Community Exposure to Tsunami Hazards in California

U.S. Geological Survey (USGS) | February 20th, 2013

Evidence of past events and modeling of potential events suggest that tsunamis are significant threats to low-lying communities on the California coast. To reduce potenti

Evidence of past events and modeling of potential events suggest that tsunamis are significant threats to low-lying communities on the California coast. To reduce potential impacts of future tsunamis, officials need to understand how communities are vulnerable to tsunamis and where targeted outreach, preparedness, and mitigation efforts may be warranted. Although a maximum tsunami-inundation zone based on multiple sources has been developed for the California coast, the populations and businesses in this zone have not been documented in a comprehensive way. To support tsunami preparedness and risk-reduction planning in California, this study documents the variations among coastal communities in the amounts, types, and percentages of developed land, human populations, and businesses in the maximum tsunami-inundation zone.  The tsunami-inundation zone includes land in 94 incorporated cities, 83 unincorporated communities, and 20 counties on the California coast. According to 2010 U.S. Census Bureau data, this tsunami-inundation zone contains 267,347 residents (1 percent of the 20-county resident population), of which 13 percent identify themselves as Hispanic or Latino, 14 percent identify themselves as Asian, 16 percent are more than 65 years in age, 12 percent live in unincorporated areas, and 51 percent of the households are renter occupied. Demographic attributes related to age, race, ethnicity, and household status of residents in tsunami-prone areas demonstrate substantial range among communities that exceed these regional averages. The tsunami-inundation zone in several communities also has high numbers of residents in institutionalized and noninstitutionalized group quarters (for example, correctional facilities and military housing, respectively). Communities with relatively high values in the various demographic categories are identified throughout the report. The tsunami-inundation zone contains significant nonresidential populations based on 2011 economic data from Infogroup (2011), including 168,565 employees (2 percent of the 20-county labor force) at 15,335 businesses that generate approximately $30 billion in annual sales. Although the regional percentage of at-risk employees is low, certain communities, such as Belvedere, Alameda, and Crescent City, have high percentages of their local workforce in the tsunami-inundation zone. Employees in the tsunami-inundation zone are primarily in businesses associated with tourism (for example, accommodations, food services, and retail trade) and shipping (for example, transportation and warehousing, manufacturing, and wholesale trade), although the dominance of these sectors varies substantially among the 94 cities.  Although the number of occupants is not known for each site, the tsunami-inundation zone contains numerous dependent-population facilities, such as schools and child daycare centers, which may have individuals with limited mobility. The tsunami-inundation zone includes a substantial number of facilities that provide community services, such as banks, religious organizations, and grocery stores, where local residents may be unaware of evacuation procedures if previous awareness efforts focused on home preparedness. There are also numerous recreational areas in the tsunami-inundation zone, such as amusement parks, marinas, city and county beaches, and State and national parks, which attract visitors who may not be aware of tsunami hazards or evacuation procedures. During peak summer months, estimated daily attendance at city and county beaches can be approximately six times larger than the total number of residents in the tsunami-inundation zone.  Community exposure to tsunamis in California varies considerably—some communities may experience great losses that reflect only a small part of their community and others may experience relatively small losses that devastate them. Among 94 incorporated communities and the remaining unincorporated areas of the 20 coastal counties, the communities of Alameda, Oakland, Long Beach, Los Angeles, Huntington Beach, and San Diego have the highest number of people and businesses in the tsunami-inundation zone. The communities of Belvedere, Alameda, Crescent City, Emeryville, Seal Beach, and Sausalito have the highest percentages of people and businesses in this zone. On the basis of a composite index, the cities of Alameda, Belvedere, Crescent City, Emeryville, Oakland, and Long Beach have the highest combinations of the number and percentage of people and businesses in tsunami-prone areas.

