Page 22 - Beaumont Basin Watermaster - 2015 Annual Report

Section 3

Status of the Basin and Administration of the

Judgment

The Beaumont Basin Watermaster is responsible for the accounting of groundwater
production, recharge of supplemental water, groundwater transfers and storage activities in
the Beaumont Basin. Since the inception of the Judgment accounting has been conducted
on a fiscal year basis starting on July 1, 2003.

Through the adoption of Resolution No. 2011-01, on September 21, 2011, Watermaster changed
the accounting from a fiscal year basis to a calendar year basis starting in CY 2011. The
conversion of Fiscal Year basis to Calendar Year basis was documented in the Annual Report
for CY 2011 adopted by the Board in early 2013. The annual report for CY 2015 builds on the
information presented in previous annual reports.

3.1 Climate, Hydrology and Hydrogeology

3.1.1 Climate
The Beaumont Basin is located in a semi-arid region characterized by warm summers and
mild winters with average summer high temperatures in the mid to upper 90s (Fahrenheit)
and average winter low temperatures in the mid to low 40s. Precipitation in the region occurs
as snowfall in the upper elevations of the San Bernardino Mountains to the north and rainfall
in the Basin. Annual precipitation in the Beaumont Basin, as recorded at the County of
Riverside’s Beaumont Station 013 averaged 17.32 inches over the 100-year period between
1916 and 2015. On the average, 70 percent of precipitation falls during the winter between
December and March.

Figure 3-1 illustrates annual precipitation at this station for the reporting period including a
plot of the cumulative departure from the mean (CDFM) precipitation. This parameter is
used to assess the occurrence, duration, and extent of wet and dry precipitation cycles.
Upper trending periods in the graph represent periods with above average precipitation such
as the 1913-46 period; average precipitation during this period was 20.5 inches or close to
16 percent above the long-term average. Other above average precipitation periods include
the 1977-83 and 1990-98 periods. Conversely, down trending periods indicate periods of
below average precipitation as in the 1947-77 period when average precipitation was only
15.2 inches. The 1984-90 period with seven consecutive years of below average
precipitation was also characterized as a dry period.

Currently, the Basin is in a dry period that began in 1999. During this 16-year period three of
the five years with the lowest precipitation ever recorded at Station 13 have occurred; 6.3
inches (lowest ever) in 1999, 7.40 inches in 2013, and 8.07 inches in 2009. It should be
noted that the average precipitation during the base period (1997-2001) used to determine
the safe yield of the Basin was 13.43 inches, close to 25 percent below the long-term
average for the Basin.

Beaumont Basin Watermaster 2015 Annual Report – Final – December 2016 3-1