the role of groundwater in geologic hazards w. richard laton, ph.d., rg assistant professor,...
TRANSCRIPT
![Page 1: The Role of Groundwater in Geologic Hazards W. Richard Laton, Ph.D., RG Assistant Professor, Department of Geological Sciences, CSUF](https://reader035.vdocument.in/reader035/viewer/2022062518/56649ec95503460f94bd66de/html5/thumbnails/1.jpg)
The Role of Groundwater in Geologic Hazards
W. Richard Laton, Ph.D., RG
Assistant Professor, Department of Geological Sciences, CSUF
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Natural Hazards• Almost every imaginable natural
hazard exists in Southern California.
• Southern California is a complex area of differing geologic and hydrologic conditions representing many differing hazards.
• Hazard identification defines the magnitude and associated probabilities of natural hazards that may pose threats to human interests in specific areas.
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Why do we need to study Natural Hazard Areas? Planning!
• Where (Identification)• Why (Understanding
the system)• What can we do
(mitigation)• Prevention
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Who’s affected
• 35 million California citizens
• City, County and State Regulators
• Builders and Contractors
• Businesses
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GIS and Natural Hazards
• Through the advanced utilization of GIS, maps of Engineering geology, shallow groundwater, surface water, liquefaction, subsidence, and landslide susceptibility can be produced.
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Groundwater
• Groundwater is usually the lost component when it comes to defining hazards.
• Through GIS, groundwater becomes an important player in hazard management.
• Susceptibility maps of Liquefaction, Subsidence and Landslide prone areas
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Example of Regional Groundwater Maps
• Riverside County shallow groundwater map was derived from over 12,000 water well records
• Used for Liquefaction and Subsidence maps
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Problems with Regional Groundwater Maps
• Comprised of incomplete well records
• Incomplete well completion records
• Not enough coverage area
• Lack of aquifer information
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Deep wells vs. Shallow wells
• Water levels less than 50-feet of most importance
• Most regional maps based on deeper wells
• Shallow well records come primarily from environmental investigations
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Natural Hazards
• Liquefaction
• Subsidence
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Groundwater and Hazard Identification
• Liquefaction – water within 50 feet of surface
• Liquefaction – over watering/irrigation
• Subsidence – groundwater withdrawal
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Liquefaction Susceptibility
• Derived from Groundwater and Engineering Geology maps
• Identifies susceptible conditions in 4 general categories
• Used for geotechnical design-level studies
• Used for Zoning and Loss estimation analysis
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Causes
• Shallow groundwater + fine grained materials + earthquakes
• Over watering - irrigation + fine grained materials + earthquakes
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Liquefaction Flow Chart
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Subsidence Susceptibility
• Derived from Groundwater and Engineering Geology maps
• Identifies susceptible conditions in 2 general categories
• Used for geotechnical design-level studies
• Used for Zoning and Loss estimation analysis
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Engineering Geologic Materials Map of Temecula, California
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Shallow Groundwater Map of Temecula, California
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Subsidence Susceptibility Map, Temecula, California
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Subsidence
• Un-regulated groundwater withdrawal
• Hydro compaction – Hydro consolidation
• Oil or gas withdrawal
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What can we do better?
• Better well records• Better logging
techniques• Sharing of records and
data• Central housing of all
records• Use regional maps for
what they were intended
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Conclusions• Regional maps should be
only used for gross planning purposes
• More detailed groundwater information is needed for less populated locations
• Need for better information gathering during soil and groundwater investigations