6. GEOTECHNICAL, SEA LEVEL RISE AND SHORELINE … · or denser sand deposits interbedded with the younger Bay Mud. The combined thickness of the sand fill and shoal sands varies between

6.2

6.3

6.1

6.4

234

238

233

240

TREASURE ISLAND AND CAUSEWAY GEOTECHNICAL IMPROVEMENTS

YERBA BUENA ISLAND GEOTECHNICAL IMPROVEMENTS

GEOTECHNICAL DOCUMENTS

SEA LEVEL RISE STRATEGY AND SHORELINE IMPROVEMENTS

6. GEOTECHNICAL, SEA LEVEL RISE AND SHORELINE IMPROVEMENTS

TREASURE ISLAND & YERBA BUENA ISLAND MAJOR PHASE 1 APPLICATION 6 - GEOTECHNICAL AND SHORELINE IMPROVEMENTS 231

6.1 GEOTECHNICAL DOCUMENTSThe documents noted below were separately distributed to agency representatives from the Department of Public Works (DPW) and the Department of Building Inspection (DBI) on February, 3, 2015, and they are also included herein as Appendix E.

1. Treasure Island Geotechnical Conceptual Design Report, February 2, 2009 2. Treasure Island Geotechnical Conceptual Design Report Appendix 4, February 2, 2009 3. Treasure Island Sub-phase 1A Geotechnical Data Report; Draft, December 31, 2014 4. Technical Memorandum 1, Preliminary Foundation Design Parameters Treasure Island Ferry Terminal Improvements, January 2, 2015 5. Technical Memorandum 2, Preliminary Geotechnical Design for Sub-Phase 1A Shoreline Stabilization, January 2, 2015 6. Treasure Island Sub-phase 1A Interim Geotechnical Characterization Report; Draft, January 5, 2015


GEOLOGIC SETTING AND DEPOSITIONAL HISTORY

The San Francisco Bay around Treasure Island is underlain by rocks of the Franciscan Complex of the Alcatraz Terrain, consisting mainly of interbedded greywacke sandstone and shale. Under Treasure Island, the Franciscan Complex bedrock is covered by Quaternary sediments and fill to depths ranging from 180 feet under the causeway to as deep as 280 feet near the north end of the island.

The Quaternary sediments at Treasure Island can generally be divided into older, Pleistocene-age marine and alluvial deposits (“Older Bay Deposits”), young Holocene-age marine clay and sand deposits (“Young Bay Mud”), native sandy shoal deposits, and hydraulic sand fills. Under Treasure Island, the Young Bay Mud varies greatly in thickness from about 20 feet near the causeway to more than 120 feet near the northwest corner of the island. The Young Bay Mud varies in thickness because it was deposited on an eroded surface of Older Bay Deposits as sea level rose over the last 12,000 years. Under the southern portions of the island, the Young Bay Mud contains many interbedded layers of fine silty sand making up as much as one-third to one-half of the thickness of the deposit. The sand lenses thin and decreases in number to the north. Near the north end of the island, sand lenses within the Young Bay Mud are very thin or absent.

Extensive windblown sand deposits are believed to have formed across the bottom of San Francisco Bay when it was exposed during low stands of sea level. Just south of Clipper Cove, Yerba Buena Island is mantled with thick (100 to 120 feet) deposits of uniform fine silty sand interpreted to be windblown deposits. The thick sand deposit has been extensively eroded by wave action at the north side of Yerba Buena Island, forming a steep sand bluff that is over 200 feet high and is still periodically shedding sand

into the Bay. The grain-size distribution of windblown sands on Yerba Buena Island is essentially the same as fine silty sands interbedded with Young Bay Mud below Treasure Island. The erosion of the windblown sand from Yerba Buena Island and surrounding areas is likely the source for both the historic sandy shoal deposits, and the fine silty sands interbedded with Young Bay Mud deposits.

