Open-File Report 2007–1255

Open-File Report 2007–1255

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Potential Out-Year Goals

We envision this project going in several productive directions depending on the fruitfulness of first-year pilot programs, community input, and funding. Setting priorities for these future research directions will be guided by the Planning and Steering Committees to take into account the research needs of partner agencies and decision makers.

Integration and Implementation Interface Working Group

Common database and urban hazard mapping. An essential need voiced by the emergency response and planning communities during the Winter 2006 workshops was the need for trustworthy hazard data pulled together in one place and made easily accessible (“integrated data management”). As a result, a map product that will result from the research and cross-discipline projects will be a space-time GIS that has multiple layers including the extents, likelihoods, temporal aspects, and regional vulnerabilities of multiple hazards that can be used as input to an urban risk assessment in southern California. The goal of the GIS is to accept and incorporate measurements from real-time monitoring networks and updated science products to assist in crises and longer term planning. A complete geotechnical database will serve as the starting point for long-term mitigation projects, short-term warning activities, hazard event emergency response, and post-event response and recovery. For example, this map product could allow end-users to conduct a geographical search of their scale of interest in order to investigate the level of risk associated with any one or multiple hazards at that location given the uncertainty of the information at the resolution of the location. Such information will improve the implementation of building codes, land-use planning decisions, and engineering design and retrofit decisions.

Hazard scenarios. We envision creating a suite of scenarios to support emergency planning for many disasters and to better manage mitigation activities. For the second year, we plan a scenario that will focus on a winter storm event that involves landslides, flooding, and coastal change. A key watershed will be selected with input from the southern California emergency managers to pilot a real-time flood-hazard modeling tool. An interactive, web-based user interface will be developed. Other earthquakes, wildfires, and combined disasters are also possible.

The third-year scenario will focus on the effects of wildfires, and subsequent floods and debris flows. The scenario will describe the consequences associated with the ignition of a fire in mountain steep lands; expected fire behavior based on vegetation type, condition, and landscape; and emergency response expectations based on transportation corridor and infrastructure impact. It will incorporate potential real-time tools to assess hazards posed by post-fire debris flows and floods to human infrastructure, wildlife, and aquatic habitats in the event of a subsequent winter storm. Risk will be evaluated in terms of probability, magnitude, and area of impact. The capabilities and limitations of existing warning systems for post-fire floods and debris flows will be illustrated.

Risk analysis for decision making. Our risk analysis work will create an environment for decision makers to assess alternative policies to improve the resiliency of southern California to multiple natural hazards. This work will take the form of an interactive simulation or game experiment embedded within a GIS that is informed by improved understanding of multiple hazards and interactions, quantification of the social and economic assets that are vulnerable, improved understanding of mitigation effectiveness, and lessons learned from work with our partners. We expect to develop tools that could be used to evaluate issues such as benefits and costs of risk-reduction options, relative roles of private insurance and government intervention, determination of acceptable risk, and scientific uncertainties for emergency response planning scenarios and long-term planning. These tools will provide an interactive approach for individual and institutional users to understand the risks and consequences of a range of multiple natural hazards and solutions. This effort also will examine how well our science products are serving or can serve decision makers and will help USGS scientists prioritize the development of future science products.

Impact of natural disasters on endangered ecosystems. Leading conservation biologists rank the California Floristic Province, especially southern California, as one of the top 18 regions on the planet for biological diversity. Many species of plants and animals are found only in California, and many are threatened or endangered. Natural disasters, especially landslides and floods, can radically alter ecosystem habitats and put further strain on endangered populations. Moreover, our data have shown that roads and fuel breaks become barriers to movement within reserves for various sensitive species in southern California. This project will assess the population and genetic consequences of natural disasters and mitigation measures to prevent losses in disasters for several target species and predict what impacts the activities will have on these species under the future build-out scenarios. After different natural disasters, the USGS will carry out studies to understand the impact on different species.

Impact of natural hazards on water supplies, ground water, and watershed stability. A disruption to water supplies in southern California is a dire threat to the economic viability and social well-being of the region. Different natural disasters pose different, but potentially significant, threats to the southern California water supply. Earthquakes on the San Andreas Fault can cut off all aqueducts carrying imported water to the region. Other earthquakes have the potential of disrupting water delivery systems. Wildfires can damage the shrubland ecosystems surrounding most urban environments in southern California that provide watershed cover. Sedimentation from debris flows and floods can impair water quality. We can analyze and compare the different threats to our water supply and evaluate the cost effectiveness of mitigable actions.

