Water Availability and Land Subsidence in California’s

San Joaquin ValleyMichelle Sneed and Claudia FauntCalifornia Water Science Center

U.S. Geological SurveyNovember 8, 2018

Land Subsidence in the San Joaquin Valley Aquifer-System Compaction

Galloway and others, 1999; USGS Circular 1182

► Concentrated in the fine-grained deposits (aquitards)

► Inelastic (irreversible) compaction occurs when the preconsolidation stress is exceeded

► Preconsolidation stress ≈ previous lowest groundwater level

► Storage capacity is reduced

Aquifer-System Structure

Faunt, 2009

Groundwater-Level Declines and

Geologic Setting are Causing High

Subsidence Rates claysiltsandgravelsoils

Water level data from USGS and Luhdorff and Scalmanini Consulting Engineers; Preliminary and subject to revision

Shallow Well (Mendota)

Deep Well (Mendota)

Historically low levels

drought droughtdrought

Subsidence Damages Natural Resources and Infrastructure

► Flood Protection and Infrastructure Damage to water conveyance systems

and other infrastructure►Reduced conveyance capacity and freeboard,

panel damage; water surface and liner misalignment; erosion/deposition in unlined channels

►Roads, rails, bridges, pipelines, wells, etc.

► Natural resources Reduces aquifer-system storage capacity Impacts to wetland, riparian, and aquatic

ecosystems Restricted land uses

Protruding Well (~0.3 m/yr)

2010

2012

Extensive withdrawal of groundwater caused widespread subsidence (1920s-1970)

Subsidence History

Galloway and others, 1999; USGS Circular 1182

Surface-water deliveries caused widespread recovery and slowing or cessation of subsidence, except when deliveries were curtailed and groundwater pumping increased to meet demand

(meters below land surface)

61

122

183

305 -Compaction (mm)

Subsidence (m)Less than 0.30.3 to 1.21.2 to 2.42.4 to 3.63.6 to 4.94.9 to 7.3Greater than 7.3

Recent Subsidence► Renewed subsidence concern during the 2007-09

drought initiated investigations Reduced surface water importation More reliance on the groundwater resources As it turns out…this is not just a problem during droughts

for some areas with limited surface-water access

CGPS data from UNAVCO; water level data from DWR, USGS, and Luhdorff and Scalmanini Consulting Engineers

Subsidence(CGPS P307)

Drought Drought

Groundwater Level

Previous lowest level (September, 1992)

Subsidence (CGPS P304)

Recent SubsidenceHistorical Subsidence

Proposed HS Rail

El Nido

Water Conveyance and Transportation Infrastructure

Proposed HS Rail

Subsidence: Eastside Bypass

A

A’

Eastside Bypass

Subsidence: GPS Measurements

CGPS data from UNAVCO and SOPAC; Preliminary and subject to revision

P303

drought drought

P307

drought drought

CHOW

Rate increasesdroughtdrought

Aquifer-System Compaction Depths: Extensometers and CGPS

Rasta: 867 ft

3.2” 1”

CGPS P304

Compaction Depths (Mendota)► Extensometer is anchored in the

top of Corcoran Clay► GPS reflects subsidence relative

to the center of the Earth► GPS measured much more

deformation than the extensometer

Extensometer (compaction)

• Conclusion: most of deformation is occurring below the top of the Corcoran Clay

GPS (subsidence)

CGPS data from UNAVCO; extensometer data from Luhdorff and Scalmanini Consulting Engineers and USGS

Extensometer (compaction from land surface to Corcoran Clay)

GPS (subsidence of land surface)

Recoverable or Permanent?Compaction &Groundwater Levels above the Corcoran Clay

Subsidence & Groundwater Levels below the Corcoran Clay

Critical Head (set Aug. 1992)Critical Head (reset Sept. 2009)

• Water levels have remained above the critical head except for short period in 2016• Likely mostly

recoverable

• Water levels have remained below the critical head• Likely mostly

permanent

DroughtDrought

Critical Head (set July 1991)

GPS data from UNAVCO; water level and extensometer data from Luhdorff and Scalmanini Consulting Engineers and USGS

Critical Head (reset fall 2013)Critical Head (reset fall 2014)Critical Head (reset fall 2015)Critical Head (reset fall 2016)

Aquifer-System Compaction: Extensometers

Rasta: 867 ft

3.2” 1”

80 Years of data…where we’ve been and where we are

Historically low levels

Sustainable Groundwater Management Act (SGMA) of 2014 • SGMA defines ‘sustainable

groundwater use’

“The management and use of groundwater in a manner that can be maintained during the planning and implementation horizon without causing undesirable results”

Undesirable Results

Surface Water

Depletion

Land Subsidence

Lowering GW Levels

Reduction of Storage

Degraded Quality

Seawater Intrusion

“Significant and unreasonable land subsidence that substantially interferes with surface land uses”

Subsidence Summary► 7,500 km2 subsided 50-540 mm during 2008-10; data indicate

these rates have continued through 2016► Adversely affecting water conveyances and other infrastructure► Compaction and resultant subsidence occurred when

groundwater levels declined as a result of pumping► Nearly all compaction occurred below the Corcoran Clay

Resulting subsidence is largely permanent► Long-term monitoring of water levels and subsidence is needed

to detect and track groundwater conditions for decision support SGMA

http://ca.water.usgs.gov/land_subsidence/For more information:

Thanks!