A.03.09 95pct_FIMI PIR 2024 DDR.pdf

FIMI PIR 2024 DDR May 2024

FIRE ISLAND INLET TO MORICHES INLET

PL 84-99 REHABILITATION PROJECT

OCEAN BAY PARK TO DAVIS PARK

SUFFOLK COUNTY, NY

DESIGN DOCUMENTATION REPORT

US ARMY CORPS

OF ENGINEERS

NEW YORK DISTRICT

May 2024 U.S. Army Corps of Engineers

New York District

Contents

I. PROJECT DESCRIPTION

II. PERTINENT DATA

III. STATUS OF AUTHORIZATION

IV. PARTNERSHIP AGREEMENT

V. POST-GRR CHANGES

VI. ENGINEERING STUDIES, INVESTIGATIONS AND DESIGN

REFERENCES

FIRE ISLAND INLET TO MORICHES INLET

PL 84-99 REHABILITATION PROJECT

OCEAN BAY PARK TO DAVIS PARK

SUFFOLK COUNTY, NY

DESIGN DOCUMENTATION REPORT

I. PROJECT DESCRIPTION

The purpose of the Fire Island Inlet to Moriches Inlet (FIMI) Ocean Bay Park to Davis Park (OBP-DP) project is to provide protection to the mainland and barrier island by reducing the potential for breaching and overwash of the barrier island. Renourishment will reinforce the existing dune and berm system along the island to help ensure the protection of property and natural resources before the next large storm event.

FIMI is a sub-project of the Fire Island to Montauk Point (FIMP) authorization. The Fire Island inlet to Montauk Point (FIMP) project area (Figure 1) extends from Fire Island Inlet east to Montauk Point along the Atlantic Coast of Suffolk County, Long Island, New York; a distance of about 83 miles. It includes the barrier island chains from Fire Island Inlet to Shinnecock Inlet, and a shorefront area east of Shinnecock Bay to Montauk Point. Behind the barrier islands, the back-bay and lands adjacent to Great South, Moriches, and Shinnecock Bays cover over 200 miles of shoreline that comprises the back bay and estuary system. The project area includes portions of the towns of Babylon, Islip, Brookhaven, Southampton, and Easthampton and 12 incorporated villages. Fire Island National Seashore, the Poospatuck Indian Reservation, and the Shinnecock Indian Reservation are all within the project area.

Construction began in September 2021 under Contract 1, which included dredging of Fire Island Inlet, and placement of sand on adjacent beaches. Contract 2, which included dredging Moriches and Shinnecock Inlets, was completed April 2023. Fire Island to Moriches Inlet Stabilization Project (FIMI) was an interim project as a response to Hurricane Sandy and P.L 113-2. FIMI has since been adopted into the overall FIMP Project. FIMI acted as a one-time stabilization project that resulted in an initial placement of 7,163,000 cy of sand as the FIMP Reformulation Study was ongoing.

FIMI includes several contracts: Contract 1 – Smith Point County Park, Contract 2 – Robert Moses State Park to Saltaire, Contract 3A – Fair Harbor to Seaview, and Contract 3B2 – Ocean Bay Park to Davis Park (Figure 2). This DDR focuses on the portion of the FIMI project covered by FIMI Contract 3B (FIMI 3B).

The FIMI 3B portion of the project extends from Ocean Bay Park (STA 455+00) through Davis Park (898+00) (Figure 3), a shoreline length of approximately 44,150 LF, which is 52% of overall length of the FIMI Project (85,100 LF).

FIMI Contract 3B, Ocean Bay Park to Davis Park includes the following communities:

OCEAN BAY PARK

Stations 455+00 to 488+00 Juniper Ave – West Walk

POINT O’WOODS

Stations 488+00 to 530+50 West Walk – Division Street

CHERRY GROVE

Stations 610+00 to 639+00 West Walk – Ivy Walk

FIRE ISLAND PINES

Station 658+00 to 719+50 Sandy Walk – Sail Walk

DAVIS PARK

Station 857+00 to 898+00 5th Walk – Whale Bone Walk

The corresponding initial fill volume for this portion of the FIMI Project is 2,105,604 CY. This area experienced extensive erosion from storm events between September 2023 and January 2024.

