1、Designation: D5981/D5981M 18Standard Guide forCalibrating a Groundwater Flow Model Application1This standard is issued under the fixed designation D5981/D5981M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This guide covers techniques that can be used tocalibrate a groundwater flow model. The calibration of a modelis the process of
3、 matching historical data, and is usually aprerequisite for making predictions with the model.1.2 Calibration is one of the stages of applying a ground-water modeling code to a site-specific problem (see GuideD5447). Calibration is the process of refining the modelrepresentation of the hydrogeologic
4、 framework, hydraulicproperties, and boundary conditions to achieve a desireddegree of correspondence between the model simulations andobservations of the groundwater flow system.1.3 Flow models are usually calibrated using either themanual (trial-and-error) method or an automated (inverse)method. T
5、his guide presents some techniques for calibrating aflow model using either method.1.4 This guide is written for calibrating saturated porousmedium (continuum) groundwater flow models. However,these techniques, suitably modified, could be applied to othertypes of related groundwater models, such as
6、multi-phasemodels, non-continuum (karst or fracture flow) models, ormass transport models.1.5 Guide D5447 presents the steps to be taken in applyinga groundwater modeling code to a site-specific problem.Calibration is one of those steps. Other standards have beenprepared on environmental modeling, s
7、uch as Guides D5490,D5609, D5610, D5611, D5718, and Practice E978.1.6 UnitsThe values stated in either SI units or inch-pound units (given in brackets) are to be regarded separately asstandard. The values stated in each system may not be exactequivalents; therefore, each system shall be independentl
8、y ofthe other. Combining values from the two systems may resultin non-conformance with the standard.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health,
9、 and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.8 This guide offers an organized collection of informationor a series of options and does not recommend a specificcourse of action. This document cannot replace education orexperience and should be
10、 used in conjunction with professionaljudgment. Not all aspects of this guide may be applicable in allcircumstances. This ASTM standard is not intended to repre-sent or replace the standard of care by which the adequacy ofa given professional service must be judged, nor should thisdocument be applie
11、d without consideration of a projects manyunique aspects. The word “Standard” in the title of thisdocument means only that the document has been approvedthrough the ASTM consensus process.1.9 This international standard was developed in accor-dance with internationally recognized principles on stand
12、ard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and C
13、ontainedFluidsD5447 Guide for Application of a Numerical GroundwaterFlow Model to a Site-Specific ProblemD5490 Guide for Comparing Groundwater Flow ModelSimulations to Site-Specific InformationD5609 Guide for Defining Boundary Conditions in Ground-water Flow ModelingD5610 Guide for Defining Initial
14、Conditions in GroundwaterFlow ModelingD5611 Guide for Conducting a Sensitivity Analysis for aGroundwater Flow Model ApplicationD5718 Guide for Documenting a Groundwater Flow ModelApplication1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of
15、 Subcommittee D18.21 on Groundwater andVadose Zone Investigations.Current edition approved Jan. 1, 2018. Published February 2018. Originallyapproved in 1996. Last previous edition approved in 2002 as D5981 96 (2008),which was withdrawn January 2017 and reinstated in January 2018. DOI: 10.1520/D5981_
16、D5981M-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of
17、 this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelo
18、pment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1E978 Practice for Evaluating Mathematical Models for theEnvironmental Fate of Chemicals (Withdrawn 2002)33. Terminology3.1 Definitions:3.1.1 For definition
19、s of technical terms in this standard,refer to Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 application verificationusing the set of parametervalues and boundary conditions from a calibrated model toapproximate acceptably a second set of field data measuredunder similar
20、hydrologic conditions.3.2.1.1 DiscussionApplication verification is to be distin-guished from code verification, which refers to softwaretesting, comparison with analytical solutions, and comparisonwith other similar codes to demonstrate that the code representsits mathematical foundations.3.2.2 cal
21、ibration targetsmeasured, observed, calculated,or estimated hydraulic heads or groundwater flow rates that amodel must reproduce, at least approximately, to be consideredcalibrated.3.2.2.1 DiscussionThe calibration target includes both thevalue of the head or flow rate and its associated error ofmea
22、surement, so that undue effort is not expended attemptingto get a model application to closely reproduce a value whichis known only to within an order of magnitude.3.2.3 fidelitythe degree to which a model application isdesigned to resemble the physical hydrogeologic system.3.2.4 hydraulic propertie
23、sproperties of soil and rock thatgovern the transmission (for example, hydraulic conductivity,transmissivity, and leakance) and storage (for example, specificstorage, storativity, and specific yield) of water.3.2.5 inverse methodsolving for independent parametervalues using knowledge of values of de
24、pendent variables.3.2.6 residualthe difference between the computed andobserved values of a variable at a specific time and location.3.2.7 sensitivity (model application)the degree to whichthe model result is affected by changes in a selected modelinput representing hydrogeologic framework, hydrauli
25、cproperties, and boundary conditions.4. Summary of Guide4.1 The steps to be taken to calibrate a flow model are:establishing calibration targets and associated acceptable re-siduals or residual statistics (as described in Section 6),identifying calibration parameters (as described in Section 7),and
26、history matching (as described in Section 8). Historymatching is accomplished by using the trial-and-error methodto achieve a rough correspondence between the simulation andthe physical hydrogeologic system, and then using either thetrial-and-error method or an automated method to achieve acloser co
27、rrespondence.5. Significance and Use5.1 Most site-specific groundwater flow models must becalibrated prior to use in predictions. In these cases, calibrationis a necessary, but not sufficient, condition which must beobtained to have confidence in the models predictions.5.2 Often, during calibration,
