Exhibit 1 has been replaced with a new Exhibit 1 (attached hereto) to include page 3 of 26, which was missing from the original Exhibit 1 posting.

Transcription

1 Raise Shorelines Request for Proposals (RFP) for Design Services Project No Contract No Addendum No. 2 May 6, 2016 To All Respondents: 1. The RFP is hereby amended as follows: Exhibit 1 has been replaced with a new Exhibit 1 (attached hereto) to include page 3 of 26, which was missing from the original Exhibit 1 posting. 2. All requirements of the original RFP shall remain in full force and effect, except as set forth in this Addendum. 3. All capitalized terms set forth in this Addendum shall have the same meaning as set forth in the RFP being amended hereby. THIS ADDENDUM MUST BE SIGNED BY THE PROPOSER AND ATTACHED TO THE TECHNICAL PROPOSAL WHEN SUBMITTED. NEW YORK CITY ECONOMIC DEVELOPMENT CORPORATION By: Maryann Catalano Title: Senior Vice President, Contracts ACKNOWLEDGED AND AGREED: Name of Proposer: By: Title: Date: 1

2 Protection Projects

3 E.1 INTRODUCTION Sea level rise protection projects and generic measures are discussed in this Appendix. The South Shore of Staten Island erosion control projects and generic measures are covered separately in Appendix F. For Phase 2 of the Study, a conceptual analysis of 85 project sites was conducted and a generic measure at each site was selected to prevent inundation due to sea level rise (SLR) during high tide in Parameters that were utilized during Phase 2 include existing elevations using 2010 LiDAR data, approximate water depths using NOAA Raster Navigation Charts (RNCs), design water level, and property ownership status. These site parameters were used to select variations of generic sea level rise protection measures. Other noted assumptions were used to complete the design of the generic measures and ultimately the cost. Site specific parameters including soil condition, exact water depth, existing ground elevation, and property delineation are to play a role only during detailed design after the Study is complete. Details for the development and design of the generic measures are provided within the following sections. E.2 DESIGN BASIS Given the wide range of shoreline conditions within the study area, a number of assumptions were made to develop a set of generic measures to mitigate inundation during high tide in E.2.1 Vertical Datum Vertical elevations (EL.) of project components and features are referenced to the NAVD88, Geoid12A vertical reference system. The Geoid12A model update allows for the transformation of NAD83 horizontal coordinates to the local NAVD88 vertical reference system based on the most current geodetic observations. All elevations throughout the report are referenced to NAVD88 Geoid12A and presented in feet unless otherwise stated. E.2.2 Bathymetry, Topography and Shoreline Elevation Bathymetric information was based on NOAA Navigation Charts (NOAA chart 12350, 12401, 12337, 12402, 12339, and 12366). Topographic data was gathered from Light Detection and Ranging (LiDAR) data that was collected for approximately 362 square miles of NYC between April 14, 2010 and May 1, 2010 (Sanborn, 2010). While actual existing ground elevations vary, a general assumption for the design of certain generic measures was made for the ground elevation at the shoreline (+4ft NAVD88). The actual project elevation is dependent on the design water level and differs from site to site. E.2.3 Design Water Level At the start of the Study, a Mean higher High Water (MHHW) raster was created with spatial coverage throughout the entire NYC area. The MHHW elevation was established using NOAA s VDATUM tool to vertically transform MHHW to NAVD88. The current tidal datum epoch is and by definition "MHHW is the average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch. Relative sea level rise for all projects is calculated analogue to the study s main goal and includes 32 inches of Sea Level Rise by the year 2050 (relative to the midpoint of the National Tidal Datum Epoch) 1. 1 The 32 inches of Sea Level Rise by 2050 corresponds to the High Estimate (90-percentile) value presented by the New York City Panel on Climate Change 2013 (New York City Panel on Climate Change, 2013). The NPCC Page 1 of 26

4 In addition to the MHHW plus sea level rise level, an additional increase in the water elevation was included to account for the effect of wave overtopping. This data was prepared during Phase 1 of the study (Moffatt & Nichol, 2015). Design water elevations for each project site were calculated by means of superimposing the three data sets: 1) The MHHW elevation; 2) Sea Level Rise (32 inches); and 3) An additional elevation to account for the effect of wave overtopping (Moffatt & Nichol, 2015). These data set rasters developed during Phase 1 were utilized during Phase 2 to determine the design water levels and the project design elevations at each project site. Design water levels are presented for each project on the Phase 2 Project Information Sheets in Appendix H and Appendix J. E.2.4 Design Wave Conditions Wave conditions vary throughout the NYC waters. Depending on the project location, the project may be subject to ocean swell (e.g. Atlantic beaches), wind waves (e.g. Jamaica Bay), ship waves (e.g. Hudson River) or little to no waves (e.g. sheltered basins or canals)... It is assumed that design waves are applicable in the design of the generic measure beach fill and groin and revetment. The projects including generic measures beach fill and groin and revetment are generally located in relatively exposed areas The majority of the shorelines throughout the study area are situated in sheltered locations that experience little to no wave action and wave loads were not investigated in detail during the development the other generic measures. E.2.5 Project Design Elevation The difference between the required design water level (the elevation of MHHW + 32 inches of sea level rise + Waves) and the existing ground elevation yields the required project design height. The required project design height varies from project to project. In Figure E-1 an example of an Elevation Profile is provided for project segment 32K (part of project 32 in the Gerritsen Beach Neighborhood). The left panel displays plan view of Project Segment 32K (depicted as the solid black line) with LiDAR elevation data in the upper left plot and the inundation extent associated with the project segment in blue in the lower left plot. The right panel displays elevations; the upper right panel displays the raw elevation data (labeled LiDAR ) and the filtered Ground Elevation data (labeled Ground Elev ) along the project segment. The elevation in blue corresponds to the design water elevation (labeled MHHW+SLR+Waves ). The lower panel displays the calculated difference between the design water elevation and the Ground Elevation and informs the project Design Height. presents a value of 31 inches by 2050 but uses as a base year. The extra 1 inch (difference between 32 and 31 inch) accounts for the Sea Level Rise between 1992 and Page 2 of 26

