B08_Attch_02a_NAMA_318722_Project_Prrogram_1thru53.pdf

NAMA 318722

ATTACHMENT 2

PROJECT PROGRAM

This document is provided to the DB Contractor for reference and to document the execution of the Schematic Design Preferred Alternative.

No additional work is expected for development of this work product.

100% DRAFT PREDESIGN SUBMITTAL

National Mall and Memorial Parks (NAMA)

Rehabilitate Seawalls and Shoreline – Design Services for Predesign (PD), Schematic Design (SD), and Design-Build (DB) Request for Proposal (RFP)

Project Program

PMIS No. NAMA 318722

August 19, 2022

THE INFORMATION IN THIS DOCUMENT IS

PROVIDED AS A REFERENCE AND FOR

CONTEXT DURING THE DEVELOPMENT OF

THE PROJECT. THE SPECIFICS HAVE BEEN

SUPERSEDED BY THE SPECIFICATIONS,

DRAWINGS, AND BASIS OF DESIGN.

i

Rehabilitate Seawalls and Shoreline National Mall and Memorial Parks

Washington, DC

PMIS Number: NAMA 318722

Project Program ii

Table of Contents

1 INTRODUCTION

1.1 Background

1.2 Project Objective

1.3 General Scope

1.4 Involved Parties

2 SITE ANALYSIS

2.1 Topographic / Bathymetric Survey

2.2 Slope Analysis

2.3 Analysis of Physical Features / Existing Conditions Assessment

2.4 Accessibility & Safety Features and Deficiencies

2.5 Access and Circulation, Traffic and Parking

2.6 Vegetation

2.7 Existing Water Bodies

2.8 Site History

2.8.1 Overall Reclaimed Lands

2.8.2 Tidal Basin

2.8.3 West Potomac Park

2.9 History of Existing Structures and Landscape

2.9.1 Original Seawall Design

2.9.2 Construction & Modification History

2.10 On-Site Utility Survey

2.11 Off-Site Utility Studies

2.12 Environmental Studies and Report

2.13 Climate Studies

2.13.1 Winds

2.13.2 Hurricanes

2.13.3 Water Levels

2.13.4 Precipitation

2.13.5 Waves and Overtopping

2.13.6 Temperature and Ice

2.14 Geotechnical / Soils

2.15 Hydrologic Studies

2.16 Project Requirements

2.17 Permitting Requirements

2.18 Project Coordination

3 SITE PROGRAM

3.1 Functional Requirements

3.2 Functional Relationships

3.3 Universal Design Features

3.4 Dimensional Requirements and/or Limitations

3.5 Unique Design Parameters

3.6 Interpretative Program

3.7 Accessibility Requirements

EXHIBIT LIST

EXHIBIT 1: TOPOGRAPHIC AND BATHYMETRIC SURVEYS

EXHIBIT 2: SLOPE ANALYSIS

EXHIBIT 3: PHYSICAL FEATURES – PHOTO LOG

EXHIBIT 4: ACCESS AND CIRCULATION

EXHIBIT 5: VEGETATION

EXHIBIT 6: EXISTING WATER BODIES

EXHIBIT 7: EXISTING UTILITIES

EXHIBIT 8: FUNCTIONAL RELATIONSHIPS

EXHIBIT 9: GEOTECHNICAL

SECTION 1

INTRODUCTION

1 INTRODUCTION

1.1 BACKGROUND

This project will rehabilitate portions of the failing Tidal Basin seawall north and south of the inlet bridge, as well as portion of the West Potomac Park seawall. The existing stone masonry seawall will be removed and reconstructed along the historic alignment and functional elevation.

Designs will include foundations that can bear the weight of additional stone and concrete, which will allow the walls to be extended vertically in response to future sea level rise or increasing storm surge elevations. Where feasible, stone masonry from the historic wall will be salvaged and reused in the reconstruction. Portions of the seawall around the Tidal Basin are the foundations for sidewalks, which will also be repaired or replaced. The Park will seek opportunities to realign and connect existing pedestrian walkways to provide a seamless and accessible route to the rehabilitated seawall.

Finally, the existing landscaping adjacent to each of the seawall systems will be removed and replaced, and the areas regraded as necessary to provide proper drainage.

