ASTM D5981-96(2008)
(Guide)Standard Guide for Calibrating a Groundwater Flow Model Application (Withdrawn 2017)
Standard Guide for Calibrating a Groundwater Flow Model Application (Withdrawn 2017)
SIGNIFICANCE AND USE
Most site-specific groundwater flow models must be calibrated prior to use in predictions. In these cases, calibration is a necessary, but not sufficient, condition which must be obtained to have confidence in the model's predictions.
Often, during calibration, it becomes apparent that there are no realistic values of the hydraulic properties of the soil or rock which will allow the model to reproduce the calibration targets. In these cases the conceptual model of the site may need to be revisited or the construction of the model may need to be revised. In addition, the source and quality of the data used to establish the calibration targets may need to be reexamined. For example, the modeling process can sometimes identify a previously undetected surveying error, which would results in inaccurate hydraulic head targets.
This guide is not meant to be an inflexible description of techniques for calibrating a groundwater flow model; 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 can be used to calibrate a groundwater flow model. The calibration of a model is the process of matching historical data, and is usually a prerequisite for making predictions with the model.
1.2 Calibration is one of the stages of applying a groundwater modeling code to a site-specific problem (see Guide D5447). Calibration is the process of refining the model representation of the hydrogeologic framework, hydraulic properties, and boundary conditions to achieve a desired degree of correspondence between the model simulations and observations of the groundwater flow system.
1.3 Flow models are usually calibrated using either the manual (trial-and-error) method or an automated (inverse) method. This guide presents some techniques for calibrating a flow model using either method.
1.4 This guide is written for calibrating saturated porous medium (continuum) groundwater flow models. However, these techniques, suitably modified, could be applied to other types of related groundwater models, such as multi-phase models, non-continuum (karst or fracture flow) models, or mass transport models.
1.5 Guide D5447 presents the steps to be taken in applying a groundwater modeling code to a site-specific problem. Calibration is one of those steps. Other standards have been prepared on environmental modeling, such as Guides D5490, D5609, D5610, D5611, D5718, and Practice E978.
1.6 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.
1.7 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.
WITHDRAWN RATIONALE
This guide covers techniques that can be used to calibrate a groundwater flow model. The calibration of a model is the process of matching historical data, and is usually a prerequisite for making predictions with the model.
Formerly under the jurisdiction of Committee D18 on Soil and Rock, this guide was withdrawn in January 2017 in accordance with section 10.6.3 of the Regulations Governing ASTM Technical Committee...
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D5981 − 96 (Reapproved 2008)
Standard Guide for
Calibrating a Groundwater Flow Model Application
This standard is issued under the fixed designation D5981; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope judgment. Not all aspects of this guide may be applicable in all
circumstances. This ASTM standard is not intended to repre-
1.1 This guide covers techniques that can be used to
sent or replace the standard of care by which the adequacy of
calibrateagroundwaterflowmodel.Thecalibrationofamodel
a given professional service must be judged, nor should this
is the process of matching historical data, and is usually a
document be applied without consideration of a project’s many
prerequisite for making predictions with the model.
unique aspects. The word “Standard” in the title of this
1.2 Calibration is one of the stages of applying a ground-
document means only that the document has been approved
water modeling code to a site-specific problem (see Guide
through the ASTM consensus process.
D5447). Calibration is the process of refining the model
representation of the hydrogeologic framework, hydraulic
2. Referenced Documents
properties, and boundary conditions to achieve a desired
2.1 ASTM Standards:
degree of correspondence between the model simulations and
D653 Terminology Relating to Soil, Rock, and Contained
observations of the groundwater flow system.
Fluids
1.3 Flow models are usually calibrated using either the
D5447 Guide forApplication of a Groundwater Flow Model
manual (trial-and-error) method or an automated (inverse)
to a Site-Specific Problem
method. This guide presents some techniques for calibrating a
D5490 Guide for Comparing Ground-Water Flow Model
flow model using either method.
Simulations to Site-Specific Information
D5609 Guide for Defining Boundary Conditions in Ground-
1.4 This guide is written for calibrating saturated porous
water Flow Modeling
medium (continuum) groundwater flow models. However,
D5610 GuideforDefiningInitialConditionsinGroundwater
these techniques, suitably modified, could be applied to other
Flow Modeling
types of related groundwater models, such as multi-phase
D5611 Guide for Conducting a Sensitivity Analysis for a
models, non-continuum (karst or fracture flow) models, or
Ground-Water Flow Model Application
mass transport models.
D5718 Guide for Documenting a Groundwater Flow Model
1.5 Guide D5447 presents the steps to be taken in applying
Application
a groundwater modeling code to a site-specific problem.