Hurricane Lee (September 2023), Tropical Storm Ophelia (September 2023, and a series of extratropical storms in December 2023 and January 2024 caused significant coastal damage along this portion of the project. The damages from these storms were cumulative resulting in the flattening of dunes and erosion of the berm along the Atlantic coastline of Fire Island. Based on reports of damages and verification of damages during a site visit on 23 January 2024, the area spanning from Ocean Bay Park through Davis Park was determined to be significantly damaged and in need of emergency repair.

Two response scenarios were considered: 1) repair of the project to pre-storm conditions; 2) repair and restoring the project to design conditions, including advance fill. The recommended work is response Scenario 2, which includes repair of the project to the original design and advance fill template with 2,003,000 CY of sand, replacement of 11,800 ft of sand fencing, planting of 8 acres of dune grass, repair of 12 elevated timber dune crossover structures, and repair of two vehicular crossovers.

Figure 1 – FIMP Project Area

Figure 2 – Fire Island to Moriches Inlet Project (FIMI HSLRR 2014) with Contracts

Figure 3 – FIMP FIMI Reach PIR Focus Area indicated by black bracket

II. PERTINENT DATA

The recommended work includes repair of the project to the original design and advance fill template, replacement of 11,800 ft of sand fencing, planting of 8 acres of dune grass, repair of 12 elevated timber dune crossover structures, and repair of two vehicular crossovers. The critically needed beachfill will restore the eroded beach between the communities of Ocean Bay Park to Davis Park.

Table 1 – Pertinent Data Length of Berm and Dune 44,150 ft Width of Design Berm 90 ft + Advanced Nourishment Elevation of Berm 8.5 ft NAVD 88 Crest Width of Vegetated Dune 25 ft Elevation of Vegetated Dune 14 ft NAVD88 Dune Slope 1V:5H Design Foreshore Slope 1V:10H Design Offshore Slope 1V:20H Renourishment None Total Initial Fill – Includes design, advance, overfill, and tolerance fill 2,003,000 cy

III. STATUS OF AUTHORIZATION

The FIMI Project was constructed pursuant to the original project authorization, described below. The Fire Island Inlet to Montauk Point (FIMP), New York, Combined Beach Erosion Control and Hurricane Protection Project was authorized by the River and Harbor Act of 14 July 1960, and subsequently modified in accordance with Section 103 of the River and Harbor Act of 12 October 1962. The project authorization was modified again by Section 31 of the Water Resources Development Act (WRDA) of 1974 (P.L. 93-251).

The authorization was further modified by section 502 of the WRDA of 1986 (P.L. 99-662). For portions of Fire Island to Montauk Point, other than the portion from Moriches Inlet to Shinnecock Inlet, Section 103 of the WRDA of 1986 (P.L. 99-662) defined the cost sharing of the first cost to be 65% Federal. In addition, Section 156 of the WRDA of 1976, as modified by Section 934 of the WRDA 1986, provides for continued renourishment not to exceed 50 years from initiation of construction of each of these reaches.

In response to extensive storm damages and increased vulnerability to future events, consistent with the Disaster Relief Appropriations Act of 2013 (Public Law 113-2; herein P.L. 113-2) and recognizing the urgency to repair and implement immediate storm protection measures, particularly in the FIMI reach of the FIMP project, USACE proposed an approach to expedite implementation of construction of necessary stabilization efforts independent of the FIMP Reformulation Study. This approach gained widespread approval from New York State, Suffolk County, NY and the local municipalities, who recognize the extreme vulnerability of the coast, and the need to move quickly to address this need. This resulted in the FIMI Hurricane Sandy Limited Reevaluation Report (HSLRR) in June 2014, recommending the FIMI Stabilization Project is a one-time, stand-alone project with its own independent utility.

Upon completion of the overall FIMP General Reevaluation Report, a Report of the Chief of Engineers was signed, dated July 9, 2020. The recommended plan, contained in the Chief’s Report was authorized for construction in Section 401 (3) of WRDA 2020. This authorized initial construction of the project, and renourishment of the project for 30 years, with sand bypassing and breach response authorized for 50 years.

