12.4: Natural Hazards of the Great Valley Province
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Natural Hazards of the Great Valley Province
Amidst its scenic landscapes and agricultural abundance, the Great Valley is also prone to various natural hazards that pose significant challenges to its residents and infrastructure. From earthquakes and floods to droughts and wildfires, the region experiences a wide range of hazards that demand careful planning, preparedness, and response.
One of the primary natural hazards that the Great Valley faces is seismic activity. Located within the seismically active Pacific Ring of Fire, the valley is susceptible to earthquakes due to its proximity to major fault lines, including the San Andreas Fault. These seismic events have the potential to cause widespread damage to buildings, roads, and other critical infrastructure, disrupting daily life and posing a significant threat to public safety.
In addition to earthquakes, the Great Valley is also vulnerable to flooding. With its extensive network of rivers and waterways, including the Sacramento and San Joaquin Rivers, the region experiences periodic flooding, especially during the rainy season. The combination of heavy rainfall, snowmelt from the nearby Sierra Nevada Mountains, and inadequate flood control measures can result in overflowing rivers, inundated farmlands, and potential damage to homes and businesses.
Furthermore, the Great Valley grapples with the challenges of drought. Despite being a major agricultural hub, the region relies heavily on limited water resources, including groundwater and surface water from rivers and reservoirs. Prolonged periods of drought, exacerbated by climate change, can lead to water shortages, impacting agricultural productivity, wildlife habitats, and the overall economic well-being of the region.
Another natural hazard, as secondary hazard of drought, that affects the Great Valley is the threat of wildfires. With its vast stretches of grasslands, forests, and agricultural lands, the region is susceptible to wildfires, particularly during the dry season when vegetation becomes highly flammable. These fires can spread rapidly, destroying crops, endangering wildlife, and posing risks to human lives and properties.
Given the magnitude and diversity of natural hazards faced by the Great Valley, it becomes crucial for residents, policymakers, and emergency management agencies to be well-prepared and proactive in mitigating risks and managing potential disasters. Through effective land-use planning, infrastructure development, early warning systems, and community engagement, the region can enhance its resilience and minimize the impact of these hazards on its communities.
In this context, understanding and studying the natural hazards specific to the Great Valley is of paramount importance. By delving into the characteristics, historical occurrences, and potential future trends of earthquakes, floods, droughts, and wildfires, we can foster a comprehensive approach to hazard mitigation, emergency response, and long-term sustainability in this vital region of California.
Water in a Sinking Valley – Land Subsidence
Completion of California's State and Federal water projects that bring water from California's wet north to its dry south allowed some groundwater aquifers to recover, and subsidence decreased in these areas. Subsidence, particularly in the San Joaquin Valley, continues today at nearly historically high rates of more than 1 ft/yr.
Land subsidence is a significant problem in California's Great Valley, characterized by the gradual sinking of the Earth's surface. This issue primarily stems from extensive groundwater extraction, agricultural practices, and geological factors. The Great Valley is an important agricultural region and one of the most productive in the United States, but the excessive pumping of groundwater has led to severe consequences. In California, large areas of land subsidence are well documented in the first half of the 20th century, as exhibited in Figure 12.4.1.
The Great Valley relies heavily on groundwater to sustain its agricultural activities due to limited surface water availability. Over the years, extensive pumping of groundwater has caused the subsurface aquifers to deplete rapidly. As groundwater is extracted, the pore spaces in the underground rock layers collapse, causing the land above to sink and resulting in land subsidence.
The consequences of land subsidence are far-reaching and detrimental. Infrastructure such as roads, bridges, and canals are damaged as the ground sinks, leading to increased maintenance costs and reduced functionality. Furthermore, subsidence increases the risk of flooding as the capacity of canals and drainage systems diminishes. This poses a significant threat to the agricultural industry, as excess water cannot be efficiently managed, potentially causing crop damage and water contamination.
The rate of land subsidence in the Great Valley has been alarming. In some areas, the land has sunk several feet over the past decades. Figure 12.4.2 exhibits land subsidence as recorded by synthetic aperture radar (SAR) in 2017 within the San Joaquin Valley. Note that negative values, complemented by the purples and blues, imply areas of recharge where water may even be seeping to the surface. Positive values associated with yellows and reds imply areas of greater subsidence or lowering of ground elevation relative to sea level. The highest rates of subsidence occur in regions with extensive agricultural activities and heavy groundwater pumping.