E978 Practice for Evaluating Mathematical Models for the
Calibration is one of those steps. Other standards have been
Environmental Fate of Chemicals (Withdrawn 2002)
prepared on environmental modeling, such as Guides D5490,
D5609, D5610, D5611, D5718, and Practice E978.
3. Terminology
1.6 This standard does not purport to address all of the
3.1 Definitions:
safety concerns, if any, associated with its use. It is the
3.1.1 application verification—using the set of parameter
responsibility of the user of this standard to establish appro-
values and boundary conditions from a calibrated model to
priate safety and health practices and determine the applica-
approximate acceptably a second set of field data measured
bility of regulatory limitations prior to use.
under similar hydrologic conditions.
1.7 This guide offers an organized collection of information
3.1.1.1 Discussion—Application verification is to be distin-
or a series of options and does not recommend a specific
guished from code verification, which refers to software
course of action. This document cannot replace education or
testing, comparison with analytical solutions, and comparison
experience and should be used in conjunction with professional
1 2
This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rock For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and is the direct responsibility of Subcommittee D18.21 on Groundwater and contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Vadose Zone Investigations. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Sept. 15, 2008. Published November 2008. Originally the ASTM website.
approved in 1996. Last previous edition approved in 2002 as D5981 – 96 (2002). The last approved version of this historical standard is referenced on
DOI: 10.1520/D5981-96R08. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5981 − 96 (2008)
withothersimilarcodestodemonstratethatthecoderepresents is a necessary, but not sufficient, condition which must be
its mathematical foundations. obtained to have confidence in the model’s predictions.
3.1.2 calibrated model—amodelthathasachievedadesired
5.2 Often, during calibration, it becomes apparent that there
degree of correspondence between the model simulations and
are no realistic values of the hydraulic properties of the soil or
observations of the physical hydrogeologic system.
rock which will allow the model to reproduce the calibration
3.1.3 calibration (model application)—the process of refin-
targets. In these cases the conceptual model of the site may
ing the model representation of the hydrogeologic framework,
need to be revisited or the construction of the model may need
hydraulic properties, and boundary conditions to achieve a
to be revised. In addition, the source and quality of the data
desired degree of correspondence between the model simula-
used to establish the calibration targets may need to be
tions and observations of the groundwater flow system.
reexamined.Forexample,themodelingprocesscansometimes
identify a previously undetected surveying error, which would
3.1.4 calibration targets—measured, observed, calculated,
results in inaccurate hydraulic head targets.
or estimated hydraulic heads or groundwater flow rates that a
model must reproduce, at least approximately, to be considered
5.3 Thisguideisnotmeanttobeaninflexibledescriptionof
calibrated.
techniques for calibrating a groundwater flow model; other
3.1.4.1 Discussion—The calibration target includes both the
techniques may be applied as appropriate and, after due
value of the head or flow rate and its associated error of
consideration, some of the techniques herein may be omitted,
measurement, so that undue effort is not expended attempting
altered, or enhanced.
to get a model application to closely reproduce a value which
is known only to within an order of magnitude.
6. Establishing Calibration Targets
3.1.5 fidelity—the degree to which a model application is
6.1 A calibration target consists of the best estimate of a
designed to resemble the physical hydrogeologic system.
value of groundwater head or flow rate. Establishment of
3.1.6 groundwater flow model—an application of a math-
calibrationtargetsandacceptableresidualsorresidualstatistics
ematical model to represent a site-specific groundwater flow
depends on the degree of fidelity proposed for a particular
system.
model application. This, in turn, depends strongly upon the
3.1.7 hydraulic properties—properties of soil and rock that
objectives of the modeling project. All else being equal, in
govern the transmission (for example, hydraulic conductivity,
comparing a low-fidelity to a high-fidelity model application,
transmissivity,andleakance)andstorage(forexample,specific
the low-fidelity application would require fewer calibration
storage, storativity, and specific yield) of water.
targets and allow larger acceptable residuals.
3.1.8 inverse method—solving for independent parameter
NOTE 1—Some low-fidelity models are not necessarily intended to
values using knowledge of values of dependent variables.
make specific predictions, but rather provide answers to speculative or
3.1.9 residual—the difference between the computed and
hypothetical questions which are posed so as to make their predictions
observed values of a variable at a specific time and location.
conditional on assumptions. An example might be a model that answers
the question: “If the hydraulic conductivity of the soil is 50 feet per day,
3.1.10 sensitivity (model application)—the degree to which
will the drawdown be more than 10 ft?” This model will not answer the
the model result is affected by changes in a selected model
question of whether or not the drawdown will, in reality, be more than 10
input representing hydrogeologic framework, hydraulic prop-
ft because the value of hydraulic conductivity was assumed. Since the
answerisconditionalontheassumption,this“what-if”typeofmodeldoes
erties, and boundary conditions.