The U.S. Army Corps of Engineers, New York District, has prepared a Project Information Report (PIR) for the Federal Coastal Storm Risk Management Project, Fire Island Inlet to Montauk Point (FIMP), New York, specifically the Fire Island Inlet to Moriches Inlet (FIMI) Reach under the District Engineer’s authority to commission a PIR, in accordance with Engineer Pamphlet 500-1-1, dated September 30, 2001. References are made to Public Law (PL) 84-99.

P.L. 84-99, Flood and Coastal Storm Emergencies (33 U.S.C. 701n) (69 Statute 186) authorizes the Chief of Engineers, acting for the Secretary of the Army, to provide emergency and disaster assistance under certain situations.

Based on the guidance contained in ER 500-1-1, paragraph 5-20 it is necessary to undertake the proposed project repair, including restoring the project to design conditions, including advance nourishment under P.L. 84-99 since there is an immediate enduring threat from winter nor’easter storms and summer tropical storms to life and the residential property on the barrier island directly behind the project, requiring immediate action. A breach of the barrier island would also negatively impact the back bay residential and commercial properties.

IV. PARTNERSHIP AGREEMENT

A fully coordinated Partnership Agreement package was signed and executed subsequent to the approval of the FIMI Hurricane Sandy Limited Reevaluation Report (HSLRR) and serves as the agreement for this phase of the project. The Partnership Agreement reflects the recommendations of the Hurricane Sandy Limited Reevaluation Report. The non-Federal partner, New York State Department of Environmental Conservation (NYSDEC), has indicated support for recommendations and its desire to execute a Partnership Agreement for the FIMI Stabilization Project TSP by letter dated July 14, 2013. The Partnership Agreement was signed on August 25, 2014.

Under the FIMP Project, a Partnership Agreement reflecting the recommendations of the Fire Island Inlet to Montauk Point Final General Reevaluation Report was signed. The non-Federal partner, New York State Department of Environmental Conservation (NYSDEC), has indicated support for recommendations and its desire to execute a Partnership Agreement for the FIMP Project TSP by letter dated July 14, 2013. The Partnership Agreement was signed on August 6, 2021.

V. POST-GRR CHANGES

Change in design slopes; GRR had 1V:12H foreshore slope to approximately MHW and followed the morphological profile from MHW to existing. During PED, design slopes are 1V:10H foreshore to elevation 1ft NAVD88 (approximately MHW), and 1V:20H offshore slope to existing. This change is based on a value engineering recommendation from FIMI VE study.

Change in construction slopes; GRR had 1V:15H construction slope. During PED, construction slopes were changed to 1V:20H to elevation -1ft NAVD88, and 1V:15H offshore slope to existing. This change is based on best practices from previous FIMP Interim projects (Westhampton, WOSI, FIMI).

Beachfill placement areas will not be the full extent as laid out in the GRR since the surveys showed existing being greater than the design template in some areas of the project. Beachfill will only be placed in the areas that showed a need for fill on the Spring 2024 surveys. Fill in the dune template will be placed as needed at the time of construction as indicated on the plans.

VI. ENGINEERING STUDIES, INVESTIGATIONS AND DESIGN

The design template includes a berm width of 90 ft at an elevation at +8.5 ft NAVD, and a vegetated dune with a crest width of 25 ft at an elevation of +14 ft NAVD (+15 ft NGVD). It also includes a dune slope of 1V:5H and a foreshore slope of 1V:12H.

This template was identified as having the highest net benefits and provides for approximately a 50-yr level of protection. The template is applied to the areas with the greatest potential for damages to oceanfront structures and will be constructed in Davis Park to Ocean Bay Park. Figure 4 shows a typical design as developed in the HSLRR.

Figure 4 – Typical Beachfill Design Section (GRR Design)

A. Berm Placement – A topographic and bathymetric survey was taken in March/April 2024 and was then developed into a three-dimensional LandXML file of the existing conditions. The LandXML was imported into Autodesk AutoCAD Civil 3D 2020 to produce an existing conditions surface. A three-dimensional surface was also created for the “design” template that included advance nourishment and uses the project reference line as the horizontal alignment. The landward slope of the design fill template was adjusted along the length of the project area to account for existing backshore conditions. The triangle volume function of Autodesk AutoCAD Civil 3D 2020 Civil3D was then used to determine the cut and fill volumes between the “design” template surface and the “existing conditions” surface. Autodesk AutoCAD Civil 3D 2020 Civil3D reports a “cut”, “fill”, and “net” volume difference. Since no reshaping of the existing beach is authorized in order to achieve the design template, only the “fill” volume difference is reported.

