The Resilience Atlas and associated analyses are intended for advisory use only. This tool is designed to provide a regional-scale illustration of sea level rise vulnerabilities, existing protections, nature-based adaptation opportunities, and to improve awareness of and preparedness for the impacts of sea level rise in the San Francisco Bay Area.
The Resilience Atlas does not constitute an adaptation plan. Additional study, planning, and engineering is necessary to develop adaptation plans using the opportunities, vulnerabilities, and other data identified herein. Mapped data are not detailed to the parcel-scale and should not be used for navigation, permitting, regulation, project review, mitigation, actuarial estimates, or other legal uses. While the maps use the best available data at the time of their publication, SFEI does not guarantee that the data remain current or accurate.
Included data are based on and limited to the methods detailed in the metadata for each layer. Details on the authorship of data layers, methods used to create data layers, and/or relevant reports or resources for more information are available within the “About // Downloads” section of this web map.
Use of the Resilience Atlas and associated data indicates that you acknowledge that you have read, understood, and agree to the terms of this disclaimer.
The Resilience Atlas visualizes the past, present and future conditions of San Francisco Bay and its local watersheds by combining layers of information, such as flood infrastructure, shoreline change over time, and sea level rise. The Resilience Atlas is an interactive platform created by the San Francisco Estuary Institute (SFEI), with funding from the Bay Area Integrated Regional Water Management (IRWM) program, managed by the San Francisco Estuary Partnership (SFEP). Ancillary funding was also contributed by the Santa Clara Valley Water District (SCVWD).
This project aims to aid regional planning efforts by providing access to an online repository of key datasets related to ecosystem resilience around the Bay shore to restoration managers, governmental organizations, nonprofits and citizens.
Our interactive interface allows users to explore the relationships between shoreline characteristics, habitats, infrastructure, adaptation strategies and vulnerable communities, overlaid with sea level rise scenarios. The Resilience Atlas will host map-based stories that highlight examples of completed adaptation projects and what can be done in areas vulnerable to sea level rise, subsidence, flooding and other challenges.
For more information on how to use the Resilience Atlas, watch the tutorial below:
Do you have ideas on how the Resilience Atlas can be improved? Email us at firstname.lastname@example.org.
To download Adaptation Atlas GIS data, visit the Adaptation Atlas Data Center page.
To delineate individual OLUs, we first identified three major geomorphic unit types along the shore: (1) headlands and small valleys, (2) alluvial fans and alluvial plains, and (3) wide alluvial valleys. These distinct units are distinguished by different underlying geology and resulting landscape morphometrics, such as slope of the shoreline, the width of the baylands, and watershed size. Once determined, geomorphic units were further divided into individual Baylands OLUs by different methods for each unit type based on topographic and bathymetric considerations in addition to landscape morphology considerations. For more information and deatiled methods on how each geomorphic unit type and Baylands OLU was delineated, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
The bayward OLU boundaries have been drawn to include parts of the Bay that could be a source of suspended fine sediment to marshes and mudflats the OLUs. In the shallow subtidal parts of the Bay, the suspended sediment concentration depends mostly on the resuspension of sediments by wind-driven waves. We calculated the maximum depth of sediment resuspension associated with the 100-year wave height in each OLU (derived from DHI 2011 & 2013). By subtracting this depth from the elevation of the water surface at MLLW (derived from AECOM 2016), we were then able to calculate the minimum elevation at which sediment resuspension is likely to occur in each OLU (ranging from -3.19 to -4.37 m NAVD88 [-10.5 to -14.3 ft NAVD88]). Finally, we calculated the average minimum elevation across all OLUs (-3.70 m NAVD88 [-12.1 ft NAVD88]) and used bathymetric data to trace the approximate location of this contour, which serves as the lower boundary of the OLUs. Boundaries between OLUs in the subtidal zone were drawn simply by connecting the boundary of the OLU at the shoreline to the lower boundary contour with a straight line. These bayward “side boundaries” are only illustrative and do not meaningfully distinguish which portions of the subtidal zone are potential sources of resuspended sediment to individual OLUs. For more information, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Contributing watershed boundaries for each Baylands OLU were delineated by using the National Hydrography Dataset (USGS 2014), local watershed/sewershed maps (Sowers et al. 2003, 2005, 2007a, 2007b, 2010), and other datasets (e.g., slope and channel maps) to identify each OLU's drainage area and side boundaries. The most challenging part of this process