Interpretations of the subsurface stratigraphy across the entire island along the north-south direction are illustrated on Figure 6.1

6.2 TREASURE ISLAND AND CAUSEWAY GEOTECHNICAL IMPROVEMENTS

FIGURE 6.1 TREASURE ISLAND GEOLOGICAL NORTH-SOUTH CROSS SECTION


6.2 TREASURE ISLAND AND CAUSEWAY GEOTECHNICAL IMPROVEMENTS

TREASURE ISLAND CONSTRUCTION

Treasure Island and the causeway that connects it to Yerba Buena Island were constructed in the late 1930s by placing over 29 million cubic yards of fine- to medium-grained sand and silty sand over a natural sand shoal and a layer of weak, compressible clay (locally known as Young Bay Mud). The sand was dredged from the shoals south of the island and from other shoals to the east. The dredged sand fill was placed hydraulically. Where the Bay floor was lower than approximately Elevation -6 feet NAVD, a bed of hydraulic fill was placed to raise the Bay floor elevation to -6 feet. A rock dike was then constructed with crest elevations between 2 and 6 feet MLLW, and sand fill was deposited in place until the elevation reached the top of the dike. Another rock dike was placed on the previously constructed dike and filling continued. This process was repeated until the interior elevation reached approximately Elevation 13 feet NAVD. Filling started at the southwest corner and progressively proceeded to the east and north. The rock dikes were faced with riprap constructed with an outboard slope of 1:1 and extended to a final grade elevation of approximately Elevation 14 feet NAVD.

SUBSURFACE STRATIGRAPHY

Subsurface materials at Treasure Island can generally be divided into five geologic units: Sand Fill, Shoal Sands, Young Bay Mud, Older Bay Deposits, and Franciscan Bedrock.

Sand Fill and Shoal Sands As described above, the hydraulic sand fills were deposited directly on native sandy shoals across most of the island footprint. In many Cone Penetration Test (CPT) probes, the contact between the base of fill and top of shoal sand can be approximately distinguished by an increase in interbedded clays and silts. Determination of the base of fill deposits is difficult in many borings. The approximate base of the hydraulic fills can be estimated from the pre-filling bathymetry, plotted on the Cross Sections. The hydraulic fill and shoal sands both consist of loose to medium-dense silty to clayey fine sand with variable fines contents. The base of sand shoal deposits was selected as the contact between loose to medium-dense sand and soft clay or denser sand deposits interbedded with the younger Bay Mud.

The combined thickness of the sand fill and shoal sands varies between approximately 30 and 50 feet.

Young Bay Mud: Onshore Fine-Grained Deposits The sandy fill and shoal materials is underlain by Young Bay Mud consisting of soft to stiff silty clay deposits with occasional interbedded sand layers. The Young Bay Mud thickness varies from 20 to 120 feet with the greatest thickness occurring under the northwest corner of the island. The Young Bay Mud is also deeper under the southeast corner of the island. The Bay Mud is generally normally consolidated and moderately compressible. Where the Young Bay Mud has been consolidated under the weight of the existing fill, it has moderate shear strength.

Young Bay Mud: Soft Offshore Deposits The Young Bay Mud deposits encountered in offshore borings are very soft to soft. The difference between onshore and offshore Young Bay Mud may be due to consolidation effects from the shoal sands and from consolidation due to placement of the island hydraulic fills. Comparison of 1926 to modern bathymetry shows that areas immediately offshore along the west margin of Treasure Island are at nearly the same elevation as 1926. Somewhat further offshore, up to approximately 25 feet of recent sedimentation may have occurred. In Clipper Cove, soft organic clays up to 20 feet thick have accumulated since 1949.

Older Bay DepositsOlder Bay deposits encountered below the Young Bay Mud deposits consist of interbedded very stiff to hard, low to high plasticity clays, silts, and dense to very dense fine silty and clayey sands. In many borings, the deep stiff/dense deposits are described as containing shell fragments or peat, suggesting that they are mainly old Bay or Bay margin deposits. Many borings note color changes from gray or dark gray to light greenish gray or brown or note mottling suggestive of oxidation and weathering. Borings just east of Sub-phase 1A note thick layers of brown gravelly sand and clay that may be of alluvial origin. The variation in thickness of these older sediments is not generally known because only a few exploratory borings on the island have penetrated to bedrock.

