land subsidence within the mojave water agency service area
TRANSCRIPT
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Land Subsidence within the Mojave Water Agency Service Area
Michelle Sneed and Justin BrandtCalifornia Water Science Center
U.S. Geological Survey
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Land Subsidence► Land subsidence is a gradual settling or
sudden sinking of the Earth’s surface owing to surface or subsurface movement of earth material
► More than 80% of the identified 17,000 square miles of land affected by subsidence in the Nation is a consequence of our exploitation of groundwater (National Research Council, 1991).
► Most of the groundwater related subsidence is caused by the compaction of susceptible alluvial aquifer systems that typically accompanies overdraft of these systems.
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Measuring SubsidenceBench Mark
Spirit Leveling
GPS
InSAR
Extensometer*
*measures part of land subsidence
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Reported subsidence caused by fluid (mostly water) withdrawal
CA Basins with Subsidence History
Subsidence is an ‘undesirable result’ in the Sustainable Groundwater Management Act (SGMA) legislation
2010
2012
Protruding Well (~2 ft in 2 yrs)
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Preliminary and subject to revision
2003-08
2008-10
2007-10
InSAR-Measured Subsidence in the San Joaquin Valley
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Subsidence along the DMC2007-10
2003-08Loss of capacity reported at Check Station 7 in April 2014, where flow was restricted because of subsidence upstream (Checks 2-6). The short-lived opportunity to fill San Luis Reservoir was impacted.
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Land Subsidence in the Mojave Desert 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
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Subsidence Damages Infrastructure & Natural Resources; Worsens Flooding
► Infrastructure damage Roads, rails, bridges, pipelines, wells,
canals, etc.► Natural resources
Reduces aquifer-system storage capacity Fissuring and channeling Rerouting/migration of riparian corridors and
wetlands (and aquatic ecosystems)
► Flooding Increased depth Longer duration Unexpected/migrating locations Restricted land uses
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Since the early 1990s, subsidence has been localized and near 5 dry lakebeds
Mojave
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Subsidence Magnitudes
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Coyote Lake
► No subsidence 1993-2004
► Shallow wells small but
persistent declines to historically low levels
► Deep wells unknown
► Clay lithology unknown
► Compaction depth unknown permanence
unknown
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Troy Lake
► Shallow and deep wells persistent declines
to historically low levels
► Clay layers range 3-100 ft in
shallow and deep parts of the aquifer system
► Compaction likely permanent in
shallow and deep parts of the aquifer system
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Harper Lake
► Shallow wells persistent declines
to historically low levels
► Deep wells recoveries after
reaching historical lows in the 1980s
► Clay layers range 8-89 ft in
shallow and deep parts of the aquifer system
► Compaction likely permanent in
the shallow system possible in the deep
system
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El Mirage► Shallow and deep
wells small but persistent
declines historical levels
(prior to 1980s) are unknown
► Clay layers range 5-295 ft in
shallow and deep parts of the aquifer system
► Compaction likely in shallow and
deep parts of the aquifer system
permanence unknown
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Lucerne► Shallow wells
persistent declines to historically low levels
► Deep wells recoveries
(historical levels unknown)
► Clay layers range 20-40 ft in
shallow part of aquifer system only
► Compaction likely permanent in
the shallow system unlikely in the deep
system
Past Subsidence: 2 ft during 1976-98
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Fissuring and Resultant Damage on Hwy247, Lucerne Valley
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GPS stations are not in the
subsiding areas, and indicate uplift
Uplift has been observed
throughout the western US… thought to be related to the
drought (loss of water weight)
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GPS stations are not in the
subsiding areas, and indicate uplift
Uplift has been observed
throughout the western US… thought to be related to the
drought (loss of water weight)
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GPS stations are not in the
subsiding areas, and indicate uplift
Uplift has been observed
throughout the western US… thought to be related to the
drought (loss of water weight)
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GPS stations are not in the
subsiding areas, and indicate uplift
Uplift has been observed
throughout the western US… thought to be related to the
drought (loss of water weight)
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The Short Story► Subsidence has been restricted to 5 localized areas
and is not regional► Subsidence rates less than 1 inch/year►Aquitards compacted in response to persistent
groundwater-level declines to historically low levels►At least some subsidence likely is permanent (not
recoverable if water-levels rise)► Subsidence in some areas may continue for some
time after water levels stabilize/recover because of the presence of thick (slowly equilibrating) aquitards
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Where To Go From Here? Continued, Periodic Monitoring
►MWA proactive at assessing subsidence Nearly 20-year record of subsidence Next round of assessment is tentatively planned for
2018-2019
►More satellites with higher measurement frequencies make the future of InSAR monitoring promising, and gaps in data availability less likely
►Coordinate groundwater-level and subsidence measurements Improved understanding of mechanisms leads to
informed management decisions that consider subsidence