ASTM D5490-93(2002)
(Guide)Standard Guide for Comparing Ground-Water Flow Model Simulations to Site-Specific Information
Standard Guide for Comparing Ground-Water Flow Model Simulations to Site-Specific Information
SIGNIFICANCE AND USE
During the process of calibration of a ground-water flow model, each simulation is compared to site-specific information to ascertain the success of previous calibration efforts and to identify potentially beneficial directions for further calibration efforts. Procedures described herein provide guidance for making comparisons between ground-water flow model simulations and measured field data.
This guide is not meant to be an inflexible description of techniques comparing simulations with measured data; other techniques may be applied as appropriate and, after due consideration, some of the techniques herein may be omitted, altered, or enhanced.
SCOPE
1.1 This guide covers techniques that should be used to compare the results of ground-water flow model simulations to measured field data as a part of the process of calibrating a ground-water model. This comparison produces quantitative and qualitative measures of the degree of correspondence between the simulation and site-specific information related to the physical hydrogeologic system.
1.2 During the process of calibration of a ground-water flow model, each simulation is compared to site-specific information such as measured water levels or flow rates. The degree of correspondence between the simulation and the physical hydrogeologic system can then be compared to that for previous simulations to ascertain the success of previous calibration efforts and to identify potentially beneficial directions for further calibration efforts.
1.3 By necessity, all knowledge of a site is derived from observations. This guide does not address the adequacy of any set of observations for characterizing a site.
1.4 This guide does not establish criteria for successful calibration, nor does it describe techniques for establishing such criteria, nor does it describe techniques for achieving successful calibration.
1.5 This guide is written for comparing the results of numerical ground-water flow models with observed site-specific information. However, these techniques could be applied to other types of ground-water related models, such as analytical models, multiphase flow models, noncontinuum (karst or fracture flow) models, or mass transport models.
1.6 This guide is one of a series of guides on ground-water modeling codes (software) and their applications. Other standards have been prepared on environmental modeling, such as Practice E 978.
1.7 The values stated in SI units are to be regarded as the standard.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.9 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word "Standard" in the title of this document means only that the document has been approved through the ASTM consensus process.
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Designation: D 5490 – 93 (Reapproved 2002)
Standard Guide for
Comparing Ground-Water Flow Model Simulations to Site-
Specific Information
This standard is issued under the fixed designation D 5490; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This guide covers techniques that should be used to
bility of regulatory limitations prior to use.
compare the results of ground-water flow model simulations to
1.9 This guide offers an organized collection of information
measured field data as a part of the process of calibrating a
or a series of options and does not recommend a specific
ground-water model. This comparison produces quantitative
course of action. This document cannot replace education or
and qualitative measures of the degree of correspondence
experience and should be used in conjunction with professional
between the simulation and site-specific information related to
judgment. Not all aspects of this guide may be applicable in all
the physical hydrogeologic system.
circumstances. This ASTM standard is not intended to repre-
1.2 Duringtheprocessofcalibrationofaground-waterflow
sent or replace the standard of care by which the adequacy of
model, each simulation is compared to site-specific informa-
a given professional service must be judged, nor should this
tion such as measured water levels or flow rates.The degree of
document be applied without consideration of a project’s many
correspondence between the simulation and the physical hy-
unique aspects. The word “Standard” in the title of this
drogeologic system can then be compared to that for previous
document means only that the document has been approved
simulations to ascertain the success of previous calibration
through the ASTM consensus process.
efforts and to identify potentially beneficial directions for
further calibration efforts.
2. Referenced Documents
1.3 By necessity, all knowledge of a site is derived from
2.1 ASTM Standards:
observations. This guide does not address the adequacy of any
D 653 Terminology Relating to Soil, Rock, and Contained
set of observations for characterizing a site.
Fluids
1.4 This guide does not establish criteria for successful
E 978 Practice for Evaluating Mathematical Models for the
calibration, nor does it describe techniques for establishing
Environmental Fate of Chemicals
such criteria, nor does it describe techniques for achieving
successful calibration.
3. Terminology
1.5 This guide is written for comparing the results of
3.1 Definitions:
numerical ground-water flow models with observed site-
3.1.1 application verification—using the set of parameter
specific information. However, these techniques could be
values and boundary conditions from a calibrated model to
applied to other types of ground-water related models, such as
approximate acceptably a second set of field data measured
analytical models, multiphase flow models, noncontinuum
under similar hydrologic conditions.
(karst or fracture flow) models, or mass transport models.
3.1.1.1 Discussion—Application verification is to be distin-
1.6 This guide is one of a series of guides on ground-water
guishedfromcodeverificationwhichreferstosoftwaretesting,
modeling codes (software) and their applications. Other stan-
comparison with analytical solutions, and comparison with
dards have been prepared on environmental modeling, such as
other similar codes to demonstrate that the code represents its
Practice E 978.
mathematical foundation.