Considerations for Management of the Mouth State of California’s Bar-built Estuaries

Southern California Wetlands Recovery Project | January 10th, 2019

Bar-built estuaries are the dominant estuary type in California, and many of these small estuaries are subject to closure with a sand barrier separating a lagoon

Bar-built estuaries are the dominant estuary type in California, and many of these small estuaries are subject to closure with a sand barrier separating a lagoon estuary from the ocean for days, months or even years. In the lagoon impounded behind the sand barrier, water levels may rise or fall depending on net water budget and water quality extremes may develop. These conditions and the obstruction of fish passage motivate managed breaching of the sand barrier in many systems statewide – an intervention that alleviates or preempts environmental problems, but which also can result in undesirable secondary impacts due to the acute effect of a single breach or the chronic effect of repeated breaching over years. Management decisions are based on an implicit trade-off between anticipated benefits and costs that depend on the values and priorities of stakeholders. This report was written to provide an overview of considerations for managed breaching in California. It presents a synthesis of processes and phenomena related to mouth closure and breaching in general and uses this to identify potential impacts of breaching, without intending any judgment of which impacts are more or less desirable. Three specific systems are reviewed in detail: Los Peñasquitos Lagoon in San Diego County, Scott Creek Estuary in San Mateo County and Russian River Estuary in Sonoma County. While there are fundamental similarities in the closure and breaching cycle across all bar-built estuaries statewide, there is also an immense diversity between these systems due to differences in size, in hydrology (wet north to dry south), and in development (rural, urban, agricultural, road/rail). The local community is likely to develop the best management strategy where there is significant effort and experience in local monitoring, science, and stakeholder consultation. However, where there is limited monitoring, science or consultation, the considerations outlined in this report provide preliminary guidance – and comparison with one of the study systems can provide more specific insight to the potential impacts of breaching management decisions. We synthesize current understanding related to how mouth state influences estuary functions and conditions, which in turn affect ecological services. While both natural and managed breaching affect many processes and phenomena in the estuary, breaching events and managed breaching regimes do not occur in isolation and many other factors affect the estuary functions and conditions, including freshwater inputs, the adjacent landscape, and stressors in the watershed. However, managed breaching is one of very few short-term management options and therefore a valuable adaptive management tool, specifically in systems that are already perturbed or impacted by human encroachment. Although emergency breaches may be required in rare occasions, our recommendation is to develop a breaching strategy for specific systems in which breaching has been used or in which it is likely to be used as a management tool. In this context, we recommend ways in which science can provide improved support for management decisions and identify a few systems in California in which there is already a well-developed, science-based management plan. Associated document: "Wetlands on the Edge: The Future of Southern California's Wetlands - Regional Strategy 2018"

Contribution of historical precipitation change to US flood damages

Publisher not available | January 26th, 2021

Precipitation extremes have increased across many regions of the United States, with further increases anticipated in response to additional global warming. Quantifying

Precipitation extremes have increased across many regions of the United States, with further increases anticipated in response to additional global warming. Quantifying the impact of these precipitation changes on flood damages is necessary to estimate the costs of climate change. However, there is little empirical evidence linking changes in precipitation to the historically observed increase in flood losses. We use >6,600 reports of state-level flood damage to quantify the historical relationship between precipitation and flood damages in the United States. Our results show a significant, positive effect of both monthly and 5-d state-level precipitation on state-level flood damages. In addition, we find that historical precipitation changes have contributed approximately one-third of cumulative flood damages over 1988 to 2017 (primary estimate 36%; 95% CI 20 to 46%), with the cumulative impact of precipitation change totaling $73 billion (95% CI 39 to $91 billion). Further, climate models show that anthropogenic climate forcing has increased the probability of exceeding precipitation thresholds at the extremely wet quantiles that are responsible for most flood damages. Climate models project continued intensification of wet conditions over the next three decades, although a trajectory consistent with UN Paris Agreement goals significantly curbs that intensification. Taken together, our results quantify the contribution of precipitation trends to recent increases in flood damages, advance estimates of the costs associated with historical greenhouse gas emissions, and provide further evidence that lower levels of future warming are very likely to reduce financial losses relative to the current global warming trajectory.

