HABITAT TECHNOLOGIES
SHORELINE COMPENSATORY MITIGATION PROGRAM FOR THE REPLACEMENT OF AN EXISTING SINGLE FAMILY HOMESITE
PARCELS 0321222022 and 0321222015 5220 Marine View Drive City of Tacoma, Pierce County, Washington
prepared for
Mr. Dale A. McLean PO Box 983 2935 Alyaska Highway Girdwood, Alaska 99587
prepared by
HABITAT TECHNOLOGIES P.O. Box 1088 Puyallup, Washington 98371-1088 253-845-5119
February 7, 2014
wetlands, streams, fisheries, wildlife – mitigation and permitting solutions P.O. Box 1088, Puyallup, Washington 98371 253-845-5119 [email protected] Table of Contents INTRODUCTION ...... 1
PROJECT SITE DESCRIPTION...... 1 CRITICAL AREAS ASSESSMENT ...... 1 CRITICAL AREAS ASSESSMENT FINDINGS ...... 3
MOVEMENT CORRIDORS ...... 5 STATE PRIORITY SPECIES ...... 5 FEDERALLY LISTED SPECIES ...... 6 SELECTED DEVELOPMENT ACTION ...... 6
PROJECT RELATED IMPACT AVOIDANCE/MINIMIZATION/RECTIFICATION ...... 6 SHORELINE COMPENSATORY MITIGATION PROGRAM ...... 9
GOAL OF THE SHORELINE COMPENSATORY MITIGATION PROGRAM ...... 9 DESCRIPTION OF THE SHORELINE COMPENSATORY MITIGATION PROGRAM ...... 10 IMPLEMENTATION INSPECTION ...... 11 POST IMPLEMENTATION MONITORING ...... 12 Vegetation Monitoring Sequence Based on a Summer 2014 Implementation ...... 13 VEGETATION MAINTENANCE PLAN ...... 13 REMOVAL OF INVASIVE NON-NATIVE VEGETATION...... 14 CONTINGENCY PLAN ...... 14 TEMPORARY IRRIGATION ...... 14 PLANTING NOTES ...... 14 FINANCIAL GUARANTEE ...... 15 FIGURES ...... 16 APPENDIX A – SHORELINE PLANT LIST ...... 17 APPENDIX B – FINANCIAL GUARANTEE WORKSHEET ...... 19 PHOTOS ...... 20 ATTACHMENT ...... 23
INTRODUCTION
This document details the Shoreline Compensatory Mitigation Program to be implemented as a part of the proposed replacement of an existing single family homesite with a new single family homesite within two existing parcels (Parcel 0321222022 and 0321222015). The existing parcels (project site) are approximately 0.12-acres in total size, irregular in shape, and located along the Marine View Drive Shoreline Area of Commencement Bay, City of Tacoma, Pierce County, Washington (part of Section 22, Township 21 North, Range 03 East, W.M.) (Figure 1). The goal of this Shoreline Compensatory Mitigation Program is to ensure that proposed planned site re-development does not result in adverse environmental impacts to identified critical areas and that the adverse impacts to shoreline habitats associated with prior site management actions are restored and enhanced.
PROJECT SITE DESCRIPTION
The project site is located within residential area along the Marine View Drive Shoreline Area of Commencement Bay. The northern boundary of the project site is formed by Marine View Drive and the southern boundary of the project site is formed by Commencement Bay. The project site is dominated by an existing, presently vacant single family homesite that was initially constructed in 1949. This existing homesite is in need of repair (see photo). Approximately one-third of this existing homesite is supported by treated wood piles and wood blocks that are waterward of the presently defined ordinary high water mark (OHWM). However, the project site is subject to southwesterly wide and wave actions across Commencement Bay and the OHWM appears to have been moving northerly and under the existing homesite for several years. An existing concrete bulkhead is present on the property immediately to the west and a large rock bulkhead is present on the property immediately to the east. This large rock bulkhead appeared present within the project site but was in need of repair to protect the existing or a future homesite.
Directions to Project Site: From SR 509 northbound through the City of Tacoma and the City of Fife continue onto Marine View Drive northbound. Follow Marine View Drive to 5220 Marine View Drive.
CRITICAL AREAS ASSESSMENT
Habitat Technologies completed a series of onsite assessments from March 2013 through March 2014. Habitat Technologies also completed a similar assessment during the early part of 2009. The objective of this evaluation was to define and delineate potential critical areas (wetlands, drainage corridors, and critical habitats) that may be present within or immediately adjacent to the project area. Onsite activities were 1 13029 completed in accordance with criteria and procedures established in the 1987 Manual with 2010 Supplement, guidance provided for the Wash. Manual, the State of Washington Department of Natural Resources (WDNR) Forest Practice Rules (WAC 222-16-030), guidance provided for defining the OHWM by the State of Washington Department of Ecology (WDOE), and the City of Tacoma Chapter 13.11 - Critical Areas Preservation.
The project site and adjacent properties had undergone prior land use manipulations over the past several decades to include vegetation clearing actions, the placement and movement of surface soils, the development of single family homesites, the development of Marine View Drive, the development of City stormwater facilities, the ditching/re-direction of seasonal surface water runoff, the construction of protective bulkheads, and the utilization of the adjacent marine areas for log-storage rafting.
Plant Communities
The entire project site had been altered by prior and ongoing land use actions which have focused on the management of onsite vegetation as a part of the onsite homesite. The area onsite upslope of the identified ordinary high water mark exhibited a limited scattering of shrubs, grasses, and herbs as a result of prior storm event wave actions. Observed species included sapling Himalayan blackberry (Rubus procera), evergreen blackberry (Rubus laciniatus), Scots broom (Cytisus scoparius), quackgrass (Agropyron repens), clover (Trifolium spp.), dandelion (Taraxacum officinale), Canadian thistle (Cirsium arvensis), daisy (Bellis spp.), bull thistle (Cirsium vulgare), pineapple weed (Marricaria lanatus), bluegrass (Poa spp.), and gumweed (Grindelia integrifolia).
The onsite shoreline area waterward of the ordinary high water mark was generally void of vegetation as a result of the areas full exposure to daily tidal wave actions and seasonal storm events. The offsite areas within the Marine View Drive right of way and within the vacant parcel to the east were dominated by dense thickets of blackberries and a scattering of small deciduous trees.
Hydrology
Seasonal hydrology patterns within and adjacent to the project site had been greatly modified by prior land use actions. That portion of the project site landward of the ordinary high water mark was identified to drain well and did not exhibit field indicators typically associated with the retention of seasonal storm event runoff.
The shoreline of Commencement Bay generally formed the southern boundary of the project site. As such, a portion of the project site was subject to daily tidal actions and the actions of seasonal storm events.
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Soils
As with the hydrology patterns discussed above, the character of the onsite soils had also been greatly modified by prior land use actions. The soil between Marine View Drive and the shoreline of Commencement Bay was dominated by native shoreline gravels and sands intermixed with imported fill materials typical of the adjacent hillside. This area appeared to drain well and did not exhibit field indicators of “hydric” soils characteristics.