BedrockThe Franciscan-Formation bedrock encountered in deep borings has been described as moderately weathered dark gray sandstone and shale. Bedrock was encountered under the south end of the causeway at an elevation of -10 feet NAVD and at an elevation of -180 feet NAVD near the middle of the causeway. Under Treasure Island, bedrock was encountered at an elevation of -255 NAVD. Under the middle of the island bedrock was encountered at an elevation of -271 NAVD.

HISTORIC PHOTO OF TREASURE ISLAND CONSTRUCTION


GEOTECHNICAL CONCERNS

There are three primary geotechnical issues that influence shoreline and site improvements at Treasure Island: liquefaction, settlement, and seismic stability.

Treasure Island was constructed in the late 1930s by placing dredged sand fill over a sand shoal located north of Yerba Buena Island. From a geotechnical perspective, there are three primary issues for any new development at Treasure Island: liquefaction settlement of the Sand Layers, settlements of the Young Bay Mud, and seismic stability of the perimeter and the causeway.

Liquefaction of Sand LayersThe combined thickness of the sand shoal and the dredged sand fill ranges from about 30 to 45 feet. These sands are generally loose to medium dense and are susceptible to liquefaction and seismic recompression settlement. Liquefaction is the reduction of the soil’s strength and stiffness by earthquake shaking.

Settlement of Young Bay Mud Beneath the sands are layers of compressible Young Bay Mud that ranges in thickness across the site from approximately 20 to 140 feet. The Young Bay Mud is generally normally consolidated and the settlement rate due to the weight of the dredged sand fill is now small. However, increases in loads due to placement of new fill or the construction of buildings will initiate a new cycle of consolidation settlements. The Young Bay Mud is underlain by dense to very dense sands and stiff to hard clays, which extend to bedrock at depths of 180 to 270 feet.

Seismic Stability of Perimeter and CausewayThe perimeter of the island and the causeway connecting Treasure Island to Yerba Buena Island are susceptible to earthquake-induced lateral spreading due to liquefaction of the fill and shoal sands. In addition, deeper lateral deformations are expected within the underlying Young Bay Mud layer.

GEOTECHNICAL MITIGATION

Mitigation of Liquefaction and Lateral SpreadingNumerous ground improvement techniques are available to mitigate the potential for liquefaction and its consequences. Some of these techniques considered in Major Phase 1 include Vibro-compaction, Vibro-replacement such as “stone columns”, and Deep Soil Mixing

Mitigation of Young Bay Mud Consolidation SettlementsSurcharging or preloading can be used both to speed primary consolidation under the weight of additional fill and to reduce the settlement caused by subsequent building loads. Surcharging is often coupled with the installation of pre-fabricated vertical drains, commonly known as wick drains, which allow excess pore pressures to drain laterally, shortening the drainage path and taking advantage of the fact that the horizontal permeability of soils is normally much greater than the vertical permeability. The rate of consolidation can be controlled by selecting the type of drain and the spacing between the drains. A horizontal drainage system can also be installed at the ground surface to collect and divert water expelled from the wicks. Wick drain and surcharge test sections can be used to confirm and refine the surcharge design.

Shoreline Stabilization As discussed previously, the shoreline may be susceptible to earthquake-induced deformation and, possibly, deep-seated slope failures in areas of deep Young Bay Mud. Lateral spreading of the island perimeter can be mitigated using vibro replacement methods, or deep soil mixing to improve approximately a zone around the island perimeter.

Causeway StabilizationThe issues potentially affecting the causeway are generally similar to those impacting the island perimeter. Lateral spreading can be mitigated using vibro-compaction or vibro-replacement methods, or deep soil mixing.

Based on historic and recent geotechnical field investigation, a conceptual geotechnical mitigation plan for Treasure Island Major Phase 1 is illustrated in Figure 6.2.