To address this issue, California has implemented various measures to manage groundwater use more sustainably. In 2014, the Sustainable Groundwater Management Act (SGMA) was enacted, which requires local groundwater sustainability agencies to develop and implement plans to achieve groundwater sustainability within 20 years. These plans aim to balance groundwater extraction with replenishment, ensuring long-term water availability while mitigating land subsidence.
In addition, work is ongoing to predict land subsidence throughout the valley. In 2009, the USGS produced the Great Valley Hydrogeologic Model (CVHM). The aim of this model was to introduce subbasin water managers to how water moves in a hydrogeologic system. This concept would then be complemented by water modelers to make predictions on water moving into and out of the basin. The CVHM has a large list of parameters for managers and modelers alike that must be set before any predictions may be made. The list of data input requirements is related to geology, topography, remote sensing, climate, land use, soils, and chemistry, to name a few. These may come in the form of measured porosity and permeability from a drill core, or the total dissolved solids measured in a water sample taken from the subsurface. Other data inputs may include annual precipitation, or even predictions of future precipitation wherein a second layer of error may be introduced into the resulting predictions. Due to how quickly each of these inputs can change, coupled with the amount of time it takes to run the model from data input to prediction output, the CVHM has not been updated since 2014. Coincidentally, this is also when SGMA was signed into California law.
Recent efforts to predict land subsidence have integrated geospatial methods with statistical modeling of geographically weighted regression with geologic and engineering variables. Such efforts have resulted in an 87% accuracy of land subsidence prediction.
However, the road to mitigating land subsidence in the Great Valley remains challenging. Reversing the effects of subsidence is a slow and costly process, and the region continues to face significant groundwater challenges. Effective water management practices, increased surface water storage, and innovative technologies are crucial in combating land subsidence and ensuring the long-term sustainability of the Great Valley's agricultural industry.
Flooding
Paradoxically, while this region is one in which subsidence due to over-extraction of groundwater is a serious challenge, this region is also under threat of flooding! Because the Great Valley is such a large, low-lying region of minimal relief with occasion gentle slopes. In fact, the whole valley averages an elevation of ~90 m (300 ft) above sea level. The valley is susceptible to the hazard of flooding by the large rivers that flow across it. The combination of heavy rainfall, snowmelt from the nearby Sierra Nevada Mountains, and inadequate drainage systems can lead to significant flooding events. Additionally. The extensive network of irrigation canals, constructed to facilitate farming, can exacerbate the flooding risk if they become overwhelmed or experience structural failures during intense rainfall or river surges. When these factors converge, the Great Valley becomes prone to overflowing rivers, breached levees, and widespread inundation, causing substantial damage to infrastructure, agriculture, and residential areas.
In addition to the natural factors, human activities in the Great Valley can intensify the flood hazard. Urbanization and development have altered the landscape, replacing permeable surfaces with impermeable ones like roads, parking lots, and buildings. This change disrupts the natural water infiltration process, increasing surface runoff and reducing the area's ability to absorb excess water (see Chapter 17 for more info on natural runoff processes). Furthermore, the construction of levees and flood control channels, while intended to protect populated areas, can create a false sense of security. If these infrastructure systems are not properly maintained or fail to withstand the forces of a severe flood event, the consequences can be devastating, leading to widespread flooding and loss of life and property.
Tulare Lake Basin
The Tulare Lake Basin is in the southern San Joaquin Valley and covers parts of Fresno, Kings, Kern, and Tulare counties. The Tulare Lake Basin includes input from the Kings, Kaweah, and Tule Rivers, as well as the Pine Flat Reservoir, Lake Kaweah, and Success Reservoir, which all drain to the historic Tulare Lake. Kern River flows into the southernmost portion of Tulare Lake. Tulare Lake was once the largest freshwater lake in California. Historically, Tulare Lake would flood during the winter months due to heavy rain and snowfall in the Sierra Nevada. The excess water would flow into Tulare Lake, causing it to expand and overflow its banks, creating a natural floodplain that was beneficial for agriculture and wildlife. Figure 12.5.3 exhibits the approximate boundary of what was once considered to be the largest freshwater lake west of the Mississippi River.