A large rock bulkhead was identified onsite. However, this bulkhead had been impacted by prior storm events and was in need of repair. As defined by a comparison of the 2013 and 2009 surveys the ordinary high water mark defined in the 2009 survey had moved landward in the 2013 survey.
The soils waterward of the ordinary high water mark were dominated by shoreline gravels, cobble, sands, and chunks of imported materials. The shoreline area was also well littered with woody debris deposited by tidal actions and storm events.
CRITICAL AREAS ASSESSMENT FINDINGS
Wetland determination was based on observations of hydrophytic vegetation, hydric soils, and wetland hydrology in accordance with the 1987 Manual with 2010 Supplement and guidance for the Wash. Manual. As identified in 2009 and again in 2013 through early 2014 no portion of the project site exhibited all three of the established criteria for designation as “wetland” and no portion of the project site exhibited characteristics typically associated with a “stream.”
The portion of the project site waterward of the ordinary high water mark was void of vegetation and dominated by a mixture of gravels, cobbles, sands, and chunks of fill materials. The shoreline area of the project site was subject to daily tidal actions and direct wave actions from tidal storm events across Commencement Bay. As such, the shoreline area also included a variety of woody materials and marine debris.
As a result of the interaction of freshwater from the Puyallup Watershed and the marine areas of Southern Puget Sound the shoreline area of the project site would best be defined as estuarine, intertidal, unconsolidated shore (E2US) (Cowardin et al. 1979).
Because of prior and ongoing land use actions the area of the project site located between Marine View Drive and the shoreline of Commencement Bay was identified to provide very limited usable habitats for wildlife species. This portion of the project site is dominated by an existing homesite, once managed yard, and thickets of invasive shrubs along the Marine View Drive right of way. Observed avian species using the habitats provided by the landward portion of the project site included violet green swallow (Tachycineta thallassina), song sparrow (Melospiza melodia), dark eyed junco (Junco 3 13029 hyemalis), American crow (Corvus brachynchos), starling (Sturnus vulgaris), American robin (Turdus migratorius), rock dove (Columbia livia), and killdeer (Charadrius vociferus). These avian species appeared to be using the landward portion of the project site for limited feed opportunities and to utilize bird feeders provided by adjacent landowners. Killdeer were also identified to nest within the open gravel area within the parcel directly to the east of the project site. The landward portion of the project site also appeared to provide usable habitats for house mouse (Mus musculus), Norway rat (Rattus norvegicus), black rat (Rattus rattus), opossum (Didelphis virginianus), raccoon (Procyon lotor), and garter snake (Thamnophis sirtalis). This portion of the project site did not provide direct habitats for amphibians or fish species.
The hillslope generally to the north of Marine View Drive is dominated by a mixed forest plant community intermixed with single family homesites. This offsite area provides habitats for a variety of wildlife species to include great blue heron (Ardea herodias), red-tailed hawk (Buteo jamaicensis), merlin (Falco columbarius), bald eagle (Haliaeetus leucocephalus), violet green swallow, tree swallow (Tachycineta bicolor), American robin, song sparrow (Melospiza melodia), white crowned sparrow (Zonotrichia leucophrys), black capped chickadee (Parus atricapillus), bushtit (Psaltriparus minimus), dark eyed junco, purple finch (Carpodacus purpureus), brown creeper (Certhia americana), black headed grosbeak (Pheucticus malanocephalus), starling, American crow, Northern flicker (Colaptes auratus), pileated woodpecker (Dryocopus pileatus), Steller’s jay (Cyanocitta stelleri), band-tailed pigeon (Columbia fasciata), opossum, raccoon, deer mouse (Peromyscus maniculatus), shrew (Sorex spp.), coyote (Canis latrans), eastern gray squirrel (Sciurus carolinensis), black tailed deer (Odocoileus hemionus), Norway rat (Rattus norvegicus), Pacific treefrogs (Hyla regilla), and garter snake.
The area waterward of the onsite ordinary high water mark provides a wide variety of habitats for resident and migratory fish and wildlife species. The area immediately waterward is dominated by intertidal and nearshore sub-tidal habitats. Further offshore the habitats include the open water and deep water habitats of Commencement Bay. The list of species associated with the habitats of Commencement Bay is fairly expansive. A very short list includes Chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), chum salmon (Oncorhynchus keta), pink salmon (Oncorhynchus gorbuscha), rainbow/steelhead trout (Oncorhynchus mykiss), cutthroat trout (Oncorhynchus clarkii), native char/bull trout (Salvelinus confluentus), sculpin (Cottus spp.), rockfish (Sebastes spp.), common mallard (Anas platyrhynchos), Canada goose (Branta canadensis), common goldeneye (Bucephala clangula), Western grebe (Aechmophorus occidentalis), shorebirds, terns (Sterna spp.), gulls (Larus spp.), scoter (Melanitta spp.), bald eagle, orca (Orcinus rectipinna), pilot whale (Globicephala scammoni), and dall porpoise (Phocoenoides dalli).
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MOVEMENT CORRIDORS
That portion of the project site between Marine View Drive and the ordinary high water mark of the shoreline of Commencement Bay is well urbanized and does not provide a movement corridor for mammals. However, the hillslope to the north and Commencement Bay to the south do provide migrational and seasonal movement corridors for a wide variety of species. In particular, the shoreline area along Marine View Drive has been documented as a movement corridor for juvenile salmonids during the late winter/spring out-migration period (Miyamoto et al. 1980 and 1985, Puyallup Tribe, unpublished). The project site is within the seasonal migratory pathways for a variety of passerine birds.
STATE PRIORITY SPECIES
Several species identified by the State of Washington as “Priority Species” were observed onsite or potentially may utilize the project site. Priority species require protective measures for their survival due to their population status, sensitivity to habitat alteration, and/or recreational, commercial, or tribal importance.
Game Species: “Game species” are regulated by the State of Washington through recreational hunting bag limits, harvest seasons, and harvest area restrictions. The list of observed or documented “game species” within and adjacent to the project site included a variety of salmonids, a variety of rockfish, a variety of ducks, band-tail pigeon, black tailed deer.
State Candidate: State Candidate species are presently under review by the State of Washington Department of Fish and Wildlife (WDFW) for possible listing as endangered, threatened, or sensitive. This list includes a number of state “game species” to include Chinook salmon, native char/bull trout, rockfish, and steelhead/rainbow trout.
State Sensitive: State Sensitive species are native to Washington, are vulnerable to decline, and are likely to become endangered or threatened throughout a significant portion of its range without cooperative management or removal of threats. Bald eagle is documented to use the habitats associated with the Commencement Bay Area.
State Threatened: State Threatened species are species native to the state of Washington and are likely to become an endangered species within the foreseeable future throughout a significant portion of its range within the state without cooperative management or removal of threats. Loggerhead sea turtle (Caretta caretta) is defined as a state threatened species.
State Endangered: State endangered species are species native to the state of Washington and are seriously threatened with extinction throughout all or a significant
5 13029 portion of its range within the state. Orca and leatherback sea turtle (Dermochelys coriacea) are defined as state endangered species.