The seawall systems included within this project date from the late 1800s to early 1900s. During this timeframe, the United States Army Corps of Engineers conducted a large-scale dredging operation within the Potomac River to improve navigation of the river adjacent to Washington, DC. A significant volume of the dredged material was used to create the lands now encompassing West Potomac Park and the Tidal Basin. A seawall was constructed around these lands to protect against the destructive forces of the surrounding waterways, especially the Potomac River. Collectively, these urban parks provide numerous opportunities for visitor recreation, including golf courses, tennis courts, a swimming pool, bicycling, fishing, and jogging. The parks are also home to the National Cherry Blossom Festival and iconic sites within Washington, DC, including the Thomas Jefferson Memorial, the Martin Luther King, Jr.

Memorial, and the Franklin Delano Roosevelt Memorial.

The dredged material was deposited on alluvial soils, and previous studies have determined that portions of the seawall have settled much as five feet since the initial construction. Based on more recent records, though, the rate of settlement has slowed significantly. Given this settlement and sea level rise, portions of the seawalls in both parks are overtopped twice daily during normal tidal conditions.

Greater areas are overtopped after extreme weather events, threatening historic resources and park infrastructure. The sidewalk on top of the Tidal Basin seawall on either side of the inlet bridge is underwater twice daily, creating a hazardous condition for the park visitors.

Due to the abovementioned settlement and subsequent decrease in elevation above mean water level, none of the overtopped areas drain effectively or quickly. When the water does recede, the overtopped areas are littered with large wood debris and other trash from the river.

The debris loads often collide with and damage the seawalls, which only accelerates their failure. Since much of the debris is manmade, this also leads to concerns for sanitation and health safety for the park’s visitors and NPS employees. Significant cost is expended by NPS staff to remove the debris load after each overtopping event.

The mortar between the blocks of stone masonry in West Potomac Park has eroded completely, and water seeps through these open joints during the normal ebb and flow of the river. When water returns through the open joints, it carries dredged material back to the river. Over time, this has led to a significant loss of material and a collapse of the integrity of the seawall into the river.

Given the current conditions described above, the West Potomac Park and Tidal Basin seawalls need to be engineered and re-built to be resilient to changing climate patterns, including storms of greater intensity and frequency which are prevalent in the National Capital Area. Otherwise, the NPS will continue to lose the seawall systems, and the material behind them, into the Potomac River. New seawall systems built to a new elevated height, above that which exists for the current seawalls, will help keep these areas from flooding during normal tidal events and minor flood stage events, and will help prevent continued loss of material to the river. Rebuilding the seawalls in a resilient manner will target a service life of 100 years.

This project directly addresses condition deficiencies on high priority assets by rebuilding portions of two seawall systems and returning these assets to new condition. It is important to note, though, that this project only rehabilitates a portion of the total seawall length in areas managed by the National Mall and Memorial Parks. This project, and potential future phases in East Potomac Park and the Tidal Basin, will increase the percentage of total park area that is open and safely accessible for public visitation and park staff. Just as importantly, at the end of all construction phases, a significant amount of deferred maintenance backlog across these systems will be eliminated.

The project will also mitigate the risks to visitor safety and health which currently exist due to both the deteriorated seawall structure, and also the debris deposition which remains prevalent even in normal tidal conditions. Visitors should feel that these parks are open in their entirety and safely accessible to all. Improved visitor satisfaction will result in increased visitation.

1.2 PROJECT OBJECTIVE

The National Park Service (NPS) is proposing rehabilitation of portions of the Tidal Basin seawall and the entire West Potomac Park seawall in accordance with the National Environmental Policy Act (NEPA) of 1969 as amended. The rehabilitation includes approximately 6,800 linear feet of seawall that is administered by the NPS through the National Mall and Memorial Parks (Park) and located in the District of Columbia (see Project Location Map below).

