Page 39 - Beaumont Basin Watermaster

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

in the northeast are assumed to be impermeable and were modeled as no-flow areas.
Groundwater flow barriers were incorporated into the southern portion of the Model Domain to
simulate head differences caused by faults. The GHB was incorporated along faults and bedrock
areas to allow subsurface inflow into the model from the mountain block. Groundwater levels at
the model boundaries in the Yucaipa, Banning and San Timoteo Creek area were constrained
using the specified head boundary package based on the historical hydrographs for wells in those
areas. Measured groundwater levels for all specified head wells are provided in Appendix F and
hydrographs for these wells are in Appendix G.

5.5 Aquifer Characteristics

5.5.1 Layer Elevations
Groundwater layers were developed based on depth-specific analysis of groundwater flow and
quality, as described in Section 3.3.2 (see Figures 18 and 19). The top of Layer 1 is the ground
surface as determined by USGS Digital Elevation Models (DEMs) (30 meter resolution) for the
Model Domain. The contoured surface of the contact between Layer 1 and Layer 2 (upper and
lower aquifers) was developed and digitized using the software package Surfer (Golden
Software, 2002) (see Figure 19).

5.5.2 Hydraulic Conductivity
Hydraulic conductivity values were spatially represented in the groundwater flow model as zones
(see Figures 30 and 31). Each zone of equal hydraulic conductivity was determined for each
model layer based on analysis of pumping test data and soil textural analysis as described in
Section 3.3.2.3 (see Figures 23 and 24). After assigning initial hydraulic conductivity values to
the zones, the values were adjusted during model calibration, within a plausible range based on
available data, until an acceptable match was obtained between measured and model-generated
groundwater levels. Final calibrated hydraulic conductivity zones are shown on Figures 30
and 31.

5.5.3 Specific Yield and Storativity

Because Layer 1 is unconfined, storage properties of the aquifer in this layer are addressed as
estimates of specific yield. Initial zones and values for specific yield were assigned to Layer 1
based on the textural analysis and literature values for the soil types (Johnson, 1967). Final
specific yield zones and values were developed during model calibration and are shown on
Figure 32.

31