5 Figure E-1. Example of the Elevation Profiles Generated for all Project Segments. Required heights for the generic measures typically ranged from 1 feet to 3 feet above the average ground elevation (EL. +4 NAVD88). In general, a generic measure comprised of two components: a main component that was below El. +4 to provide shoreline stability (bulkhead, revetment, etc.) and a secondary component that was above El. +4 to provide protection against sea level rise inundation. E.2.6 Project Life The design life for the generic measures is 30 years. E.3 GENERIC MEASURES To prevent inundation due to sea level rise during high tide in 2050, the following generic measures were investigated: 1. Crown Wall 2. Bulkhead 3. L-Wall 4. Revetment 5. I-Wall Page 3 of 26

6 6. Berm 7. Road Raising 8. Tide Gate 9. Beach Fill with Groins 10. Low Dune The generic measures were assigned to projects based on shoreline type, shoreline condition, property ownership, and land use. Typical application opportunities, constraints, and existing conditions were considered as well. Existing shoreline features for all the project sites were assessed using publically available satellite images. In general, the shoreline features were classified into the categories shown in Table E-1. This table presents the applicability of the generic measures by shoreline type. Prototype/ Existing Shoreline Features Table E-1. Generic Measure Applicability by Existing Shoreline Type Concrete Abutment/ Gravity Wall/ Curb Beach Bulkhead Flood Plane and Inland Areas Natural Shoreline Revetment Roadway Estuary Outlet/Culvert Unprotected Urban Waterfront Crown Wall Bulkhead L-Wall Revetment I-Wall Berm Road Raising Tide Gate Fill with Groins Low Dune E.3.1 Generic Measures Combinations The generic measures were subdivided into two types: 1) a new shoreline structure and 2) a retrofit wall on an existing shoreline structure. New construction measures were assigned where there appeared to be no existing structure that would prevent inundation or an existing structure that appeared structurally unsound to support a retrofit installation. New measures consisted of a shoreline stabilization component below existing ground elevation and a secondary component above existing ground elevation to prevent future high tide inundation. Retrofit measures were assigned to shorelines where there appeared to be an existing structure in sufficient condition to maintain a stable shoreline, but not high enough to prevent inundation in These structures consisted of only a component above existing ground elevation. Table E-2 summarizes all the generic measures and the combination of components. Page 4 of 26

7 Generic Measure L-Wall Crown Wall Bulkhead Berm Table E-2. List of Prototypes and Components Main Component below Secondary Drainage El.+4 Component above El. +4 Existing Revetment or L-Wall New Revetment Existing or New Vertical Crown Wall Structure New Steel Sheet Piling Crown Wall with Concrete Cap Underground Berm/ Above ground berm Excavation Retrofit Structure New Structure Revetment New Revetment L-Wall I-Wall New Steel Sheet Piling Concrete Cap Beach Fill & Beach Fill and Groins Groins Low Dune Existing Beach Low Dune Tide Gate Self-Regulating Tide Gate Road Raising of Existing Roadway Raising E.3.2 Drainage Considerations Structures such as an L-wall, crown wall, bulkhead, revetment, berm, and I-wall have the potential to trap rainfall runoff associated with storms on the landward side, creating an additional flooding hazard. To reduce this additional hazard, drainage infrastructure was considered for such projects. During Phase 2, a uniform cost per linear foot was developed using standard inlet spacing and pipe sizes. Because of the large number and variations of projects, only Phase 3 included a site specific watershed delineation and conceptual design including drop inlets, reinforced concrete pipes (RCP), outfall vaults, outfall pipes and outfall tide valves to be installed along the length of the structure. The design of these structures are detailed in the following sections. E Watershed Delineations In order to lay out conceptual storm drainage designs that could collect runoff from areas currently draining overland directly to the surface water, the size of the direct drainage areas had to be determined. Approximate watershed boundaries were determined using LiDAR topographic data in conjunction with Google Earth to determine the locations of any storm drainage inlets. It was found that most of the direct drainage watersheds were fairly narrow. E Inlet Spacing Since the direct drainage watershed areas were typically long and narrow, inlets were spaced based upon practical considerations, like allowing maximum pipe lengths between access points for maintenance or as necessary for making turns in the pipe system, rather than as necessary to provide adequate flow collection capacity. Inlets were typically spaced 200 feet apart or less. Page 5 of 26

