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Errors in the input depth files to the high resolution model along the sand spit of Bodega Bay resulted in inaccurately predicted flooding extents and over-predicted velocity in this region. Many SLR scenarios (075-175 cm) show flooding extents greater than larger SLR scenarios for corresponding storm events in small areas along the sand spit.
The boundary between different modeling systems within CoSMoS (XBEACH and high-resolution flood generation) along the southern end of Bodega Bay prevents complete generation of flood extents for certain scenarios in the region and results in under-predicted flooding extents for large SLR scenarios (greater than SLR 125 cm with 20-year storm) and most flooding uncertainty fields on the eastern side of sand spit.
The boundary between different modeling systems within CoSMoS along the main sand spit prevents complete calculation of flooding uncertainty extents for several scenarios; many flooding uncertainty fields are under-predicted on small portions of the sand spit as a result.
In small areas of the western bays of Drakes Estero, flooding uncertainty fields exhibit irregular flooding behavior, producing cut-off extents.
Two embayments inside the bay (near White Gulch and Sacramento landing) are not correctly depicted within the DEM. Consequential flooding extents are not properly projected, likely under-predicting the flooding extent.
Several scenarios (SLRs 000 cm, 025 cm, 175 cm, and 200 cm for most storm conditions) show irregular flooding behavior and exhibit non-progressive flooding along portions of Lagunitas Creek and Walker Creek.
Point Reyes Beach
The DEM shows small inconsistencies in elevation along portions of Point Reyes Beach; consequential flooding extents in scenarios up to SLR 150 cm are not accurately predicted and projected in these areas. The magnitude of velocity is over-predicted along this shoreline for all scenarios.
Projected flooding, low-lying coverage, and uncertainty flooding fields all exhibited irregular flooding behavior in this area and produced cut-off flooding extents. These sections have been amended to indicate likely and complete flooding coverages based on topography and flooding performance for varied SLR-storm scenarios along the surrounding coastal area.
Certain scenarios (including SLR 000 cm with 100-year storm, SLR 025 cm with a 100-year storm, and SLR 100 cm with a 100-year storm) exhibited exaggerated flooding extents in small areas east of Seadrift and a parking lot at the end of Marine Way. Other scenarios (including SLR 050 with a 20-year storm and SLR 200 cm with a 1-year storm) showed likely under-predicted flooding extents in the aforementioned areas given beach profiles and adjacent flooding behavior. Sections with particularly disproportionate predictions in flooding extents have been corrected to reflect probable flooding extents based on beach topography and flooding performance of comparative scenarios.
Non-progressive flooding behavior is also exhibited at small portions of these areas during stronger storm events (20-year and 100-year events).
Small portions of the DEM within Seadrift Lagoon contain elevation inconsistencies, due to originating LIDAR picking up docks within the lagoon; flooding extents and depths are not accurately predicted at these locations.
Certain scenarios (including SLR 000 cm with 20-year storm, SLR 050 cm with 20-year and 100-year storms, and SLR 125 cm with 1-year and 20-year storms) exhibit likely over-predicted flooding extents in small areas along the edges and sand spit at the entrance of the lagoon.
Particular scenarios (including SLR 025 cm with 20-year event and SLR 150 cm with 20-year event) showed evidence for consistent under-prediction of flooding within the lagoon. Specific sections have been revised to indicate probable flooding extents based on beach profiles at the spit and progressive flooding behavior.
Low-lying and uncertainty flooding fields all exhibited irregular flooding behavior and produced cut-off flooding extents. These sections have been amended to indicate likely and complete flooding coverages based on topography and wave run-up performance for varied SLR-storm scenarios along the coastal area.
Low-lying and uncertainty flooding fields for certain scenarios exhibited irregular flooding behavior within the lake area, producing cut-off flooding extents. Cut-off sections have been corrected to reflect probable and complete flooding coverage.