Contribution of the Pacific Decadal Oscillation to global mean sea level trend

American Geophysical Union (AGU) | October 3rd, 2013

Understanding and explaining the trend in global mean sea level (GMSL) have important implications for future projections of sea level rise. While measurements from sa

Understanding and explaining the trend in global mean sea level (GMSL) have important implications for future projections of sea level rise. While measurements from satellite altimetry have provided accurate estimates of GMSL, the modern altimetry record has only now reached 20 years in length, making it difficult to assess the contribution of decadal to multi-decadal climate signals to the global trend. Here, we use a sea level reconstruction to study the 20 year trends in sea level since 1950. In particular, we show that the Pacific Decadal Oscillation (PDO) contributes significantly to the 20 year trends in GMSL. We estimate the PDO contri-bution to the GMSL trend over the past 20 years to beapproximately 0.49 ± 0.25 mm/year and find that removing the PDO contribution reduces the acceleration in GMSL estimated over the past 60 years. 

Contributions of Climate Change and ENSO Variability to Future Precipitation Extremes Over California

American Geophysical Union (AGU) | June 14th, 2023

CVFPP Conservation Strategy Appendix A. Regulatory Setting

California Department of Water Resources (DWR) | July 14th, 2016

Section 7.0 of the Conservation Strategy describes regional permitting efforts that are being developed by the California Department of Water Resources (DWR) in v

Section 7.0 of the Conservation Strategy describes regional permitting efforts that are being developed by the California Department of Water Resources (DWR) in various stages of implementation. This appendix provides a more thorough description of the State and federal regulatory approvals that will be required for implementation of the Central Valley Flood Protection Plan (CVFPP), including the Conservation Strategy.

CVFPP Conservation Strategy Appendix B. Advance Mitigation

California Department of Water Resources (DWR) | July 14th, 2016

Section 7.0 of the Conservation Strategy presents methods for coordinating the acquisition of permits for implementation of the Central Valley Flood Protection Plan (CVFP

Section 7.0 of the Conservation Strategy presents methods for coordinating the acquisition of permits for implementation of the Central Valley Flood Protection Plan (CVFPP). These approaches have been initiated and are expected to be used in the future to mitigate impacts on species and habitats that result from CVFPP actions. As explained in Section 7.0, one regional permitting tool used by the California Department of Water Resources (DWR) is the development of advance mitigation projects.  This appendix further describes the purpose and benefits of advance mitigation, DWR’s efforts to date, and the process for selecting the first set of advance mitigation projects that will support the CVFPP. Each advance mitigation project has been, or will be, carefully selected in collaboration with permitting agencies to mitigate the effects of activities that will be implemented by DWR and Local Maintaining Agencies in the Systemwide Planning Area (SPA). DWR and the resource agencies are continuing to develop the mechanisms for crediting and a process for tracking the credits. Future advance mitigation projects are likely to follow the same process described herein. 

CVFPP Conservation Strategy Appendix C. Description of Construction Activities for Structural Modifications

California Department of Water Resources (DWR) | July 14th, 2016

This appendix [to the CVFPP Conservation Strategy] provides a general description of construction activities, focused on levee construction. It is based on the Program En

This appendix [to the CVFPP Conservation Strategy] provides a general description of construction activities, focused on levee construction. It is based on the Program Environmental Impact Report (PEIR) for the 2012 Central Valley Flood Protection Plan (CVFPP) (California Department of Water Resources [DWR] 2012). 

CVFPP Conservation Strategy Appendix D. Vegetation Management Strategy

California Department of Water Resources (DWR) | August 17th, 2017

When the 2012 Central Valley Flood Protection Plan (2012 CVFPP) and Conservation Framework were adopted by the Central Valley Flood Protection Board (CVFPB), the CVFPB co