Advance nourishment fill is a sacrificial quantity of sand which acts as an erosion buffer against long-term and storm-induced erosion as well as beachfill losses cause by “spreading out” or diffusion. The required advance berm width was computed based on representative erosion rate shown in Table 2.

The representative erosion rate was calculated based on the historical sediment budget, volumetric changes in measured profiles between 1988 and 2012, the performance of recent beach fill projects on the island, and anticipated beachfill spreading.

The advance nourishment berm width is the representative erosion rate (ft/yr) from the MIDU (Updated Middle Alignment), the beachfill alignment used for the project, column of Table 2 below, multiplied by four for a typical four-year renourishment cycle.

Table 2 - Advance Berm Widths

Project Design Reaches

Length (ft)

MIDU Representative Erosion Rate (ft/yr)

Advanced Nourishment Berm Width (ft)

Ocean Bay Park to Point O’ Woods

GSB-2D 7,400 5 20

Cherry Grove GSB-3A 3,000 0 0 Fire Island Pines GSB-3C 6,400 10 40

Water Island GSB-3E 1,200 1 4 Davis Park GSB-3G 4,200 12 48

Since the design profile below MLW cannot be directly constructed, a construction template will be utilized for placement. The construction template contains the same total initial fill as the design profile with advance nourishment but will have an approximate 1 on 20 foreshore slope and 1 on 15 offshore slope. Once fill is placed within this template, natural wave action on the beach will result in an onshore of 1 on 12 slope to MLW, achieving the design profile (Figure 4). An additional 0.5 ft vertical tolerance (to account for constructability concerns) is added to the construction template.

This tolerance is added to the volume developed from the comparison between the design template and existing conditions to arrive at the required construction quantity.

The required construction quantity for construction for the project area is 2,003,000 cy.

B. Dune Placement – The dunes will be constructed with a 1V:5H slope on both landward and seaward sides. Landward dune slopes will intersect with the existing landward topography. The dunes will be vegetated with 18” spacing on the crest and both the seaward and landward slopes throughout the entire length of the project.

C. Pedestrian Dune Crossings and Vehicular Crossings – The project will include repair of 12 elevated Timber Dune Crossings, either ADA Compliant, or Non- ADA Compliant, as shown on plan sheets. There will be repairs to two Vehicle Access Crossings as shown on plan sheets.

D. Borrow Area – The sand required for initial construction will be obtained from offshore borrow site 2C (Figure 5). Borrow Area 2C is located approximately 2 miles offshore of Point O’ Woods and contains a total estimated 9 million cy of compatible sediment. Sand will be dredged offshore by a hopper dredge, shipped to a pump out location, and placed hydraulically on the beach. Earth moving equipment, such as dozers and excavators, will be used for final shaping.

Although sediment analysis was conducted no later than 1997, sand from borrow area 2C has been previously used for construction at this site an at a site just to the west. The grab samples taken during the construction process confirm that the borrow area is suitable for use on Fire Island.

Further details on sediment analysis of Borrow Area 2C can be found in the FIMP GRR Borrow Area Appendix.

USACE is in full support of using adaptive borrow area management practices, should any other than negligible impacts be quantified or confirmed. These practices can include dredging in shallow lifts, changing the order the ridge borrow areas are accessed during the project life, allowing further time in between operations at these areas to allow maximization of infilling, minimizing surface area impacted in a borrow area, etc.

USACE welcomes further collaboration on future research from the community of coastal sedimentation scientists. Additional information can be found in the FIMI HSLRR Borrow Area Appendix and in Appendix A of this report. References found in the FIMI HSLRR Borrow Area are included in this DDR.

Figure 5 – Borrow Area 2C Location

E. Sea Level Rise – This contract is emergency PL84-99 repair work due to storm damage that occurred over the 2023-2024 storm season to a previously constructed FIMI Contract. Sea level rise considerations are taken from the FIMP Project to which this FIMI work will be incorporated into in the future. The relative sea level rates considered a low rate based on an extrapolation of the historic rate, and intermediate and high rates which include future acceleration of the eustatic sea level change rate. These rates of rise correspond to 0.64 feet, 1.12 feet, and 2.65 feet from 2021 – 2071 under the low, intermediate, and high rates of USACE RSLC projections, respectively.

