Static Files

The static directory contains a set of MODFLOW-2000 input files that do not change with time. Most of the files date from V12p7, while others are closely related to the V12p7 files. The following table describes the static files.

02.ibound IBOUND array used to define active model cells
11.etsurf Ground surface array used to calculate depth-to-water for ET Aquifer bottom array used to calculate aquifer saturated thickness Top of saturation array used to calculate aquifer saturated thickness
annual.lpf Layer Property Flow package input file
12p.k Aquifer hydraulic conductivity array Aquifer specific storage array Aquifer specific yield array (not used)
12p.pcg Preconditioned Conjugate Gradient (PCG2) solver control parameters
annual.drn Drain package input file
12.hyd HYDMOD file for V12p7 streams
12s.hyd HYDMOD file for V12s streams
annual.oc Output Control

It should never be necessary to modify any of these files.

Aquifer property files

Aquifer properties of the RRCA Groundwater Model are set in the Layer Property Flow (LPF) package input file annual.lpf. File references in this file are set up to access the appropriate files in the static directory.

The extent of the active aquifer is defined by 02.ibound. This file remains unchanged from model version 2.

The aquifer is simulated as having a constant saturated thickness, calculated as the difference between the top and bottom of the saturated aquifer specified in the files and, respectively. The aquifer hydraulic conductivity is specified in the file 12p.k in units of feet per day, which the LPF package then uses to calculate an aquifer transmissivity.

The aquifer is in reality a phreatic aquifer. However, in order to simulate the aquifer as having a constant transmissivity, the LPF package treats the aquifer as being confined. The specific yield of the aquifer is contained in the file However, the LPF package requires a specific storage, defined as specific yield divided by aquifer thickness. These values are contained in the file and it is this file that is read by the LPF package.

Note that the top of saturation and ET ground surface are quite different. The ET ground surface array represents the actual ground surface, while the top of saturation array represents an average water table elevation.

Except for changes to the LPF package file necessitated by changes to the directory structure, all the aquifer property files remain unchanged from V12p7.

The files and are referenced from the MODFLOW-2000 discretization package. However, since this package also contains the time step information which differs year to year because of leap years, the discretization package file is generated for each year.

Drain Package Input

The drain package is used to simulate springs and seeps in the model. The file annual.drn contains the parameters as they appear in the transient portion of the V12p7 model.

The V12p7 model consisted of a steady state pre-development period, and a transient period from 1918 to 2000. The drain package contained a different set of data for the pre-development steady state and the transient periods. The file annual.drn contains the V12p7 drain parameters as well as a repeat flag for 1199 stress periods so that this file can be used in simulations for up to 100 years of monthly stress periods.

HYDMOD Package Input

The files 12.hyd and 12s.hyd are input files to the HYDMOD package. The HYDMOD package is used to extract stream flows at a set of locations along the stream network. These stream flows are the used by post-processing programs to determine changes in stream flows which translate to stream depletions.

The 12.hyd file contains the set of locations corresponding the the V12p7 stream package. An error in the V12p7 stream package was discovered after the model was officially adopted by the RRCA. A corrected model, known as V12s, was adopted for use starting with model year 2001. The correction in the streams required a different set of stream locations, which are contained in 12s.hyd.

For model simulations from 2001 onwards, the 12s.hyd should be used. For the year 2000, the 12.hyd was used to verify that model simulations exactly match those obtained during model calibration, while 12s.hyd was used to evaluate the differences introduced by the V12s stream correction.

Output Control

The annual.oc output control file is used to save model predicted heads and cell by cell flows at the end of each month. The file differs from the V12p7 output control file only in that it does not have the initial steady state step. The file contain enough entries for multi-year simulations up to 100 years.

PCG Solver

The file 12p.pcg contains control parameters to the PCG2 solver. When MODFLOW-2000 is run in double precision, these parameters generally result in a mass balance better than 0.01 percent.

In order to provide for a stable solution algorithm, a damping factor of 0.8 is used. This allows most numerical oscillations to be overcome without excessively slowing down the convergence.

A maximum of 100 outer iterations are permitted. Occasionally, this maximum number of iterations will be reached without satisfying the head and residual criteria, but with a very good mass balance, usually better than 0.01 percent. The version of MODFLOW-2000 used has the Mass Balance Override feature enabled to continue the simulation when this occurs.

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Model Units
Directory Structure
Precipitation Data Entry
Colorado Data Entry
ET Data Entry
Stream Data Entry
Kansas Data Entry
Nebraska Data Entry
Running the Model