When the 2012 Central Valley Flood Protection Plan (2012 CVFPP) and Conservation Framework were adopted by the Central Valley Flood Protection Board (CVFPB), the CVFPB considered the levee vegetation management strategy contained in the 2012 CVFPP as interim. CVFPB Resolution No. 2012-25 directed the California Department of Water Resources (DWR) to further develop the interim strategy into a more comprehensive approach. Resolution No. 2012-25 further directed that the approach be adaptive and responsive to the results of ongoing and future research regarding vegetation on levees, knowledge gained from levee performance during high-water events, and the need to conserve critical riparian habitat. The DWR vegetation management approach described in this appendix reflects efforts to develop a more comprehensive levee vegetation management strategy that consists of efforts to manage levee vegetation, channel vegetation, and invasive plants. Levee vegetation management is particularly important because levee vegetation can impede visibility and accessibility for inspections and flood fighting, and in some limited cases, it may pose an unacceptable threat to levee integrity. In channel areas in between State Plan of Flood Control (SPFC) levees, the floodplain and channel may provide opportunities for important riparian and wetland habitat, as well as agricultural operations. However, land uses in these areas also need to be managed to maintain the channel’s ability to convey high flows during flood events. Finally, invasive plants can adversely affect operations and maintenance (O&M) of the SPFC and are a documented stressor on the species, habitats, and ecosystem processes targeted by this Conservation Strategy. Management of invasive species, and eradication of them where feasible, reduces O&M needs by increasing channel capacity and provides important ecosystem benefits.  DWR water resources managers have been implementing the interim strategy to balance public safety with environmental quality. Current and future work will focus on improving public safety by providing for integrity, visibility, and accessibility for inspections, maintenance, and flood fight operations; at the same time, protecting important and critical environmental resources. DWR’s approach also includes ongoing policy discussions regarding potential compatibility with United States Army Corps of Engineers (USACE) levee vegetation guidance through recognition of regional variations and prioritization of levee remediation based on risk assessment. Retaining lower waterside vegetation is a leading example of how risk assessment is coupled with recognition that widespread loss of habitat on levees, particularly on the lower waterside slope, is unmitigable. The Conservation Framework identified roughly two-thirds of the riparian habitat that occurs on SPFC levees is found on the lower waterside slope. On-going DWR analyses are further evaluating this assumption. In addition, risk assessment has shown that removing this vegetation, and conducting required levee remediation, likely would not be a worthwhile investment of flood risk reduction dollars. On the contrary, vegetation in this area has long been recognized as offering protection to levees from wind and wave wash erosion (USACE 1955). Expending resources to address factors contributing to lower risk would have to be considered against expending these resources to address other levee conditions that pose a significantly higher risk (DWR 2011). Similarly, DWR is assessing how to identify trees that may pose an unacceptable risk to levee integrity in a manner that retains the majority of existing habitat over its normal life span. Ongoing research, as well as knowledge gained from levee performance during high water events, will continue to inform how vegetation management within and around the SPFC may continue to evolve toward meeting multiple objectives, including sustainability of critical environmental resources. DWR anticipates revising vegetation management policy and guidance as needed in the ongoing five year updates to the CVFPP. 

CVFPP Conservation Strategy Appendix E. Invasive Plant Management Plan

California Department of Water Resources (DWR) | July 14th, 2016

The California Department of Water Resources (DWR) developed this Invasive Plant Management Plan (or Plan) as part of the Conservation Strategy of the Central Valley Floo