8 Outlet Vault Spacing Regular discharge points from the drainage system had to be incorporated in order to avoid very long pipe runs and thus excessively deep pipes and structures. The assumption was made that the upstream ends of pipe runs would have a minimum of 1.5 feet of cover. This would result in a 15-inch pipe having an invert depth of approximately 3 feet. Assuming a pipe slope of 0.5 percent, the pipe invert would be 5 feet deep on a 400-foot run and 6 feet deep on a 600-foot run. Since a high water table is likely be present in most of the system locations, pipe depths were limited to 5 or 6 feet deep, thus pipe run lengths were limited to between 400 and 600 feet until reaching an outlet vault. Pipe Sizing Pipe where not sized in detail at this conceptual stage of the project. General assumptions were made about widths of direct drainage watershed areas and watershed impervious percentages based on surveys of the project locations. Using these assumptions, it was estimated that a 15-inch pipe on a 0.5- percent slope would reach flow capacity during the 10-year, 5-minute storm peak intensity (crown of the pipe) after collecting runoff from approximately 500 feet of project length. Since the maximum pipe runs until reaching an outlet vault are 400 to 600 feet, 15 or 18-inch diameter pipes along the runs should suffice. An 18-inch pipe diameter for the full run length was assumed during cost estimating to be conservative and to potentially size the system to route larger storm events. Discharge pipes leaving the vaults were assumed to be 24-inch diameter when collecting runoff from long lengths of sea level rise protection structures and were assumed 18-inch when collecting short lengths. Vault Design Vaults were sized based upon assumed invert depths of incoming pipes (5 or 6 feet) and the length and width necessary to house a Tideflex valve that fits a 24-inch diameter outlet pipe. The vault was assumed to include two chambers. The first chamber functions as a junction box for the incoming pipes, with a single outlet opening to the second chamber. Within the second chamber, the Tideflex valve is mounted to the outlet opening from the first chamber. The second chamber thus serves the function of containing the valve. A single 24-inch outlet pipe then leaves the second chamber and discharges to the surface water. The vault dimensions assumed were 6 feet wide by 12 feet long by 8 feet deep. Treatment Opportunities Some of the sites allow for simple and inexpensive opportunities to treat surface runoff before discharging it to the surface water through the construction of stormwater BMPs. This is primarily the case where there is open space near the intended inlet locations. There is a variety of BMP options available, like vegetated swales to direct runoff to the inlets, and basins constructed around the inlets to infiltrate runoff into the soil rather than pipe it to the surface water or to treat it before collections. Types of basins could include stormwater wetlands, bioretention cells using engineered filtration media, or bioretention cells constructed in the in-situ soil. In-situ soil bioretention cells could also vary in design to be drier or more like a wetland area. The primary factors that will determine which of these basin designs is most appropriate for a given site are the depth to the water table, soil hydraulic conductivity and the desired level of aesthetic appeal. E.4 GENERIC MEASURE COSTS Conceptual design and parametric cost estimates were developed for the ten generic measures identified. Quantity takeoffs were estimated from the conceptual design cross-sections. Unit costs for all construction items were established using available cost information for similar existing projects and bottom-up estimates as presented in Table E-3. The quantity takeoffs (per linear foot) together with the construction unit costs define the construction unit costs for each measure. The unit cost per linear foot Page 6 of 26

9 of generic measure was used to compute the Total Project Construction Cost. The project costs were used to develop a cost score, which was used to compute a benefit to cost index for each project. Table E-3 Construction Unit Costs Item Unit Cost Concrete CY $2,000 Steel Sheeting TON $4,500 Architectural Handrail LF $400 Pile Cap Rehabilitation and Epoxy LF $150 Drill and Grout Reinforcement (depending on wall height) LF $90 or $100 Repair Spalled Concrete LF $31 Rehabilitation of Existing Bulkhead (Steel Coating or Concrete LF $1,000 Encasement) Armor Stone TON $200 Filter Stone TON $112 Filter Layer (Groin) SY $15 Soil Backfill CY $35 Excavation (General) CY $40 Excavation for Concrete Formwork and Pour CY $75 Impervious Clay CY $200 Berm Soil CY $55 Geotextile SY $54 Grass/Mat SF $5 Trucked Sand CY $75 Beachfill CY $25 Renourishment (Dune) LF $406 Beach Renourishment (Beach Fill & Groin) LF $2,750 Structural Fill CY $35 Top Course (HMA) TON $120 Vehicular Guardrail LF $80 Maintenance and Protection of Traffic LS $750,000 Self-Regulating Tide Gate EA $62,500 Temp Cofferdam EA $125,000 Drainage costs for Phase 2 were assigned using a uniform $80 per linear foot. Table E-4 presents the unit costs for drainage infrastructure materials used in Phase 3. Table E-4 Drainage Unit Costs Item Unit Cost Inlet/Junction Box EA $3,000 Outfall Vault EA $15,000 Tide Valve EA $4, Inch Pipe LF $52 24-Inch Pipe LF $65 Page 7 of 26

