Open-File Report 2006–1104
U.S. GEOLOGICAL SURVEY
Open-File Report 2006–1104
Since publication of the DVRFS model, the authors have responded to model users regarding questions about predictive pumping scenarios and conversion of the model from a transient to a steady-state simulation. Both of these scenarios are addressed in following sections which pertains to editing the model archive files. The required editing of model inputs to achieve these model modifications for execution in forward model mode with observations and parameter-value substitution (Hill and others, 2000, p. 12) is described. The observation packages (CHOB, DROB, and HOB) are not required to conduct model simulations in forward mode when the OBS Process is inactive. However, conducting model simulations in the forward mode with the OBS Process active produces additional output that aids model evaluation. If a user is not utilizing the OBS Process, inactivate the OBS Process and the CHOB, DROB, and HOB Packages in the name file and disregard editing instructions for these files.
To simulate predictive pumping scenarios, or pumping that extends beyond the last stress period of the DVRFS model, the DIS file and the WEL1 Package (or the MNW1 Package) are the primary two files that require editing. The total length of the model simulation may be changed by adding additional stress periods in the DIS file. Any pumping that occurs during these additional stress periods can be included in the WEL1/MNW1 Package by specifying pumping rates, well locations, and time of pumping. All other packages which contain parameter information by stress period (CHD, HFB6, DRN, and RCH Packages) also need to reflect an increase in the total number of stress periods. Parameter definitions from the previous time step may be repeated for each of the new stress periods.
In the DIS file, extend the number of stress periods by adding a line, at the end of the file, for each additional stress period, and increase the total number of stress periods (variable NPER).
# DIS Package Line 0: Text
16 194 160 90 4 2 Line 1: NLAY NROW NCOL NPER ITMUNI LENUNI
Next, specify the length of each of the three additional stress periods (variable PERLEN), the number of time steps (variable NSTP), the time step multiplier (variable TSMULT), and identify the additional stress period as transient (TR).
1462 3 1 TR Line 7: PERLEN NSTP TSMULT (stress period 88) 1462 3 1 TR Line 7: PERLEN NSTP TSMULT (stress period 89) 1462 3 1 TR Line 7: PERLEN NSTP TSMULT (stress period 90).
Well locations are identified by model layer, row, and column. Approximate well locations by row and column can be calculated from Universal Transverse Mercator (UTM) coordinates using the following equations:
Column = INT((easting - 437,000)/1500) + 1, (1)
Row = INT((4,219,000 - northing)/1500) + 1, (2)
where
INT is a function which converts a real number to an integer
by truncating values after the decimal point, and the easting and northing coordinates
are UTM zone 11.
To add additional pumping or well injection during the three new stress periods, add to the end of the WEL1 Package the number of non-parameter wells read for the current stress period (variable ITMP), and the layer, row, and column of the well followed by the pumping rate (variables Layer, Row, Column, and Q) for each stress period. A negative pumping rate indicates discharge from the ground-water system. For example, to add a pumping well (model layer 1, row 141, column 100) and another pumping well (model layer 1, row 147 and column 104) that each pump at a rate of 2.36 m3/d in each of the three additional stress periods, the following lines would be added to the end of the WEL1 Package:
2 1 141 100 -2.36 1 147 104 -2.36 2 1 141 100 -2.36 1 147 104 -2.36 2 1 141 100 -2.36 1 147 104 -2.36
After editing files, execute MODFLOW-2000 in the forward mode with observations and parameter-value substitution.
For users who wish to compare DVFRS hydraulic properties with an existing model, it may be an advantage to run the model with steady-state conditions, instead of transient conditions, for faster sensitivity analysis computations. Oftentimes in ground-water modeling, a steady-state solution is approximated with a long transient stress period. Significant drawdown occurs at some locations in the DVRFS model and adding a long final transient stress period to the existing model would require re-wetting if pumping was turned off during a long final stress period. As rewetting may result in numerical instabilities (Harbaugh and others, 2000), a different approach is proposed.
To convert the DVRFS model from a transient to a steady-state simulation, some transient information must be removed. To simulate only a single initial steady-state stress period, change the total number of stress periods to 1. In this case, model stresses during the existing transient stress periods do not need to be removed as they are effectively turned off leaving only a single steady-state stress period. The observation files, the DIS file which specifies time discretization, and storage parameters in the HUF2 Package and SEN Process require editing. The OC Option also requires editing so that printing and saving does not occur from the transient stress periods that have been removed from the model simulation. Additionally, all observation packages (CHOB, DROB, and HOB) must be edited so that no observations are specified in times that extend beyond the period of the steady-state simulation.
