Transcript Overdraft Of the Central Valley Aquifer

Overdraft Of the Central Valley Aquifer
Nate Holdsworth
The valley is in a structural trough about 400 miles long and from 20
to 70 miles wide and extends over more than 20,000 square miles
3 regions Redding, Central
valley, Tulare separated by
different ground water flow
systems
The most drastic decrease in
water levels have taken place
in the Tulare Basin and San
Joaquin Valley.
Sacramento Valley does not
pump as much because they
have more surface
water.
Tulare Basin is the deepest
part of the aquifer
(continental deposit)
Also takes the longest to
recharge.
Geologic Setting of the Aquifer
•
THE CENTRAL VALLEY AQUIFER IS A BASIN FILL AQUIFER
•
THE CENTRAL VALLEY ACTS AS A TROUGH. IT HAS ACCUMULATED CONTINENTAL
DEBRIS AND MARINE SEDIMENT OVER MILLIONS OF YEARS AS MOUNTAINS ERODE
AND THE VALLEY IS SUBMERGED BENEATH OCEAN WATERS.
•
OCEAN SEDIMENT DEPOSITED DURING THE LAST INUNDATION OF THE CENTRAL
VALLEY DURING THE PALEOCENE(65 MILLION-56.5 MILLION Y.A.) AND EOCENE
(56.5-35.4 MILLION Y.A.) IS RELATIVELY IMPERMEABLE.
•
THE CONTINENTAL MATERIAL(ABOVE OCEAN SEDIMENT) CARRIED INTO THE
VALLEY BY MOUNTAIN STREAMS, CONSISTS PRIMARILY OF SAND, GRAVEL, AND
CLAY. THIS MATERIAL MAKES UP THE MAJORITY OF THE AQUIFER.
•
THE AQUIFER VARIES IN DEPTH (CONTINENTAL MATERIAL) FROM 9,000 FT. AT THE
DEEPEST. TOWARDS THE SOUTHERN END AND HAS AN AVERAGE THICKNESS OF
2,4OO FT.
•
Before humans came along and developed the area, the Central Valley Aquifer
fully recharged the water table every year in the valley and percolated up into
the Sacramento and San Joaquin River’s as well as other small streams and
wetland areas that existed throughout the valley.
AGRICULTURE IS A HUGE FACTOR IN AQUIFER DEPLETION
“The Central Valley is one of the most important
agricultural areas in the world. No single region of
comparable size in the United States produces more fruits,
vegetables, and nuts. More than 7 million acres are
currently (1995) under irrigation. During 1985, crop
irrigation accounted for 96 percent of the surface water and
89 percent of the ground water withdrawn in the Central
Valley. 8 percent of the U.S. food supply produced in the
central valley.”(USGS)
California’s Central Valley covers about 20,000 square miles,
and is one of the most productive agricultural regions in the
world.
More than 250 different crops are grown in the Central
Valley, with an estimated value of $17 billion per year.
Approximately one-sixth of the Nation’s irrigated land is in
the Central Valley.
About one-fifth of the Nation’s groundwater pumpage is
from the Central Valley aquifer system.
Compaction and Land Subsidence as a result of aquifer overdraft
“During the period 1961 through 1977, the rate of ground-water withdrawals from
the aquifer system was greater than the net recharge from all sources. Withdrawals in
excess of recharge resulted in a loss of water from storage in the aquifer of 800,000
acre-feet per year. In the case of the Central Valley aquifer system, some of the loss
from storage is permanent because some of the water was removed from beds of
fine-grained materials, which, when drained, become compacted and cannot store
water again. Compaction of fine-grained materials led to land subsidence in the
Central Valley.”(USGS)
Drought and decreased availability of
surface water have led to increased
pumping of the central valley aquifer.
Climate change and increased population
will likely cause current trends to continue
or increase
“The Sacramento Valley is expected to have sufficient supplies to meet
agricultural demand until at least 2010. However, without increased surfacewater imports, the San Joaquin Valley (exclusive of the Tulare Basin) and the
Tulare Basin might require withdrawals of 150,000 and 2,400,000 acre-feet
per year, respectively, in excess of recharge. Those estimates probably
underestimate additional increased demand that would result from
sustained dry weather. Occasional large withdrawals from an aquifer are a
viable solution to the problem of reduced surface-water supplies in dry
periods, provided the aquifer is replenished during wet years. However,
continual withdrawal of ground water in excess of recharge can increase the
cost of pumping, reduce water availability, and, in certain hydrogeologic
settings, can cause land subsidence.”(USGS)
Another consequence of aquifer overdraft
Reverse of groundwater flow because of aquifer overdraft causes rivers and
lakes to sink into unconfined aquifers in areas where the water table has
been lowered by pumping.
CALIFORNIA IS FACING IT’S FOURTH YEAR OF DROUGHT CONDITIONS!!!
http://www.water.ca.gov/drought/
Subsidence can cause surface structure damage
Over time, but more importantly compaction
Decreases the amount of water the aquifer
Can hold meaning less water availability
In the future, even if the aquifer was fully
recharged.
When fine-grain groundwater layers of
permeable clay, silt, and sand lose water from
their pore space they are compacted by the force
of the land above and become impermeable.
Coarser grain compact as well but can recover,
fine grain compaction is usually permanent.
The land surface declined nearly 30 feet from the 1920's to the late 1970's in an
area southwest of Mendota
SOLUTIONS?
More efficient irrigation techniques
Artificial recharge of aquifer
Education and conservation
sources
• http://pubs.usgs.gov/ha/ha730/ch_b/B-text3.html
• http://www.alternet.org/water/144676/stealing_water_fro
m_the_future:_california%27s_massive_groundwater_over
draft_newly_revealed
• http://articles.sfgate.com/2009-1215/news/17224129_1_central-valley-water-supplygroundwater
• http://pubs.usgs.gov/fs/2009/3057/
• http://www.uwsp.edu/geo/faculty/ritter/geog101/textboo
k/hydrosphere/subsurface_water_groundwater.html
• http://ks.water.usgs.gov/studies/equus/
• http://connect.in.com/california-raisins/photos-1-1-12df7bc2408988dbf75fb74c25d6b09eb.html