was identifying tidal watershed boundaries within the baylands. Whenever possible, we used contemporary maps of tidal channels (BAARI version 2.1; SFEI-ASC 2017a) to elucidate these tidal watershed boundaries, but in areas where the baylands have been diked and extensively modified we sometimes relied on maps of historical tidal channel networks (e.g., SFEI 1998). Some minor exceptions to the guidelines described above and other details associated with identifying boundaries between OLUs are described in Appendix 2 of the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Subtidal areas with conditions that could support oysters and would be suitable for restoration projects were identified by the San Francisco Bay Subtidal Habitat Goals Project (Subtidal Goals 2010). Specifically, the areas mapped as suitable for nearshore reefs are those that were identified through the Subtidal Goals Project as “potential restoration sites” based on the best professional judgment of scientists considering water depth (sites were only mapped where depth is <2 m), salinity, substrate type, oyster recruitment potential, and site access. For more information, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Areas mapped as appropriate for submerged aquatic vegetation restoration were derived from a predictive model developed by Merkel & Associates (Merkel 2005), which identified potentially suitable eelgrass habitat based on water residence time, salinity, and hours of light saturation. Specifically, the areas shown as suitable for submerged aquatic vegetation are those with a modeled habitat suitability index greater than zero. These areas were digitized from a low-resolution geo - referenced copy of the suitability map. For more information, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Areas mapped as suitable for beaches were identified by selecting shoreline reaches that are fronted by existing beaches or wetlands, or are currently fortified by rip rap, sea walls, or other structures indicative of high wave energy environments. Results were refined by removing buffers that overlap channel openings, marinas, and ports, which assumes beaches would not be appropriate in these areas based on current land use. Existing beaches, wetlands, fortified areas, and channel openings were mapped using SFEI’s Bay Shore Inventory dataset (SFEI 2016). Marina and port locations were digitized based on photo interpretation of 2018 aerial imagery from Google Earth. Areas suitable for beaches were only mapped within historical beach provinces (e.g., where evidence of beaches exist circa 1800) based on historical beach locations as mapped by EcoAtlas (SFEI-ASC 1997) and expert opinion (Peter Baye, personal communication). Areas that fell outside of the historical beach province boundary include the north shore of San Pablo Bay, Carquinez Strait, Suisun Bay, and the far South Bay demarcated by Dumbarton Bridge. Beach crest elevations were calculated for each 100 m shoreline segment based on the runup of the 100-year significant wave height (DHI 2011, 2013). The low-tide terrace elevation was set at MLLW. Beach slope was assumed to be 30:1 (horizontal:vertical) and representative of a mixture of sand, shell, cobble, and gravel. For more information, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Areas mapped as suitable for tidal marsh restoration were identified by selecting areas between the approximate elevation of MSL and highest astronomical tide (HAT) (with a z* value between -0.14 and 1.38), which is the range determined by Thorne et al. (2018) as supporting tidal marshes at Petaluma Marsh in San Francisco Bay (the range corresponds to the area between the lowest extent of tidal marsh vegetation and the highest extent flooded on average at least once per year). To assess the appropriateness of defining potential marsh across the whole Bay using a relative marsh elevation (z*) range from only Petaluma Marsh, we calculated the elevation range of 11 other marshes with tidal datum and marsh elevation data from USGS (Takekawa et al. 2013). Finding that the mean relative elevation (z*) range of these sites was comparable to the relative elevation range of Petaluma Marsh determined by Thorne et al. (2018), we felt comfortable using the Petaluma Marsh values to identify areas at the right elevation for tidal marshes across the Bay. Future iterations of this work could incorporate data from additional sites (particularly Suisun Marsh) to define different elevation ranges for each OLU. For more information on methods and data limitations, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Areas mapped as suitable for polder management were identified by selecting any contiguous areas with elevations below MSL and disconnected from tidal inundation by dikes—i.e., areas that would be inundated on most tides if dikes were not present. This was accomplished in a GIS by isolating all areas with a z* value <0 and then deselecting the portions of this area that are contiguous with (i.e., connected to) the Golden Gate. In a few areas we were required to add or subtract connections to reflect known landscape modifications that have occurred since the underlying DEM was generated (e.g., adding the Hamilton Wetlands breach). In the final map we only show polders with surface areas greater than 0.3 ha. For more information on methods and data limitations, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