Earthquakes and Tsunamis Working Group

Earthquake-rupture chronology and slip rates for the southern San Andreas system in the last 2,000 years. The southern San Andreas Fault is recognized as southern California’s most likely source of future great earthquakes, with 20 million people likely to be affected by such an event. Evidence is increasing that the fault has already exceeded the average time between great (magnitude about 8) events by more than 50 percent; however, recent geologic studies suggest that the hazard from this significant fault is uncertain by a factor of three. A systematic study of the earthquake history of the southernmost 550 kilometers of the fault through geologic studies (paleoseismology) to determine the rate of past events and how regularly they occurred will constrain the rate of earthquakes and the hazard of this catastrophic event.

Time-dependent earthquake-hazard maps.The methodologies employed in producing the USGS national and urban seismic hazard maps assume the hazard does not change with time. However, the potential for an earthquake on a fault increases with time from the last earthquake and may be modified by nearby conditions. Time-varying hazard maps are needed throughout the Nation. In addition, the occurrence of one earthquake makes another more likely. The USGS has developed significant capability in quantifying the increase in hazard likelihood and has a prototype product (daily earthquake hazard maps) that shows the chance of earthquake shaking in the next 24 hours.

Earthquake site effects. Assessing the damage potential of earthquakes depends critically on local soil conditions and the structures of basins and valleys that can amplify the shaking from earthquakes. Three of the fastest growing areas of southern California are the Antelope Valley, the San Bernardino Valley, and the Coachella Valley—all valleys where site amplification could play a major role in increasing damage from big earthquakes. To better understand the nature of this risk, we must determine the subsurface structure of these basins. Seismic refraction techniques (such as used for oil exploration) will be used to determine the shape of the basins. This can then be modeled to understand which areas are most susceptible to resonance and other shaking amplification mechanisms. The same data will be useful in modeling ground-water systems to better understand local water resources in case a disaster cuts off outside water supplies.

Mapping of Probabilistic earthquake-induced landslide hazards. Current hazard maps only provide a binary landside susceptibility rating that does not provide a basis for prioritizing the risk or possible mitigable responses. Applied research is needed to determine what controls the relative likelihood of earthquake-induced landsliding, including the relative contributions of slope, bedrock geology, alluvial cover, and intensity, frequency, and duration of earthquake shaking in southern California. The results of this research could be combined with probabilistic earthquake hazard information to give a picture of the comparative likelihood of landsliding during earthquakes.

Earthquake early warning. Most damage in earthquakes is caused by the shaking from seismic waves. These waves travel at the speed of sound in rocks from the fault that produces the earthquake, dying off with distance from the fault. In very large earthquakes, the fault can produce the shaking for many minutes and these waves can cause substantial damage even at great distances from the fault. Thus, in very large earthquakes it is possible to transmit (at the speed of light) the information that an earthquake is underway and receive that information at more distant sites before the earthquake waves themselves arrive. This type of system has recently been created in Japan and Mexico. Knowing that an earthquake will begin in 10-60 seconds can be used in automatic systems to reduce losses by actions such as securing hazardous materials, stopping trains, and shutting down nuclear reactors.

Assessing the potential for local tsunamis from earthquake-induced offshore landslides and fault movement. Given the relative rarity of direct observations in any specific locale, the assessment of tsunami hazard potential depends on model formulations linking geologic processes and structures to tsunami generation, propagation, and impact. We know that past earthquakes have triggered offshore landslides that have in turn produced locally damaging tsunamis. A local tsunami that damages the Ports of Los Angeles and Long Beach and concentrated coastal developments will have major financial and social impact on the region. Research is needed to quantify the hazard magnitudes and likelihoods to better understand how large such a tsunami could be. Significant offshore bathymetric mapping has been completed in the last few years, but about one-third of the mainland slope has not been mapped using state-of-the-art technology. Quantification of the tsunami hazard needs a completion of the bathymetric mapping, assessment of the data to identify potentially tsunamic landslide deposits and active faults, determination of the ages of these landslides and time of most recent fault movement, modeling of the movement of these landslides, and modeling of associated tsunamis and synthesis of data within a probabilistic framework. These tsunami research and hazard assessment studies will be coordinated with partners in the Southern California Coastal Ocean Observing System (SCCOOS).

