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Frequently Asked Questions about

Our Coast, Our Future (OCOF)

Please click on a question to reveal the answer.

GENERAL

What is OCOF?

Our Coast, Our Future (OCOF) is a collaborative, user-driven project focused on providing San Francisco Bay Area coastal resource managers and planners locally relevant, online maps and tools to help understand, visualize, and anticipate vulnerabilities to sea level rise and storms.

Project objectives include: modeling vulnerabilities from sea level rise and storm hazards, including factors such as water levels, wave heights, flooding, and erosion; using a collaborative product development process to meet stakeholders’ information needs; mapping infrastructure and ecosystem vulnerabilities at scales relevant to planning and management; developing products in accessible, user-friendly formats that can be easily applied to local planning efforts; and providing training and targeted in-depth technical assistance on the use of the decision-support tools.

Final products include: Seamless Digital Elevation Model (DEM) at 2 meter horizontal resolution for the San Francisco Bay Area; suite of sea level rise projections between 0 - 2 meters, with a 5 meter extreme, plus storm scenarios using the Coastal Storm Modeling System (CoSMoS); interactive maps overlaying infrastructure and ecosystem vulnerabilities; online and downloadable data access for use in restoration, adaptation and response planning, tailored to stakeholders’ information needs; and report presenting the project findings and assessing impacts.

How can the OCOF scenario models and flood map help me?

OCOF provides science-based decision-support tools to help understand, visualize, and anticipate local impacts from sea level rise and storms. Examples of planning efforts that could benefit from this information include: determination of infrastructure vulnerability (such as buildings, parking lots, public bathrooms, sewer systems, public transportation stations, rail lines, roads, etc.); determination of community vulnerability; emergency response plans; implications for levee, wetland, shoreline, and infrastructure protection; understanding long-term potential for wetland migration; and prioritization of conservation acquisition and restoration areas.

How is this tool different from other sea level rise mapping efforts?

  1. NOAA Sea-level Rise Viewer: The NOAA Coastal Services Center’s Sea Level Rise and Coastal Flooding Impacts Viewer provides users the ability to visualize areas potentially impacted by sea level rise side-by-side with other data such as critical infrastructure, roads, ecologically sensitive areas, demographics, and economics. This is a sophisticated screening level tool that models coastal flooding from the combination of a high tide and sea level rise only. The data and maps do not include storm surges nor do they account for erosion, subsidence, or future construction. The tool uses a modified bath-tub approach that accounts for local tidal variability using the NOAA VDATUM model and includes hydraulic connectivity.
  2. FEMA California Coastal Analysis and Mapping Project (CCAMP): The CCAMP study area covers the entire California open Pacific coast, including the nine San Francisco Bay Area counties. The new detailed coastal engineering analyses and mapping will revise and update the flood and wave hazard data shown on the coastal Flood Insurance Study reports and Flood Insurance Rate Maps based on existing conditions for each of the twenty coastal counties. Through Risk MAP, CCAMP will develop enhanced products and tools to help communities understand and mitigate existing coastal flood hazards and risks, while OCOF’s online decision support tools project future flood hazards and risks resulting from sea level rise and storms within the San Francisco Bay Area.

What is the difference between the Point Blue Future San Francisco Bay Tidal Marsh website and OCOF?

The Point Blue Future San Francisco Bay Tidal Marsh seeks to understand how tidal marshes and the biota in those marshes are responding to sea level rise. OCOF seeks to understand the extent of flooding expected with sea level rise and various storm scenarios. These are two different approaches to answering a complex set of questions about San Francisco Bay and sea level rise. Scientists from all research organizations are sharing models and best practices for answering these complex questions about the effects of sea level rise on our world.

If I have questions about sea level rise in San Francisco Bay, should I use OCOF or Point Blue’s Future Marshes website?

OCOF tools will be available for the Outer Coast now and for the San Francisco Bay in Summer 2014. The Point Blue Future Marshes website is available for use today. These tools are designed to answer different questions with respect to climate change and sea level rise so ultimately the most appropriate tool will depend upon your specific question.

GEOGRAPHIC COVERAGE

What is the current geographic extent and resolution of the Digital Elevation Model and decision support tool?

