

摘要

Uncertainty of groundwater model predictions has in the past mostly beenrelated to uncertainty in the hydraulic parameters, whereas uncertainty inthe geological structure has not been considered to the same extent. Recentdevelopments in theoretical methods for quantifying geological uncertaintyhave made it possible to consider this factor in groundwater modeling. Inthis study we have applied the multiple-point geostatistical method (MPS)integrated in the Stanford Geostatistical Modeling Software (SGeMS) forexploring the impact of geological uncertainty on groundwater flow patternsfor a site in Denmark. Realizations from the geostatistical model were usedas input to a groundwater model developed from Modular three-dimensionalfinite-difference ground-water model (MODFLOW) within the Groundwater Modeling System(GMS) modeling environment. The uncertainty analysis was carried out in threescenarios involving simulation of groundwater head distribution and traveltime. The first scenario implied 100 stochastic geological models allassigning the same hydraulic parameters for the same geological units. Inthe second scenario the same 100 geological models were subjected to modeloptimization, where the hydraulic parameters for each of them were estimatedby calibration against observations of hydraulic head and stream discharge.In the third scenario each geological model was run with 216 randomized setsof parameters. The analysis documented that the uncertainty on theconceptual geological model was as significant as the uncertainty related tothe embedded hydraulic parameters.