To convert the transient simulation to a steady-state simulation, specify a single steady-state stress period in the DIS file. If a single steady-state stress period is specified, the additional transient stress periods, which are specified on subsequent lines in the file, will not be read.
For example, replace the 87 stress periods in DIS file:
# DIS Package Line 0: Text
16 194 160 87 4 2 Line 1: NLAY NROW NCOL NPER ITMUNI LENUNI
with a single steady state stress period as indicated by the gray highlighting:
# DIS Package Line 0: Text
16 194 160 1 4 2 Line 1: NLAY NROW NCOL NPER ITMUNI LENUNI.
To convert from a transient to a steady-state simulation, specific storage parameters (parameter types SS and SYTP) must be removed from the HUF2 Package (HUF2_CONFINED.txt) and the SEN Process (SENSITIVITY.txt) files. The removal of these parameters also must be reflected in the total number of HUF2 Package parameters (variable NPHUF) and the total number of parameters in the SEN Process (variables NPLIST and MXSEN). If the seven storage parameters (STOR_12, STOR_34, STOR_4VUP, STOR_4C, SY_OTHER, SY_PAH, and SY_PUMP) are removed from the HUF2 Package (lines 246 to 283) and the SEN Process (lines 97 to 103), the variable NPHUF, which specifies the total number of parameters in the HUF2 Package (HUF2_CONFINED.txt), also must decrease by seven (from 69 to 62) as indicated by the gray shading in the first data row in the HUF2 Package:
# HUF2 Package
#
36 -9999 27 62 0 IHUFCB HDRY NHUF NPHUF IOHUF.
Additionally, the total number of parameters in the SEN Process must be decreased from 100 to 93 as indicated by the gray shading in the first data row.
# SEN Package Line 0: Text (Line 3: PARNAM ISENS LN B BL BU BSCAL) 93 -1 0 93 Line 1: NPLIST ISENALL IUHEAD MXSEN
As steady-state conditions were defined as pre-development conditions with no pumping, the MNW Package should be deactivated in the name file.
In the OC Option, remove all references to stress periods after stress period 1.
After the above editing is complete, model simulations will be executed with steady-state conditions if the OBS Process is deactivated in the name file. To run the model with steady-state conditions and an active OBS Process, edit the DROB and HOB Packages. The CHOB Package does not require editing because all observations occur during the steady-state stress period.
Most observations in the DROB Package are specified during stress period 86. Because only two discharge locations have flows that diminish with time, the observation flows in stress period 86 also reflect steady-state conditions, and only the observation time requires editing.
For example, for the drain observation at Furnace Creek Wash springs in Death Valley (OBS-DV-FRNFN) highlighted below in gray, the change is from stress period 86:
1 9
OBS-DV-FRNFN 1 86 -11522. 0.280 2 3
1 122 50 1.00
1 123 49 1.00
1 123 50 1.00
1 124 49 1.00
1 124 50 1.00
1 125 49 1.00
1 125 50 1.00
1 126 50 1.00
1 126 51 1.00
to stress period 1:
1 9
OBS-DV-FRNFN 1 1 -11522. 0.280 2 3
1 122 50 1.00
1 123 49 1.00
1 123 50 1.00
1 124 49 1.00
1 124 50 1.00
1 125 49 1.00
1 125 50 1.00
1 126 50 1.00
1 126 51 1.00
Four drain observations at two locations (Manse and Bennetts Springs in Pahrump Valley), which reflect decreasing flows over time, must be removed as they do not reflect steady-state conditions: OB-PAH-BENT (stress period 48), O-PAH-BENT (stress period 87), OB-PAH-MANS (stress period 48), and O-PAH-MANS (stress period 87). The change in the total number of observations (from 49 to 45) must be reflected in the first data row of DROB Package.
#Observations in the 1997=86 stress period and stress period 1. 49 769 49
to:
#Observations in the 1997=86 stress period and stress period 1. 45 769 45
as indicated by the gray highlighting.
In the HOB Package, remove observations that do not reflect steady-state conditions. This can be accomplished by removing hydraulic head observations with PLOT-SYMBOL values of 2 or 3 (so that just PLOT-SYMBOL values of 0 and 1 remain) or by deleting entries that occur at times other than during the steady-state stress period. Update the change in the total number of head and head change observations (variable NH) in the first data row of the HOB Package.
After editing, execute MODFLOW-2000 in the forward mode with observations and parameter-value substitution (table 7).
For more information about USGS activities in Nevada, visit the USGS Nevada Water Science Center home page.
U.S.
Department of the Interior | U.S. Geological
Survey
Persistent URL: http://pubs.water.usgs.gov/ofr20061104
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