Page 38 - Beaumont Basin Watermaster

Beaumont Basin Watermaster
2013 Reevaluation of the Beaumont Basin Safe Yield 3-Apr-15

MODFLOW is modular such that similar program functions (called “packages”) are grouped and
kept independent of other functions, which enables incorporating site-specific boundary
conditions into any given model. The packages utilized for the groundwater flow model
included:

 Basic Package (McDonald and Harbaugh, 1988);

 Block Centered Flow Package (BCF2; McDonald et al., 1991);
 General Head Boundary Package (McDonald and Harbaugh, 1988);
 Constant Head Boundary Package (McDonald and Harbaugh, 1988);
 Recharge Package (McDonald and Harbaugh, 1988);
 Well Package (McDonald and Harbaugh, 1988);
 Streamflow Package (STR6; Prudic, 1989); and
 Evapotranspiration Package (McDonald and Harbaugh, 1988)

Development of the groundwater flow model was accomplished using Visual MODFLOW, a
pre- and post-processing software package (Schlumberger Water Services, 2011). This program
allows for efficient pre-processing of model input files and post-processing of simulation output
files. Many of the aquifer parameter arrays and other data were initially developed using ArcGIS
(ESRI, 2009), a Geographic Information System (GIS) that is compatible with Visual
MODFLOW . For model calibration, parameter estimation software (PEST) was used to refine
the match between measured and model-generated groundwater levels (Doherty, 2002).

5.3 Model Size and Grid Geometry
The Model Domain is approximately 6.5 miles in the north-south direction and 12.2 miles in the
east-west direction (approximately 79 square miles). The model domain has been discretized
into 393 columns and 210 rows with 164 ft by 164 ft cells (see Figure 29). There are a total of
82,530 cells in the two layer model. The site coordinate system was established in State Plane
Zone 6.

5.4 Boundary Conditions

A boundary condition is any external influence that adds or removes water from the groundwater
system. Boundary conditions applied to the groundwater flow model included no-flow cells
(inactive areas), groundwater flow barriers, time-varying specified head boundaries, general head
boundaries (GHB), wells, recharge zones, a stream boundary (San Timoteo Creek), and an ET
zone (see Figure 29). The sedimentary bedrock of the San Timoteo Formation in the
southwestern portion of the Model Domain and the igneous and metamorphic crystalline bedrock

30