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Evaluation of the hydrologic system and selected water-management alternatives in the Owens Valley, California

January 1, 1998

The Owens Valley, a long, narrow valley
along the east side of the Sierra Nevada in eastcentral
California, is the main source of water for
the city of Los Angeles. The city diverts most of
the surface water in the valley into the Owens
River?Los Angeles Aqueduct system, which
transports the water more than 200 miles south to
areas of distribution and use. Additionally, ground
water is pumped or flows from wells to supplement
the surface-water diversions to the river?
aqueduct system. Pumpage from wells needed to
supplement water export has increased since 1970,
when a second aqueduct was put into service, and
local residents have expressed concerns that the
increased pumping may have a detrimental effect
on the environment and the native vegetation
(indigenous alkaline scrub and meadow plant
communities) in the valley. Native vegetation on
the valley floor depends on soil moisture derived
from precipitation and from the unconfined part of
a multilayered ground-water system. This report,
which describes the evaluation of the hydrologic
system and selected water-management alternatives,
is one in a series designed to identify the
effects that ground-water pumping has on native
vegetation and evaluate alternative strategies to
mitigate any adverse effects caused by pumping.
The hydrologic system of the Owens Valley
can be conceptualized as having three parts: (1) an
unsaturated zone affected by precipitation and
evapotranspiration; (2) a surface-water system
composed of the Owens River, the Los Angeles
Aqueduct, tributary streams, canals, ditches, and
ponds; and (3) a saturated ground-water system
contained in the valley fill.
Analysis of the hydrologic system was
aided by development of a ground-water flow
model of the ?aquifer system,? which is defined as
the most active part of the ground-water system
and which includes nearly all of the Owens Valley
except for the area surrounding the Owens Lake.
The model was calibrated and verified for water
years 1963?88 and used to evaluate general
concepts of the hydrologic system and the effects
of past water-management practices. The model
also was used to evaluate the likely effects of
selected water-management alternatives designed
to lessen the adverse effects of ground-water
pumping on native vegetation.
Results of the model simulations confirm
that a major change in the hydrologic system was
caused by the additional export of water from the
valley beginning in 1970. Average ground-water
pumpage increased by a factor of five, discharge
from springs decreased almost to zero, reaches of
the Owens River that previously had gained water
from the aquifer system began losing water, and
total evapotranspiration by native plants decreased
by about 35 percent. Water-management practices as of 1988
were defined and evaluted using the model. Simulation
results indicate that increased ground-water
pumpage since 1985 for enhancement and mitigation
projects within the Owens Valley has further
stressed the aquifer system and resulted in
declines of the water table and reduced
evapotranspiration. Most of the water-table
declines are beneath the western alluvial fans and
in the immediate vicinity of production wells. The
water-table altitude beneath the valley floor has
remained relatively constant over time because of
hydrologic buffers, such as evapotranspiration,
springs, and permanent surface-water features.
These buffers adjust the quantity of water
exchanged with the aquifer system and effectively
minimize variations in water-table altitude. The
widespread presence of hydrologic buffers is the
primary reason the water-table altitude beneath the
valley floor has remained relatively constant since
1970 despite major changes in the type and
location of ground-water discharge.
Evaluation of selected water-management
alternatives indicates that long-term variations in
average runoff to the Owens Valley of as much as

Publication Year 1998
Title Evaluation of the hydrologic system and selected water-management alternatives in the Owens Valley, California
DOI 10.3133/wsp2370H
Authors Wesley R. Danskin
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Water Supply Paper
Series Number 2370
Index ID wsp2370H
Record Source USGS Publications Warehouse