FEDERALLY LISTED SPECIES
A number of species documented to use the habitats of Commencement Bay or potentially may use these habitats are listed as endangered or threatened pursuant to the Endangered Species Act. A partial list of these species includes Chinook salmon, native char/bull trout, Orca, leatherback sea turtle, a few rockfish species, and steelhead/rainbow trout.
SELECTED DEVELOPMENT ACTION
The Selected Development Action (see Attachment) for the project site (Parcels 0321222022 and 031222015) focuses on the replacement of the existing homesite with a new single family homesite consistent with the City of Tacoma Comprehensive Plan and local zoning. The homesite replacement would remove a number of existing creosote treated wood piles and creosote treated wood blocks located waterward and landward of the OHWM that are presently supporting the existing homesite. The new homesite would be supported by five (5) new concrete structural piles waterward of the OHWM, six (6) new concrete structural piles located landward of the OHWM, and a concrete wall located along the boundary of Marine View Drive. In addition, the new homesite would face generally southwesterly and the homesite would be elevated to allow daily sunlight to hit the exposed intertidal area under the homesite.
All work waterward of the ordinary high water mark would be accomplished between August 1st and February 1st (outside of the protective “fish window of February 1st through July 31st) to ensure protection of out-migrating juvenile salmonids and other fish species along the shoreline of Commencement Bay. Homesite construction would also remove existing marine debris and garbage along the shoreline. No adverse impacts to critical areas or habitats for critical species have been identified for this proposed homesite replacement. The homesite replacement would not increase the about of existing overwater coverage waterward of the OHWM.
PROJECT RELATED IMPACT AVOIDANCE/MINIMIZATION/RECTIFICATION
As defined by survey and the identified location of the OHWM verified by the Washington Department of Ecology the existing homesite covers 349 square feet of area waterward of the verified OHWM. The area of waterward coverage is within the upper reaches (above mean high water – MHW) of the intertidal shoreline area which provides limited habitats for fish species and is not vegetated. The proposed new homesite would not result in greater than 349 square feet of overwater coverage 6 13029 waterward of the OHWM which is also within the upper reaches (above MHW) of the intertidal shoreline area. In addition, slotted decking material that allows for a minimum of 60% light penetration would also be used in the development of the new homesite.
The replacement of the existing single family homesite would require the removal of the existing homesite structure and 12 existing creosote treated wood piles. Of the total of 12 existing creosote treated piles to be removed nine (9) are located waterward of the OHWM. In addition, a number of creosote treated wood block presently support the existing homesite and are also located waterward of the OHWM. All existing treated wood piles and treated wood blocks shall be removed from the project site, along with all other existing homesite materials. Since the majority of the existing treated wood piles are old and degraded, when full pile removal is not possible the pile removal may require breaking the existing wood pile off a least a few feet below the substrate surface and then refilling the hole with clean sand/small gravel following Best Management Practices.
The proposed new homesite would be supported by 11 new, pre-stressed concrete piles. However, only five (5) of these new concrete piles would be located at or waterward of the OHWM. The use of the pre-stressed concrete piles provides a low- impact, structural support alternative that minimizes potential short-term and long-term adverse impacts to the intertidal area of the project site. Upon the placement of the new concrete piles a replacement homesite would be constructed on these supportive structures. The bottom floor elevation of the replacement homesite would be located at a higher elevation that the existing homesite. This elevation together with the southwesterly aspect to project site would allow natural sunlight to reach the shoreline substrate in an area presently covered by the existing homesite. The addition of natural sunlight to the shoreline would promote the growth of aquatic and terrestrial vegetation and organisms which form the base of the aquatic food wed.
With the exception of a potential minor, short-term encroach onto the upper shoreline area to removal treated wood piles and treated wood blocks with small track equipment, all replacement and repair actions would be completed from the area landward of the OHWM and would further avoid/minimize potential adverse impacts to the shoreline environment. In addition, all materials removed from the project site and all new materials used to create the replacement homesite would exit and enter the project site via the existing driveway connection to Marine View Drive.
All work waterward of the OHWM would be accomplished during lower tidal cycles when the work area is fully exposed. As the high tide recedes a small backhoe, or similar equipment, shall be used to remove the existing homesite, treated wood piles, and treated wood block. The placement of the new concrete piles shall be accomplished using mechanical means during lower tidal cycles. All equipment shall be on tracks rather than rubber tires to provide greater protection of the shoreline substrate. In addition, the size of the equipment shall be held to the minimum possible which would safely complete the removal and replacement actions. Where required to re-fill holes
7 13029 formed by the removal of existing degraded piles, clean sand/small gravel shall be used.
The timing of pile removal and new pile placement shall follow the approved in-water construction window (i.e. no in-water work between February 1st and July 31st) even though the majority of the work would be landward of the OHWM to ensure that there are no adverse effects to juvenile salmonids or other species within or adjacent to the project site. It is presently expected that the removal of the existing homesite, the removal of the existing creosote treated wood piles, and the placement of new homesite supportive piles would be accomplished during a one-week period. There shall be no onsite maintenance or fueling of equipment during the onsite activities. Best Management Practices typical of the type of work being completed shall also be undertaken to protect local water quality and aquatic habitats during all onsite activities. In addition, appropriate silt fencing shall also be used during onsite removal and constructions actions.
Because of the timing of pile and homesite removal along with homesite replacement these actions would avoid or minimize potential impacts to the intertidal habitats. The proposed project is not expected to result in the direct or indirect mortality to juvenile, sub-adult, or adult salmonids or other fish species along the shoreline of the project site. The proposed project may, however, result in a very limited decrease in the short-term production of epibenthic fauna following old pile removal and new pile installation in the area waterward of the OHWM. This limited short-term decrease in the production of epibenthic and attached fauna would be expected to be very minimal and the project area would be expected to become quickly colonize and provide habitats for benthic fauna, aquatic insects, and terrestrial insects.
POTENTIAL IMPACT CONCLUSIONS: The selected homesite redevelopment action follows the mitigation sequencing guidelines provided within City of Tacoma 13.11.206.
Avoidance – The homesite redevelopment shall avoid adverse impacts to the shoreline and aquatic habitats by focusing actions primarily within the area of the existing homesite and within the area landward of the OHWM to the greatest extent practicable.
Minimization – The homesite redevelopment minimizes potential adverse impacts to the shoreline and aquatic habitats by focusing unavoidable encroachments into the shoreline and aquatic habitats only within the very upper tidal areas and does not proceed waterward of the mean high water mark. In addition, were possible slotted decking materials shall be used to allow a minimum of 60% light penetration onto the intertidal substrates. Best Management Practices shall also be followed for all shoreline activities.
Rectification/Mitigation – The homesite redevelopment provides shoreline and aquatic habitats rectification through the removal of existing creosote treated wood piles and creosote treated wood blocks. The new homesite would be
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supported by new pre-stressed concrete piles. The number of new concrete piles to be placed waterward of the ordinary high water (i.e. five) has been held to the minimum necessary to provide safe support for the new homesite. Additional rectification/mitigation actions include the elevation of the new homesite to allow for the intertidal areas below the new homesite to be exposed to daily sunlight; the elevation of the new homesite to allow unimpeded movement of fish, other aquatic organisms, and terrestrial organisms along the shoreline area; and the removal of existing debris along the shoreline.