The California Department of Water Resources (DWR) developed this Invasive Plant Management Plan (or Plan) as part of the Conservation Strategy of the Central Valley Flood Protection Plan (CVFPP). The Conservation Strategy tiers from the Conservation Framework, which was an integral part of the State’s preferred SSIA, identified in the 2012 CVFPP. The Conservation Strategy describes how to make progress toward meeting the environmental objectives of the Central Valley Flood Protection Act of 2008 (Act) and related legislation throughout the flood management system in the Systemwide Planning Area (SPA). The SPA comprises five Conservation Planning Areas (CPAs) in California’s Central Valley: the Feather River CPA, the Upper and Lower Sacramento River CPAs, and the Upper and Lower San Joaquin River CPAs (Figure 1-1). The SSIA includes developing and implementing multipurpose projects, and this Plan will guide the invasive plant management approaches undertaken as part of these projects.  The Conservation Strategy recognizes invasive plants as a primary stressor on the habitats, species, and ecosystem processes that are the focus of conservation planning. As of 2014, at least 68 plant species considered to be invasive by the California Invasive Plant Council (Cal-IPC) potentially occur in upland, riparian, wetland, and open water habitats in the Sacramento and San Joaquin Valleys (Cal-IPC 2013a). Many are widespread and abundant in vegetation managed as part of State Plan of Flood Control (SPFC) operation and maintenance (O&M). These species degrade riverine and floodplain habitats by altering ecosystem processes and displacing native plants. In addition, some of these invasive species, such as tamarisk (or saltcedar) (Tamarix spp.), giant reed (Arundo donax), and red sesbania (Sesbania punicea), are stressors that increase the cost and difficulty of operating and maintaining the SPFC.  These species can alter hydrology and sedimentation rates in riparian and aquatic systems (Cal-IPC 2011a) and can degrade flood system effectiveness. Importantly, recent studies have shown that certain invasive plant species have greater impacts on channel conveyance than native species adapted to the same areas (Stone et al. 2013). Dense stands of certain invasive species can alter channel morphology by retaining sediments and increasing the hydraulic roughness of the channel, which restricts flows and reduces flood conveyance (Bossard et al. 2000). For example, saltcedar traps and stabilizes alluvial sediments, narrowing stream channels and contributing to more frequent flooding (Bossard et al. 2000). Species with shallow root systems, such as giant reed and red sesbania, promote bank undercutting, collapse, and erosion (Bossard et al. 2000; Cal-IPC 2011b). Invasive terrestrial plants can reduce groundwater availability by transpiring large amounts of water, leaving less water available for native riparian vegetation (Bossard et al. 2000).  Invasive plants can also reduce the integrity of native riparian plant communities by outcompeting native plants, reducing habitat quality and food supply for wildlife, and interfering with wildlife management (Bossard et al. 2000; Cal-IPC 2011a). Nationally, invasive species are the second greatest threat to endangered species, after habitat destruction (Cal-IPC 2011a), and approximately 42 percent of the species listed as threatened or endangered by the federal Endangered Species Act (ESA) are at risk primarily because of the adverse effects of invasive species (Pimentel et al. 2005). Aquatic invasive plants can degrade aquatic habitat by reducing areas of open water used by waterfowl for resting, by shading out algae in the water column and thereby diminishing the basis of the aquatic food web, and by displacing native aquatic plants that are used for food or shelter by wildlife (Bossard et al. 2000). In addition, invasive aquatic plants often form dense mats that kill fish by lowering pH, dissolved oxygen, and light levels and by increasing carbon dioxide and turbidity (Bossard et al. 2000).  Because of these adverse effects and the threats they pose to achieving the goals of the Conservation Strategy, this Plan is driven by the following vision: to reduce the impact of invasive plants as a stressor on conservation targets and as an impediment to the operation and maintenance of the State Plan of Flood Control.  This Plan seeks to increase DWR institutional support for an SPA-wide invasive plant treatment program, and facilitate consistent invasive vegetation treatment actions by levee maintaining agencies and other partners such as the California Department of Fish and Wildlife and the United States Fish and Wildlife Service who are also conducting invasive plant control efforts. SPA-wide implementation of invasive plant treatment faces challenges that include ever-decreasing O&M budgets, regulatory requirements to protect sensitive resources, and the need to meet multiple and sometimes conflicting management objectives. This Plan recognizes those challenges, but it is beyond the scope of a single plan to resolve them all. Instead, the Plan provides first steps toward addressing the challenges through a series of goals, objectives, and implementation actions. The Plan includes measurable objectives for the treatment of four target species (Initial Priority Species) in Channel Maintenance Areas within the SPA (Channel Maintenance Areas; Figure 1-2) and identified in the DWR State Plan of Flood Control Descriptive Document (DWR 2010). It is the intent of this Plan to increase the resources available for invasive plant treatment actions by fashioning an approach that meets multiple needs and, therefore, may take advantage of funding sources not previously available for these actions.