10 A summary of the generic measure designs and costs are summarized in the following sections. In the cross section drawings, the current Mean Sea Level (MSL) elevation is provided for reference (El NAVD88) at the Battery, New York (NOAA gage # ). E.4.1 Crown Wall Generic Design A crown wall is a rectangular reinforced concrete wall constructed on top of a new or existing vertical structure (bulkhead, seawall, curb, or gravity wall) as shown in Figure E-2. Dowels would be grouted in the holes drilled in the existing concrete. The required design heights for projects with crown walls varied from 0.5 ft to over 3 ft. A wall height of 1 feet or 3 feet was included in the generic measure designs. For existing structures on a public property, it was assumed that the existing structures are being maintained to a reasonable extent or otherwise would be the responsibility of the appropriate agency to improve. Nevertheless, repair work associated with the tie-in between the new crown wall and the existing structure was accounted for in the cost estimate. For privately-owned structures, especially in project areas that cover numerous privately-owned buildings, a lack of uniformity among various existing waterfront structures is likely to result in more extensive rehabilitation work prior to dowelling-in the new crown wall. Some deterioration of the existing privately-owned structures is expected, and therefore, substantial repairs such as coating re-application and concrete encasement were assumed and accounted for in the parametric unit cost-estimates. Lastly, project locations with existing architectural handrails were assumed to include the cost of reinstalling a similar handrail. Figure E-2: Crown Wall Cross-Section Unit First Construction Cost Designs and costs are developed for a crown wall height of 1 foot and 3 feet, costs are shown in Table E-5. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit Page 8 of 26

11 markup at 21% as well as drainage costs. Additional costs for architectural handrails ($400/LF) were applied to two projects: East River Esplanade (project 84) and Roosevelt Island (project 83). Table E-5. Crown Wall Parametric Cost Estimate Measure Description $/Linear Foot New 1 ft 1 high concrete wall installed on a new bulkhead $97 New 3 ft 3 high concrete wall installed on a new bulkhead $242 Retrofit 1 ft (Public) Retrofit 3 ft (Public) Retrofit 1 ft (Private) Retrofit 3 ft (Private) 1 high concrete wall installed on an existing structure on public land. Includes cost of repair of the pile cap. 3 high concrete wall installed on an existing structure on public land. Includes cost of repair of the pile cap. 1 high concrete wall installed on an existing structure on public land. Includes cost of rehabilitation of the structure. 3 high concrete wall installed on an existing structure on public land. Includes cost of rehabilitation of the structure. $505 $662 $1,715 $1,872 E.4.2 Bulkhead Generic Design A bulkhead is comprised of a steel sheet piling wall and a reinforced concrete pile cap that terminates at a design elevation of El. +4 (equal to the existing ground elevation for the generic measures). Above El. +4, a crown wall anchored into the pile cap is provided. Backfill would be provided to fill in the gap between the new sheet piling and the existing bulkhead/shoreline. The crown wall would either be 1 foot high or 3 feet high depending on the design elevation, which is location dependent. While their main function is usually to retain and prevent sliding of land, bulkheads if build to elevation can also protect the upland area against inundation due to sea level rise. Bulkheads on poor soil requires longer sheet pilings. Because flood-prone waterfront areas are likely to have poor soil material, it was assumed that the soil in front of the sheet piling is characterized by poor clay. Soil behind the sheet piling is assumed to be backfill of medium sand up to El. +4. Three different existing mudline elevations, El. - 4, El. -9, and El. -14, for shallow water depth, medium water depth and deep water depth respectively; were evaluated. This was done to capture the varying conditions throughout NYC in which bulkheads would be applied as generic measure. The deeper the water (lower mudline elevation), the heavier and longer the sheet piling required. Sheet size and length for the shallow, medium and deep water bulkheads are shown in Figure E-3 through Figure E-5. The relatively small footprint of a bulkhead renders it a preferred solution to urban waterfront areas that are exposed to inundation. At urban waterfront, the shoreline is typically dotted by discontinuous and heterogeneous existing bulkheads that are privately owned by different individuals with limited real estate for new structures. In order to develop a generic measure, as in the case of bulkhead construction, the existing bulkhead is assumed to be non-functional. In fact, privately-owned bulkheads typically have no comprehensive maintenance program in place and hence likely experience some deterioration. Page 9 of 26

12 Figure E-6 shows a bulkhead wall along urban waterfront. Figure E-3 Bulkhead (Shallow Water Depth) Cross-Section Page 10 of 26

13 Figure E-4 Bulkhead (Medium Water Depth) Cross-Section Figure E-5 Bulkhead (Deep Water Depth) Cross-Section Figure E-6 Bulkhead along Urban Waterfront Page 11 of 26

