ASCE 50-08 / 51-08


Standard Guideline for Fitting Saturated Hydraulic Conductivity Using Probability Density Functions (50-08) / Standard Guideline for Calculating the Effective Saturated Hydraulic Conductivity (51-08)American Society of Civil Engineers / 01-Sep-2008 / 36 pages ISBN: 9780784409930

ASCE 50-08:
This standard guideline outlines a procedure to optimizethe fitting and goodness-of-fit testing of a probabilitydensity function (pdf) to a sample of saturatedhydraulic conductivity (K) measurements. The procedureassumes a uniform scale of observation (similarmeasuring device) and statistically homogeneous andindependent hydraulic conductivity measurements.Two pdfs are recommended for fitting purposes whensuch a sample of saturated hydraulic conductivitymeasurements is available. The first is the lognormalpdf, recommended when logarithmically transformedK data have coefficient of skew (CsY) in the range< or = 0.05 CsY < or = 0.05. The second is the (threeparameter)log-gamma pdf, recommended whenlogarithmically transformed K data have coefficientof skew CsY > 0.05. Testing the goodness-of-fit to Kdata achieved by the lognormal or the log-gamma pdfsis performed with the chi-squared method.
ASCE 51-08:
This standard guideline outlines a procedure to calculatethe effective saturated hydraulic conductivity inlocal-scale groundwater flow. The effective saturatedhydraulic conductivity is a parameter that relates theaverage groundwater specific discharge to the averagehydraulic gradient. This standard guideline procedureassumes
1. a uniform scale of observation (that is, the use of asimilar measuring device for all saturated hydraulicconductivity measurements) and
2. statistically homogeneous saturated hydraulic conductivity(K) with axisymmetric or isotropic spatialcovariance.
Two situations are considered in estimating theeffective saturated hydraulic conductivity. The firstconcerns the case in which the saturated hydraulicconductivity follows a lognormal distribution withvery small log conductivity variance. Log conductivityis the natural logarithm of saturated hydraulicconductivity. Log normality and smallness of thelog conductivity variance are assumptions that havebeen widely used in the stochastic groundwaterhydrologyliterature (Gutjahr et al. 1978; Gelhar1993). The second situation concerns saturatedhydraulic conductivity with arbitrary probabilitydensity function (pdf) and variance. ASCE/EWRIStandard 50-08 (2008, in this volume) outlines a procedurefor fitting the saturated hydraulic conductivitydata with skewed pdfs.

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