Fire and Debris-Flow Working Group

Post-fire flood and debris-flow hazard assessment and early warning. Web-based tools to characterize post-fire debris-flow and flash-flood susceptibility, magnitude, and inundation area in response to storm rainfall conditions can be used to assess these potential hazards on a basin scale. Because the tools developed in this task will rely on data that are readily available both before and immediately after wildfires, they will be useful to land management agencies both in pre-fire planning and post-fire response. Application of the predictive models before the occurrence of wildfires can help identify sensitive drainage basins and thus direct forest restoration efforts. Rapid application of these tools post-fire will provide information necessary to provide warnings and to make effective and appropriate mitigation and planning decisions. Assessments of risks from post-fire floods and debris flows to human life and property, and to wildlife and aquatic habitats both immediately post-fire and over longer time periods can be used to create response plans.

Evaluation of how pre-fire fuel manipulations affect watershed stability and subsequent downstream impacts. Shrubland ecosystems surround most urban environments in southern California and provide many important benefits to communities. One of the more critical values is as a watershed cover, and this ecosystem service becomes more apparent following wildfires when the vegetative cover has been temporarily eliminated. Twentieth-century urban expansion has used much of the desirable coastal plain real estate and forced development ever closer to steep slopes in the surrounding mountain ranges, typically adjacent to federal lands. Increased potential for flooding, sudden debris flows, and erosion are factors that pose major hazards for these urban environments and affect natural resources. There are three areas where new research is needed: (1) Using several decades of sediment-production data in the Los Angeles Basin, coupled with past fire history data, we will analyze the extent to which vegetation-age and landscape-fuel mosaics can alter rates of erosion following fires; (2) We will relate remote-image algorithms using Landsat images to assess fire intensity to both real potential for sediment loss and vegetation recovery after fire; and (3) Debris-flow events have reduced or removed sensitive and endangered frogs and fish from entire watersheds. Understanding and predicting where these events will take place and what resources are at risk is a priority for managing the last remaining populations of these formerly widespread species and communities.

Integrated approach to watershed risk assessment. We can apply an integrated approach to watershed risk assessment that examines all potential natural hazards expected to impact an area, and considers the spatial and temporal aspects of a hazard and the potential for interaction among hazards. Specific to the fire hazard, this approach will consider fuel loadings, effects of fuel treatment programs, pre-event long-term climatic conditions and rainfall regime, and potential resources at risk at the site of the hazard and downstream. The potential for deleterious effects on water resources including impacts on municipal water supplies, both surface and subsurface, will receive special attention.

Impact of past fire activity on vegetation type conversion. Accelerated fire activity is responsible for major losses of natural shrubland ecosystems and replacement by non-native annual grasses and forbs. Type conversion has implications both for conservation and human safety through impacts to ecosystem functioning and fire regime. Loss of native shrublands greatly decreases the structural complexity of ecosystem communities and landscapes, and is responsible for the loss of critical components of the flora and fauna, including rare species and keystone species. When these shrublands are displaced by non-native grasslands, the functional types change from deeply rooted shrubs to shallow-rooted annuals, which alters the water-holding capacity and erosion potential of watersheds. This sometimes increases the potential for debris slides in the absence of other disturbances such as fire. These types of conversions also alter the risk of fires owing to the easily combustible nature of grasses relative to shrublands, often greatly extending the normal fire season. Two tasks are anticipated: The first task will take advantage of a 35-year remote imaging database (Landsat), which is capable of detecting vegetation changes at a relatively fine scale. Documenting the massive scale of past type conversion will be a critical first warning to future hazards. The second task will examine biodiversity and trophic response and recovery from landscape fires in San Diego. This five-year study addresses these presumed changes in flora and fauna to the vegetation type conversion and takes advantage of extensive pre-fire USGS data.

Assess effectiveness of pre-fire fuel management strategies on southern California fire behavior and reducing urban impacts from fire. California leads the Nation in fire losses. Since 1970, 12 of the Nation’s 15 most destructive wildfires have occurred in California, costing the insurance industry $4.8 billion, the most destructive being the southern California firestorms of October 2003. We will conduct an empirical study of how past fuel-manipulation projects in southern California have affected the progression of historical fires in the region. In addition, fire behavior models will be used to relate landscape patterns of fuels, topography, climate, and wind patterns to predictions of fire spread under different scenarios of fuel placement. This project also will include consideration of land planning scenarios of future build-out provided by urban growth models. The most useful product will be maps that distinguish important topographic fire corridors that are most likely to affect urban environments and placement of fuel treatments to minimize vulnerability of communities. This research will involve USGS researchers collaborating with land managers and scientists from the U.S. Forest Service and the U.S. Bureau of Land Management.