not necessarily require calibration, and, therefore, there would be no
3.1.11 simulation—in groundwater flow modeling, one
calibration targets.
complete execution of a groundwater modeling computer
6.2 For a medium- to high-fidelity model application, estab-
program, including input and output.
lish calibration targets by first identifying all relevant available
3.2 Forotherdefinitionsusedinthisguide,seeTerminology
data regarding groundwater heads (including measured water
D653.
levels, bottom elevations of dry wells, and top of casing
4. Summary of Guide elevations of flowing wells) and flow rates (including records
of pumping well or wellfield discharges, estimates of baseflow
4.1 The steps to be taken to calibrate a flow model are:
to gaining streams or rivers or recharge from losing streams,
establishing calibration targets and associated acceptable re-
discharges from flowing wells, springflow measurements,
siduals or residual statistics (as described in Section 6),
and/or contaminant plume velocities). For each such datum,
identifying calibration parameters (as described in Section 7),
include the error bars associated with the measurement or
and history matching (as described in Section 8). History
estimate.
matching is accomplished by using the trial-and-error method
to achieve a rough correspondence between the simulation and
6.3 Establish calibration targets before beginning any simu-
the physical hydrogeologic system, and then using either the
lations.
trial-and-error method or an automated method to achieve a
6.4 For any particular calibration target, the magnitude of
closer correspondence.
the acceptable residual depends partly upon the magnitude of
5. Significance and Use
the error of the measurement or estimate of the calibration
5.1 Most site-specific groundwater flow models must be target and partly upon the degree of accuracy and precision
calibrated prior to use in predictions. In these cases, calibration required of the model’s predictions. All else equal, the higher
D5981 − 96 (2008)
the intended fidelity of the model, the smaller the acceptable ductivities; whereas, when the flow rates are changed, repre-
absolute values of the residuals. senting a different condition, then the range of hydraulic
6.4.1 Head measurements are usually accurate to within a conductivitiesthatproduceacceptableresidualsbecomesmuch
few tenths of a foot. Due to the many approximations em- more limited.
ployed in modeling and errors associated therewith (see Guide
6.5.1.1 Otherwaystoaddresstheuniquenessproblemareto
D5447), it is usually impossible to make a model reproduce all
include groundwater flows with heads as calibration targets,
heads measurements within the errors of measurement. There-
and to use measured values of hydraulic properties as model
fore, the modeler must increase the range of acceptable
inputs.
computed heads beyond the range of the error in measurement.
6.5.2 Verification (Similar Hydrologic Conditions) —When
Judgment must be employed in setting these new acceptable
data are available for two times of similar hydrologic condi-
residuals. In general, however, the acceptable residual should
tions, only one of those data sets should be used as calibration
be a small fraction of the difference between the highest and
targets because they are not distinct. However, the other data
lowest heads across the site.
set can be used for application verification. In the verification
process, the modeled data are compared, not to the calibration
NOTE 2—Acceptable residuals may differ for different hydraulic head
calibration targets within a particular model. This may be due to different data set, but to the verification data set.The resulting degree of
errors in measurement, for example, when heads at some wells are based
correspondence can be taken as an indicator or heuristic
on a survey, but other heads are estimated based on elevations estimated
measure of the uncertainty inherent in the model’s predictions.
from a topographic map. In other circumstances, there may be physical
reasons why heads are more variable in some places than in others. For
NOTE 4—When only one data set is available, it is inadvisable to
example, in comparing a well near a specified head boundary with a well
artificially split it into separate “calibration” and “verification” data sets.
near a groundwater divide, the modeled head in the former will depend
It is usually more important to calibrate to data spanning as much of the
lessstronglyupontheinputhydraulicpropertiesthantheheadinthelatter.
modeled domain as possible.
Therefore, acceptable residuals near specified head boundaries can be set
NOTE 5—Some researchers maintain that the word “verification”
lower than those near divides.
impliesahigherdegreeofconfidencethantheverificationprocessimparts
NOTE 3—One way to establish acceptable hydraulic head residuals is to
(3). Used here, the verification process only provides a method for
use kriging on the hydraulic head distribution. Although kriging is not
heuristically estimating the range of uncertainty associated with model
usually recommended for construction of hydraulic head contours, it does
predictions.
result in unbiased estimates of the variance (and thus standard deviation)
NOTE 6—Performing application verification protects against over-
of the hydraulic head distribution as a function of location within the
calibration. Over-calibration is the fine-tuning of input parameters to a
modeled domain. The acceptable residual at each node can be set as the
higher degree of precision than is warranted by the knowledge or
standard deviation in the hydraulic head at that location. Some researchers
measurability of the physical hydrogeologic system and results in artifi-
question the validity of this technique (1). An alternative is to perform
cially low residuals. With
...
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