The first FIMP contract, constructed in 2021, marks the start of monitoring sea level change for the FIMP project. There are multiple contracts to FIMP’s “initial construction” because it stretches along ~83 miles of the Atlantic Coast of NY; starting to monitor sea level change after initial construction was completed would result in not accounting for change in that duration, therefore possibly under designing the project if sea levels are rapidly rising.

The design accounts for 1ft of relative sea level rise based upon the middle of the current tidal epoch – year 1992. Based upon the analysis of variation of monthly mean sea level, the determined project adaptations will start when the five-month average MSL observations exceed the threshold value plus a buffer for a sequential duration of six months or more. The metric takes into account both variation in mean sea level and a time window and gives the trigger point referenced in the study a tangible value.

As part of the physical monitoring aspect of the monitoring and adaptive management plan (MAMP), the Engineering Division (EN) FIMP MAMP team will track the tidal gage at Sandy Hook for the five-month average MSL observations twice a year and report annually, until the threshold is exceeded. At that point, the team will track the data monthly, and if the threshold continues to be exceeded for a sequential duration of 6 months, the adaptation measures will go into the pre-engineering and design phase. Brief memoranda of the data collection will be compiled, distributed to the Adaptive Management Team, and kept as part of the project records.

REFERENCES

Coastal Planning & Engineering of NY, PC, 2013. “2009 Fire Island Beach Renourishment Project Post- Sandy Storm Report”, prepared for Sponsoring Communities on Fire Island, New York.

Hapke, C. J., Brenner, O., Hehre, R., Reyonlds, B. J., 2013. “Coastal Change from Hurricane Sandy and the 2012-13 Winter Storm Season: Fire Island, New York”, Open- File Report 2012-1231, U.S. Department of the Interior, U. S. Geological Survey.

John Milner Associates. 2000. Cultural Resources Baseline Study, Fire Island to Montauk Point, Suffolk County, New York, Reformulation Study. Prepared for the US Army Corps of Engineers.

Larson and Kraus, 1989. SBEACH: Numerical Model for Simulating Storm-Induced Beach Change; Report 1, Empirical Foundation and Model Development. TR CERC-89-9, USACE.

Sanders and Kumar, 1975. “Evidence of Shoreface Retreat and in Place Drowning during Holocene Submergence of Barriers, Shelf off Fire Island, New York,” Geological Society of America Bulletin, Volume 86.

U.S. Army Corps of Engineers, New York District (USACE-NAN), 1999. “Barrier Island Breach and Overwash Impacts, Position Paper for Fire Island to Montauk Point Storm Risk Management Reformulation Study,” U.S. Army Corps of Engineers, New York District.

U.S. Army Corps of Engineers, New York District (USACE-NAN), 2018. “Fire Island Inlet to Moriches Inlet Contract 3B2 Design Documentation Report”, U.S. Army Corps of Engineers, New York District.

U.S. Army Corps of Engineers, New York District (USACE-NAN), 2021. “Fire Island Inlet to Montauk Point Contract 2 Design Documentation Report”, U.S. Army Corps of Engineers, New York District.

U.S. Army Corps of Engineers, New York District (USACE-NAN), 2020. “Fire Island Inlet to Montauk Point, Long Island, New York: General Reevaluation Report”, U.S. Army Corps of Engineers, New York District.

U.S. Army Corps of Engineers, New York District (USACE-NAN), 2024. “Fire Island Inlet to Montauk Point, Long Island, New York, Fire Island Inlet to Moriches Inlet Reach: Project Information Report”, U.S. Army Corps of Engineers, New York District.

United States Geological Survey (USGS), 2012. http://coastal.er.usgs.gov/hurricanes/sandy/field-measurements/

WL | Delft Hydraulics, 2008. “Delft3D-FLOW: Simulation of Multi-Dimensional Hydrodynamic Flows and Transport Phenomena, Including Sediments.”

http://coastal.er.usgs.gov/hurricanes/sandy/field-measurements/ http://coastal.er.usgs.gov/hurricanes/sandy/field-measurements/