Hosted/Sea_Level_Rise_0_8ft_2050__BCDC_RSAP_

View In: ArcGIS JavaScript ArcGIS Online Map Viewer

Service Description:

All Layers and Tables

Has Versioned Data: false

MaxRecordCount: 2000

Supported Query Formats: JSON

Supports Query Data Elements:

Layers:

Sea Level Rise 0.8ft 2050 (BCDC RSAP)_master (0)

Description: <DIV STYLE="text-align:Left;"><DIV><DIV>Note: This layer is a copy of data hosted in BCDC's Regional Shoreline Adaptation Plan Atlas. "Coastal Flood Hazards" features service available online at: https://services2.arcgis.com/4Z9x989NrBVrvFwm/arcgis/rest/services/RSAP_Coastal_Flood_Hazards/FeatureServer------Data from the ART SLR flood maps is used to represent future flooding from sea level rise and storm surge/extreme tides, while the USGS CoSMoS groundwater hazard maps are used to represent shallow groundwater rise and groundwater emergence/flooding. The ART SLR flood maps use a Total Water Level (TWL) approach for estimating flood extent that differs from FEMA and other established engineering practices. For the ART SLR flood maps, TWL refers to the combination of tides, storm surge, and sea level rise to contribute to a water level and flood extent above Mean Higher High Water (MHHW) but does not include wave run up. TWL is not used to describe the combined hazard scenarios in the RSAP. A comparison of the USGS CoSMoS Coastal Flood data and ART SLR flood data (by BCDC staff) concluded that at low water levels the ART SLR flood maps better reflect the dynamics associated with flooding in urbanized/developed shorelines, due to the extensive ground truthing that was conducted as part of the mapping methodology as well as better inclusion of local flood protection structures. For these reasons, the ART SLR flood data was identified as the best available data source on sea level rise for the San Francisco Bay. Shallow groundwater mapping includes areas that will experience emergent (surface) groundwater flooding as well as estimates of the depth to groundwater (below surface) for future SLR scenarios. At the time of analysis, USGS CoSMoS-GW is the only source of shallow groundwater maps available for the whole region. CoSMoS-GW is a hydraulic model based on USGS’s MODFLOW model calibrated for the San Francisco Bay. Additional Groundwater modeling has been completed by SFEI and the Pathways Climate Institute for Alameda, Marin, San Francisco, and San Mateo Counties, but is not yet available for the whole nine county Bay Area. Where subregional groundwater modeling exists we encourage jurisdictions to analyze the shortcomings and advantages of each model and choose the analysis that best fits their jurisdiction. If local models do not exist we encourage supporting local groundwater rise modeling. Where that is infeasible, we recommend carefully reviewing the assumptions in CoSMoS-GW model and assumptions in the hazard layers assembled in the combined hazard layer to ensure that planners understand and are comfortable with those assumptions. In general, the CoSMos-GW model is intended as a screening tool to identify locations that may experience increasing groundwater hazards as sea levels rise and is not a substitute for local hydraulic modeling for project development. A key modeled parameter in the USGS CoSMoS-GW shallow groundwater model results is a measure of groundwater geology called hydraulic conductivity (K). Hydraulic conductivity measures how permeable the subsurface is. For purposes of the regional shallow groundwater rise hazard maps and exposure analysis, a Moderate hydraulic conductivity value of K = 1.0 meter/day was chosen. USGS CoSMoS recommends K = 1 as the default assumption when little is known, or there is significant variation in the subsurface geology. The Bay Area has highly variable geology, so using the moderate hydrologic connectivity minimizes maximum error. However, this assumption is unlikely to be precisely accurate for some regions in the Bay Area because of the highly variable conditions. Where better local information exists, we highly encourage adjusting the assumptions. As an additional evaluation step, three CoSMoS hydraulic conductivity models (K=0.1, K=1.0, and K=10) were compared to the SFEI modeling. This confirmed the decision to use the K=1.0 data. While mapped depth to groundwater can exceed 15 ft in areas, for the purposes of the RSAP Minimum Categories and Assets (Section 3.3.2), groundwater depths deeper than 9 ft were excluded from