FIGURE 6.2 MAJOR PHASE 1 TREASURE ISLAND CONCEPTUAL GEOTECHINCAL MITIGATION


6.3 YERBA BUENA ISLAND GEOTECHNICAL IMPROVEMENTS

EXISTING GEOLOGIC CONDITIONS

Yerba Buena Island is underlain by Franciscan rock. On the island, the majority of the Franciscan Complex bedrock is covered with unconsolidated windblown sand and alluvial deposits, along with localized areas of artificial fill. Windblown sand deposits in the Bay Area are typically of Pleistocene to Holocene age, and are believed to have formed by Aeolian (windblown) re-working of sandy shoals exposed during low stands of sea-level. The most extensive deposits of unconsolidated sandy soils are found on the windward north and northwest sides of the Yerba Buena Island.

The steep perimeter slopes appear to be the result of a combination of wave erosion and mass wasting, including landslides, slope creep and surficial erosion. Along the western and southern perimeter of the island, the lower slopes are steep, wave-cut bluffs exposing bedrock. The highest steep perimeter slopes occur below Macalla Road, where a 1.5:1 (h: v) slope as high as 240 feet has been eroded into deep deposits of windblown sand, colluvium and landslide debris. Bedrock is exposed only sporadically at the base of this slope, suggesting that unconsolidated deposits may locally extend below sea level. The original island topography has been altered by man-made excavations for roadways and building pads.

CONSTRUCTION HISTORY

Construction of United States Naval facilities began on Yerba Buena Island in the late 1800s and continued through the 1960s. Existing improvements include Coast Guard facilities on the east side of the island, residential units, and utility infrastructure. There are numerous underground utilities, many of which have been abandoned in place, as well as two existing above-ground water storage tanks and two below-grade water reservoirs.

The abutments for the eastern and western spans of the San Francisco-Oakland Bay Bridge (Bay Bridge) occupy considerable portions of the island adjacent to the Yerba Buena Tunnel, which passes through the southeastern portion of the island. Access around Yerba Buena Island is provided by perimeter roadways, including Macalla Road, Treasure Island Drive, and Hillcrest Road. Secondary roads provide access to the residential area on the central portion of the island and to the western abutment

of the eastern span of the Bay Bridge. Construction of access ramps for the eastern span of the Bay Bridge is currently in progress by Caltrans.

The western portion of Treasure Island Drive is supported on the Yerba Buena Island Viaduct, which is a complex of cantilevered steel structures, concrete spans and retaining walls. The viaduct was originally constructed in the late 1930s to provide access

FIGURE 6.3 YERBA BUENA ISLAND GEOLOGIC MAP


from the eastbound Bay Bridge to Yerba Buena Treasure Islands. Portions of the original structures were removed and replaced in the 1960s, 1970s and 1990s. In 2011, the San Francisco Metropolitan Transportation Agency (SFMTA) started the design for the seismic retrofit of the viaduct structures. Construction of the viaduct retrofit is anticipated to commence in 2017.

Level areas for roadways and building pads were constructed by making side hill cuts and fills. Side hill cut slopes are typically inclined between 1:1 and 2:1 (h: v). Many side hill cut excavations are supported by retaining walls that are typically between 5 and 15 feet high, but are locally as high as 20 feet. The majority of existing walls are cast-in-place concrete structures or concrete crib walls. On the southwest slopes of the Island, between Yerba Buena Road and Treasure Island Drive, there is an area of terraced slopes and abandoned foundations associated with past site uses.

SUBSURFACE CONDITIONS

Areas of artificial fill were created by grading associated with past development activities on Yerba Buena Island. Artificial fills on much of the island consist of sliver fills under building pads and roadways. Bay margin fills underlie the Treasure Island Causeway and Coast Guard facilities on the east side of the island. On the upper portions of the island, the existing fills appear to consist of sand and mixtures of sand and rock fragments, derived from local cuts. The Bay margin fills were reportedly constructed with a combination of dredge spoils and possibly excavated material from the Bay Bridge tunnel.

