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On the applicability of analytical methods for estimating solute travel time statistics in nonuniform groundwater flow
Author(s) -
Destouni Georgia,
Simic Eva,
Graham Wendy
Publication year - 2001
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2001wr000348
Subject(s) - groundwater recharge , log normal distribution , cumulative distribution function , groundwater flow , probability density function , groundwater , statistics , flow (mathematics) , gaussian , mathematics , advection , probability distribution , geology , hydrology (agriculture) , mechanics , geotechnical engineering , physics , aquifer , geometry , quantum mechanics , thermodynamics
Groundwater recharge from the unsaturated zone results in a nonuniform mean groundwater flow. We report closed‐form expressions for the mean and variance of advective solute travel time under such nonuniform flow conditions. These expressions are derived directly from velocity statistics, based on an analytical direct evaluation method (DEM). An alternative, indirect evaluation method (IEM) has previously been used for deriving and evaluating the cumulative distribution function of solute travel time in nonuniform mean flow, through its relation to an assumed Gaussian probability density function of solute displacement. For negative groundwater recharge we argue that neither of the two analytical methods DEM and IEM can be considered reliable. For positive groundwater recharge we show that (1) the DEM results reported here remain as reliable for nonuniform as for uniform mean groundwater flow; (2) an assumed lognormal cumulative distribution function based on the DEM‐derived travel time moments is consistent with the IEM‐derived solute travel time cumulative distribution function (cdf), which is in turn consistent with numerical simulation results reported in the literature; and (3) the detailed differences between the DEM‐based lognormal cdf and the IEM‐derived cdf for nonuniform flow are such that the former (DEM) may exhibit even better agreement with reported numerical simulation results than the latter (IEM).