The area displays non-progressive flooding behavior and several low SLR scenarios have flooding extents greater than larger SLR scenarios in select small portions of the lake and neighboring coastline. Certain scenarios (including SLR 125 cm with 20 year storm and SLR 150 cm with 100-year storm) exhibited excessively under-predicted flooding extents within the lake area compared to surrounding topography and comparable scenario flooding performance. These extents have been corrected to show probable flooding given the aforementioned evidence. Select areas along the coast with disproportionate flooding extent behavior have been similarly revised to show probable flooding extents based on beach profiles and adjacent flooding performance.
Non-progressive flooding behavior is consistently exhibited at the northern portions of Pacifica for several SLR scenarios (including SLR 025 cm, SLR 075 cm, SLR 125 cm, and SLR 150 cm). Certain scenarios (including SLR 125 cm with 20-year storm event) show likely under-predicted flooding in small portions in this region in comparison to neighboring SLR and storm scenario flooding behavior. Conversely, the flooding extent for SLR 025 cm with 100-year storm event is likely over-predicted in small areas given other scenario flooding performance and local beach profiles. Select areas with disproportionate flooding extents have been corrected to reflect probable flooding extents based on comparable scenarios’ flooding behavior.
Flood extents and depths in some marshes may be under-predicted due to vegetation related elevation-offsets. Non-progressive flooding is displayed in small areas, primarily with larger SLRs and the major storm events.
Flooding displayed in the 5m SLR scenarios may show cut-off behavior is select locations (including north of Suisun City and in select areas in the far western portions of the Suisun region) as flooded extents were so large in this low-lying area it exceeded model boundaries in small sections.
Select tide-controlled marshes in the far eastern portions of the region (east of Honker Bay) appear flooded during King Tide and average condition scenarios, as some control-related levees in this location may not be effectively captured in the model framework.
100-year storm scenarios likely show under-predicted extents in some portions of the region. These areas have been manually adjusted to reflect likely flooding extents more consistent with storm conditions.
Average conditions (i.e. no storm) for lower SLR scenarios may show over-predicted extents in particular marsh areas. These have been amended to show probable flooding behavior in line with given atmospheric and wave conditions.
San Pablo Bay (including Napa and Petaluma Rivers)
The flooding extents in the marshes of this area are under-predicted due to dense vegetation related elevation offsets. Maximum flood potential indicates more probable flooding extents in these locations.
Multiple instances of non-progressive flooding behavior are exhibited in this region. Areas affected included ponds and leveed marshes to the north of San Pablo Bay in vicinity Russ Island, areas surrounding Napa River, and some marshes neighboring the upper portions of Petaluma River and near Novato.
100-year storm scenario flooding extents in vicinity Petaluma River and Novato may be under-predicted, while flooding extents for the 20-year storm scenarios may be under-predicted in the upriver portions (north of China Slough) neighboring Napa River. Particularly disproportionate flooding extents have been manually adjusted to show more probable flooding behavior.
SFO and OAK airports
Very small areas around both San Francisco and Oakland airports display non-progressive flooding behavior with the storm scenarios. This is due to directional differences of the storm waves, wind, and currents in relation the levees in the location.
Foster City and Redwood City
Very small areas in vicinity Foster City and Redwood City show non-progressive flooding behavior.
SLR 000 cm Suite
Differences between average condition flooding extents and visible wet/dry lines are noted along many open beaches and sand spits including: Bodega Bay, Drakes Estero, entrance to Valley Ford, Bolinas, entrance to Rodeo Lagoon, Point Reyes Beach, Muir Beach, Point Pillar, northern Pacifica, and Half Moon Bay State Beach. Probable beach profile changes and variation in tide elevation, surge level, and wave run-up conditions between retrieval of topographic data for generation of DEM and when aerial imagery was taken contribute to these visible conditions.
Small sections of beach near Half Moon Bay State Beach, Pillar Point, Ocean Beach and an area east of Seadrift in Stinson Beach, showed evidence for over-predicted flooding extents for the 100-year event. These sections were revised to reflect likely flooding extents based on beach profiles, flooding performance in adjacent locations, and comparable scenarios’ flooding behavior. Flood extents from 100-year event appear slightly over-predicted and consistently display nonprogressive flooding behavior in areas of coast near Half Moon Bay, Moss Beach, and portions of Lagunitas Creek.