The resolution is 2 m (a single elevation value is assigned to each 2 x 2 m grid cell) and it extends alongshore from Bodega Head to just south of Pillar Point Harbor in Half Moon Bay. In the cross shore direction it extends from an elevation of +20 meters and offshore to at least the 3 nautical mile limit of state waters The report and data can be downloaded from http://pubs.usgs.gov/ds/684/

How did you choose the OCOF project boundary?

The boundaries cover all the high-interest sites on the North-central Coast that are vulnerable to present and future coastal storms, including harbors (e.g., Pillar Point, Bodega), popular beaches (e.g., Ocean Beach, Linda Mar), sensitive ecosystems and embayments (e.g., Drakes Estero, Muir Beach, Bolinas Lagoon), and National Park Service Lands (e.g., Point Reyes National Seashore, Golden Gate National Recreation Area).

DATA

Which LIDAR data do you use?

LIDAR data comes from three 2010 surveys: USGS, California State Ocean Protection Council (OPC), and the Golden Gate Lidar Project. See http://pubs.usgs.gov/ds/684/ for the spatial coverage of each survey.

The other primary data for the DEM are depth soundings recently collected using multibeam bathymetry as part of the California Seafloor Mapping Project, a collaborative, multi-institutional campaign (http://seafloor.csumb.edu/csmp/csmp.html).

What are the sources for other data layers shown on the map?

What is the accuracy of the mapping used in this tool?

The DEM and all derived data layers have a horizontal resolution of 2 meters. The elevation data has a vertical accuracy of approximately 18 cm. The horizontal accuracy of the 2010 lidar (the bulk of the topography) has an RMSE of 1m.

How often is the mapping updated with new elevation data?

The DEM utilizes the latest and greatest topography and bathymetry available. There are no current plans to collect new data over this region.

How do I get a copy of the data layers for my own use?

You can download all data layers through the OCOF mapping tool. Select Flood Map from the main menu to get to the mapping tool. Select the model, sea level rise and storm scenario you want to download through the left panel, or open the Detailed Layers and make one of the layers active by selecting the radio button next to the layer name. In the upper right corner of the map, select the right most button, which provide additional instructions through a tool tip. Once selected, drag a box for the area of the map you want to download. You will receive a Zip file with the data in standard formats along with metadata for your reference.

Can I get the digital elevation model (DEM) that was used to create the layers, and how is it different from most other DEMs?

Yes. All the grids and metadata are available at http://pubs.usgs.gov/ds/684/ and also at http://topotools.cr.usgs.gov/topobathy_viewer/. At 2 m grid resolution, this is the highest resolution DEM available along the coast in the state of California. Standard regional DEMs are 90 m resolution, with a few locations having resolution as high as 10 m that have been developed for tsunami inundation modeling by NOAA.

MODELING

Which global climate models are used, and why did you choose them?

We use the latest and most sophisticated Global Climate Models from the Coupled Model Intercomparison Project Phase 5 (CMIP5: http://cmip-pcmdi.llnl.gov/cmip5/). These are a set of international climate models with a standard set of boundary conditions designed to collectively simulate the future climate for the 5th assessment report of the Intergovernmental Panel on Climate Change (AR5) , due in 2013. We chose the 4 of the 32 models (BCC-CSM1.1, INM-CM4, MIROC5, and GFDL-ESM2M) that have fine enough temporal resolution (3 hours) to adequately capture the maximum wind speeds so we can model the largest, most realistic waves. The remaining models only output our key parameters from storm modeling, wind and pressure fields, at 6-24 hour intervals, not adequate for resolving the peaks of coastal storms.

Is this based on a “bathtub” modeling approach?

No. Not only are we including both the static (i.e., tides and global sea level rise) and dynamic components of water levels (i.e., surge and wave-driven set-up and run-up), we are also explicitly modeling the flow of the flood waters as well.

Why does the tool show inundation starting at Mean Higher High Water (MHHW)?

Below the Mean Higher High Water are elevations that are wet at some point every day due to expected tidal activity. Elevation alone is not enough to tell you whether you are expected to be flooded due to sea level rise and storm surge activity on top of tides.

Does this tool show timing of inundation levels (e.g., 3 feet by 2100)?

From the OCOF Flood Map, select the Help me with Sea Level Rise projections link. A tool will cover the map that compares expert opinion about when sea level rise estimates will happen. You can ask questions about the range of years when sea level rise scenarios are expected to happen, as well the range of sea level rise scenarios expected for a given year.