In the years since their construction, the seawalls have significantly settled and been compromised, leading to overtopping of the seawalls in some sections twice daily during normal tidal conditions which does not dissipate in a timely manner due to poor drainage. This has led to reduced public access, damage to historic cultural landscapes and Park infrastructure, resulting in negative impacts to visitor use and experience. When the water does recede, the overtopped areas are littered with large wood debris and other trash from the river that often collides with and damages the seawalls, causing further failure and is unsightly. The failing seawalls, standing water, and debris are concerns for visitor safety. The Tidal Basin and West Potomac Park experience large numbers of visitors every day of the year with peak visitation during the spring with the blooming of the Cherry Blossoms. The current condition of the seawalls affect visitor use and experience since the pedestrian trails in many areas have degraded creating trip and fall hazards, are inaccessible due to standing water and mud, and debris left behind from daily flooding. Significant cost is expended by the NPS staff to remove the debris load after each overtopping event.

The purpose of the proposed action is to restore the historic functional height of the seawalls, improve the historic cultural landscape and visitor experience along the shorelines, minimize soil erosion and safety hazards, and provide some flood protection. The proposed action is primarily needed because the existing structural deficiencies of the seawalls negatively impacts the experience and safety of park visitors and drowns out vegetation, which affect the landscapes.

The NPS proposes to rebuild and elevate the seawalls to re-establish the historic functional height of the walls in such a way as to provide for a sustainable solution that extends the lifecycle of the seawalls and future extensions of the wall to respond to changing climate patterns, including storms of greater intensity and frequency. The proposed action would help keep these areas from flooding during normal tidal events, minor flood stage events, and would help prevent continued loss of upland material. The existing masonry seawall would be removed and a new wall would be constructed along the historic alignment. The stone from the historic wall would be salvaged and reused in construction of the new walls. The existing sidewalk on top of the seawall along the Tidal Basin will be replaced. Finally, the existing landscaping adjacent to each of the seawall systems would be rehabilitated. Repairs to the surrounding infrastructure may include grading, stormwater control, pedestrian/multi-use paths, curbing, and replacement in-kind of any construction damage to the landscape and trees.

Figure 1 – Project Location Map

According to the PMIS, current available construction funding for this project is $109,993,000.The work of this task order shall be performed in accordance with the Denver Service Center (DSC) Design- Build (DB) Workflows Website:

https://www.nps.gov/dscw/designbuild.htm

Construction is expected to start in FY 2023.

1.3 GENERAL SCOPE

For this project, work shall consist of the preparation of the Predesign (PD), Schematic Design (SD), and Design Build Request for Proposal (RFP) Documents. Predesign will define the function and requirements (preliminary sizing, existing routing, materials) required to support the modifications to the seawall. Schematic Design will explore the location, layouts, and options for development to provide to the Design Build contractor for the modifications to the seawall construction.

1.4 INVOLVED PARTIES

National Park Service Staff

Name/Title Role/Responsibility Organization(s) Phone E-mail

Brent Nagen Portfolio Manager, Design and Construction Division

NPS DSC 303.358.0772 brent_nagen@nps.gov

Marcello Arroio NPS DSC Project Specialist

NPS DSC 720.701.0146 marcello.arroio@nps.gov

Kaetlyn Jackson Natural Resources Specialist

NPS DSC 303.905.5248 kaetlyn_jackson@nps.gov

Sean Kennealy Deputy Superintendent NAMA 202.359.1551 sean_kennealy@nps.gov

Yue Li Park Planner NAMA 202.570.8430 yue_li@nps.gov

Catherine Dewey Chief of Resource Management

NAMA 202.510.1117 catherine_dewey@nps.gov

Doug Jacobs Associate Regional Director

NPS 202.441.9142 doug_Jacobs@nps.gov

Tammy Stidham Dep. ARD Lands & Planning

NPS NCA 202.438.0028 tammy_stidham@nps.gov

Paula Aldrich

NPS

paula_aldrich@nps.gov

Jason Jimenez-Pisani Civil engineer NAMA 202.744.9509 jason_jimenez-pisani@nps.gov

HDR Engineering [JV Partner]

Name/Title Role/Responsibility Phone E-mail

Kent Brogger, PE Program Manager 303.318.6336 720.552.3119 kent.brogger@hdrinc.com

