Open-File Report 2006–1104
U.S. GEOLOGICAL SURVEY
Open-File Report 2006–1104
The source code used in the DVRFS model (mf2k_13_00-dp.exe) is MODFLOW-2000 version 1.13 compiled to run in double precision. A model simulation is conducted by executing “mf2k_13_00-dp.exe” in a DOS window and entering “name.txt” when prompted for the name file. The source code is available from the USGS website at URL: http://pubs.water.usgs.gov/sir20045205/, accessed on December 22, 2005, under model archive. Single precision simulations result in inaccurate water budgets due to rounding errors. The most recent version of MODFLOW-2000, version 1.15.01, is available at URL: http://water.usgs.gov/nrp/gwsoftware/modflow2000/modflow2000.html, accessed on December 22, 2005. The executable file available at the website is single precision, and the source code must be recompiled in double precision.
Various simulation modes are available in MODFLOW-2000 depending on the file types activated in the name file, and the values assigned to variables in the SEN and PES Processes. In general, four types of model modes are thought to be most relevant to simulations with the DVRFS model: (1) forward with observations and parameter-value substitution, (2) parameter sensitivity with observations, (3) sensitivity-analysis, and (4) the parameter-estimation mode (table 7) (Hill and others, 2000, p. 12). The two parameter-sensitivity modes (modes 2 and 3) produce similar output files; however, depending on the parameter-sensitivity mode, different statistics are written to the GLOBAL file (table 6).
For discussion, it is assumed that the OBS Process is always active, and parameter-value substitution (values from the SEN Process are always used) occurs. In all modes, a LIST file and a GLOBAL file are created. However, different information is written to these two files depending on the mode and which processes (OBS, SEN, PES) are active (table 6).
Forward mode generally is the simplest mode and also is the mode most similar to MODFLOW-96. To execute a simulation in forward mode with observations and parameter-value substitution (Hill and others, 2000, p. 12), include the SEN and PES Process file types in the name file (for example, see the archived model name file). In the SEN Process (SENSITIVITY.txt), set the second variable (first data row, second column entry variable INSENALL) to –1. Shown below are the first few lines of the SEN Process with the ISENALL variable shaded in gray:
# SEN Package Line 0: Text
100 -1 0 100 Line 1: NPLIST ISENALL IUHEAD MXSEN
0 0 0 3 Line 2: IPRINTS SEN_ISENSU (binary or text file = unit 42) SEN_ISENPU
(text file = unit 43) ISENFM.
The forward mode with observations and parameter value substitution can generate head and drawdown arrays for contouring, water-budget terms, and the fit of simulated equivalents to observations. Model time steps for which output is saved and printed are determined by the OC Option. In the DVRFS model, arrays of simulated head and drawdown by layer and time, as specified in the OC Option, are contained in the files HEADSOUT.TXT and DRAWDOWN.TXT, respectively. The HEADSOUT.txt and DRAWDOWN.txt files are specified as the file type “DATA” in the name file.
Output files created in the forward mode with observations and parameter value substitution include GLOBAL, LIST, HEADSOUT.txt, DRAWDOUT.txt and the “underscore” output files (dvr._* files) are listed in table 5.
