WriteModflowInput: Write MODFLOW Input Files
In USGS-R/wrv: Wood River Valley Groundwater-Flow Model

Description Usage Arguments Details Value Author(s) References Examples

This function generates and writes input files for a MODFLOW simulation of groundwater flow in the Wood River Valley (WRV) aquifer system.

WriteModflowInput(
  rs.model,
  rech,
  well,
  trib,
  misc,
  river,
  drain,
  id,
  dir.run,
  is.convertible = FALSE,
  ss.perlen = 0L,
  tr.stress.periods = NULL,
  ntime.steps = 4L,
  mv.flag = 1e+09,
  auto.flow.reduce = FALSE,
  verbose = TRUE
)

`rs.model`	RasterStack. Collection of RasterLayer objects with the same extent and resolution, see ‘Details’ for required raster layers.
`rech`	data.frame. Areal recharge rate, in cubic meters per day. Variables describe the model cell location (`lay`, `row`, `col`) and volumetric rate during each stress period (`ss`, `199501`, `199502`, ..., `201012`).
`well`	data.frame. Well pumping at point locations in cubic meters per day. Variables describe the model cell location and volumetric rate during each stress period.
`trib`	data.frame. Incoming flows from the major tributary canyons. Variables describe the model cell location and volumetric rate during each stress period.
`misc`	data.frame. Direct recharge from miscellaneous seepage sites in cubic meters per day. Variables describe the model cell location and volumetric rate during each stress period.
`river`	data.frame. River conditions. Variables describe the model cell location, river conductance (`cond`) in square meters per day, river bottom elevation (`bottom`) in meters above the North American Vertical Datum of 1988 (NAVD 88), and a numeric river reach identifier (`id`).
`drain`	data.frame. Drain conditions for groundwater outlet boundaries. Variables describe the model cell location, drain threshold elevation (`elev`) in meters above the NAVD 88, drain conductance (`cond`) in square meters per day, and a numeric identifier (`id`) indicating the drains general location.
`id`	character. Short identifier for the model run.
`dir.run`	character. Path name of the directory to write model input files.
`is.convertible`	logical. If true, indicates model layers are ‘convertible’, with transmissivity computed using upstream water-table depth. Otherwise, model layers are ‘confined’ and transmissivity is constant over time.
`ss.perlen`	integer or difftime. Length of the steady-state stress period in days.
`tr.stress.periods`	Date. Vector of start times for each stress period in the transient simulation. If missing, only steady-state conditions are simulated.
`ntime.steps`	integer. Number of uniform time steps in a stress period.
`mv.flag`	numeric. Missing value flag for output reference data files.
`auto.flow.reduce`	logical. If true, a simulated well will adjust pumping according to supply under bottom-hole conditions. Pumping rates that have been automatically reduced will be written to a model output file (‘.afr’).
`verbose`	logical. If true, additional information is written to the listing file (‘.lst’) and budget file (‘.bud’)

Groundwater flow in the WRV aquifer system is simulated using the MODFLOW-USG groundwater-flow model. This numerical model was chosen for its ability to solve complex unconfined groundwater flow simulations. The solver implemented in MODFLOW-USG incorporates the Newton-Raphson formulation for improving solution convergence and avoiding problems with the drying and rewetting of cells (Niswonger and others, 2011). A structured finite-difference grid is implemented in the model to (1) simplify discretization, (2) keep formats and structures for the MODFLOW-USG packages identical to those of MODFLOW-2005, and (3) allow any MODFLOW post-processor to be used to analyze the results of the MODFLOW-USG simulation (such as Model Viewer).

Model input files are written to dir.run and include the following MODFLOW Package files: Name (‘.nam’), Basic (‘.ba6’), Discretization (‘.dis’), Layer-Property Flow (‘.lpf’), Drain (‘.drn’), River (‘.riv’), Well (‘.wel’), Sparse Matrix Solver (‘.sms’), and Output Control (‘.oc’). See the users guide (Description of Model Input and Output) included with the MODFLOW-USG software for details on input file formats and structures.

Data within the rech, well, trib, and misc arguments are combined in the MODFLOW Well Package and identifiable with added id values of 1, 2, 3, and 4, respectively.

The Layer-Property Flow file includes options for the calculation of vertical flow in partially dewatered cells. For the WRV model, where there is no indication that perched conditions exist, CONSTANTCV and NOVFC options are used to create the most stable solution (Panday and others, 2013, p. 15-16). Options for the Sparse Matrix Solver were set for unconfined simulations by implementing an upstream-weighting scheme with Newton-Raphson linearization, Delta-Bar-Delta under-relaxation, and the χMD solver of Ibaraki (2005).

The raster stack rs.model includes the following layers:

lay1.top: elevation at the top of model layer 1 (land surface), in meters above the NAVD 88.
lay1.bot: elevation at the bottom of model layer 1, in meters above the NAVD 88.
lay2.bot: elevation at the bottom of model layer 2.
lay3.bot: elevation at the bottom of model layer 3.
lay1.strt: initial (starting) hydraulic head in model layer 1, in meters above the NAVD 88.
lay2.strt: initial hydraulic head in model layer 2.
lay3.strt: initial hydraulic head in model layer 3.
lay1.zones: hydrogeologic zones in model layer 1 where values equal to 1 is unconfined alluvium, equal to 2 is basalt, equal to 3 is clay, and equal to 4 is confined alluvium.
lay2.zones: hydrogeologic zones in model layer 2.
lay3.zones: hydrogeologic zones in model layer 3.
lay1.hk: horizontal hydraulic conductivity in model layer 1, in meters per day.
lay2.hk: horizontal hydraulic conductivity in model layer 2.
lay3.hk: horizontal hydraulic conductivity in model layer 3.

Used for the side-effect of files written to disk.

J.C. Fisher, U.S. Geological Survey, Idaho Water Science Center

Ibaraki, M., 2005, χMD User's guide-An efficient sparse matrix solver library, version 1.30: Columbus, Ohio State University School of Earth Sciences.

Niswonger, R.G., Panday, Sorab, and Ibaraki, Motomu, 2011, MODFLOW-NWT, A Newton formulation for MODFLOW-2005: U.S. Geological Survey Techniques and Methods 6-A37, 44 p., available at https://pubs.usgs.gov/tm/tm6a37/.

Panday, Sorab, Langevin, C.D., Niswonger, R.G., Ibaraki, Motomu, and Hughes, J.D., 2013, MODFLOW-USG version 1: An unstructured grid version of MODFLOW for simulating groundwater flow and tightly coupled processes using a control volume finite-difference formulation: U.S. Geological Survey Techniques and Methods, book 6, chap. A45, 66 p., available at https://pubs.usgs.gov/tm/06/a45/.