Brent Moore, PE Project Manager 361.696.3374 361.779.6587 brent.moore@hdrinc.com

Aaron Zdinak, PE Geotechnical Engineer

804.799.6875 804.205.6375 aaron.zdinak@hdrinc.com

Dan Garza, PE Project Engineer 713.576.3541 361.779.7571 dan.garza@hdrinc.com

Scott McCoy, PE Project Engineer 361.696.3355 954.401.2448 scott.mccoy@hdrinc.com

Tamara Bradley Program Admin 303.318.6301 303.764.1520 tamara.bradley@hdrinc.com

Maggie Hatcher Project Scheduler 713.576.3505 703.403.5711 maggie.hatcher@hdrinc.com

Oana Salas Project CADD 361.696.3348 oana.salas@hdrinc.com

Bill Beining Commercial Manger 412.497.6258 bill.beining@hdrinc.com

Moffatt & Nichol [JV Partner]

Name/Title Role/Responsibility Phone E-mail

Rob Sloop, PE Assistant Program Manager

562.590.6500 562.506.4975 rsloop@moffattnichol.com

Margaret Boshek, PE Coastal Engineer 984.239.2765 608.327.9952 mboshek@moffattnichol.com

Annapolis Landscape Architects [Historic Landscape Architecture]

Name/Title Role/Responsibility Phone E-mail

Shelley Rentsch Historic Landscape Architecture

443.995.8361 shelley@annapolisla.com

Biohabitats, Inc. [Environmental Planning and Compliance]

Name/Title Role/Responsibility Phone E-mail

Chris Streb, PE Wetlands Delineation 667.401.8485 443.414.2647 cstreb@biohabitats.com

CCM - Construction Cost Management [Cost Engineering/Estimating]

Name/Title Role/Responsibility Phone E-mail

Keith Kothmann Vice President / Lead Cost Estimator

817.625.6200 817.706.3431 keith@constructioncostmanagement.com

Nishant More Estimating Manager / Project Manager

817.625.6200 nishant@constructioncostmanagement.com

Katy Abraham CEO katy@constructioncostmanagement.com

The Cultural Landscape Foundation [Cultural Landscape Preservation]

Name/Title Role/Responsibility Phone E-mail

Charles Birnbaum Cultural Landscape Preservation

202.483.0553 info@tclf.org

Dutton and Associates [Archaeology]

Name/Title Role/Responsibility Phone E-mail

David Dutton Archaeology 804.897.1960 ddutton@dutton-associates.com

E2CR [Geotechnical Investigation/Drilling]

Siva Balu Geotech Drilling 410.737.9100 sivabalu@e2cr.com

Edgewater Projects [Constructability Reviews]

Mike Bruce Constructability Review

813.484.2229 mbruce@edgewater-projects.com

EHT Traceries [Cultural Resources and Architectural Conservation]

Name/Title Role/Responsibility Phone E-mail

Laura Hughes Cultural Compliance 202.393.1199 703.244.1504 laura.hughes@traceries.com

GEI Consultants [Geotechnical/Monitoring Design]

Name/Title Role/Responsibility Phone E-mail

Paul Landers Geotechnical Engineering – Tidal Basin

202.609.7678 703.898.7072 planders@geoconsultants.com

GEOmatx [Hydrographic Surveys]

Name/Title Role/Responsibility Phone E-mail

Tom McElroy Hydrographic Survey 443.562.7136 tmcelroy@geomatx.com

Institute for Human Centered Design [ABBAAS Specialist]

Name/Title Role/Responsibility Phone E-mail

Jan Majewski Accessibility Review 671.259.1654 571.245.4403 jmajewski@ihcdesign.org

InterAgency [Permitting, Cultural and Natural Resources]

Name/Title Role/Responsibility Phone E-mail

Doug Chapin Compliance, Regulatory, and Permitting

703.951.3246 doug.chapin@interagency.biz

Amanda Tyrrell Compliance, Regulatory, and Permitting

415.994.4271 Amanda.tyrrell@interagency.biz

Kirk Associates [Value Analysis]

Name/Title Role/Responsibility Phone E-mail

Steve Kirk Value Analysis 313.701.2084 kirkassociates@aol.com

Lowe Engineers [Surveying]