For the San Francisco Bay Shoreline Adaptation Atlas (2019) report, areas mapped as suitable for ecotone levees were identified by selecting areas at the proper elevation for tidal marsh that are both adjacent to developed areas and wide enough to support a levee with a 1:30 slope, assuming a crest height equal to the height of the 100-year storm surge plus 2.1 m of sea level rise. The version mapped here is based on a similar, updated method developed in 2021 to expand and refine the range of opportunity sites for ecotone levees originally identified in the 2019 Adaptation Atlas. The “developed areas” layer and the “marsh” layer used as inputs to the analysis were expanded from the 2019 Adaptation Atlas versions. The development layer was updated with the most recent available National Land Cover Database from 2016 and development types not accounted for previously (e.g. wastewater infrastructure) were added. The marsh layer was expanded to include existing marsh as well as areas of potential future marsh, including undeveloped areas that are at marsh elevation today, low-elevation areas where restoration is planned, and undeveloped inland areas at marsh migration space elevations. An extensive review process was undertaken to identify missed opportunities not captured in the 2019 Adaptation Atlas and remove opportunities now recognized as infeasible. See Appendix A of Ecotone levees and wildlife connectivity: A technical update to the Adaptation Atlas for a complete description of the updated method.
Locations mapped as suitable for migration space preparation were identified by selecting undeveloped areas expected to be inundated with 2.0 m of sea level rise (CoSMoS Model SF Bay Product Suite, Barnard et al. 2014) that are above today’s highest astronomical tide (z* > 1.34). Results were refined by removing areas of existing tidal marsh by using SFEI-ASC (2017a) data to map tidal ditch, tidal marsh flat, tidal panne, and tidal vegetation classification types. We then distinguished protected migration space from unprotected migration space using the California Protected Areas Database (CPAD 2017). Note that the 2.0 m sea level rise scenario utilized in the analysis is slightly less severe than the 2.1 m assigned 0.5% probability of occurring by 2100 under high emissions scenarios by OPC (2018). Undeveloped areas were distinguished from developed areas using the 2011 National Land Cover Database (Homer et al. 2015) using the crosswalk developed by Collins (2015). For more information, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Mudflats were mapped by selecting areas categorized as "Bay Tidal Flat" in version 2.1 of the Bay Area Aquatic Resources Inventory (2017). Tidal flat extents within this dataset are largely based on interpretation of NAIP imagery from 2009.
Existing tidal marsh areas were mapped by selecting habitats categorized as "tidal ditch", "tidal marsh flat", "tidal panne", and "tidal vegetation" in version 2.1 of the Bay Area Aquatic Resources Inventory (2017). Tidal marsh extents within this dataset are largely based on interpretation of NAIP imagery from 2009.
To map developed areas in the San Francisco Bay Area, we extracted all areas classified in the National Land Cover Database (2011) as “Developed- Low Intensity,” “Developed- Medium Intensity,” or “Developed- High Intensity” and then corrected developed feature edges by erasing any wetland or aquatic features mapped in the higher resolution Bay Area Aquatic Resources Inventory (SFEI-ASC 2017a; see Goals Project 2015). For more information, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Although the DEM utilized to calculate z* values and identify polders, potential tidal marsh, and potential migration space is topobathymetric (containing elevation for both dry and submerged parts of the study extent), there are submerged areas (including some lakes, marinas, and current/former salt ponds) without true bathymetric data. To identify these areas, we first identified portions of the DEM likely quantifying the elevation of the water surface (instead of the land surface) by using a neighborhood filter to identify flat areas. Flat areas with an z* value >0 were then flagged as potential false negatives and shown on the suitable areas map as data gaps (areas that may or may not be polders). It is likely that most of these flagged areas are, in fact, polders and suitable for polder management. For more information, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
Newly restored or planned restoration areas are defined by the area mapped as planned future tidal marsh habitats in the Baylands Ecosystem Habitat Goals Science Update (2015). As detailed in that report, this area is based on Bay Area Aquatic Resource Inventory (BAARI) data from 2009 and includes projects in progress and planned projects that have been funded and/or permitted as of 2015 (i.e., projects that have a high likelihood of completion within the next 20 to 30 years). We refined this layer based on feedback through personal communciations with USFWS staff (2019). These areas include restoration sites that have been breached and are in the process of accreting to intertidal elevations. For more information, see the San Francisco Bay Shoreline Adaptation Atlas (2019) report.