However, since the overall homesite replacement action shall result in an increase in onsite impervious surface the homesite replacement program includes additional shoreline improvement actions. These shoreline improvement actions focus on the narrowing and relocation of the existing driveway to maximize the area immediately adjacent to the shoreline for the planting of a variety of native trees and shrubs to support shoreline habitats and provide detrital materials to the aquatic environment.
Through the process of impact avoidance, minimization, and rectification/mitigation the overall redevelopment of the homesite would not significantly impact existing critical areas.
SHORELINE COMPENSATORY MITIGATION PROGRAM
GOAL OF THE SHORELINE COMPENSATORY MITIGATION PROGRAM
The GOAL of the selected Shoreline Compensatory Mitigation Program to be implemented as a part of the re-development of the existing single family homesite is to create a viable native plant community along the shoreline of Commencement Bay. The identified shoreline area shall be planted with a variety of native trees and shrubs to provide habitats for local wildlife, support onsite and offsite aquatic and shoreline habitats, and ensure protection of local water quality. To achieve the defined GOAL the following OBJECTIVE and PERFORMANCE CRITERIA are defined:
Objective A. To establish a viable plant community composed of native species along the shoreline area within the project site.
Performance Criterion #A1: As defined by direct counts of installed native trees and shrubs within the mitigation area, 100% of the plants installed during the initial planting phase shall be alive at the end of the first growing season.
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Performance Criterion #A2: As defined by direct counts of installed native trees and shrubs, 80% (cumulative total) of the plants installed within the mitigation area during the initial planting phase shall be alive at the end of the third and fifth growing seasons following initial planting.
Performance Criterion #A3: Invasive shrubs shall not exhibit more than 10% aerial coverage within the mitigation area at the end of the first, third, and fifth growing seasons following initial planting.
DESCRIPTION OF THE SHORELINE COMPENSATORY MITIGATION PROGRAM
As outlined above, the re-development of the new homesite would not result in an increase of overwater coverage waterward of the OHWM than presently existing onsite as a result of the existing homesite. All of the overwater coverage is within the upper reaches (above MHW) of the intertidal shoreline area. In addition, slotted decking material that allows for a minimum of 60% light penetration would also be used in the development of the new homesite. In addition, the existing homesite is supported by creosote treated wood piles (9 of which are waterward of the OHWM) that shall be removed following Best Management Practices and replaced with new concrete supportive piles (5 of which are waterward of the OHWM). The present project does not include the repair of an existing rock bulkhead landward of the identified OHWM as initially discussed.
The homesite re-development would create additional impervious homesite coverage within the project site and would create both pervious and impervious driveway areas within the project site (see project site plan description). As compensation for these increases the Shoreline Compensatory Mitigation Program would establish a native plant community within the shoreline area of the project site. Best Management Practices typical of the type of work being completed shall be undertaken to protect local water quality during all onsite activities. In addition, appropriate silt fencing shall also be used during onsite removal and constructions actions.
1. Old treated pile removal and the placement of new piles shall be completed during low tidal cycles and shall follow Best Management Practices. Protective silt fencing shall be utilized to protect local water quality and capture any work related debris. All treated wood and removed homesite material shall be taken offsite to an approved disposal location.
2. The existing driveway in the eastern portion of the project site shall be narrowed and relocated to generally follow the northern project boundary – adjacent to Marine View Drive. This relocation increases the restorable area immediately adjacent to the shoreline and allows for the onsite treatment of seasonal stormwater runoff from the relocated driveway area prior to entry into the aquatic environment.
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3. The project biologist shall define the onsite area to be restored through the planting of native trees and shrubs. All planting areas shall be clearly marked and protected by appropriate silt fencing.
4. Prior to planting all invasive shrubs, while limited is presence, shall be hand-pulled and removed from the identified shoreline planting areas.
5. The identified shoreline planting areas shall be planted with a variety of native trees and shrubs. The selected native species (Appendix A) would increase species diversity and wildlife habitats (i.e. feeding, nesting, cover), while also enhancing the local water quality through increased biofiltration and increased detrital inputs into the aquatic system.
6. All onsite actions shall be completed only at the direction of the project biologist.
7. Upon the initial completion of the Shoreline Compensatory Mitigation Program an implementation report with associated graphics and photo documentation shall be prepared by the project biologist and submitted to the City of Tacoma.
8. Following City of Tacoma acceptance of the implementation report a five-year monitoring program shall occur to ensure that the onsite actions successfully meet the GOAL, OBJECTIVE, AND PERFORMANCE CRITERIA. This monitoring shall include a contingency plan to remedy created features that do not meet the project's GOAL, OBJECTIVE, and PERFORMANCE CRITERIA.
9. An annual monitoring report shall be prepared for monitoring years one, three, and five. Each monitoring report shall be provided to the City of Tacoma and shall include a summary of the observations (i.e. plant communities, hydrology, wildlife), associated sample plot data, photo documentation, and general comments. Each annual report shall include documentation as to whether or not the project site is meeting or in not meeting the established performance criteria.
IMPLEMENTATION INSPECTION
Essential to the success of the Shoreline Compensatory Mitigation Program is the accurate inspection of onsite activities immediately prior to and during the pile removal/replacement and shoreline planting phases. These activities include pre- construction and pre-planting site inspection, onsite inspection and technical direction during pile removal and shoreline activities, and post-planting site inspection and evaluation. The pre-planting site inspection allows the project proponent, the planting team, and the onsite biologist to evaluate and, if necessary, make minor adjustments in the onsite planting steps. These steps include analysis of project site elevation features, project sequencing and timing, unforeseen required minor modifications to the original planting plan, and the establishment of environmental protections (silt fences). 11 13029
Onsite technical inspection during all shoreline activities shall be implemented by the project biologist. The project biologist shall perform project oversight and address minor unforeseen planting difficulties to ensure that the goal of the mitigation program is met. The project biologist shall be responsible for ensuring that the species and sizes of native plants selected and noted within the planting plan are utilized during planting. If selected native species become unavailable, the project biologist shall consult with City of Tacoma staff for substitute plant species to assure that the intent of the mitigation plan is met. Post-construction site inspection/evaluation shall include the preparation of an implementation report which shall be submitted to City of Tacoma.
All onsite actions shall be completed only at the direction of the project biologist. The project biologist shall completed onsite inspections, verify, and approve the following project tasks (at a minimum):
1. Marking of work areas and access corridors. 2. Removal of existing piles, wood debris, and invasive species. 3. Soil augmentation within planting pits. 4. Nursery stock acceptance. 5. Modification of plant species and sizes. 6. Installation of the temporary irrigation system (if required). 7. Installation of protective fencing and buffer boundary signs.