Name/Title Role/Responsibility Phone E-mail

Josh Daniel Topo Survey and

SUE

985.809.4109 josh.daniel@loweengineers.com

SaLUT – Soil and Land Use Technology [Geotechnical Laboratory Analysis]

Name/Title Role/Responsibility Phone E-mail

Ed Dalton Geotechnical Lab Testing

443.791.1334 edalton@salutinc.com

Schnabel Engineering [Geotechnical Analysis and Engineering]

Name/Title Role/Responsibility Phone E-mail

Bill Khouri Geotechnical Engineering – West Potomac

202.677.4123 240.882.4711 bkhouri@schnabeldc.com

SECTION 2

SITE ANALYSIS

2 SITE ANALYSIS

2.1 TOPOGRAPHIC / BATHYMETRIC SURVEY

1. Topographic survey of the Tidal Basin and West Potomac Park was performed by Lowe Engineers, LLC, and was collected from 04/18/2022 through 04/29/2022.

2. Hydrographic survey for the Potomac River was performed by Geomatx and was collected on 04/22/2022. Hydrographic survey for the Tidal Basin was performed by Geomatx and was collected on 05/05/2022.

3. Elements shown on drawing that are outside of the construction site boundaries are based on information from previous LiDAR dated 2020.

See Exhibit 01.

2.2 SLOPE ANALYSIS

The slopes extending landward from the Tidal Basin and the West Potomac Park vary depending on the location along the waterway. The Tidal Basin East slope is falling in elevation from the seawall top near the Jefferson Memorial and rising in elevation near the Inlet Bridge and towards the FDR Memorial. The West Potomac Park slopes rise from the top of the seawall elevation to Ohio Drive.

See Exhibit 02.

2.3 ANALYSIS OF PHYSICAL FEATURES / EXISTING CONDITIONS ASSESSMENT

The existing conditions vary depending on the location of the seawall within the project limits.

The Tidal Basin East seawall and surrounding site has settled since its construction allowing the water to overtop the seawall eroding and damaging vegetation. The same condition is occurring at the Tidal Basin West seawall but to a much lesser degree. The West Potomac Park South Seawall has been over topped and eroded. The wall has fallen, and rip rap has been placed to reduce the continued erosion of the bank. The West Potomac Park North seawall is in better condition partially due to the concrete added to the wall section in a past repair. All seawalls have settled and lost stones from their face, and there has been loss of soil material from behind the walls.

See Exhibit 03.

2.4 ACCESSIBILITY & SAFETY FEATURES AND DEFICIENCIES

Accessibility & Safety Features o ADA paved pathways with ramps o Handrails on sloped approaches o Lighting on main roadways

Accessibility & Safety Deficiencies o Pathway flooding o Pathway differential subsidence and cracking o No curbs, handrails, or lighting along seawall o No emergency response equipment (ladders, life rings, beacons, etc.)

o No egress from the water in the Tidal Basin o Tripping hazards – roots and rocks o Slipping hazard – mud o Stagnate water landward of the seawall o Buildup of soft mud and bird droppings o Low hanging tree limbs o Mixed pedestrian, bike, scooter traffic o No directional or safety signage

2.5 ACCESS AND CIRCULATION, TRAFFIC AND PARKING

There are several roads, parking lots, sidewalks, bike lanes and visitor paths through and around the project site. Construction access may be by truck or by barge from the river.

See Exhibit 04.

2.6 VEGETATION

There are a number of trees that will be impacted by this project, but the final tally has not been completed. Based on the impacted trees, there will be a replacement plan with a ratio that varies from 6:1 to 1:1, with variable caliper trees, as defined by the NCPC. The final ratio will be determined after the evaluation and coordination with the NPS and other stakeholder agencies.

The current exhibits assume a replanting plan at a 1:1 ratio.

See Exhibit 05.

2.7 EXISTING WATER BODIES

The project water bodies include the Tidal Basin, and Potomac River.

See Exhibit 06.

2.8 SITE HISTORY

The lands which now comprises West & East Potomac Parks were historically not part of L’Enfant’s Plan for the City of Washington and did not even exist prior to 1880. Below is chronological history of the site with a focus on the development and upkeep of the seawalls.