analysis because they were not considered to have a potential impact to the topic area asset data. Including a depth to 9ft is a highly conservative assumption, because most underground infrastructure will not be affected by groundwater rise at that depth. However, in some cases, such as a location with hazardous material at or near the groundwater table, awareness of potential groundwater rise may assist planners in considering adaptation options. To provide more options to planners related to the impact of groundwater rise on their particular asset for the purposes of a vulnerability assessment, the combined hazard maps bin “Shallow” groundwater as three depth classes: Very Shallow (0-3 ft), Shallow (3-6 ft), and Moderately Shallow (6-9 ft). To further refine the accuracy of the groundwater rise data to areas where groundwater depth was most impacted by sea level rise, BCDC staff also confined the groundwater rise hazard maps based on methodology developed by Hill et al. (2023). This constrained the data set to areas where a change in groundwater between existing conditions and the future scenario was greater than 4 in and areas where the groundwater table is within 10 m of the surface. This is because impacts below 4 in are considered nominal and likely will not require region-wide adaptation actions. Using ArcPro and ArcPy (the ESRI Python extension), the ART SLR flood data and USGS CoSMoS Groundwater data were combined to create the coastal hazard maps for four sea level rise scenarios based on the California Sea Level Rise Guidance (2024) statewide averages:<UL><LI>0.8 feet (2050)</LI><LI>3.1 feet (2100 Intermediate)</LI><LI>4.9 feet (2100 Intermediate-High)</LI><LI>6.6 feet (2100 High)</LI></UL>For each scenario, a 100-year storm surge value was added that is approximately 3.5 ft greater than the sea level rise value. This value comes from the AECOM Tidal Datums and Extreme Tides Study (2016) that was produced for the San Francisco Bay. Only groundwater rise data for SLR scenarios and not for the added storm surge water levels were included in the analysis. This is due to a lack of scientific consensus of how acutely storm surge affects groundwater, how the ffects of storm surge on groundwater diminish as you move inland, and variation in how quickly groundwater returns to pre storm depths. As seen in Table 1, California Sea Level Rise Guidance (2024) recommendations did not always perfectly reflect the water levels available in either the ART SLR flood data or the CoSMoS data. In both cases, the closest value to the recommended California Sea Level Rise Guidance (2024) scenario was chosen. All tidal inundation and groundwater values were within 0.6 feet of the California Sea Level Rise Guidance (2024), with most being significantly closer (Table 1). One limitation of choosing to use the ART data was that it caps out at 108” or 9 feet (Table 1). This led to a greater disparity between the predicted storm surge level for the California Sea Level Rise Guidance (2024) 2100 High (10.1 feet) and the mapped storm surge (9 feet). These hazards combined created the following 10 categories which show where multiple hazards are present in the same area:<UL><LI>Tidal Inundation + Emergent Groundwater</LI><LI>Emergent Groundwater</LI><LI>Storm Surge + Emergent Groundwater</LI><LI>Storm Surge + Very Shallow Groundwater (0-3 ft)</LI><LI>Storm Surge + Shallow Groundwater (3-6 ft)</LI><LI>Storm Surge + Moderately Shallow Groundwater (6-9 ft)</LI><LI>Storm Surge</LI><LI>Very Shallow Groundwater (0-3 ft)</LI><LI>Shallow Groundwater (3-6 ft)</LI><LI>Moderately Shallow Groundwater (6-9 ft)</LI><LI>Existing Bay</LI></UL>While the data distinguishes between three levels of shallow groundwater, for legibility, the Coastal Hazard Maps in the Coastal Flood Hazards and Sea Level Rise Scenarios Standard Section combine the shallow groundwater categories into one (0-9 ft). Python scripts and step by step analysis can be found on the BCDC-GIS Github.</DIV></DIV></DIV>

Service Item Id: 23a457a48e0e4669acd6fc4b8a1101b1

Copyright Text:

Spatial Reference: 102642 (2226) LatestVCSWkid(0)

Initial Extent:

Full Extent:

Units: esriFeet

Document Info:

N/A Enable Z Defaults: true

Supports ApplyEdits With Global Ids: false

Supports Dynamic Layers: false

Child Resources: Info Relationships

Supported Operations: Query Query Contingent Values Append Get Estimates

Hosted/Sea_Level_Rise_0_8ft_2050__BCDC_RSAP__master (FeatureServer)