SLR 025 cm Suite
Along portions of coast in vicinity the entrance to Valley Ford flooding extents exhibit non-progressive flooding behavior, and the 1-year and 20-year extents are greater in small areas than the 100-year event. The 20-year event showed evidence of under-predicted flooding extents within Rodeo Lagoon given beach elevations and comparable scenario flood extents. This specific section has been amended to indicate probable flooding extents based on beach profiles and comparative flooding performance. In general, flooding extents for the storm event scenarios of this SLR suite appear slightly over-predicted in relation to comparative SLR 050 cm and SLR 075 cm scenarios in select areas, such as areas near Stinson Beach and portions of Pacifica.
SLR 050 cm Suite
Along portions of Lagunitas Creek flooding extents exhibit non-progressive flooding behavior. Flooding extent for the 100-year event shows slight under-prediction in comparison to other SLR flooding and wave run-up in areas along Thornton Beach, north of Laguna Salada, and small portions of Pacifica. The 100-year event exhibited exaggerated flooding extents along a portion of Half Moon Bay State Beach. This area has been corrected to a probable flood extent based on progressive flooding behavior, beach profile, and neighboring scenarios’ flooding coverage.
SLR 075 cm Suite
Along portions of coast near Pacifica and Rodeo Lagoon flooding extents exhibit non-progressive flooding behavior. Flooding extent for the 20-year event showed evidence for over-predictive behavior along a section of Half Moon Bay State Beach. The section was revised to reflect a more probable extent based on beach profile and commensurate SLR scenarios’ flooding coverage.
SLR 100 cm Suite
In general, flooding extents for the storm event scenarios of this SLR suite appear slightly over-predicted in relation to comparative SLR 075 cm and SLR 125 cm scenarios in select areas, such as areas near Laguna Salada, Half Moon Bay, and Bolinas.
A portion of flooding along Half Moon Bay State Beach for the 20-year event has been amended, as it exhibited disproportionally over-predicted extents in relation to neighboring scenarios’ flooding behavior.
SLR 125 cm Suite
Along small portions of coast near Rodeo Lagoon and Pacifica, flooding extents exhibit non-progressive flooding behavior.
SLR 150 cm Suite
Flooding extent for the 20-year event showed evidence of being disproportionately over-predicted in relation to other SLR and wave conditions along a small portion of Ocean Beach. This area has been corrected to a probable flood extent based on progressive flooding behavior, beach profile, and neighboring scenarios’ flooding coverage.
SLR 175 cm Suite
Along small sections of coast near Valley Ford, Rodeo Lagoon, and portions of Lagunitas and Walker Creeks, flooding extents exhibit non-progressive flooding behavior.
SLR 200 cm Suite
Flooding extents for storm event scenarios of this SLR suite are slightly under-predicted in relation to comparative SLR 175 cm scenarios in select areas, such as sections of coast near Bodega Bay, Muir Beach, Walker Creek, and Half Moon Bay State Beach.
SLR 500 cm Suite
Flooding extent from the 20-year event is greater than the extent from 100-year event along small portions of coast near Pacifica.
Corrected flooding extents for noted areas have coincident flood depths that are inaccurate for the amended location. Similarly, projected flooding depths in regions prone to cut-off flooding behavior (such as Abbott Lagoon or Laguna Salada) likely have under-predicted quantities throughout the area.
Wave maps within some bays show varying footprints
Wind generated waves were not included in these model simulations. The only waves accounted for in the model runs were swell waves generated far offshore. These waves propagate across large distances to the shore and in some cases penetrate through lagoon inlets and into bays (such as Bolinas Lagoon). Because spits and barriers provide protection to lagoons from open coast swell waves, there isn’t much wave energy within these areas during any big event relative to the outer coast. At present, very low wave heights, even those that are within the margin of model error, are shown in the tool whereas all model output points with wave heights near zero have been removed. This sometimes results in large variations of the wave footprint within lagoons and non-systematic transitions between scenarios. It should be noted that these variations are small and have negligible impact on the resulting flooding scenarios.
Updated: July 14, 2013