The OCOF mapping tool and underlying flood hazard data do not give any time frames directly.

Does the model take into account levees and/or hydraulic features (culverts, pipes, levees, bridges)?

The models included all features with a footprint of at least 1 square meter that were captured as part of the LIDAR surveys, which should capture all levees and bridges. If you want to see if a particular feature was included, go to the OCOF Flood Map, open the Detailed Layers on the left side of the map, and select the layer Base > 2m Digital Elevation Model, and turn off other modeling layers. Zoom into the feature of interest and see if you can discern them, or download the area of interest with the upper right most button on the map and examine the data in a GIS package.

Does the model take into account land use changes on the shoreline, and the addition of infrastructure like seawalls?

Yes, indirectly. Coastal slopes greater than 30 degrees are assumed to be hard structures, such as jetties and seawalls, and are assumed to not erode over the time scale of the storms being simulated.

Does the model take into account future changes in geomorphology, shoreline change, etc.?

No, it only models the changes during a single storm. However, the future shoreline position has been projected for 2030, 2050, and 2100 based on the historical rates of change reported in the USGS National Assessment of Shoreline Change for the California coast (http://pubs.usgs.gov/of/2006/1219/).

Are the cumulative impacts from sea level rise and storm surge modeled together?

Yes. Each simulation includes all the relevant components of each storm scenario, including sea level rise, tidal currents, surge (driven by wind and atmospheric pressure), and waves.

How do you model inputs such as rivers and stormwater?

We did not include river and stormwater in the outer coast analysis, as we did not have enough data available to include these components. Anecdotally, however aside from a few very site specific locations, these flows are not known to be important on a regional scale in this study area.

We expect to include these factors when we expand this research to San Francisco Bay.

Why doesn't the flood extent reach the wet-dry line on the background image for the 0cm Sea Level Rise (SLR) with average wave conditions (0-year/no storm) in my study area?

Projected flood extents are intended to represent the maximum landward extent where standing water is expected for the duration of several minutes or more. This is usually below the maximum wave run-up line, where intermittent wave uprush is expected to reach and recurrent wetting and drying occurs.

Beach profiles change frequently, both seasonally and from year to year. Although the digital elevation model (DEM) used in this study has the latest comprehensive data available, it does not capture any recent changes in beach profiles or necessarily coincide with profiles indicated in aerial imagery. Changes in beach profile can yield variations in flooding extent and maximum wave run-up that might be especially noticeable in relation to the visible wet/dry lines on beaches in the imagery. When viewing SLR 000 cm results, flood extents affected by such beach profile changes are observable in the DEM and in relation to the visible wet/dry line in many locations, particularly on sand spits such as at the mouth of Bodega Bay, Tomales Bay, Drakes Estero, entrance to Valley Ford, Bolinas, entrance to Rodeo Lagoon, and open beaches along Point Reyes Beach, Muir Beach, northern Pacifica, Pillar Point and Half Moon Bay State Beach.

What is storm scenario frequency and what do 0-year (i.e., no storm), 1-year, 20-year, 100-year storm event wave conditions represent?

Simply stated, a storm scenario frequency is an estimate of how long it will be between storms of a given magnitude. For example, the 20-year storm event is expected to occur once in 20 years. Equivalently, one can say that there is a 5% chance that a storm of that magnitude will occur in any one year.

It is important to remember that this is based on statistics - there is no guarantee that once such a storm has hit the coast it will not happen again for another 20 years. If you had measurements of wave heights covering 100 years, there would be five such storms in that data series (an average of once every 20 years). These storms could occur in consecutive years or several in a single year.

The 0-, 1-, 20-, and 100-year storm events used in this work were derived from numerically modeled wave heights using projected winds for the 21st century. Statistical analysis of the wave height record offshore of San Francisco indicates that the median wave height in deep water (0-year storm, i.e., average daily conditions) will be on the order of 2.4 m while offshore wave heights associated with a 100-year storm will exceed 9.8 m.

Why does the flood extent for certain low SLR/storm scenarios sometimes seem to flood more than a higher SLR/storm scenario in my study area?