To execute a model simulation in a parameter-sensitivity mode, activate the SEN Process and inactivate the PES Process in the name file (parameter sensitivity with observations mode), or make the PES Process active with the variable MAX-ITER set to zero (sensitivity-analysis mode). To calculate sensitivities for all parameters, activate the parameter sensitivity with observations mode by setting the second variable (ISENALL) in the first data row of the SEN Process to 1. The first few lines of the SEN Process are shown below with the ISENALL variable shaded in gray:
# SEN Package Line 0: Text(Line 3: PARNAM ISENS LN B BL BU BSCAL)
100 1 0 100 Line 1: NPLIST ISENALL IUHEAD MXSEN
0 0 0 3 Line 2: IPRINTS SEN_ISENSU (binary or text file=unit 42)
SEN_ISENPU (text file = unit 43) ISENFM
B_LVVSZ_1 0 1 9.0E-4 0.100000E-07 10.0000 0.100000E-08
B_HWY95 0 1 2.95E-4 0.100000E-07 10.0000 0.100000E-08
B_DVFC_FCR 0 1 1.0E-7 0.100000E-07 10.0000 0.100000E-08
B_LVVSZ_IS 0 1 1.1E-8 0.100000E-07 10.0000 0.100000E-08
B_LVVSZ_I2 0 1 4.19E-8 0.100000E-07 10.0000 0.100000E-08
B_PAHRUMP 0 1 5.52E-7 0.100000E-07 10.0000 0.100000E-08
B_DV_N 0 1 2.4E-7 0.100000E-07 10.0000 0.100000E-08
Calculating sensitivities for individual parameters, or a subset of parameters, is much faster than calculating sensitivities for all parameters. If only a part of the DVRFS modeling area is of interest to a user, sensitivities can be calculated only for parameters in the subarea of interest. To calculate sensitivities for only select parameters, set the second variable (INSENALL) in the first data row of the SEN Process to 0. Next, for each parameter for which sensitivity output is desired, set the second column (variable ISENS) to 1. Shown below are the first few lines of the SEN Process with the ISENALL variable shaded in gray. As designated by the Boolean flag in the second column (variable ISENS), sensitivities will only be calculated for the fault conductance parameters B_HWY95 and B_DV_N:
# SEN Package Line 0: Text(Line 3: PARNAM ISENS LN B BL BU BSCAL)
100 0 0 100 Line 1: NPLIST ISENALL IUHEAD MXSEN
0 0 0 3 Line 2: IPRINTS SEN_ISENSU (binary or text file=unit 42)
SEN_ISENPU (text file = unit 43) ISENFM
B_LVVSZ_1 0 1 9.0E-4 0.100000E-07 10.0000 0.100000E-08
B_HWY95 1 1 2.95E-4 0.100000E-07 10.0000 0.100000E-08
B_DVFC_FCR 0 1 1.0E-7 0.100000E-07 10.0000 0.100000E-08
B_LVVSZ_IS 0 1 1.1E-8 0.100000E-07 10.0000 0.100000E-08
B_LVVSZ_I2 0 1 4.19E-8 0.100000E-07 10.0000 0.100000E-08
B_PAHRUMP 0 1 5.52E-7 0.100000E-07 10.0000 0.100000E-08
B_DV_N 1 1 2.4E-7 0.100000E-07 10.0000 0.100000E-08
In addition to all the output created in the forward mode, additional output files (dvr._sc, dvr._sd, and dvr._s1) are produced when the SEN Process is active (table 7). These output files list composite scaled sensitivities (dvr._sc) and dimensionless scaled sensitivities (dvr._sd) for each selected parameter, and prediction scaled sensitivities (dvr._s1) for each observation for each selected parameter. Statistics written to the GLOBAL file in the parameter-sensitivity mode that are not produced during a forward model simulation include the calculated error variance, the standard error of the regression, and parameter correlation coefficients (Hill, 1998).
To execute a model simulation in parameter-estimation mode, activate the SEN and PES Processes in the name file. In the PES Process, also set the variable MAX-ITER to 1. Parameter-sensitivity mode output includes one-percent scaled sensitivity arrays (set additional print flags in the SEN Process and OC Option), the fit of simulated equivalents to observations, composite scaled sensitivities, and prediction scaled sensitivities. Parameter-estimation mode will produce optimal parameter values for the observation weights if convergence is achieved. When the PES Process is activated in the name file, the method of running this mode for all parameters or for a set of parameters is the same as previously described for the parameter-sensitivity mode.
Output produced only in the parameter-estimation mode, including the dvr. pa and dvr._pc files, contains information about parameter estimation by iteration and only final parameter estimates, respectively. With an active PES Process, additional statistics, such as estimated parameter values, standard deviations, coefficients of variation, and 95 percent linear confidence intervals, are written to the GLOBAL file (table 7) (Hill, 1998).
For more information about USGS activities in Nevada, visit the USGS Nevada Water Science Center home page.
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