Assess effectiveness of pre-fire fuel management strategies on southern California biodiversity and ecosystem stability.The impact of fuel treatments and fuel breaks to biodiversity and fragmentation within the remaining wildlands will be assessed with an emphasis on the recently formed Habitat Conservation Plans authorized by the Endangered Species Act. USGS data have shown that roads and fuel breaks become barriers to movement within reserves for various sensitive species in southern California. This project will assess the population and genetic consequences of these types of barriers for several target species and predict what impacts the fuel modifications will have on these species under the future build-out scenarios and how urban fire risk-reduction strategies can be successfully integrated into the reserve design for maintaining biodiversity in the region. This research will involve USGS researchers collaborating with other Department of the Interior scientists.

Winter Storm Events Working Group

Developing tools for predicting flooding and debris flows at ungaged sites. After flood-frequency information is updated at gaged sites, new predictive equations for estimation of flood magnitude and probability at ungaged sites in southern California will be developed using Generalized Least Squares regression techniques. Equations will be incorporated into a web-based program (StreamStats) that enables users to quickly obtain flood estimates at ungaged sites by simply clicking the site locations on a web map. Similar predictive equations currently under development for estimating the probability of occurrence and volume of deposited material from debris flows also will be incorporated into the StreamStats program. Research will be initiated to understand and better determine risk in watersheds subject to both floods and debris flows (mixed-population analysis). As the risk from both processes becomes better understood, predictive methods in the StreamStats program will be modified as necessary to better convey the risk information. Insofar as possible, the StreamStats application for Southern California will be designed to provide flood and debris-flow risk information to local officials in easy-to-understand, non-technical terms.

Real-time model predictions of coastal erosion and flooding. This will involve taking our short-term goal of generally assessing coastal vulnerability to erosion and flooding, and integrating these data into a fully operational, real-time coastal warning system. The web-based interface will feature a real-time model driven by the most up-to-date coastal conditions (specifically, wind, waves, and tides) with the product being an hourly hazard assessment of the southern California coastline. Using the state-of-the-art Delf3D integrated hydrodynamic and wave model and the most up-to-date topographic (specifically, Light Detection And Ranging - LIDAR) and bathymetric (specifically, multi-beam) data, this operational model will provide invaluable information to the full range of coastal users, particularly during the winter storm season. It will allow resources to be allocated in areas of greatest risk, and warnings to be issued to beachgoers where dangerous conditions exist. Development of this warning system will be closely coordinated with partners in the Southern California Coastal Ocean Observing System (SCCOOS). 

Rapid assessment of methods for characterizing and assessing errors in streamflow data. Many planning and design decisions are predicated on assumptions that streamflow data are complete and accurate. In fact there are multiple sources of error in streamflow records. A rapid and accurate method to estimate and evaluate these uncertainties is needed. The inherent difficulties of collecting streamflow records in southern California make it a prime area to design and develop methods for characterizing and assessing errors in flow measurements, instruments, and rating curves.

Forcing mechanisms on changes in streamflow. Time series of streamflow records in many areas indicate decade-scale changes in flow volumes and flow duration curves. The frequency of extreme events may be changing. El Niño signals may offer an opportunity to predict some of these changes, and paleoflood techniques may offer a chance to document trends over long periods of time. Many basins in southern California have evolved from undisturbed to agricultural to urban in the last 50–100 years, and some stream-gaging stations have operated throughout these changes. These sites need to be studied to evaluate the impacts of changes in land use and regulation on flow statistics such as duration series and flood frequencies.

Comprehensive assessment of landslide hazards and early warning. Although landslides often result in millions of dollars of damage, and even deaths, during rainy winters in southern California, no comprehensive evaluation of landslide hazards exists for the region. We propose the development and application of reliable and accurate landslide prediction tools that are appropriate to southern California. We will develop methods and models that use LIDAR and other high-resolution remotely sensed data to characterize landslide susceptibility or probability in response to seismic, climatic, or artificial disturbances. Physically based models of landslide processes can be coupled with methods for identifying the hydrologic precursors to landslide failure (either of large, deep-seated landslides or shallow landslides that generate debris flows), and with methods for real-time monitoring of hill-slope hydrologic conditions. Incorporation of quantitative precipitation forecasts and measurements into these models can result in spatially and temporally specific real-time warnings for landslides. Models that can be used to define potential areas that can be inundated by debris flows will be developed and integrated into the warning system. The improved hazard assessment approaches developed here will provide critical information on landslide occurrence at appropriate spatial and temporal scales to planners, decision makers, and emergency managers.

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