Windblown Sand The bedrock across most of the island is mantled by uncemented to partially cemented silty to clayey sand, (Qs) interpreted to be a combination of wind-blown sand, alluvium and marine terrace deposits (Wagner, 1991, Blake, et al., 2000). Within the proposed development area the Qs deposits consist of relatively uniformly-graded silty sand that appears to be of windblown origin. The thickest deposits of Qs occur on the north side of the island along Macalla Road, where previous explorations and this investigation have encountered up to 120 feet of silty sand. Geotechnical explorations along the Viaduct alignment

have encountered colluvium and silty sand to depths of up to 66 feet. Surface exposures of Qs deposits typically consist of loose light brown silty sand locally overlain by thin organic surface soils. Test pits and borings typically encountered denser, reddish-brown silty sand with weak clay cementation below the surficial sand layers. These clay-cemented layers may represent local development of weathering profiles. Deeper borings in Qs deposits did not encounter uniform cementation in Qs deposits. The consistency of Qs sands ranges from loose near the surface to very dense in deep deposits; however, along portions of Macalla Road, medium dense sands extend to depths of 50 to 100 feet. Where borings have penetrated to bedrock, a layer of stiff rocky clay has locally been encountered at the base of the Qs deposits.

Landslides and Colluvium The steep island perimeter slopes are mantled with sandy colluvium and landslide deposits, as shown on Figure 6.4. The mapped landslides include relatively shallow debris flows and more deep-seated debris slides triggered by a combination of natural processes such as over-steepening of coastal bluffs by erosion, seasonal rainfall, poor drainage associated with runoff from roadways and unstable fills associated with roadway grading. Shallow debris flows have also locally occurred in overly steep cut slopes associated with roadways and building pads in the residential areas of the island. Existing improvements such as roadways and retaining walls around the island perimeter have been damaged by slope movements several times since the late 1940s. The most extensive area of landslide deposits and colluvium occurs along the north island perimeter below Macalla Road, where there are several steep arcuate scarps interpreted to be the heads of older landslides (See Figures 6.2 and 6.3). Landslide activity has also occurred below portions of the Viaduct and on slopes below Hillcrest Drive.

Franciscan Formation The Franciscan Complex bedrock consists of graywacke sandstone, interbedded with siltstone and shale in varying proportions (Blake, et al, 2000). The rocks are slightly metamorphosed, with localized intra-formational tectonic shearing. According to regional and local geologic mapping, the bedrock layering exhibits a relatively consistent northwest strike and typically dips northeast at 20 to 80 degrees. In cut

slope exposures, the Franciscan bedrock is moderately to slightly weathered and appears relatively stable at inclination of as steep as ½:1. In many borings directly below surficial deposits, the upper portions of the bedrock are highly weathered.

GEOTECHNICAL CONCERNS

Geotechnical concerns at Yerba Buena Island are associated with: • Loose surficial soils and undocumented existing fills • Slope stability issues along the existing steep perimeter slopes

GEOTECHNICAL IMPROVEMENTS

Mitigation measures for the above geotechnical concerns may require re-grading to remove weak soils. Potential slope-stability hazards adjacent to the steep northern perimeter slopes can beaddressed with combinations of re-grading to remove weak soils and using setbacks from the existing top of slope when siting new improvements.

Macalla RoadA segment of Macalla Road will be realigned due to its proximity to steep perimeter slopes with potential instability concerns. The new road alignment will be set back from the top of the perimeter slopes by constructing a retaining wall into the existing hillside, removing all the weak soils will be removed and constructing the roadway will be constructed as engineered fill to provide vehicular access to the Bay Bridge, and stable ground conditions for the new mainline utilities.

Water TanksThe three new water tanks will be located on the western facing slopes of YBI, at a super-pad that will be constructed by cutting a retaining wall into the existing hillside. During the grading of the pad, all weak soils will be removed and placed back as engineered fill. The major considerations in foundation design for the water tanks will include the effects of potential differential movement of on-site soils as a result of their shrink-swell characteristics, settlement associated with deep fills, and the distance of the tanks from the top of slopes.


6.4 SEA LEVEL RISE STRATEGY AND SHORELINE IMPROVEMENTSSHORELINE PROTECTION

The existing rock slope at the shoreline will be augmented with additional rock to create elevated protection. The higher berm crest will prevent excessive wave overtopping. Setbacks will allow future rock to be added to raise the elevation as sea level rise requires.