14 Unit First Construction Cost Designs and costs are developed for three bulkhead mudline elevations, El. -4, El. -9, and El. -14 ; the costs for each design, excluding the crown wall, are shown in Table E-6. The cost per linear foot for shallow, medium and deep water bulkheads are approximately $2,752, $5,486 and $7,169, respectively. Cost for the bulkhead crown walls, 1 foot high and 3 feet high, are shown in Table E-6. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21%. Table E-6. Bulkhead Parametric Cost Estimate Measure Description $/Linear Foot Bulkhead - Shallow New bulkhead with steel piles down to -30 ft, NAVD88 $2,752 Bulkhead - Medium New bulkhead with steel piles down to -45 ft, NAVD88 $5,486 Bulkhead - Deep New bulkhead with steel piles down to -65 ft, NAVD88 $7,169 E.4.3 L-Wall Generic Design The L-wall was considered as both a new prototype and a retrofit generic measure and was developed to be installed a new or an existing revetment. An L-Wall is an L-shaped reinforced concrete wall with a shear key at the base as shown in Figure E-7. The L-wall would be founded on top of a layer of filter stone. The filter stone would provide a flat surface for the L-wall and increase the friction between the L- wall and the revetment. The revetment, whereas effective at dissipating wave energy, would not prevent sea level rise inundation since it is porous. An impervious concrete L-wall of 2 feet or 3 feet high, depending on the required height, would be installed on a revetment with an assumed design crest elevation of El. +4. Figure E-7. L-Wall Cross-Section Page 12 of 26

15 In the case of an existing revetment, it was assumed that a maintenance program is in place; the revetment was properly designed and constructed and therefore, fully functional. Some preparation work associated with the integration of a new L-wall to the existing revetment such as excavation was accounted for in the cost. Unit First Construction Cost Designs and costs were developed for an L-wall of 2 feet and 3 feet high. Costs are shown in Table E-7. The cost per linear foot for a 2-ft and 3-ft L-wall are about $1,067 and $1,261, respectively. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21% as well as drainage costs. Table E-7. L-Wall Parametric Cost Estimate Measure Description $/Linear Foot New - 2 feet 2 high L wall installed on a new or existing revetment $1,067 New - 3 feet 3 high L wall installed on a new or existing revetment $1,261 E.4.4 Revetment Generic Design Revetments are onshore structures with the principal function of protecting the shoreline from erosion and typically consist of a cladding of stone, concrete, or asphalt to armor sloping natural shoreline profiles (U.S. Army Corps of Engineers, 2002). They consist of an armor layer, filter layer(s), and toe protection. The filter assures drainage and retention of the underlying soil. Filter-type structures such as stone revetments are preferable where groundwater is part of the erosion process. Toe protection is needed to provide stability against undermining at the bottom of the structure (U.S. Army Corps of Engineers, 1995). Figure E-8. Revetment at Poplar Island Figure E-8 shows an example of a revetment at Poplar Island in Chesapeake Bay, MD (U.S. Army Corps of Engineers, 2002). The generic revetment geometry is comprised of toe protection, rock armor units (i.e. the seaward slope) and a short horizontal crest also comprised of rock as shown in Figure E-9. It was assumed that a revetment with 2-ft diameter armor stone, 5-inch diameter underlayer stone, 1.3-ft diameter toe armor stone and a slope of 2 (Horizontal):1(Vertical) would provide sufficient stability. The protective rock armor Page 13 of 26

16 serves to hold the revetment in place and was assumed to consist 2 layers of rock. The underlayer acts as a drain parallel to the slope to prevent a build-up of water pressure under the armor layer and a filter to prevent the underlying soil from washing out. The 2-layer underlayer would be on top of a geotextile. Toe protection is normally an integral part of the revetment structure and was designed to prevent the structural component from undermining as a result of wave and/or current-induced scour. The toe was comprised of 2 layers of toe armor stone with a width of 3.8 feet. The crest would be 10 feet wide; at El. +4 (equal to the existing ground elevation for the generic measures). Above El. +4, an L-wall founded on top of a layer of filter stone would be provided. The L-wall, would either be 2 feet high or 3 feet high depending on the project location and design elevation. One of the more important variables of the revetment design is the seaward side slope which, together with the crest height, is generally dictated by soil conditions and revetment construction methods. For the purposes of this study, it is assumed that the revetment is founded on reasonably competent soils which do not require foundation/ground improvements. Bottom elevation of the revetment was assumed to be at El Actual elevations will vary widely across the study area, but for Phase 2 of this study it is this considered a reasonable elevation for revetments along interior estuarine shorelines. In order to develop a generic revetment design for Phase 2 it was also assumed that revetments are only applicable to estuarial environments as distinct from open ocean environments. In some locations the design wave will be controlled by exposure to ship wake and in others by locally generated wind-waves. The design waves were assumed to be characterized by a significant wave height, Hs, of 3 ft and a peak spectral period, Tp, of 5 seconds. The revetment, whereas effective at dissipating wave energy, cannot prevent sea level rise induced inundation since it is porous. The impervious concrete L-wall would be installed to prevent inundation due to sea level rise. Revetments, especially the ones with stone armor, integrate well with the natural shoreline, their natural look in particular has a high aesthetic appeal; they also provide a valuable habitat for marine life. Figure E-9. Revetment Cross-Section Page 14 of 26