Over the years, Tulare Lake has gradually disappeared due to a combination of factors, including, damming of rivers, diversions for irrigation, increase water demand for agriculture, and climate change—a great example being the drought that has stricken most of the Great Valley. Today, most of Tulare Lake is a dry lakebed and is predominantly used for agriculture, with the surrounding areas being some of the most productive agricultural regions in the world. However, these rich soils do not come without risk. During the winter of 2022, the Tulare Lake Basin experienced an unprecedented amount of precipitation, with much of the Sierra Nevada snowpack melting in the higher April temperatures, leading to large volumes of runoff and a rapid resurgence of Tulare Lake (Figure 12.4.4). A March 2023 pineapple express storm, brought a resurgence of Tulare Lake where floodwaters covered 6th Avenue south of Corcoran, Kings County, CA. Heavy precipitation and runoff is shown having flooded communities and agricultural fields in former Tulare Lake. Before 2023, Tulare Lake emerged in 1997, 1983, and 1969, with 1969 and 1983 holding the records for the wettest years until being broken by the 2023 events. American settlers drained the lake, dammed key rivers that provided recharged to the lake, and then planted crops on the dried lakebed. Figure 12.4.5 is what many citizens of the San Joaquin Valley are accustomed to seeing.
Overall, the Great Valley in California faces a significant hazard of flooding due to a combination of natural factors, such as heavy rainfall, snowmelt, and inadequate drainage, as well as human modifications to the landscape. As previously stated, due to the low-lying relief in the Great Valley makes it difficult for excess water to flow away quickly. Many of the streams throughout the valley can be a flood hazard during a wet season. For this reason, it is crucial for the region to implement comprehensive flood management strategies, including improved infrastructure maintenance, land-use planning, and effective emergency response systems, to mitigate the risks and protect the communities and resources within the Great Valley.
Seismicity
The Great Valley is relatively seismically stable compared to the surrounding regions, but seismicity still poses as a hazard. This stability is primarily due to the Valley’s location away from major active faults. However, it is still influenced by seismic hazards originating from nearby faults. One of the significant faults near the eastern edge of the Great Valley is the Sierra Nevada frontal fault system. This fault system includes the Owens Valley Fault and the Garlock Fault, which pose a potential seismic hazard to the eastern parts of the Great Valley. However, in recent years the USGS has made an effort to better define what is known as the Great Valley fault system.
The Great Valley fault system defines a tectonic boundary between the Coast Ranges and the Great Valley in California, as the rock types go from hard igneous and metamorphic rocks to softer sedimentary rocks. This fault has been active throughout the Quaternary, and has been the source of several significant (greater than magnitude 6) historic earthquakes, including the 1983 M 6.5 Coalinga earthquake and the 1892 Vacaville–Winters earthquake sequence. However, the locations and geometries of individual faults in the Great Valley fault system are poorly constrained, and fault slip rates and paleoearthquake chronology are largely unknown. Figure 12.4.6 shows ground shaking potential throughout California. Notably, the Great Valley has a low shaking potential.
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In terms of faults within the Great Valley itself, the most prominent one is the Concord-Green Valley Fault. It runs through the western part of the valley, southwest of Sacramento, and is an active fault with an estimated age of several million years. The Green Valley Fault has the potential to generate moderate earthquakes and is a significant consideration for seismic hazard assessment within the Great Valley. The probability for one or more magnitude 6.7 or greater earthquakes between 2003 to 2032 is 4%
Additionally, the Winters Fault is another fault system located within the Great Valley. It runs along the western side of the valley near the town of Winters. While it is considered a minor fault, it can still contribute to seismic hazards in the region.
It is important to note that the Great Valley is predominantly characterized by tectonic forces related to the Pacific-North American plate boundary, rather than major fault activity within the valley itself. The Buena Vista fault, the Plieto fault, the Wheeler Ridge fault, and of course the San Andreas fault are all great examples of active faults that exist due to plate interaction and form the boundary between the Central Valley and the Coast Ranges. The primary seismic hazards in the Great Valley come from the transmission of seismic energies from surrounding fault systems and the amplification of ground shaking due to the valley's sedimentary basin. All the more reason to understand how faults propagate energy through brittle and ductile failure.
While faults on the fringes of the Great Valley province have been zoned by the Alquist-Priolo Earthquake Fault Zoning Act (AP Act), most faults are concealed by younger rocks and are not zoned as an active seismic hazard. This does not mean that larger, dormant faults are not present in the valley. Understanding the seismic hazards associated with these faults within and near the Great Valley is crucial for implementing effective mitigation measures and ensuring the safety and resilience of the communities in the region.
