Page 29 - Beaumont Basin Watermaster

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

Timoteo area were assigned values ranging from 0.07 to 0.12. Initial specific yield values were
adjusted during the model calibration process.

3.3.2.6 Storativity

Storativity is a measure of the volume of water an aquifer can release from, or take into, storage
per unit surface area of aquifer per unit change in hydraulic head (Fetter, 1994). Storativity is
derived from long-term pumping tests where pumping interference is measured in a monitoring
well located a known distance from the pumping well. Only limited storativity values from
pumping tests were available in the Study Area (see Figure 24; Appendix C). Available data
indicates storativity values ranging from 0.0003 to 0.007. These values suggest confined to
semi-confined aquifer conditions although it is noted that many of the storativity values derived
from pumping tests are based on wells perforated through both the Upper and Lower Aquifers.

3.3.3 Groundwater Movement
Groundwater flow within the Beaumont Basin generally depends on location with respect to a
groundwater flow divide which occurs in the center of the basin approximately coincident with
the Noble Creek drainage (see Figure 25). Initially groundwater flows south, away from the San
Bernardino Mountains, before diverging away from the Noble Creek Drainage. West of the
Noble Creek drainage, groundwater generally flows to the northwest and ultimately towards San
Timoteo Wash. East of the Noble Creek drainage, groundwater flows to the southeast towards
the City of Banning.

Since approximately 1927, groundwater levels in the Study Area have generally declined 120 to
180 ft (see Figure 26). Between approximately 1930 and 1970, groundwater levels dropped as
much as 90 ft at a relatively consistent rate. Between approximately 1970 and 2000, the rate of
groundwater level decline decreased but continued a downward trend. Between 2000 and 2012,
the rate of groundwater level decline increased again as a result of increased groundwater
pumping in the Beaumont Basin and surrounding areas (see Figure 26).

The more stable groundwater levels observed between 1970 and 2000 are interpreted to result
from the delayed arrival of percolating return flow and recharge in stream channels resulting
from urban development of the area. Despite average groundwater production that was higher
between 1970 and 2000 relative to the 1930s and 1940s, groundwater levels were relatively
stable (see Figure 27). Given that average precipitation did not change significantly and artificial
recharge had not begun yet, the only other sources of recharge would be return flow from
increased urban landscape irrigation and increased runoff and associated infiltration in unlined
stream channels.

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