POST IMPLEMENTATION MONITORING
Following the successful completion of the Shoreline Compensatory Mitigation Program the onsite planting actions shall be monitored for a period of five years. The purpose of this monitoring program is to ensure the success of the selected mitigation program as measured by an established set of performance criteria. Annual reports shall be produced and provided to City of Tacoma following years one, three, and five. These reports shall provide valuable information on the effectiveness of mitigation procedures, along with the overall success of the completed mitigation program. Onsite monitoring shall be completed twice for year one and once a year for the third and fifth growing seasons following initial planting.
The plant species selected shall be obtained as nursery stock. The specific regional nursery may vary according to plant species and nursery availability. The selected species are native and commonly occur in the local area. The plant species prescribed were selected to increase plant diversity, match offsite communities, increase wildlife habitats, and increase shoreline protection. The proposed plant species list (Appendix A) presents the list of species to be planted and the selected size and spacing for initial planting. All onsite activities and plant placements shall be supervised by the onsite biologist.
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The evaluation of the success of the Shoreline Compensatory Mitigation Program shall be based on the performance criteria. The percent survival rate shall be based on combined counts of planted and volunteer desirable species.
1. As a part of each monitoring period the project biologist shall count (100% plant count) the number of live plants which were planted within the shoreline mitigation area. Plants shall be identified to species and observations of general plant condition (i.e., plant health, amount of new growth) are to be recorded for each plant.
2. As a part of each monitoring period the project biologist shall count the number of undesirable invasive plants and estimate the aerial coverage (as if the observer were looking straight down from above) of these invasive plants. Undesirable plants include blackberries, Scot’s broom, tansy ragwort, and other such plants listed in the Washington State Noxious Weed List.
3. As a part of each monitoring period the project biologist shall count the number of desirable "volunteer" plants and estimate the aerial coverage of these plants.
4. As a part of each monitoring period the project biologist shall take photographs that show the shoreline mitigation area. During the five-year monitoring period photos shall be taken in the same direction and at the same location to provide a series of photos. These photos shall show plant growth, plant species, and plant coverage.
5. Upon the completion of each annual monitoring period the project biologist shall prepare a report defining methods, observations, and results along with the date the observations were completed.
Vegetation Monitoring Sequence Based on a Summer 2014 Implementation MONITORING PLANT COMMUNITY MONITORING SUBMITTAL OF MONITORING YEAR REPORT YEAR-1 April 15, and Sept. 15, 2015 Oct. 10, 2015 YEAR-3 Sept. 15, 2014 Oct. 10, 2014 YEAR-5 Sept. 15, 2016 Oct. 10, 2016
VEGETATION MAINTENANCE PLAN
Maintenance of the established shoreline mitigation area plant community may be required to ensure the long-term health and welfare of the environmental functions. The overall objective is to establish undisturbed plant communities that do not require maintenance. Activities may include, but are not limited to, the removal of invasive non- native vegetation and the irrigation of selected areas. Maintenance activities shall include the removal of any trash within the shoreline mitigation area.
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REMOVAL OF INVASIVE NON-NATIVE VEGETATION
As a contingency, should the removal of invasive non-native vegetation become necessary the homeowner shall enact a program to remove the invasive vegetation. Removal actions shall be undertaken at the direction of the project biologist and shall not adversely impact desirable species.
CONTINGENCY PLAN
As a contingency, should the proposed program fail to meet the PERFORMANCE CRITERIA, the homeowner shall undertake and complete required remedial actions.
1. Replacement at the end of the first year following initial planting of all plants that did not survive this first year. Such replanting may also be required prior to the end of the first year if onsite monitoring determines that such planting is required to ensure 100% survival at the end of the first year following initial planting. Such replanting shall be held to the same requirements as the initial planting.
2. Additional planting shall be undertaken if monitoring identified that the 80% survival criteria would not be obtained at the end of the third and fifth monitoring periods.
TEMPORARY IRRIGATION
The homeowner shall ensure that a minimum of one (1) inch of water is supplied each week to each plant within the shoreline mitigation area between May 1 and October 15 for a least the first two years following initial planting. The calculated amount of required water shall include both natural rainfall and temporary irrigation. The need for additional years of irrigation shall be determined based on site conditions and overall plant survival. The amount of water supplied to the shoreline mitigation area shall be increased if onsite monitoring defines such a need.
PLANTING NOTES
All plant materials utilized within the shoreline planting areas shall be native to the southern Puget Sound Region. The onsite biologist shall inspect plant materials to assure the appropriate plant schedule and plant characteristics are met. The homeowner shall warrant that all plants would remain alive and healthy for a period of one year following completion of planting activities. The homeowner shall replace all dead and unhealthy plants with plants of the same specifications.
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FINANCIAL GUARANTEE
A financial guarantee shall be established for the implementation of the shoreline mitigation program and for the five-year monitoring program. The associated costs for the financial guarantee are outlined in the City of Tacoma Bond Worksheet (Appendix B).
Thank you for allowing Habitat Technologies to assist with your project needs. Please contact us with any questions.
Sincerely,
Thomas D. Deming Thomas D. Deming, PWS Habitat Technologies
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FIGURES
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The map features are approximate and are intended only to provide an indication of said feature. Additional areas that have not been mapped may be present. This is not a survey. The orthophotos and other data may not align. Pierce County and Habitat Technologies assume no liability for variations ascertained by actual survey. All data is expressly provided AS IS and WITH ALL FAULTS. Pierce County and Habitat Technologies make no warranty of fitness for a particular purpose. Map Legend
Figure 1 Site Vicinity 0 125 250 ft.
Habitat Technologies 5/31/13 9:20 AM
APPENDIX A – Shoreline Plant List
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SHORELINE COMMON NAME (ID) PROPOSED PLANTING SCIENTIFIC NAME SIZE 5 Pacific madrone 2 gal Arbutus menziesii 8 Shore pine 2 gal Pinus contorta 5 Hawthorne 2 gal Crataegus douglasii 6 Oceanspray 1 gal Holodiscus discolor 10 Baldhip rose 1 gal Rosa gymnocarpa 10 Tall Oregon grape 1 gal Berberis aquifolium 5 Hooker willow 1 gal Salix hookeri 5 Evergreen huckleberry 1 gal Vaccinium ovatum 4 Black twinberry 1 gal Lonicera involucrata 58 TOTAL
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APPENDIX B – Financial Guarantee Worksheet
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Project Name: McLean/Pleasants Homesite Project Owner: Mr. McLean Project Address: 5220 Marine View Drive Owner Address: 5220 Marine View Drive Tacoma Wetland Permit Number: Owner Phone Number: Prepared by: Habitat Technologies
City of Tacoma Bond Quantity Worksheet Performance and Maintenance Plant material Seed/ ounce whips and QTY Plugs QTY 6” pots QTY 1 Gallon QTY 2 gallon QTY ball and QTY Total bare root burlap Trees NA $2.00 NA NA $13.00 $23.00 18 $45.00 $414.00 Shrubs $30.00 $2.00 NA $13.00 40 $23.00 NA $520.00 Herbacous $3.00 NA $2.00 $2.00 $13.00 NA NA $0.00 Ferns & NA NA NA $4.00 $13.00 $23.00 NA $0.00 Ground cover MATERIAL PRICE UNIT QTY Grading $1.50 cy $0.00 6” to 12” soil $2.00 cy $0.00 decompaction Topsoil $38.00 cy $0.00 Vegetable $38.00 cy 10 $380.00 compost delivered and spread Hydroseeding $0.60 sy $0.00 Log 20’ with $500.00 each $0.00 root wad Log 20’ w/o $250.00 each $0.00 root wad Log weir $1,500.00 each $0.00 Erosion fence $1.50 lf 150 $225.00 Chain link $20.00 lf $0.00 fence Wood fence $11.00 lf $0.00 CA signs $3.48 each $0.00 Temporary $2,000.00 acre $0.00 Irrigation Other pond seal clay $50.00 cy Performance subtotal $1,539.00 50% contingency $769.50 Performance total $2,308.50
Plant price estimates are from Sound Native Plants, Storm Lake Growers and Frosty Hollow. Plant material cost includes labor, installation, contractor markup and sales tax.
