Page 32 - Beaumont Basin Watermaster - 2015 Annual Report

Section 3
Status of the Basin and Administration of the Judgment

year. In the north central portion of the basin (TW-1), groundwater levels increased slightly
before declining. In the south-central portion of the basin, groundwater levels at Oak Valley
No. 1 decreased in 2015. At Beaumont-Cherry Valley Water District (BCVWD) Well No. 2,
groundwater levels rose in March 2015 to the highest levels in eight years, declined in the
summer, and then rose again in September. At Banning Well C-4 (southeast Beaumont
Basin), groundwater levels have rising and falling throughout 2015. However, the overall
trend in this well since 2013 is downward. Groundwater levels in the northeast portion of the
basin (335714116565002) have been trending upward since 2010.

3.6.2 Analysis of Change in Groundwater Storage

Basin-wide change in groundwater storage between Fall 2013 and Fall 2015 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 Fall 2014 and Fall 2015 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 a decrease in groundwater storage within the adjudicated basin
of approximately 1,679 acre-ft between Fall 2014 and Fall 2015.

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

Beaumont Basin Watermaster 2015 Annual Report – Final – December 2016 3-11