2.8.1 OVERALL RECLAIMED LANDS

Pre- 1860s – Upstream inland industry operations, including mining, timber logging, and charcoal production, result in sedimentation of the once navigable Potomac River resulting in nearshore shallows called the Potomac Flats. Lack of city sanitation results in “giant smelly mudflat.”

1870 – 1879 – US Army Corp of Engineers (USACE) begin dredging Potomac River to re-establish shipping channels, later opting to fill the Potomac Flats to reclaim land while maintaining the Washington Channel. Design of reclaimed lands goes through many iterations. Major W.J. Twining proposed a tidal basin at the north end of Washington Channel as a device to flush and clear the Washington Channel of pollutants and sediment.

1882 – 1896 – USACE dredges more than 12 million cubic yards of sediment to create more than 600 acres of reclaimed land.

1897 – Congress declares reclaimed Potomac Flats to be a public park, named Potomac Park.

1903 – 1909 – Park lands transferred from USACE to the jurisdiction of Office of Public Buildings and Grounds.

FIGURE 2 – MAP OF CITY OF WASHINGTON, 1839 (LIBRARY OF CONGRESS)

FIGURE 3 – PROPOSED AREA TO BE RECLAIMED, 1882 (LIBRARY OF CONGRESS)

FIGURE 4 – PROGRESS MAP 1884 (CHIEF OF ENGINEERS, UNITED STATES NAVY)

FIGURE 5 – PROGRESS MAP 1894 (CHIEF OF ENGINEERS, UNITED STATES NAVY)

FIGURE 6 – ORIGINAL CONTAINMENT OF DREDGE MATERIAL

(PROGRESS MAP 1884, CHIEF OF ENGINEERS, UNITED STATES NAVY)

2.8.2 TIDAL BASIN

1885 – Foundations of the seawalls within the Tidal Basin started.

1888 – Foundation piles for outlet gates are driven 74ft below low tide before reaching bedrock.

1887 – 1891 – Construction of outlet gate.

1893 – Riprap foundation for seawall completed.

1893 – 1896 – Construction of seawalls throughout the basin.

1896 – USACE reconstructed parts of the wall above the level of high tide and laid it in cement mortar in response to top stones being lost to malicious removal.

1902 – Seawall to the “north and west of the Tidal Basin” heightened to 6ft above mean high tide (3ft increase) constructed entirely out of Portland-cement concrete. This modification can be most clearly seen along the northeast wall. This section later called “high north wall.”

1909 – Construction of inlet bridge. Removal and reconstruction of walls adjacent to gate “which had settled.”

1912 – Japanese Cherry Trees gifted from the People of Japan to the People of the United States.

1915 – Office of Public Buildings and Grounds orders the paving the surface of the seawalls above mean low tide so that vegetation could not grow through the stones of the wall.

1918 – Tidal Basin bathing beach constructed along southern shore in the location of present-day Jefferson Memorial requiring removal of stacked seawall section.

1922 – New seawall constructed along Independence Avenue, SW reusing salvaged stone and foundation.

1925 – Bathing beach closed, and seawall reassembled.

1940 – Plans for relocation of seawall to account for Jefferson Memorial Construction.

This work consisted of 775 ft of rubble wall to the east of the memorial, 500 ft of ashlar wall north of the memorial, and 925 ft of rubble wall to the west and southwest of the memorial.

1941 – Seawall modifications and construction started.

o Seawall coping of 8-inch cement added to existing seawalls.

o Tidal Basin filled out to new seawall from approximately elevation -10 to elevation

+10.5 resulting in 20.5ft of new fill.

o Rubble seawall is a random stone faced reinforced concrete wall founded on a riprap foundation.

1942 – Railing ordered to be extended around entire Tidal Basin. Pipe sleeves placed as receptacles on all walls but railings were only installed on northeast basin wall between the outlet bridge and Kutz Bridge.

1943 – Kutz Bridge built.

1945 – Seawall within the Tidal Basin is noted to need considerable repair by National

Capital Parks (NCP).

1963 – Seawall is noted to be missing many large stones.

1965 – Inspection of seawalls in and around Jefferson Memorial result in recommendations of removal and reconstruction of wall in select locations with patching and pointing in others. No indication whether this work was undertaken.

