Page 37 - Beaumont Basin Watermaster

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

5.0 Groundwater Flow Model

The Safe Yield of the Beaumont Basin was reevaluated using a calibrated three-dimensional
numerical groundwater flow model. The model boundaries are the same as the Study Area,
which is hereafter referred to as the Model Domain (see Figure 2).

5.1 Conceptual Model

Conceptualization of the groundwater flow model was based on Rewis et al. (2006) and updated
with more recent geological and hydrogeological data, as summarized in this report. Consistent
with Rewis et al. (2006), two model layers were identified for the alluvial aquifer system:

Layer 1 This layer represents the Upper Aquifer and generally includes the
upper approximately 1,000 ft of alluvial sediments. This layer is
modeled as unconfined.

Layer 2 This layer represents the Lower Aquifer and ranges from 150 to 730 ft
thick. Layer 2 is less permeable than the overlying layer and is
modeled as confined. Only the deepest wells in the Beaumont Basin
are perforated into Layer 2.

Groundwater flow is assumed to occur horizontally within each model layer while vertical
communication between model layers is addressed through assignment of vertical hydraulic
conductivity values for each layer.

Both recharge and discharge were applied to the model in annual stress periods from 1927
through 2002, then as monthly stress periods for the period between January 2003 and December
2012.

5.2 Description of Model Codes

The numerical groundwater flow model code selected for use in this evaluation was
MODFLOW. MODFLOW is a block centered, finite difference groundwater flow modeling
code developed by the USGS for simulating groundwater flow (McDonald and Harbaugh, 1988;
Harbaugh, 2005). MODFLOW is one of the most widely used and critically accepted model
codes available (Anderson and Woessner, 2002).

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