Page 35 - Beaumont Basin Watermaster

Section 3
Water Quality Conditions

The variability of groundwater levels at BCVWD Well No. 2 and Banning Well C4 are likely due
to seasonal pumping patterns in these areas. Groundwater levels in the northeast portion of
the basin (USGS Highland Springs Monitoring Well - 335714116565002) have been trending
upward since 2010 and have remained mostly stable in 2018.

3.6.2 Analysis of Change in Groundwater Storage
Basin-wide change in groundwater storage between December 2017 and December 2018 was
analyzed as a function of the difference in groundwater levels across the basin and the
specific yield of the aquifer sediments. Groundwater level change across the basin was
analyzed using the following procedure:

1. The December 2017 and 2018 model-generated groundwater contour maps were each
converted into three-dimensional raster surfaces.
2. The basin was discretized into 100-ft by 100-ft grid cells.
3. Attributes were assigned to each grid cell including groundwater level change and
specific yield.

4. The resulting attribute table was processed in a Geographic Information System (GIS)
for calculating the change in storage.

The specific yield distribution used for the analysis was obtained from the calibrated
groundwater flow model used to evaluate the Safe Yield of the Beaumont Basin, as
summarized in TH&Co (2015).

Results of the analysis show an increase in groundwater storage within the adjudicated basin
of approximately 173 acre-ft during this one-year period. The model may be underestimating
the positive storage change in the Noble Creek Recharge area. Most of the western area
showed decreases in groundwater in storage

3.7 Operating Safe Yield

For purposes of this annual report, the annual operating Safe Yield (OSY) describes the net
infiltration to the adjudicated groundwater basin (not including artificial recharge) for any given
year. It is noted that the OSY is different than the Operating Yield, which is a function of the
unused overlyer production (Appropriative Water) and Temporary Surplus, as described in the
Beaumont Basin Judgment (San Timoteo Management Authority v. Banning et al., 2004).

Operating Safe Yield is estimated based on the following equation:

OSY = ΣP + ΔS - ΣAR
ΔT

where: ΣP = The sum of groundwater production (ac-ft)
ΔS = The change in groundwater storage (ac-ft)

ΣAR = The sum of groundwater recharge (ac-ft)

Beaumont Basin Watermaster 2018 Annual Report – DRAFT - February 2019 3-13