1.7 The values stated in SI units are to be regarded as the
3.1.2 calibration—the process of refining the model repre-
standard.
sentation of the hydrogeologic framework, hydraulic proper-
1.8 This standard does not purport to address all of the
ties, and boundary conditions to achieve a desired degree of
safety concerns, if any, associated with its use. It is the
correspondence between the model simulations and observa-
tions of the ground-water flow system.
This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rock
and is the direct responsibility of Subcommittee D18.21 on Ground Water and
Vadose Zone Investigations. Annual Book of ASTM Standards, Vol 04.08.
Current edition approved Nov. 15, 1993. Published January 1994. Annual Book of ASTM Standards, Vol 11.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5490
3.1.3 censored data—knowledgethatthevalueofavariable 4.3.3 Assessment of the reasonableness or justifiability of
in the physical hydrogeologic system is less than or greater the input aquifer hydrologic properties given the aquifer
than a certain value, without knowing the exact value. materials which are being modeled. Modeled aquifer hydro-
3.1.3.1 Discussion—For example, if a well is dry, then the logic properties should fall within realistic ranges for the
potentiometricheadatthatplaceandtimemustbelessthanthe physical hydrogeologic system, as defined during conceptual
elevation of the screened interval of the well although its model development.
specific value is unknown.
5. Significance and Use
3.1.4 conceptual model—an interpretation or working de-
scription of the characteristics and dynamics of the physical
5.1 Duringtheprocessofcalibrationofaground-waterflow
system. model, each simulation is compared to site-specific informa-
3.1.5 ground-water flow model—an application of a math-
tion to ascertain the success of previous calibration efforts and
ematical model to represent a ground-water flow system. to identify potentially beneficial directions for further calibra-
3.1.6 hydrologic condition—a set of ground-water inflows
tion efforts. Procedures described herein provide guidance for
or outflows, boundary conditions, and hydraulic properties that making comparisons between ground-water flow model simu-
cause potentiometric heads to adopt a distinct pattern.
lations and measured field data.
3.1.7 residual—the difference between the computed and
5.2 This guide is not meant to be an inflexible description of
observed values of a variable at a specific time and location.
techniques comparing simulations with measured data; other
3.1.8 simulation—in ground-water flow modeling, one
techniques may be applied as appropriate and, after due
complete execution of a ground-water modeling computer consideration, some of the techniques herein may be omitted,
program, including input and output.
altered, or enhanced.
3.1.8.1 Discussion—For the purposes of this guide, a simu-
6. Quantitative Techniques
lation refers to an individual modeling run. However, simula-
tion is sometimes also used broadly to refer to the process of
6.1 Quantitative techniques for comparing simulations to
modeling in general.
site-specific information include calculating potentiometric
3.2 For definitions of other terms used in this guide, see
headresiduals,assessingcorrelationamongheadresiduals,and
Terminology D 653.
calculating flow residuals.
6.1.1 Potentiometric Head Residuals—Calculate the residu-
4. Summary of Guide
als(differences)betweenthecomputedheadsandthemeasured
4.1 Quantitative and qualitative comparisons are both es-
heads:
sential. Both should be used to evaluate the degree of corre-
r 5 h 2 H (1)
i i i
spondence between a ground-water flow model simulation and
site-specific information.
where:
4.2 Quantitativetechniquesforcomparingasimulationwith
r = the residual,
i
site-specific information include:
H = the measured head at point i,
i
h = the computed head at the approximate location where
4.2.1 Calculation of residuals between simulated and mea-
i
sured potentiometric heads and calculation of statistics regard- H was measured.
i
ing the residuals. Censored data resulting from detection of dry If the residual is positive, then the computed head was too
or flowing observation wells, reflecting information that the high; if negative, the computed head was too low. Residuals
head is less than or greater than a certain value without cannot be calculated from censored data.
knowing the exact value, should also be used.
NOTE 1—For drawdown models, residuals can be calculated from
4.2.2 Detection of correlations among residuals. Spatial and
computed and measured drawdowns rather than heads.
temporal correlations among residuals should be investigated.
NOTE 2—Comparisons should be made between point potentiometric
Correlations between residuals and potentiometric heads can heads rather than ground-water contours, because contours are the result
of interpretation of data points and are not considered basic data in and of
be detected using a scattergram.
themselves. Instead, the ground-water contours are considered to reflect
4.2.3 Calculation of flow-related residuals. Model results
features of the conceptual model of the site.The ground-water flow model
should be compared to flow data, such as water budgets,
should be true to the essential features of the conceptual model and not to
surface water flow rates, flowing well discharges, vertical
their representation.
gradients, and contaminant plume trajectories.