The existing perimeter protection was analyzed for protection against coastal flooding. The recommended perimeter berm crest at different locations around Treasure Island, prior to adding allowance for sea level rise, is the highest of the following three cases: • The one percent annual chance runup elevation; • The maximum elevation at which the one percent annual chance overtopping rate is not dangerous to pedestrians walking along the perimeter; • Two feet above the ten percent annual chance still water level allowing for vessel wakes, which are of short duration and are not required to be included in the coastal flooding analysis, but which could cause nuisance flooding.

The wave runup analysis was performed around the perimeter of Treasure Island with the following criteria for a compound shoreward slope: • 2H:1V below +12 feet NAVD88, • 3H:1V slope above +12 feet, NAVD88.

The resulting crest elevations for specific reaches around TI are shown in Table 6.1.

It is not practical to build a high wall around the project for a design condition that may not happen for several decades, because it will pose a visual obstruction and severely limit public access. Therefore, an allowance of 16-inches of sea level

rise will be built into the initial construction, and the design will be adaptable to higher levels of sea level rise by leaving a significant development setback such that improvements can be made.

The following table show the results of the runup analysis for present conditions and with 16 inches of sea level rise.

ISLAND CENTER

Existing elevations within the Island Center are among the highest on the island and will allow the historic buildings within the district to remain in use through the time frames cited above.

STORM DRAIN OUTFALLS

Stormwater runoff from streets and paved areas on Treasure Island and Yerba Buena Island is currently discharged untreated directly to the Bay through 31 outfalls around the perimeter of Treasure Island and 32 outfalls from Yerba Buena Island. The existing stormwater system will be replaced with a new collection system, which will include gravity pipelines, force

mains, lift stations, pump stations and the reconstruction of existing outfalls. Refer to Section 5.2, Storm Drain, for more information about this system.

Existing outfalls will be replaced, renovated or abandoned in place during each of the four Major Phases. A total of 14 outfalls will be replaced or renovated from existing outfalls on Treasure Island and Yerba Buena Island. The outfalls will penetrate the rock slope into the Bay water.

SEA LEVEL RISE STRATEGY

Estimates of sea-level rise (SLR) in literature vary widely based on the methods used and it is clear that the science of climate change and sea level rise is evolving. It is prudent to develop community designs that can accommodate various levels of SLR over the planning horizon rather than design to a specific report or estimate. Features that have been incorporated into project planning documents and design criteria are summarized below.

• Given the relatively high elevation of over half the island, the decision was made to raise the development footprint to be higher than extreme Bay water levels. All streets and entrances to subterranean parking will be set at an elevation that is 36 inches higher than the Base Flood Elevation (BFE, current 100-yr return period water level). All buildings will have a finished floor elevation that is 42 inches higher than the BFE (includes a 6-inch freeboard). This will ensure that even in the event of deficiencies along the perimeter, habitable structures will not be flooded for water levels 42 inches higher than the BFE. This will put it beyond the 2080 time frame according to the most aggressive sea level rise, and close to or beyond 2100 according to National Research Council (NRC) and Intergovernmental Panel on Climate Change (IPCC) projections.

ExistingElevation

Recommended Crest Elevation for Runup associated with 1% event + minimal overtopping + 16” of SLR

(feet, NAVD88) (feet, NAVD88)

Southwest 10 to 13 14.3

West 10 to 11 14.6

Northwest 11 to 13 15.1

North 12 16.8

Northeast 10 to 11 13.3

East 11 to 13 11.7

South 11 to 13 11.7(Proposed embankment sliope = 3H:1V above +12' NAVD and 2H:IV below +12')Table 6.1 - Recommended Perimeter Crest Elevations

Location

FIGURE 6.1 RECOMMENDED PERIMETER CREST ELEVATIONS


• The perimeter of the island will be geotechnically improved such that existing coastal flooding from various combinations of tides, waves, surges and tsunamis will be mitigated. The crest elevation of shoreline structures will be set at an elevation that is 16 inches higher than what will be needed at the present time, and the design will be adaptable to higher levels of SLR by leaving a significant development setback such that improvements can be made. This will ensure that visual obstructions and public access limitations do not occur for a condition that will not happen for several decades in the future.