Inset Box \(\PageIndex{1}\): 1983 Coalinga-Naschmarkt Earthquake
The 1983 Coalinga earthquake, also known as the Coalinga-Naschmarkt earthquake, struck central California on May 2, 1983. It was a magnitude 6.5 earthquake that originated near the city of Coalinga. The earthquake caused significant damage to the region, with the epicenter located in a sparsely populated area, reducing the impact on human life. However, the effects were felt over a wide area, and the earthquake caused several injuries and one fatality. The damage was mainly concentrated in Coalinga, where buildings suffered structural failures, roads were cracked, and water and gas lines were disrupted. Figure 12.5.7 displays the Nunez fault being located northwest of the city of Coalinga (pink shape represents the city limits of Coalinga). The San Andreas fault is in the lower left corner of the map (to the southwest of Coalinga).
The Coalinga earthquake was notable for its unique fault behavior. It occurred on a previously unrecognized fault known as the Elkhorn Scarp, which is a branch of the active San Andreas Fault system. The fault ruptured the ground surface along a 24-kilometer-long (15 miles) segment, causing a prominent surface rupture. This surface rupture was well-documented and studied by geologists, providing valuable insights into earthquake mechanisms. The earthquake also triggered numerous aftershocks in the following weeks, which further contributed to the seismic activity in the region.
Despite the significant damage caused by the Coalinga earthquake, the response and recovery efforts were relatively efficient. Emergency services were promptly deployed, and local authorities quickly assessed the damage and aided affected residents. The earthquake served as a wake-up call for seismic awareness in the region, leading to increased efforts in earthquake preparedness and building code revisions. The Coalinga earthquake highlighted the ongoing seismic risk in California and underscored the importance of implementing measures to mitigate future damage and protect the population from the potential devastation of larger earthquakes.
NC 4.0. Constructed in a GIS using data from California Open Data Portal. Access a detailed description.
Figure Inset Box\(\PageIndex{2}\): Building at 187 South 6th Street, Coalinga, CA, severely damaged by the May 1983 Coalinga-Nunez earthquake by USGS and is in the public domain. Access a detailed description.
References
- Bawden, G. W., Sneed, M., Stork, S. V., & Galloway, D. L. (n.d.). Measuring human-induced land subsidence from space. U.S. Geological Survey Fact Sheet, 069–03, 4. http://water.usgs.gov/pubs/fs/fs06903/New Data Shows Subsidence Continued in Water Year 2021, But Pace Slower than Seen in Previous Droughts. (2022, February 16). California Department of Water Resources. Retrieved July 10, 2023, from https://water.ca.gov/News/News-Releases/2022/Feb-22/New-Data-Shows-Subsidence-Continued-in-Water-Year-2021-Pace-Slower-than-Previous-Droughts
- CGS Map Sheet 48: Earthquake Shaking Potential for California (revised 2016). (1999, May 11). Retrieved July 10, 2023, from https://data.ca.gov/dataset/cgs-map-sheet-48-earthquake-%20shaking-potential-for-california-revised-20161
- Faunt, C. C., Sneed, M., Traum, J., & Brandt, J. T. (2016). Water availability and land subsidence in the Great Valley, California, USA. Journal of Hydrogeology, 24, 675-678.
- Garone, P. (2011). The Fall and Rise of the Wetlands of California’s Great Great Valley (1st ed.). University of California Press.
- Muarry, K. D., & Lohman, R. B. (n.d.). Short-Lived Pause in Central California Subsidence after Heavy Winter Precipitation of 2017. Science Advances, 4(8). doi:10.1126/sciadv.aar8144
- Pond, J. F. (1972). Land subsidence in the western states due to ground-water overdraft. Water Resources, Bulletin 8, 113-118.
- Shakal, A. F., & Ragsdale, J. T. (1983). Strong Motion Data From the Coalinga, California Earthquakes and Aftershocks. The 1983 Coalinga, California Earthquakes, CDMG Special Publication 66(OSMS 83-04).
- SGMA Data Viewer. (n.d.). SGMA Portal. Retrieved May 5, 2023, from https://sgma.water.ca.gov/webgis/?appid=SGMADataViewer#currentconditions
- Subsiding Areas in California | USGS California. (n.d.). California Water Science Center. Retrieved March 5, 2023, from https://ca.water.usgs.gov/land_subsidence/california-subsidence-areas.html