Page 1 of 2 Project Name: McLean/Pleasants Homesite Project Owner: Mr. McLean Project Address: 5220 Marine View Drive Owner Address: 5220 Marine View Drive Tacoma Wetland Permit Number: Owner Phone Number: Prepared by: Habitat Technologies
City of Tacoma Bond Quantity Worksheet Performance and Maintenance
Type Unit Price Quantity Total Annual $500.00 3 $1,500.00 monitoring. Annual $100.00 5 $500.00 maintenance City review fee $600.14 4 $2,400.56 (should include as-built review) implementation $500.00 1 $500.00 report
Maintenance subtotal $4,900.56 50% contingency $2,450.28 Maintenance total $7,350.84
Page 2 of 2
PHOTOS
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The existing homesite is supported by treated wood and treated wood piles. This shall be replaced as a part of the proposed action.
The existing homesite is supported by old creosote piles and a number of wood chunks. These creosoted materials would be removed as a part of the homesite replacement. 21 13029
The eastern portion of the project site is dominated by a variety of invasive shrubs, herbs, and grasses. Portions of this area shall be restored through the planting of native trees and shrubs.
View from the east along the existing driveway towards the existing onsite home. The driveway shall be narrowed and relocated to the north and then planted with a variety of native trees and shrubs.
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ATTACHMENT
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TECHNICAL REPORT MCLEAN-PLEASANTS PROPERTY, MARINE VIEW DRIVE, TACOMA, WA WAVE FORCE DETERMINATION FOR STABILITY OF PILE FOUNDATION
Technical Report
MCLEAN-PLEASANTS PROPERTY, MARINE VIEW DRIVE, TACOMA, WA WAVE FORCE DETERMINATION FOR STABILITY OF PILE FOUNDATION
Prepared for Owners:
Dale McLean Grace Pleasants 5220 Marine View Drive Tacoma, Washington 98422
This document was prepared for the purpose of establishing force magnitudes applied by waves and debris carried by waves during the one-percent-annual-chance wave storm applicable to existing piles supporting the structure at 5220 Marine View Drive. Results of calculations contained in this Technical Report conform to requirements of a City of Tacoma building permit application. This Technical Report is released under the direction of David Simpson, P .E. This document is not to be used for construction documents.
Prepared by:
David Simpson, P .E.
~ COAST & HARBOR ~ ENGINEERING 110 Main Street, Suite I 03 Edmonds, WA 98020 Ph 425 359.8634 Fax 425 778.6883
TABLE OF CONTENTS
1. Introduction...... 1 1.1. Purpose...... 1 1.2. Background...... 1 1.3. Scope...... 1 2. Project Site...... 2 3. Data...... 3 3.1. V Zone Elevation ...... 3 3.2. Structure...... 4 3.3. Wind...... 6 3.4. Waves...... 7 3.5. Tide ...... 7 4. Analysis...... 8 4.1. Winds ...... 8 4.2. Waves...... 8 4.2.1. Lateral Wave Forces ...... 9 4.3. Debris Loading...... 10 4.4. Breaking Wave Force ...... 10 4.4.1. Wave Uplift Forces...... 11 5. Summary of Forces...... 11 6. References...... 11
FIGURES
Figure 1. Location map of McLean-Pleasants property...... 2 Figure 2. Existing structures and shoreline at site ...... 3 Figure 3. Portion of effective Flood Insurance Rate Map containing project site...... 4 Figure 4. Analysis transects and pile locations at planned redevelopment...... 5 Figure 5. Transect A profile...... 5 Figure 6. Transect B profile...... 5 Figure 7. Browns Point wind rose...... 6 Figure 8. City of Tacoma Coastal Flood Elevation Data (Source: Tacoma Municipal Code) .7 Figure 9. 100-year recurrence interval wave height and direction ...... 8
TABLES
Table 1. Calculated forces and pressures for the 100-yr wave storm ...... 11
Technical Report McLean-Pleasants Property, Marine View Drive, Tacoma, WA Wave Force Determination for Stability of Pile Foundation
1. Introduction
1.1. Purpose This technical report provides background information and coastal engineering analysis of a pile and pile cap system designed to support a house, deck, and garage at the shoreline of Puget Sound. The analysis will serve as the basis for a structural engineering determination of the lateral load capacity of piles and the uplift resistance of a pile cap system that have been designed to support a habitable structure in the wave and tide environment of Commencement Bay.
1.2. Background A single family dwelling at 5220 Marine View Drive, in Tacoma, Washington, known as the Pleasants and McLean property, is being redeveloped by designing and constructing a new residence, garage, and connecting deck that is pile supported at the seaward side. A Site Plan provided by CBAY Consulting, Tacoma, Washington shows the building site to be in the Federal Emergency Management Association (FEMA)-designated Velocity Hazard Zone (V Zone). Preliminary design of the concrete piles to support the new construction show the piles are in the V Zone. The City of Tacoma permitting process relative to flooding hazards in the V Zone places restrictions on the elevation of the lowest horizontal member of the building and structural requirements on the piles to resist forces developed during the Base Flood event. The coastal Base Flood event is by convention the one-percent-chance wave storm, or the 100-year storm from the direction that would generate the highest waves at the site.
1.3. Scope This engineering study derives the hydrodynamic forces that would be developed laterally against piles and pile caps making up the pile foundation of the planned residential addition. The study also develops magnitudes of vertical forces caused by wave crests propagating under the pile supported structure and coming in contact with the pile caps and underside of the floor. The study quantifies lateral loading against piles caused by timber debris which would be expected to be carried by storm waves against the pile foundation. The study provides a qualitative assessment of the shore processes that are relevant to shoreline change or lowering of the ground line in the vicinity of the piles. The study does not analyze the structural strength of the components and connections of the foundation system.
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2. Project Site The property is located at the shoreline at 5220 Marine View Drive on the northeast side of Commencement Bay in Tacoma, Washington. Figure 1 shows the site location with respect to surrounding features. The site is exposed to winds, waves, and tides, but is partially sheltered from the predominant wind directions of this portion of Puget Sound. Sheltering is by the land mass of Browns Point to the north, and the City and Port of Tacoma on the east and south. The shoreline is intensely developed, with residences and water-dependent industrial activities adjacent to and seaward from the site. Log storage and rafting is carried on seaward of the site, the presence of which has an attenuating effect on waves approaching the site from the northwest. The property is situated on glacial marine sediments and fill. The local shore sediments are comprised of mixed sand and gravel. A photograph of the subject property is shown in Figure 2.
