1、Designation: D5981 96 (Reapproved 2008)Standard Guide forCalibrating a Groundwater Flow Model Application1This standard is issued under the fixed designation D5981; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers techniques that can be used tocalibrate a groundwater flow model. The calibration of a modelis the process
3、 of 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 hydrogeolo
4、gic 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
5、. This 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
6、as 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
7、, such as Guides D5490,D5609, D5610, D5611, D5718, and Practice E978.1.6 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 and health practices and determine the
8、applica-bility of regulatory limitations prior to use.1.7 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 used in conjunction with professionaljudgment.
9、 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 applied without consideration of a projects manyuniqu
10、e aspects. The word “Standard” in the title of thisdocument means only that the document has been approvedthrough the ASTM consensus process.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD5447 Guide for Application of a Groundwater Flow Modelt
11、o a Site-Specific ProblemD5490 Guide for Comparing Ground-Water Flow ModelSimulations to Site-Specific InformationD5609 Guide for Defining Boundary Conditions in Ground-water Flow ModelingD5610 Guide for Defining Initial Conditions in GroundwaterFlow ModelingD5611 Guide for Conducting a Sensitivity
12、Analysis for aGround-Water Flow Model ApplicationD5718 Guide for Documenting a Groundwater Flow ModelApplicationE978 Practice for Evaluating Mathematical Models for theEnvironmental Fate of Chemicals (Withdrawn 2002)33. Terminology3.1 Definitions:3.1.1 application verificationusing the set of parame
13、tervalues and boundary conditions from a calibrated model toapproximate acceptably a second set of field data measuredunder similar hydrologic conditions.3.1.1.1 DiscussionApplication verification is to be distin-guished from code verification, which refers to softwaretesting, comparison with analyt
14、ical solutions, and comparison1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.21 on Groundwater andVadose Zone Investigations.Current edition approved Sept. 15, 2008. Published November 2008. Originallyapproved in 1996.
15、Last previous edition approved in 2002 as D5981 96 (2002).DOI: 10.1520/D5981-96R08.2For 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 pa
16、ge onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesNOTICE: This standard has either been superseded and replaced by a new version or
17、 withdrawn.Contact ASTM International (www.astm.org) for the latest information1with other similar codes to demonstrate that the code representsits mathematical foundations.3.1.2 calibrated modela model that has achieved a desireddegree of correspondence between the model simulations andobservations
18、 of the physical hydrogeologic system.3.1.3 calibration (model application)the process of refin-ing the model representation of the hydrogeologic framework,hydraulic properties, and boundary conditions to achieve adesired degree of correspondence between the model simula-tions and observations of th
19、e groundwater flow system.3.1.4 calibration targetsmeasured, observed, calculated,or estimated hydraulic heads or groundwater flow rates that amodel must reproduce, at least approximately, to be consideredcalibrated.3.1.4.1 DiscussionThe calibration target includes both thevalue of the head or flow
20、rate and its associated error ofmeasurement, 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.3.1.5 fidelitythe degree to which a model application isdesigned to resemble the physical hydrogeolog
21、ic system.3.1.6 groundwater flow modelan application of a math-ematical model to represent a site-specific groundwater flowsystem.3.1.7 hydraulic propertiesproperties of soil and rock thatgovern the transmission (for example, hydraulic conductivity,transmissivity, and leakance) and storage (for exam
22、ple, specificstorage, storativity, and specific yield) of water.3.1.8 inverse methodsolving for independent parametervalues using knowledge of values of dependent variables.3.1.9 residualthe difference between the computed andobserved values of a variable at a specific time and location.3.1.10 sensi
23、tivity (model application)the degree to whichthe model result is affected by changes in a selected modelinput representing hydrogeologic framework, hydraulic prop-erties, and boundary conditions.3.1.11 simulationin groundwater flow modeling, onecomplete execution of a groundwater modeling computerpr
24、ogram, including input and output.3.2 For other definitions used in this guide, see TerminologyD653.4. 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),iden
25、tifying calibration parameters (as described in Section 7),and 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 thetria
26、l-and-error method or an automated method to achieve acloser correspondence.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 conf
27、idence in the models predictions.5.2 Often, during calibration, 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
28、 or the construction of the model may needto be revised. In addition, 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 inaccurat
29、e hydraulic head targets.5.3 This guide is not meant to be an inflexible 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.6. Establishing Cal
30、ibration 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 proposed for a particularmodel application. This, in turn, depends s
31、trongly 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 residuals.NOTE 1Some low-fidelity models are not necessarily inten
32、ded 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 hydraulic conductivity of the soil is 50 feet per day,will the
33、drawdown be more than 10 ft?” This model will not answer thequestion of whether or not the drawdown will, in reality, be more than 10ft because the value of hydraulic conductivity was assumed. Since theanswer is conditional on the assumption, this “what-if” type of model doesnot necessarily require
34、calibration, and, therefore, there would be nocalibration targets.6.2 For a medium- to high-fidelity model application, estab-lish calibration targets by first identifying all relevant availabledata regarding groundwater heads (including measured waterlevels, bottom elevations of dry wells, and top
35、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, springflow measurements,and/or contaminant plume velocities). For each such
36、 datum,include the error bars associated with the measurement orestimate.6.3 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
37、 of the calibrationtarget and partly upon the degree of accuracy and precisionrequired of the models predictions. All else equal, the higherD5981 96 (2008)2the intended fidelity of the model, the smaller the acceptableabsolute values of the residuals.6.4.1 Head measurements are usually accurate to w
38、ithin afew tenths of a foot. Due to the many approximations em-ployed in modeling and errors associated therewith (see GuideD5447), it is usually impossible to make a model reproduce allheads measurements within the errors of measurement. There-fore, the modeler must increase the range of acceptable
39、computed heads beyond the range of the error in 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 2Acceptable residuals may
40、differ for different hydraulic headcalibration targets 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,
41、there may be physicalreasons why heads are more 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 th
42、e latter.Therefore, acceptable residuals near specified head boundaries can be setlower than those near divides.NOTE 3One way to establish acceptable hydraulic head residuals is touse kriging on the hydraulic head distribution. Although kriging is notusually recommended for construction of hydraulic
43、 head contours, it doesresult in unbiased estimates 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. Som
44、e researchersquestion the validity of this technique (1).4An 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 magnitud
45、e of theresiduals from the trend analysis should 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 (2). For example,baseflow estimates are generally accurate only to within anorder of ma
46、gnitude. In such cases, the upper and lower boundson 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
47、are represented by theavailable data sets. Include 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
48、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 addressnonu
49、niqueness, because one set of heads can be matched withthe proper ratio of groundwater flow rates to hydraulic con-ductivities; whereas, when the flow rates are changed, repre-senting a different condition, then the range of hydraulicconductivities that produce acceptable residuals becomes muchmore limited.6.5.1.1 Other ways to address the uniqueness problem are toinclude groundwater flows with heads as calibration targets,and to use measured values of hydraulic properties as modelinputs.6.5.2 Verification (Similar Hydrologic Conditions) Whendata are