This composite picture is based upon hundreds of independent sources of data. These include eighteenth- and nineteenth-century maps, sketches, paintings, photographs, engineering reports, oral histories, explorers' journals, missionary texts, hunting magazines, interviews with living elders, and other sources. Click here for more information.
Download the data here.
The coverages of the Modern Landscape View of the EcoAtlas Baylands share common aerial photography origin. They are based on the best available existing regional digital information on baylands habitats. However, substantial local inaccuracies in this existing digital data have been revealed through intensive local reviews held by SFEI in December 1996 through the present. The following documentation summarizes the origin of version 1.0 of the EcoAtlas Modern Landscape View. Substantial revision of the Modern Landscape View to incorporate hundreds of changes recommended by local experts through truthing sessions, changes in the landscape since 1985, and to implement the more detailed and regionally-representative Habitat Typology of the Goals Project is currently taking place. As a result of these changes a substantially more detailed and accurate Modern Landscape View will be available. Click here for more information.
Download the data here.
This dataset represents a reconstruction of the historical landscape and prevailing conditions of different study areas in the Bay Area and Delta prior to Euro-American modification. It integrates many sources of data describing the historical features of different regions. This layer is the product of numerous historical ecology projects including Napa Valley, Alameda Creek, South San Francisco Baylands Tsheets, EcoAtlas Historical Baylands, South Santa Clara Valley, Western Santa Clara Valley, Coyote Creek Watershed, East Contra Costa County, and the Sacramento-San Joaquin Delta. Extensive supporting information, including bibliographic references and research methods, can be found for each individual project.
This layer shows tidal marsh patches by size in 2009, originally created for The Baylands and Climate Change: What We Can Do report, an update to the 1999 Baylands Ecosystem Habitat Goals report. Tidal marshes in the Bay have become more fragmented, with much more edge relative to interior or core areas and some isolated habitat patches. Fragmentation has reduced the baylands’ ability to support wildlife by decreasing the connectivity between populations and increasing edge effects that promote predation and anthropogenic issues. These changes are likely to reduce some support functions for resident marsh wildlife above and beyond the loss in habitat extent. In this data layer, “Edge habitat” is defined as within 50 meters (164 feet) of the marsh edge, and the rest of the marsh interior is defined as “core habitat”. Habitat patches are considered separate if they are greater than 60 meters (197 feet) apart. For more details about this methodology, see pages 20-24 and Appendix C in the Baylands Ecosystem Habitat Goals Science Update (2015).
Understanding lateral shoreline change is a critical indicator of shoreline resilience, also providing data input for sea level rise models, and helping to prioritize appropriate restoration adaptation strategies. Given the large continuing investment in San Francisco Bay wetlands restoration, this information is critical to informing regional planning, preservation and prioritization of habitat restoration in light of sea level rise and changing sediment availability. Without this basic understanding of shoreline dynamics, the region is likely to extend valuable resources in unsustainable places.
Using a systematic, empirical, and repeatable approach, we mapped the location of the shorelines in San Pablo Bay at three points in time: 1855, 1993, and 2010. We then measured rates of change over the long (1855-1993) and short-term (1993-2010) to identify zones of erosion, progradation, and areas that have remained stable.
The purpose of this report is to increase our understanding of the rate, distribution, and mechanisms of marsh edge shoreline erosion and describe current understanding of changes of the mudflat-marsh transition, describe several types of shoreline edges, and provide recommendations for next steps in tracking shoreline change. The results of this pilot study provide a new level of understanding about the dynamics of our shorelines and the ways they are likely to respond to local actions. Read more about the project here
Download the full report here.