Project Site
Port of Tacoma
Figure 1. Location map of McLean-Pleasants property
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Figure 2. Existing structures and shoreline at site
3. Data
3.1. V Zone Elevation The effective Flood Insurance Study (F.I.S.) is dated December 1, 1983. Figure 3 is a portion of the FIRM and shows the site is in a V Zone with elevation +9.0 feet referenced to the National Geodetic Vertical Datum of 1929 (NGVD29). The V Zone represents the area where the velocity of the advancing wave is sufficient to cause structural damage to conventionally framed walls, approximated as the wave swash zone with depth greater than 3 feet. The V Zone elevation represents, to the nearest whole foot, the level to which water may rise within the zone. At this type of shoreline that maximum level is the vertical extent of wave runup on the shore or on a shore structure. That flooding hazard elevation applies to the portion of the project site lying seaward of the +9.0-ft elevation (NGVD29) contour on the effective map. No information could be found in the F.I.S. on the wave height and period with which the V Zone elevation was calculated. The 100-year return-period water level was calculated by FEMA Region 10 for locations in Puget Sound (Weber, personal communication, 2005). The 100-year water level currently in effect for the project site is +9.0 feet NGVD29, interpolated using levels from Des Moines and Tahlequah. Tidal information indicates the flooding hazard zone is determined by tidal inundation and not wave runup. Although tidal inundation is inconsistent with V Zone criteria, the area is mapped as a V Zone and City ordinances are keyed to that designation.
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Figure 3. Portion of effective Flood Insurance Rate Map containing project site
3.2. Structure A Site Development Plan has been provided for this study. Figure 4 is a partial copy of the Plan, which shows the location of each pile relative to the structure and the site. Twelve existing piles are to be replaced with 11 new plumb piles. Also shown are transect locations for developing profiles for coastal engineering analysis. Figure 5 is transect profile A showing designed improvements at the southeastern wall of the garage. Figure 6 is transect profile B showing designed improvements at the location of a pile that supports the house. Drawings provided by CBAY Consulting (the project architect) indicate the piles are 14-inch octagonal concrete pre-stressed piles. We will hereafter refer to seaward-most piles in Figures 5 and 6 as Pile A and Pile B, respectively.
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Figure 4. Analysis transects and pile locations at planned redevelopment
Figure 5. Transect A profile
Figure 6. Transect B profile
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3.3. Wind The focus of this analysis is wind-generated waves. Wave energy distribution by direction is approximately represented by the fetch and wind speed and direction. A wind rose representing the occurrence frequency of wind speed and direction at Browns Point is shown in Figure 7. The relative exposure to waves at the site is indicated by superposing the wind rose with the project shoreline. Moderate wind speeds blow from the longest fetch to the project location. The strongest winds blow from a shorter fetch, but produce higher waves at the site.
Figure 7. Browns Point wind rose
Wind speed statistics for the project area were analyzed for modeling wave growth and transformation. Wind data analyzed were measured at the National Data Buoy Center C-MAN Station WPOW1 at West Point, Washington. The data consists of hourly two-minute averages of wind speed and direction measured 42 feet above land from 1984 through 2008. Wind speeds were sorted for maximum speed from each 10 degrees of azimuth each year and analyzed for exceedance frequency of extreme wind speeds. Wind speed data collected at Sitcum Waterway in Commencement Bay, Brown’s Point, SeaTac Airport, and West Point were analyzed previously by Coast & Harbor Engineering (CHE 2004). Based on a review of this data, it was determined that although the Sitcum measurement site is located closest to the project, it represents a sheltered wind source and could cause underestimation of wave heights at the project location. Topographic and elevation effects would cause measurements at Browns Point to be not representative of winds for wave predictions in Dalco Passage. The
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West Point winds are preferable to the SeaTac winds because West Point is located on Puget Sound, has superior quality data, and better represents the wave-generating winds of this elevation and location.
3.4. Waves Wave measurements of the type and in the location that would be useful for this study are not known to exist. Therefore, waves were modeled numerically and are described in the Analysis section below.
3.5. Tide Tidal datums derived using the NOAA program VDATUM show the mean higher high water level as 11.90 feet above mean lower low water (MLLW) for the project location. The highest observed tide at Tacoma is 14.98 feet above MLLW. Elevations for the current work are referenced to NGVD29, which is also the New Tacoma City Datum. Figure 8 illustrates the relationship of the NGVD29 geodetic datum to the tidal datum, as adopted by the City of Tacoma. The Still Water Level adopted for analysis of wave runup and wave force calculation is +9.0 feet NGVD29.
Figure 8. City of Tacoma Coastal Flood Elevation Data (Source: Tacoma Municipal Code)
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4. Analysis
4.1. Winds Extreme value statistics of the West Point data were calculated by fitting the annual maximum sustained wind speeds recorded at West Point in the period 1984 - 2008 to a Weibull distribution. Wind speed statistics were generated with winds from the sector south through northwest for purposes of initial modeling of controlling waves at the site. Maximum 100-year wind speed from the southern sector (51.5 knots) was applied over Commencement Bay to the direction 180 degrees for simulating design waves for the project site. Winds from two other directions with longer fetch (210 and 320 degrees) were analyzed to find the governing design wave height. Characteristics of modeled waves reaching the Pleasants residence are the basis of the wave force calculations presented below. The resulting wave pattern is described below.
4.2. Waves The two-dimensional model SWAN (Delft University of Technology, 2012) was applied for simulating wave growth, propagation, and transformation with input of the wind field, bathymetry of Dalco Passage and Commencement Bay (provided by Finlayson 2005), and the design water level. The wind direction input to the model was from the 210-degree direction. The pattern of significant wave height and direction that produces the most energetic 100-year wave at the project site is shown in Figure 9. Wave modeling results for a deep water location (-35 feet NGVD29) just seaward of the project site are a significant wave height (Hs) of 3.09 ft and peak period (Tp) of 3.30 sec.
Hsig (ft),180TN_51.5knots_12.5ftNAVD 5244850 5
4.5
4 5241963 3.5
3
5239075 2.5
2
1.5
Northing, m (NAD83, UTM10) m (NAD83, Northing, 5236188 1
0.5
0 5233300 530500 534100 537700 541300 544900 Easting, m (NAD83, UTM10) Figure 9. 100-year recurrence interval wave height and direction
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Waves reaching the project site are expected to be unaffected by log rafts or other features. Wave transformation for calculating forces impacting the project site is based only on depth effects on waves. 4.2.1. Lateral Wave Forces Assessment of wave forces on the pile foundation, and particularly effects of floating debris on the piles, is a necessary part of the evaluation by the structural engineer of the ability of the structure to resist damage during the Base Flood event. Wave height, period, and direction, and the tide level presented above were input to force calculation procedures. The methods and results are presented below. Morison’s equation was applied to evaluate wave loading on octagonal piles using a conservative estimate of coefficients of drag and inertia. The equation is expressed as, 1 D 2 dv F C Dv 2 C x (1) 2 D x m 4 dt
In Equation 1 F is horizontal force on the pile per unit length of the pile, CD and Cm are drag and inertia coefficients, is water density, D is pile diameter, and vx is horizontal velocity. Pile diameter for all piles is given as 14 inches were input to this analysis. Values for CD and Cm were interpolated between those recommended for a square section and a rhombus shaped section, and are 1.8 and 2.3, respectively.
