Page 31 - Beaumont Basin Watermaster

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

During storm events, a portion of the precipitation falling on the land surface in the Study Area
runs off and is routed into the stream channels. All of the streams in the Study Area are unlined
except for an approximate 2,600 ft section of Noble Creek immediately downstream of its
confluence with Little San Gorgonio Creek. A portion of the surface water runoff that occurs in
unlined stream channels infiltrates into the subsurface and becomes groundwater recharge.
Although there are no stream gages in the Study Area, observations of surface water flow in the
stream channels during minor precipitation events suggests that surface water flow in Noble
Creek generally infiltrates into the subsurface before reaching San Timoteo Creek (see Figure 10
for stream channel locations). Surface water flow in Noble Creek reaches San Timoteo Creek
during flash flood events and prolonged periods of precipitation. Surface water flow in Marshall
Creek does not typically reach San Timoteo Creek except during flash flood events or during
prolonged periods of precipitation (Personal communication with BCVWD staff, 2013).

Deep infiltration and groundwater recharge from runoff in stream channels was estimated based
on the USGS Infil v3 model. The model provided the magnitude and location of recharge within
the stream channels. The resulting recharge was incorporated into the groundwater flow model
using the recharge package and adjusted during calibration. It is noted that deep infiltration in
San Timoteo Creek was not estimated using the Infil v3 model but was instead simulated based
on stream discharges from the City of Beaumont’s WWTP and assumptions for streambed
conductance using the MODFLOW stream package (see Section 5.8.2).

4.1.3 Subsurface Inflow from Outside the Study Area

Subsurface inflow to the aquifers in the Study Area occurs primarily from the Yucaipa area with
a lesser amount from the South Beaumont area. Subsurface inflow is addressed via a time-
varying specified head boundary condition in the groundwater flow model and estimated as a
result of the calibration process. The groundwater flow model boundary conditions are shown
on Figure 29.

4.1.4 Subsurface Inflow from the Mountain Block
Mountain block recharge represents the water that enters the hydrologic groundwater basin along
the bedrock alluvial interface plus subsurface underflow where Little San Gorgonio Creek,
Noble Creek, and Smith Creek enter the basin (see Figure 29). Groundwater recharge along the
bedrock alluvial interface was simulated in the groundwater flow model using a General Head
Boundary condition with initial estimates based on Rewis et al. (2006) which were then adjusted
during calibration. Subsurface underflow in the alluvial area where Little San Gorgonio Creek
and Noble Creek enter the groundwater basin was estimated based on a flownet analysis of this

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