NOTE 3—It is desirable to set up the model so that it calculates heads at
4.3 Qualitative considerations for comparing a simulation
the times and locations where they were measured, but this is not always
with site-specific information include: possibleorpractical.Incaseswherethelocationofamonitoringwelldoes
not correspond exactly to one of the nodes where heads are computed in
4.3.1 Comparison of general flow features. Simulations
thesimulation,theresidualmaybeadjusted(forexample,computedheads
should reproduce qualitative features in the pattern of ground-
may be interpolated, extrapolated, scaled, or otherwise transformed) for
water contours, including ground-water flow directions,
use in calculating statistics.Adjustments may also be necessary when the
mounds or depressions (closed contours), or indications of
times of measurements do not correspond exactly with the times when
surface water discharge or recharge (cusps in the contours).
heads are calculated in transient simulations; when many observed heads
4.3.2 Assessment of the number of distinct hydrologic
conditionstowhichthemodelhasbeensuccessfullycalibrated.
It is usually better to calibrate to multiple scenarios, if the
Cooley, R. L., and Naff, R. L., “Regression Modeling of Ground-Water Flow,”
scenarios are truly distinct. USGS Techniques of Water Resources Investigations, Book 3, Chapter B4, 1990.
D 5490
are clustered near a single node; where the hydraulic gradient changes
where sisthestandarddeviationofresiduals.Smallervalues
significantlyfromnodetonode;orwhenobservedheaddataisaffectedby
of the standard deviation indicate better degrees of correspon-
tidal fluctuations or proximity to a specified head boundary.
dence than larger values.
6.1.2.5 If weighting is used, calculate the weighted standard
6.1.2 Residual Statistics—Calculate the maximum and
deviation:
minimum residuals, a residual mean, and a second-order
statistic, as described in the following sections.
n
w ~r 2 R!
6.1.2.1 Maximum and Minimum Residuals—The maximum (
i i
i 5 1
s 5 (5)
residual is the residual that is closest to positive infinity. The
n
5 6
minimumresidualistheresidualclosesttonegativeinfinity.Of ~n 2 1! w
(
i
i 5 1
two simulations, the one with the maximum and minimum
NOTE 6—Other norms of the residuals are less common but may be
residuals closest to zero has a better degree of correspondence,
5,6
revealing in certain cases. For example, the mean of the absolute values
with regard to this criterion.
of the residuals can give information similar to that of the standard
deviation of residuals.
NOTE 4—When multiple hydrologic conditions are being modeled as
NOTE 7—In calculating the standard deviation of residuals, advanced
separate steady-state simulations, the maximum and minimum residual
statistical techniques incorporating information from censored data could
can be calculated for the residuals in each, or for all residuals in all
be used. However, the effort would usually not be justified because the
scenarios, as appropriate. This note also applies to the residual mean (see
standard deviation of residuals is only one of many indicators involved in
6.1.2.2) and second-order statistics of the residuals (see 6.1.2.4).
comparing a simulation with measured data, and such a refinement in one
indicator is unlikely to alter the overall assessment of the degree of
6.1.2.2 Residual Mean—Calculate the residual mean as the
correspondence.
arithmetic mean of the residuals computed from a given
simulation: 6.1.3 Correlation Among Residuals—Spatial or temporal
correlation among residuals can indicate systematic trends or
n
r
bias in the model. Correlations among residuals can be
( i
i 5 1
R 5 (2)
identified through listings, scattergrams, and spatial or tempo-
n
ral plots. Of two simulations, the one with less correlation
where:
among residuals has a better degree of correspondence, with
R = the residual mean and
regard to this criterion.
n = the number of residuals.
6.1.3.1 Listings—List residuals by well or piezometer, in-
Of two simulations, the one with the residual mean closest to
cluding the measured and computed values to detect spatial or
zero has a better degree of correspondence, with regard to this
temporal trends. Figures X1.1 and X1.2 present example
criterion (assuming there is no correlation among residuals).
listings of residuals.
6.1.3.2 Scattergram—Useascattergramofcomputedversus
6.1.2.3 If desired, the individual residuals can be weighted
measured heads to detect trends in deviations. The scattergram
to account for differing degrees of confidence in the measured
is produced with measured heads on the abscissa (horizontal
heads. In this case, the residual mean becomes the weighted
axis) and computed heads on the ordinate (vertical axis). One
residual mean:
point is plotted on this graph for each pair. If the points line up
n
along a line with zero intercept and 45° angle, then there has
wr
(
i i
i 5 1
been a perfect match. Usually, there will be some scatter about
R 5 (3)
n
this line, hence the name of the plot.Asimulation with a small
n w
( i
i 5 1
degree of scatter about this line has a better correspondence
where w is the weighting factor for the residual at point i. with the physical hydrogeologic system than a simulation with
i
a large degree of scatter. In addition, plo
...
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