Calculation of Ftot = FDrag + FInertia accounts for the phase difference between drag and inertia components. At the time of occurrence of the maximum drag force FDrag, the inertial term will be zero or near zero. The maximum inertia force FInertia occurs when the water surface elevation is at or close to the static design tide level. To evaluate the maximum total force, the force must be calculated for various time intervals (i.e., phases) during the passage of the wave train. The 100-year wave height, transformed to the site, was input with the pile diameter at each pile location to the calculation procedure to determine forces on each pile.
The values of vx and dvx/dt have been calculated through use of the Stream Function Theory for this modeling case. The water column was divided into 2-in deep layers (bins) and Equation 1 was used to calculate wave force for each bin. The force on the pile was evaluated by integrating all the values for the bins over the length of the pile, according to Equation 2.
N F F(i)z(i) (2) tot i1
where N is the number of bins and z is the height of the bin. The calculated force on piles A and B is 353 and 119 lbf, respectively. The forces on other seaward piles will be bounded by the above two forces. The rest of the piles that are somewhat behind the most seaward piles will be to some degree protected
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from the wave front and it can be assumed that the forces listed for them will not develop to the stated level.
4.3. Debris Loading Floating debris will exert a lateral load on the piles upon impact. Weight of the flood-borne debris is one of the most important factors in determining debris impact load. The force exerted by a drift log impacting a pile (Fi) at the Stillwater elevation was calculated following provisions of FEMA P-55 (2011) using the following Equation:
Fi = WVCDCbCStr (5)
where W is the weight of the object, V is the velocity of water, CD is the drag coefficient, CB is the blockage coefficient, and CStr is the building structure coefficient. In absence of local provisions, both FEMA P-55 and ASCE 7-10 suggest using 1000 lb as weight of the floating debris. The debris impact force was calculated for the worst case scenario, which is the most seaward pile in Section A. The lateral debris impact load on piles A and B was calculated to be 2,353 and 1,564 lbf respectively, which is significantly larger than wave forces.
4.4. Breaking Wave Force Because FEMA is the source of regulations pertinent to coastal flooding hazards, methodology applied by CHE (Section 4.2.1.) has been compared with the FEMA specified methodology contained in Chapter 11 of the Coastal Construction Manual (FEMA P-55) released in 2011, as follows:
2 Fbrkp = 0.5CdbwDHb (6)
where Fbrkp is the drag force acting at the Stillwater elevation, Cdb is the breaking wave drag coefficient, w is the specific weight of water, D is the pile diameter, and Hb is the breaking wave height. The above equation (Equation 8.5 in FEMA P-55) is of the general form of the Morison Equation, a standard procedure that calculates force based on the velocity head of a fluid impinging on the projected area of a solid surface, with a factor to account for the shape effects of the solid body on resistance to flow. Equation 1 above is the complete form of the Morison Equation for wave force, with coefficients that are applicable to the piles at the project site. Separate terms, with applicable coefficients, are in the working equation to account for the instantaneous velocity as well as the acceleration of the fluid past the pile. FEMA P-55 recommends that all wave force calculations for piles should assume a breaking wave condition (which produces greater forces than non-breaking waves). Equation (6) contains a few simplifications to the Morison Equation. The formula substituted the variable wave height for the terms fluid velocity and fluid acceleration that appear in the CHE equation, and contains a different value for the drag
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coefficient. By basing the formula on breaking wave height, it contains implicit assumptions of fluid velocity and water depth and the depth-limited breaking process. Breaking wave height does not have a simple relationship with fluid velocity. The breaking wave force calculated with Equation (6) for piles A and B is equal to 864 and 169 lbf, respectively, acting at the still water level. It is observed that with increasing depth, forces due to breaking waves significantly exceed that of non-breaking waves. The overriding consideration, however, is the load developed during impact by wave-carried debris. This force magnitude was calculated to be about 6 times that calculated assuming wave-only impact with Equation (6). Therefore, piles supporting the over-water structure at the project location that resist log impact will far exceed the ability to withstand wave forces corresponding to breaking and non-breaking waves. 4.4.1. Wave Uplift Forces Tirindelli et al. (2004) and McConnell et al. (2004) established guidelines to evaluate wave forces on bridge decks and beams. This guideline proposes a formulation for calculating quasi-steady vertical force associated with impact of waves on nearshore decks/girders. Here, to estimate forces on pile caps, we will use the formulation for decks. It should be noted that FEMA P-55 does not address wave uplift forces on structural elements. The calculated pressures on the bottom of the pile caps were estimated to be 168 and 75 psf for piles A and B, respectively.
5. Summary of Forces Forces calculated in the above analyses are generated by direct wave impact on the piles that will support the new over-water construction, wave uplift applied by the waves to the underside of the pile-supported deck, and wave-carried debris impact against the piles. Magnitudes at the wave maximum are summarized below in Table 1 for the 100-year wave storm. The term “pounds force” is abbreviated “lbf”.
Table 1. Calculated forces and pressures for the 100-yr wave storm Force Force/Pressure Seaward-most Pile Seaward-most Pile Direction Component in Section A in Section B
Non-Breaking Wave 353 (lbf) 119 (lbf) Lateral Breaking Wave 864 (lbf) 169 (lbf) Debris Impact 2,353 (lbf) 2,353 (lbf) Vertical Uplift Pressure on Pile Cap 168 (psf) 75 (psf)
6. References ASCE. 2010. Minimum Design Loads of Buildings and Other Structures. ASCE Standard ASCE 7-10.
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Coast & Harbor Engineering. October 4, 2004. Point Defiance and Tahlequah Terminals, Coastal Engineering Analysis for Siting Feasibility Study. Prepared for Jacobs Civil and Washington State Ferries. Delft University of Technology, Environmental Fluid Mechanics Section. April 2012. SWAN – User Manual, Version 40.91. FEMA (Federal Emergency Management Agency). August 2011. Coastal Construction Manual Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in Coastal Areas (Fourth Edition) FEMA P-55. Volume I and II. Finlayson, D. 2005. Combined Bathymetry and Topography of the Puget Lowland, Washington State. http://www.ocean.washington.edu/data/pugetsound/ McConnell K.J., Allsop N.W.H. & Cruickshank I.C. 2004. “Piers, jetties and related structures exposed to waves” Thomas Telford, London. Tirindelli, Matteo, Giovanni Cuomo, William Allsop, and Kirsty McConnell. 2004. Physical Model Studies of Wave-Induced Loading on Exposed Jetties: Towards New Prediction Formulae, Proceedings ISOPE 2003, Honolulu, Hawaii. pp. 823-830.
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