17 Unit First Construction Cost Cost for the revetment prototype is approximately $3,694/LF as shown in Table E-8. The cost for the revetment do not include the cost for the L-Wall these are presented separately in Table E-7. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21%. Table E-8. Revetment Parametric Cost Estimate Measure Description $/Linear Foot Revetment New Revetment installed to stabilize shoreline $3,694 E.4.5 I-Wall Generic Design An I-wall is defined as a slender cantilever wall, embedded in the ground or in an embankment. The wall rotates when loaded and is thereby stabilized by reactive lateral earth pressures. The I-wall is comprised of a relatively light steel sheet piling and a reinforced concrete cap of 2 feet wide extending above ground elevation. Due to its relatively small footprint and the need to be embedded on both sides, the I-wall is deemed suitable for project location that are not directly at the shoreline, but more inland where there is no existing structure or along an existing roadway embankment. In the situation where an I-wall was to be constructed along an existing roadway embankment, it was assumed the existing structure was wellmaintained and fully functional. A typical cross-section of an I-wall is shown in Figure E-10. The size and length of the sheet piling depends on soil condition. It was assumed the soil was of poor clay. Designs and costs were developed for a low and a high I-Wall equal to an elevation of 2 feet and 3 feet above the existing ground, respectively. Figure E-10. I-Wall Cross-Section Page 15 of 26

18 Unit First Construction Cost Costs for the low and high I-Wall prototypes are $2,060 and $2,229, respectively. Costs are shown in Table E-9. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21% as well as drainage costs. Table E-9. I-Wall Parametric Cost Estimate Measure Description $/Linear Foot I-Wall - Low New I Wall with 2 high concrete cap $2,060 I-Wall - High New I Wall with 3 high concrete cap $2,229 E.4.6 Berm Generic Design Berms are typically constructed by compacting soil into a large earthen structure that is wide at the base and tapers at a 2.5 on 1 slope toward the top as shown in Figure E-11. Grass or some other type of nonwoody vegetation are usually planted on the berm to add stability and aesthetic appeal to the structure. The interior of the berm is a core composed of impervious material, usually clay, to form a watertight barrier to prevent seepage. Berms on poor foundation are subject to instability and settling, and therefore, require deeper excavation prior to construction. For this study, it was assumed the berm is founded on soil of medium quality and 3 feet of material would be excavated from the design existing ground elevation of El. +4 to El. +1. Figure E-11 Typical Berm Construction Due to the berm width and required setbacks, relatively large tracks of real estate are usually required. For this reason, berms are best suited along natural shoreline or parallel to the course of streams and rivers in floodplains away from the developed areas. Figure E-12 shows a typical berm. Page 16 of 26

19 Figure E-12 Berm Cross-Section Unit First Construction Cost Designs and costs were developed for low berms of 2 feet high and high berms of 3 feet high. Costs are shown in Table E-10. A drainage ditch is part of the design of the generic measure and is included within the cost of the structure. The berm, constructed to a uniform top elevation, would have a width varying between 10 and 20 feet. For berm construction, first Parametric Cost Estimate for the low and high berm are $662 per linear foot and $910 per linear foot. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21% as well as drainage costs. Table E-10. Berm Parametric Cost Estimate Measure Description $/Linear Foot Berm - Low New berm 2 high $662 Berm - High New berm 3 high $910 E.4.7 Road Raising Generic Design The road raising generic design for sea level rise projects was developed to account for situations where an existing roadway is vulnerable to saturation with the increasing water table associated with sea level rise. Given a satisfactory subgrade material and depth, it was assumed that the new roadway could be constructed directly on top of the existing roadway to the desired elevation. At a higher elevation built up by structural fill and HMA pavement, a wider shoulder and embankment is required to support the raised road, increasing the roads footprint. A typical section of road raising is provided in Figure E-13. Page 17 of 26

20 Figure E-13: Road Raising Section Unit First Construction Cost Construction costs for raising and repaving a road, including the lump sum cost assumed for the protection and maintenance of traffic during construction is approximately $632 per linear foot and $750,000 lump sum for the maintenance and protection of traffic, which would vary based on location and is shown in Table E-12. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21%. Table E-11. Tide Gate Parametric Cost Estimate Measure Description Construction ($/Project) Road Raising Raised and repaved road constructed 3 above existing road. Lump sum cost for protection and maintenance of traffic. $632/ Linear Foot + $750,000 Lump Sum E.4.8 Tide Gate Generic Design Tide gates typically consist of a series of movable gates that stay open under normal hydrological conditions to allow flow to pass in both directions but are closed when tides exceed the design threshold level. The gates are sliding or rotating steel constructions supported on a frame founded on pile foundations or directly mounted to the existing culvert. Figure E-14 shows a typical self-regulated tide gate (Waterman USA, 2015). In order to develop a parametric cost, it was assumed that the tide gates were a series of four self-regulated tide gates (SRTs) as shown in Figure E-15. Each of the SRT was 6 feet wide by 6 feet high and are supported on steel sheet pilings. Figure E-14. Self-Regulating Tide Gate Page 18 of 26