In certain locations, flooding does not progress in a consecutive manner with regard to SLR or storm event. There are two main reasons why this occurs:

  • Direction of incoming waves: The first is due to changes in wave height as they approach the shore from different angles. Within the CoSMoS structure, each storm event generated waves of different heights and directions offshore central California (see above for more information). 100-year event waves approached from a northwest direction, while 20-year event waves approached from the west. As waves approach the shore, bathymetric variability along the coast causes waves to change direction and approach different locations at different angles resulting in focusing or de-focusing of wave energy relative to other locations. Additionally, as waves change direction to approach the shore nearly straight on, some energy is lost in the form of decreasing wave height. Differences in wave approach angles for particular locations can result, for example, in flooding extent from the 20-year storm event, when waves may approach an area of coast more directly, exceeding 100-year storm event extents, when the generated waves may be larger but approach from a more oblique angle (see Figure right). This is particularly noticeable along south and southwest-facing coastlines such as Drakes Estero, Stinson Beach, Muir Beach, Horseshoe Cove, Rodeo Lagoon, and Pillar Point.

  • Eroding shoreline: The other reason that non-consecutive flooding occurs and small SLR/storm scenarios may have flooding extents greater than larger SLR/storm scenarios in limited areas is because of the complex nature of beach profile erosion simulated within the models. For each storm event, the same starting beach profile was used for a specific location along the coast. This profile was allowed to erode for the given storm within the model structure. Because of differences in wave height, length, and angle of wave approach, the erosion and deposition along the profile evolved in a nonprogressive fashion and subtle changes caused differences in the calculated extent of standing floodwater and maximum run-up. Most of this behavior is notable during stronger storm events (20-year and 100-year events) when there is considerable shoreline change.

What does ‘flood risk’ mean? How was it determined?

In order to provide a more comprehensive evaluation of possible flooding hazards at a particular location, flood risk was developed for each SLR scenario. This risk is determined as a percentage estimate that a location would be flooded in any given year given the wide range of storm and wave conditions that can affect an area. It was calculated using the probabilities of storm occurrences along with corresponding flood areas

Coastal planning is an evolving science and the models will continue to develop. Will there be new versions in the future?

The framework and approach of the modeling system will be expanded geographically into San Francisco Bay, but for the open coast there are no definitive plans to update the model system and presented results. It is important to note that all models are simplifications of the physics that that cause changes in the natural environment and can only provide approximations to the currents, shoreline erosion, and flooding extents presented in this work. Although different results might be attained with different models and a different approach to the overall strategy, the models and framework used in this work are considered to be state-of-the-art at this time.

DECISION SUPPORT TOOL

Is the resolution high enough to visualize impacts to a single parcel or building?

The DEM resolution of 2 m was selected to enable the possibility of asking questions at a parcel scale. We suggest you examine all modeled data layers and understand the assumptions that are behind these models when using these data.

Can I add my own layers with data specific to my project or site?

No. We have made the data used in the tool available for downloading from the OCOF mapping tool in standard GIS formats.

What types of maps or other products can be exported?

We have developed a standardized pdf report which summarizes model results for a user defined area. The report will include summaries and graphs of area you select interactively and a copy of the map.

Can I build mashups with the tool?

The OCOF mapping tool is built with open source technologies with map data delivered through Open Geospatial Consortium standards (http://www.opengeospatial.org/). If you are interested in mashing up portions of OCOF, please contact Michael Fitzgibbon at Point Blue Conservation Science (mfitzgibbon@pointblue.org).

Is there a mobile app to access this information in the field?

You can access the OCOF web site on a tablet computer with internet access. We are looking at the possibilities of mobile applications in the future.

Can I get the tool source code?

Yes. Please contact Michael Fitzgibbon at Point Blue Conservation Science (mfitzgibbon@pointblue.org).

USER FEEDBACK

How do I provide feedback on this tool?

Look for the “Feedback” link on each page for sending the team your thoughts, issues and ideas about the research, website and interactive tools. We would love to hear from you!

MISCELLANEOUS

Will there be an endorsement by the State of California that this is approved for CEQA analysis?

It is unlikely that the State of California will endorse any specific tool for sea level rise analysis within CEQA. State policies and guidance regarding climate change considerations are constantly evolving, so you should contact the appropriate agency for more information.

Updated: November 25, 2013

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