The transition zones between our watersheds and the Bay are often occupied by flood control channels that provide a variety of societal and driven in large part by a combination of high watershed sediment yield and excess tidal sediment accumulation due to decreased tidal scour.
As part of the Flood Control 2.0 project, SFEI gathered and collated key sediment data for the past 50+ years from the major flood control channels around the Bay. The effort focused on data related to the supply of watershed sediment entering these channels and environmental services but can require sediment removal to maintain flood conveyance capacity. The causes of sedimentation problems in these channels are often complex, the details of individual sediment removal events for each channel (e.g., location, volume, sediment grain size, and cost). This information is intended to help clarify the amount of sediment trapped in flood control channels that could be used to restore baylands and support long-term bayland resilience as sea level continues to rise.
An interactive map displaying the summary flood control channel sediment data can be found here. A report synthesizing these data with other Flood Control 2.0 regional analyses will be released in December 2016. Click here to read more.
Download the dataset here.
San Francisco Bay’s connections to local creeks are integral to its health. These fluvial-tidal (F-T) interfaces are the points of delivery for freshwater, sediment, contaminants, and nutrients. The ways in which the F-T interface has changed affect flooding dynamics, ecosystem functioning, and resilience to a changing climate. As the historical baylands have been altered, the majority of contemporary F-T interface types have changed leading to additional F-T interface types within the present-day landscape. Illustrations of each F-T interface type and methods for classification are available here.
This project is part of Flood Control 2.0. For further information please visit this project page.
This layer is part of the Bay Area Aquatic Resources Inventory (BAARI) project which provides a detailed base map of the Bay Area's aquatic features that have been mapped using a standard mapping protocol developed by SFEI's GIS team.
BAARI v2 includes all wetlands, open water, streams, ditches, tidal marshes and flats, and riparian areas. BAARI can be used to track changes in the amount, extent and condition of aquatic resources, serve as the base map for environmental monitoring study designs, and support resource planning and management efforts. BAARI is viewable on EcoAtlas, where users can browse the area's aquatic features and restoration projects on an interactive map. Details about the methodology can be found here.
BAARI data can be downloaded here.
To provide a comprehensive and consistent picture of today’s Bay shore, SFEI mapped and inventoried Bay shore features that could affect flooding and flood routing for all nine Bay Area counties. While many different detailed levee layers exist, the region currently lacks a standardized regional dataset of elevated Bay shore features, accredited or not.
Mapping extends up to 10 feet above Mean Higher High Water and includes many shore features: engineered levees, berms, embankments, transportation structures, wetlands, natural shoreline, channel openings, and water control structures. Features were attributed with elevation, FEMA accreditation, how a structure was armored, whether a structure was fronted by a wetland or beach, ownership, and the entity responsible for maintenance, if known. The methodology was originally piloted in BCDC’s Adapting to Rising Tides (ART) project in Alameda and San Francisco counties. SFEI refined and extended the methodology to the whole Bay to complete a coherent and comprehensive dataset. The dataset is available in ESRI ArcGIS and Google Earth formats. For more information on the shoreline inventory dataset, please contact Jeremy Lowe.
Click here for a full description of the methodology used to create this dataset.
Download the data here.
This layer is a slightly modified version of the Pacific Institute’s dataset of wastewater treatment plants near the California coast. Modifications were made to remove outfall locations and only keep physical locations of wastewater treatment plants. In addition, some wastewater treatment plants near the San Francisco Bay were manually added to this dataset. The original dataset can be accessed here.
The sea-level rise projections used in this viewer were created by Our Coast Our Future using the CoSMoS model. More information on how these layers were created can be found on the OCOF website. These layers are courtesy of Our Coast Our Future.
This project focused on addressing the lack of detailed assessments of stormwater infrastructure and flood hazards in disadvantaged communities (DACs), where adequate stormwater conveyance was not constructed when the community was built, or not fully improved in subsequent years. These activities were conducted in support of the Bay Area Integrated Regional Water Management Plan (IRWMP) Coordinating Committee objectives to advance local and regional water resource management goals through synergistic collaboration of agencies, communities, and other project partners. IRWMP objectives included assessment of DAC water quality and flood protection needs, such that resultant information would be of benefit within the San Francisco Bay Area region.