21 The gate consists of rotating steel construction. Moreover, SRTs are equipped with floats and counter floats that are fully adjustable to meet the required gate closure water levels on a site-specific basis. The gate is placed on the tidal or the exposed side of the estuary. Its float system responds to any tidal change allowing tidal flow exchange up to a predetermined water level and closes to incoming flows when the tide reaches the design threshold elevation. For this reason, SRTs are often a preferred alternative where tidal flow into the estuary is important yet risk due to upland inundation is to be reduced. SRTs can be installed on existing concrete structures Figure E-15. Tide Gate Cross-Section Unit First Construction Cost Construction cost for the tide gates, including steel sheet pilings and construction of a cofferdam for installation is approximately $572,100. The tide gate cost is shown in Table E-12 and includes the costs of the gates and use of a temporary cofferdam. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21%. Table E-12. Tide Gate Parametric Cost Estimate Measure Description ($/Project) Tide Gate Series of four tide gates installed on an existing concrete structure. $572,100 Page 19 of 26

22 E.4.9 Beach Fill and Groin Generic Design Groins are structures that extend perpendicularly from the shoreline. They are usually built to stabilize a stretch of natural or artificially nourished beach against erosion that is primarily due to a net longshore loss of beach material. The effect of a single groin is accretion of beach material on the updrift side and erosion on the downdrift side; both effects extend some distance from the structure. Consequently, a groin system (series of groins) results in a saw-tooth-shaped shoreline within the groin field and a differential in beach level on either side of the groins (USACE 2002). In most cases, groins are sheetpile or rubble-mound constructions. In this study rubble mound stone groins were selected for design. The relatively high initial construction costs with groins may be offset by a reduction in the quantity and frequency of future renourishments over the project life. Figure E-16 shows a groin field at Westhampton, NY. Given the wide range of conditions within the study area, and in order to develop a generic design for the beach fill and groin it was assumed that beach fill and groin would be most applicable to sheltered environments (beaches on the bay or on the backside of the barrier islands). The design waves were assumed to be characterized by a significant wave height, Hs, of 6 ft and a peak spectral period, Tp, of 6 seconds. An assumed erosion rate of 3 feet per year was used. Figure E-16. Groin Field at Westhampton, NY Groin design is summarized as: (1) a horizontal shore section (HSS) extending from a crest elevation of +5 feet NAVD; (2) an intermediate sloping section (ISS) extending from a crest elevation of +5 to +2 feet NAVD at a slope of 1V:18H; and (3) an outer sloping section (OS) extending from a crest elevation of +2 feet NAVD to a bottom elevation of -10 feet NAVD. Figure E-17 depicts the three groin sections and the length of each section. Armor stone sizes increase along the groin with water depth and were determined based on the design wave conditions. The groin trunk consists of side slopes of 1V:1.5H, one layer of armor stone with a nominal weight, W50, of 3 ton, underlayer with 2 layers of stone, core and blanket layer comprised of 9 to 180 pound stone, and geotextile filter. At the groin head a minimum of two armor stone layers (4 ton) are placed. The nominal armor stone weight (W50) was calculated based on the Hudson formula using a stability coefficient, Kd, of 2 along the trunk and a Kd, of 1.8 at the head (USACE, 1984). Typical sections at the HSS, OS, and Head are shown in Figure E-18. Page 20 of 26

23 Figure E-17. Beach Fill and Groin Elevation and Cross-Sections Page 21 of 26

24 Figure E-18. Beach Fill and Groin Cross-Sections Unit First Construction Cost Sand quantities are determined by comparing the existing survey profiles to the design template. Sand quantities are site specific and will vary considerably depending on the existing beach geometry. In order to develop parametric costs it was assumed that a trailer-suction hopper dredge would be used. Unit sand costs may vary considerably based on the type of dredge used and distance to the sediment source (e.g. borrow area). An additional cost associated with the beach fill and groin projects is renourishment costs. Beach fill renourishment is typically required every 10 years to address the continued loss of sand as a result of natural processes. Regular beach renourishment was assumed to be part of the project cost. Total annual costs are estimated using a 30-year project life and the Federal Discount Rate for Fiscal Year 2015 of 3.375%. Table E-13 presents the initial construction cost ($5,307) and renourishment cost Page 22 of 26

25 ($2,750). The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21%. Table E-13. Beach Fill and Groin Parametric Cost Estimate Measure Description $/Linear Foot Beach Fill and Groin New groins with beach fill including renourishment $5,307 (Initial Construction) + $2,750 (Renourishment) E.4.10 Low Dune Generic Design An artificial low dune is typically constructed by placing sediment similar to the native sand on a beach. The deposited dredged sediment would then be reshaped, using bulldozers or other, into a low dune with a toe elevation above the design water level. The design of the generic measure is defined by the dune elevation, the dune width and slope. It was assumed that a dune crest width of 25 feet, height of 2 feet, and dune slope of 1V:5H would provide sufficient stability to a low dune as shown in Figure E-20. Since sand is readily available in beach nourishment projects, low dune construction is most frequently carried out at the same time as beach nourishment. In this study however, the low dune was designed and costed as a standalone generic measure with the assumption that the shoreline of the selected project sites is stable, based on the following two possibilities for the existing project site: 1. There is an existing, gently sloping, sandy beach having a natural source of sand to help sustain the beach. The volume of sand is relatively stable and the beach demonstrates no significant shoreline erosion over time; 2. There is a beach nourishment program currently in place for a gently sloped sandy beach where the shoreline has been eroding at a moderate rate. The volume of sand is technically stable due to the regular renourishments. A low dune alone is a viable solution to sea level rise inundation at only those locations where shoreline erosion is not severe. It is a natural method to raise the elevation of a beach, but is limited in its effectiveness in areas where nourishment/rehabilitation is required frequently. At highly erosive locations such as adjacent to inlets or erosional hot spots, it is often advisable to combine beach fill, dune and groins as discussed in Section E.4.9. Low dunes may be considered as having both ecological and recreational importance. Due to their wide footprint, low dunes are generally used in locations where the use of hard structures is not acceptable and the beach is sufficiently flat and wide. Figure E-19 shows a typical low dune. Page 23 of 26