28、 it becomes apparent that thereare no realistic values of the hydraulic properties of the soil orrock which will allow the model to reproduce the calibrationtargets. In these cases the conceptual model of the site mayneed to be revisited or the construction of the model may needto be revised. In add
29、ition, the source and quality of the dataused to establish the calibration targets may need to bereexamined. For example, the modeling process can sometimesidentify a previously undetected surveying error, which wouldresults in inaccurate hydraulic head targets.5.3 This guide is not meant to be an i
30、nflexible description oftechniques for calibrating a groundwater flow model; othertechniques may be applied as appropriate and, after dueconsideration, some of the techniques herein may be omitted,altered, or enhanced.NOTE 1Users of the inverse method should be aware that the methodmay have several
31、solutions, all equally well calibrated. (1)46. Establishing Calibration Targets6.1 A calibration target consists of the best estimate of avalue of groundwater head or flow rate. Establishment ofcalibration targets and acceptable residuals or residual statisticsdepends on the degree of fidelity propo
32、sed for a particularmodel application. This, in turn, depends strongly upon theobjectives of the modeling project. All else being equal, incomparing a low-fidelity to a high-fidelity model application,the low-fidelity application would require fewer calibrationtargets and allow larger acceptable res
33、iduals.NOTE 2Some low-fidelity models are not necessarily intended tomake specific predictions, but rather provide answers to speculative orhypothetical questions which are posed so as to make their predictionsconditional on assumptions. An example might be a model that answersthe question: “If the
34、hydraulic conductivity of the soil is 50 feet per day,will the drawdown be more than 3 m 10 ft?” This model will not answerthe question of whether or not the drawdown will, in reality, be more than3 m 10 ft because the value of hydraulic conductivity was assumed.Since the answer is conditional on th
35、e assumption, this “what-if” type ofmodel does not necessarily require calibration, and, therefore, there wouldbe no calibration targets.6.2 For a medium- to high-fidelity model application, estab-lish calibration targets by first identifying all relevant availabledata regarding groundwater heads (i
36、ncluding measured waterlevels, bottom elevations of dry wells, and top of casingelevations of flowing wells) and flow rates (including recordsof pumping well or wellfield discharges, estimates of baseflowto gaining streams or rivers or recharge from losing streams,discharges from flowing wells, spri
37、ngflow measurements,and/or contaminant plume velocities). For each such datum,include the error bars associated with the measurement orestimate.3The last approved version of this historical standard is referenced onwww.astm.org.4The boldface numbers in parentheses refer to a list of references at th
38、e end ofthis standard.D5981/D5981M 1826.3 Establish calibration targets before beginning any simu-lations.6.4 For any particular calibration target, the magnitude ofthe acceptable residual depends partly upon the magnitude ofthe error of the measurement or estimate of the calibrationtarget and partl
39、y upon the degree of accuracy and precisionrequired of the models predictions. All else equal, the higherthe intended fidelity of the model, the smaller the acceptableabsolute values of the residuals.6.4.1 Head measurements are usually accurate to within afew tenths of a foot. Due to the many approx
40、imations em-ployed in modeling and errors associated therewith (see GuideD5447), it is usually not practicable to make a model reproduceall heads measurements within the errors of measurement.Therefore, the modeler must increase the range of acceptablecomputed heads beyond the range of the error in
41、measurement.Judgment must be employed in setting these new acceptableresiduals. In general, however, the acceptable residual shouldbe a small fraction of the difference between the highest andlowest heads across the site.NOTE 3Acceptable residuals may differ for different hydraulic headcalibration t
42、argets within a particular model. This may be due to differenterrors in measurement, for example, when heads at some wells are basedon a survey, but other heads are estimated based on elevations estimatedfrom a topographic map. In other circumstances, there may be physicalreasons why heads are more
43、variable in some places than in others. Forexample, in comparing a well near a specified head boundary with a wellnear a groundwater divide, the modeled head in the former will dependless strongly upon the input hydraulic properties than the head in the latter.Therefore, acceptable residuals near sp
44、ecified head boundaries can be setlower than those near divides.NOTE 4One way to establish acceptable hydraulic head residuals is touse kriging on the hydraulic head distribution. Although kriging is notusually recommended for construction of hydraulic head contours, it doesresult in unbiased estima
45、tes of the variance (and thus standard deviation)of the hydraulic head distribution as a function of location within themodeled domain. The acceptable residual at each node can be set as thestandard deviation in the hydraulic head at that location. Some researchersquestion the validity of this techn
46、ique (2). An alternative is to performtrend analysis of regions of similar heterogeneity. Since a model willusually only be able to represent trends over length scales larger than thescale of local heterogeneity that is causing variations, the magnitude of theresiduals from the trend analysis should
47、 approximate the magnitude ofresiduals in the model in that region.6.4.2 Errors in the estimates of groundwater flow rates willusually be larger than those in heads (3). For example,baseflow estimates are generally accurate only to within anorder of magnitude. In such cases, the upper and lower boun
48、dson the acceptable modeled value of baseflow can be equal tothe upper and lower bounds on the estimate.6.5 Multiple Hydrologic ConditionsWhen more than oneset of field measurements have been collected, identify thedifferent hydrologic conditions that are represented by theavailable data sets. Inclu
49、de only one data set from eachhydrologic condition in the set of calibration targets. Use theremaining data sets for verification.6.5.1 Uniqueness (Distinct Hydrologic Conditions)Thenumber of different distinct hydrologic conditions that a givenset of input aquifer hydraulic properties is capable of repre-senting is an important qualitative measure of the performanceof a model. It is usually better to calibrate to multiplehydrologic conditions, if the conditions are truly distinct.Matching different hydrologic conditions is one way to addressnonuniqueness, bec
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