This project was prepared for The Watershed Project by Balance Hydrologics and managed by SFEP under the same IRWMP grant that supported the creation of the Resilience Atlas.
Click here to download the report.
Download the data here.
This layer is a slightly modified version of the Disadvantaged Community Census Block Group layer created by the California Department of Water Resources (DWR) using the definition created by Proposition 84 IRWM Guidelines (2015). “Severely Disadvantaged Communities” (SDAC) are defined as census block groups with an annual median household income (MHI) less than 60 percent of the Statewide annual MHI, and “Disadvantaged Communities” (DAC) are defined as census block groups with an annual MHI less than 80 percent of the Statewide annual MHI. Annual MHIs are based on the US Census American Community Survey (ACS) 5-year data for 2010-2014 (with an MHI of $61,489 and hence calculated DAC and SDAC thresholds of $49,191 and $36,893, respectively). Modifications to this layer include omitting areas that fall within the Bay water body, omitting block groups with a population of zero, and limiting the extent to the nine Bay Area counties.
Click here for a full description of the original layer.
Download the data from DWR here.
The Habitat Projects data layer contains habitat restoration, mitigation, and conservation projects tracked on EcoAtlas. The wetland mitigation projects are located in the San Francisco Bay Area, North Coast, Central Coast, South Coast, and Lake Tahoe Basin. In the San Francisco Bay Area, project information is collected for all projects that have received a 401 Certification and/or Waste Discharge Order from the Regional Water Quality Control Board. Basic information is provided through the 401 Certification application or through subsequent inquiries with project sponsors. Habitat projects are tracked and updated by the San Francisco Bay Joint Venture, Central Valley Joint Venture, and Sacramento-San Joaquin Delta Conservancy.
Projects can be viewed in the landscape context along with other data layers on an interactive map. Individual project information pages summarize the status, events, contacts, funding, and habitat plan for each project. Some projects consist of multiple sites, each of which can have a different status. In addition, supporting materials including monitoring reports, permits, photos, videos, and links to other websites can be uploaded and stored in a project’s file repository.
Project Tracker is an online data entry tool for submitting new projects to EcoAtlas. Once approved by regional managers, project boundaries are displayed on the map and can be viewed within the larger landscape context. Project information is summarized on individual project pages and in the Landscape Profile Tool. Project data can be downloaded here.
As we rethink land management in the face of climate change, we know well-functioning resilient landscapes can protect development and sustain native ecosystems. SFEI has created a series of Resilient Landscape Vision reports that explores ways to restore and support natural processes, and, in turn, provide multiple benefits such as flood risk management, water quality improvements, sediment reuse, recreational opportunities and more. The process for developing a vision typically has three components. First, we build a baseline understanding of the historical and contemporary geomorphic and ecological conditions, and assess the likely impacts of future drivers (e.g., sea level rise, increased flood intensity). Second, we convene a workshop to bring together engineers, planners, state and local natural resource agency staff, and an advisory panel of regional science experts. Finally, following the workshop, we analyze the potential improvements to habitat, flood conveyance and other important considerations to the study area associated with the developed Vision. Ultimately, these Visions can be used to guide planning efforts to promote long-term landscape resilience and ecosystem functioning under a changing climate.
The Baylands and Climate Change: What We Can Do (2015) is the update to the 1999 Baylands Ecosystem Habitat Goals, which for the first time set comprehensive restoration goals for the San Francisco Bay estuary. Produced by a collaborative of 21 management agencies working with a multi-disciplinary team of over 100 scientists, the new report synthesizes the latest science— particularly advances in the understanding of climate change and sediment supply— and incorporates projected changes through 2100 to generate new recommendations for achieving and sustaining healthy baylands ecosystems. This layer was created based on the recommended actions for each bayland segment detailed in the 2015 BEHGU report. For more details, access the report here.
Boundaries for the individual watersheds that drain to the Bay. Disclaimer: Due to limitations data limitations, the watershed boundaries here may contain delineation errors. As such, this layer only serves to convey a general sense of the major watersheds draining to the Bay.