26 Figure E-19: Typical Low Dune The low dunes were designed to prevent inundation due to sea level rise. It was not designed to reduce risk to the structures and populations behind it by providing a buffer against the increased wave energy and storm surge generated during a coastal storm event. In the event of a coastal storm, damage to the low dunes and subsequent flooding was expected; reshaping the low dunes with bulldozers or other means is assumed to be part of the renourishment program. For the development of the cost estimate it was assumed that a major dune renourishment program would be carried out every 10 years. Figure E-20. Low Dune Cross-Section Page 24 of 26

27 Unit First Construction Cost Sand quantities are estimated assuming a gentle beach slope in the vicinity of the low dune. Sand quantities are site specific and will vary considerably depending on the existing beach width and dune heights. In order to develop parametric costs it was estimated the low dune would be constructed on a flat beach. Unit sand costs may vary considerably based on the type of dredge used and distance to sediment source (e.g. borrow area). The Low Dune generic measure was expected to be constructed using sand trucks and bulldozers. Fill material is typically obtained from borrow areas located in the vicinity of the project area. An additional cost associate with the low dune measure is renourishment costs. Renourishment is typically required every 10 years to address the continued loss of sand as a result of natural processes Total annual costs are estimated using a 30-year project life and the Federal Discount Rate for Fiscal Year 2015 of 3.375%. Table E-14 presents the initial construction cost, $236, and renourishment cost, $406. The Unit First Construction cost presented includes the General Contractor s Overhead and Profit markup at 21%. Table E-14. Low Dune Parametric Cost Estimate Measure Description $/Linear Foot Low Dune $236 $236 (Initial Construction) + $406 (Renourishment) E.5 SUMMARY This appendix present the design of the generic measures to prevent inundation during high tide inundation in For each generic measure a parametric unit cost was established. The parametric construction unit costs for the generic measures are shown in Table E-15. Before a total Unit First Construction Cost is calculated Drainage features are accounted for and 21% is added to account for General Contractor Requirements, Overhead and Profit. Construction costs for drainage features are listed separately for the measures where drainage features are applicable. Drainage costs were approximated at $80 per linear foot. Renourishment cost are also included for the Beach Fill and Groin and Low Dune generic measures. Page 25 of 26

28 Table E-15 Summary of Parametric Construction Unit Costs per linear foot Measure Type Variation Unit Material And Labor Unit Material And Labor (including GCOP) Drainage features Unit First Construction Cost Renourishment Unit Cost Crown Wall Retrofit -Public, Low $351 $425 $80 $505 Crown Wall Retrofit -Public, High $481 $582 $80 $662 Crown Wall Retrofit -Private, Low $1,351 $1,635 $80 $1,715 Crown Wall Retrofit -Private, High $1,481 $1,792 $80 $1,872 Bulkhead Shallow Water, Low Crown Wall $2,354 $2,848 $80 $2,928 Bulkhead Medium Water, Low Crown Wall $4,614 $5,583 $80 $5,663 Bulkhead Deep Water, Low Crown Wall $6,005 $7,266 $80 $7,346 Bulkhead Shallow Water, High Crown Wall $2,474 $2,994 $80 $3,074 Bulkhead Medium Water, High Crown Wall $4,734 $5,728 $80 $5,808 Bulkhead Deep Water, High Crown Wall $6,125 $7,411 $80 $7,491 L Wall Retrofit - Low $816 $987 $80 $1,067 L Wall Retrofit - High $976 $1,181 $80 $1,261 Revetment Low L-Wall $3,869 $4,681 $80 $4,761 Revetment High L-Wall $4,029 $4,875 $80 $4,955 I Wall Low $1,636 $1,980 $80 $2,060 I Wall High $1,776 $2,149 $80 $2,229 Berm Low $481 $582 $80 $662 Berm High $686 $830 $80 $910 Road Raising $632 $765 $765 + $750,000 Tide Gate $473,000 $572,075 $572,075 Beach Fill & Groin $4,386 $5,307 $5,307 $2,750 Low Dune $195 $236 $236 $406 Appendix H presents the total costs for each project and provides measure type(s) and length(s) that are included for each project. E.6 FURTHER WORK The generic measures were developed based on the assumptions as detailed in this appendix. Site specific information such as tie-in to the existing structures, assumed integrity of the existing structures, permit requirements and drainage requirements were considered when refining conceptual designs and cost estimates in Phase 3 for selected projects. Information about ecological impacts, soil conditions, wave conditions, and water depths are items that must be accounted for during detailed design. Page 26 of 26