• The storm drain system will be improved such that runoff from the island will flow out to the Bay under gravity and not result in flooding of the development parcels. The gravity-drained storm drain system will be constructed with an initial SLR allowance of 16 to 24 inches, which will be adaptable to higher levels of SLR with minimal intervention. It will thus function as a gravity-drained system for several decades, beyond which adaptations will be implemented consisting of installing storm drain pumps.

ADAPTIVE MANAGEMENT

Future SLR will be accommodated within each of the above proposed improvements, such that future improvements will be necessary only after a significant amount of SLR has occurred in the Bay. Due to differences in adaptive capacity, different planning horizons were adopted for the various elements of the project.

Low Adaptive CapacityAreas that cannot tolerate flooding (low adaptive capacity such as urban promenades, building pads, City parks) will accommodate a higher amount of SLR because building structures for example are generally “immovable.”

High Adaptive CapacityPassive use, open space areas where infrequent flooding can be tolerated (high adaptive capacity such as natural areas oriented to habitat creation and passive open space uses) will accommodate a lower amount of SLR, with provisions for

relatively easy adaptations in the future, for example by raising the perimeter. Development setbacks are included along the perimeter to allow these future improvements to be constructed within the island footprint rather than encroaching into the Bay. Funding

A stream of funding will be set up for the community to construct these improvements as part of an Adaptive Management Plan. The Adaptive Management Plan is a project-specific Plan that identifies stakeholders, provides guidance, defines appropriate triggers and management actions, and establishes long-term specific funding mechanism. The Plan will be administered by Treasure Island Development Authority which will have taxing authority and funding responsibility. It will lay out the elements of a monitoring program for incorporating ongoing measurements of SLR from the scientific community into periodic perimeter system inspection reports that will guide the decision making process for future improvements. The Plan will also define specific triggers for action, based on observed changes in sea level.


A1

A2

B1

B2

C

C

C

Major Phase 1 Boundary

1000’ 2000’

N

Elevated Development Lands

Clipper Cove - Ferry Terminal

Island Core (Existing Grades)

KEY

Shoreline Park - Recreational Areas

Northern Shoreline Park - Wilds - Adaptive Habitat Areas

Yerba Buena Island elevationspreclude the need for sealevel rise adapations.


FIGURE 6.4 SEA LEVEL RISE STRATEGY SITE PLAN DIAGRAM



SECTION A1 FERRY TERMINAL

SECTION A2 CLIPPER COVE PROMENADE

SECTION B1 CITYSIDE WATERFRONT PARK TYPICAL CONDITION

SECTION B2 EASTERN SHORELINE PARK

WRU Wave Run-Up

SLR Sea Level RiseBFE Base Flood Elevation

MHW Mean High Water

LEGEND

MHWBFESLRWRU

MHWBFESLRWRU

MHWBFESLR

WRU

MHWBFESLR

WRU

FIGURE 6.5 SEA LEVEL RISE SECTIONS A1, A2, B1 AND B2

EXISTING GRADE

EXISTING GRADE

EXISTING GRADE

EXISTING GRADE



SECTION C NORTHERN SHORELINE PARK - OPTIONS

OPTION A PROTECT

OPTION B CENTRAL MARSH

OPTION C TIDAL MARSH

FIGURE 6.6 SEA LEVEL RISE SECTION C

MHWBFESLR

WRU

MHWBFESLR

WRU

MHWBFESLR

WRU


TREASURE ISLAND & YERBA BUENA ISLAND MAJOR PHASE 1 APPLICATION 7 - LAND TRANSFER AND IMPLEMENTATION 246

Documents

6. GEOTECHNICAL, SEA LEVEL RISE AND SHORELINE … · or denser sand deposits interbedded with the younger Bay Mud. The combined thickness of the sand fill and shoal sands varies between