1968 – Slippage of Tidal Basin’s “high north wall” listed as a hazard to public safety.

Shifting of stone evident in cracks and excessive putty. Drawings suggest wall section is set on timber pilings.

2.8.3 WEST POTOMAC PARK

1884 – Foundations of West Potomac Park North started.

1890 – Construction of stone seawalls commences. Described as dry stone 6ft high, 4ft thick at base, by 2.5ft at top with vertical back and batter face.

1891 – Riprap foundation for seawall completed.

1893 – Construction of seawalls modified to include a coarse gravel backing, approximately 2ft thick, to protect it from frost and washout.

1896 – USACE reconstructed parts of the wall above the level of high tide and laid it in cement mortar in response to top stones being lost to swell from passing steamers and malicious removal.

1890 – 1899 – Construction of seawalls throughout West Potomac Park. During that time, multiple sections were taken down and rebuilt.

1908 – Last section of seawall built across the old sewer canal.

1913 – Changes proposed to West Potomac Park seawall from Easby’s Point to a point

4,560ft south due to construction of Lincoln Memorial. This pushes the land further into the Potomac and requires new fill which continued through 1922.

1917 – Construction of foundations for new seawall complete. All surrounding seawall sections noted to be in good condition.

1918 – Major ice jam damages approximately 2,400 linear feet of seawall south of the Lincoln Memorial. Repaired by 1920.

1930 – Major Potomac River flood flows result in proposed levee for Potomac Park spanning north end of Tidal Basin and West Potomac Park.

1932 – Construction of Arlington Memorial Bridge.

1936 – Major flood results in extensive damage. Floodwaters covered West Potomac

Park seawalls to a depth of approximately 8ft.

1939 – Potomac Park levees completed. Not intended to protect areas south of Lincoln

Memorial from flooding.

1942 – Second major flood event. Floodwaters covered West Potomac Park seawalls

1.5ft higher than in 1936.

1945 – Seawall from the “mole” to the inlet bridge noted as being deteriorated in some places and in need of major repairs.

1946 – Seawalls in both East and West Potomac Park are recommended to be raised to

“protect them.”

1957 – NCP accepts Potomac Electric Power Company’s (PEPCO) proposal to replace portion of seawall to the south of Arlington Memorial Bridge.

1958 – USACE makes some repairs to seawalls. Nature and extent of repairs unknown.

1971 – NCP requests permit to place riprap along the shoreline behind the seawalls at various locations to stabilize shoreline from being eroded and undermined.

1994 – Hydraulic Report authored by the Federal Highway Administration provides recommendations for addressing erosion concerns within West Potomac Park, south of the PEPCO repair. Site photos show a large volume of riprap placed along the shoreline which matches Alternative 1 within the report. Exact date of riprap placement unknown.

2.9 HISTORY OF EXISTING STRUCTURES AND LANDSCAPE

The documented history of the construction and modifications to the seawalls and surrounding landscape is listed in chronological order below. A number of documents, photographs, and new reports were used to develop the below understanding. It should be noted that agreement did not always follow between sources and therefore the most accurate understanding was based on original historic documents and photos from the site.

2.9.1 ORIGINAL SEAWALL DESIGN

Foundation:

o Riprap stone base approximately 20ft wide on the bottom and 5ft thick with the top set at an elevation of low tide.

FIGURE 7 – RECLAMATION OF POTOMAC FLATS, (HAINS, 1885)

Seawall:

o Built of “Potomac River Stone” of a size “rather larger than ordinary building stone” Approximate stone size is 8” T x 1.5’ W x 2’ L o Stone came from quarries along the banks of the Potomac River, “about four miles from the work.”

o Original seawall is 6ft in height above low tide.

o Wall batter ranges from 1 to 2 (early construction), 1 to 3 (a majority of construction), to 1 to 6 (final constructed areas) with a base of 4 – 4.5 ft wide and top of 2.5 – 3 ft wide.

o A majority of the construction includes a backing of coarse gravel or oyster shell approximately 1.5 – 2 ft thick.

FIGURE 8 – ORIGINAL SEAWALL CONSTRUCTION (DOI, 1940)

2.9.2 CONSTRUCTION & MODIFICATION HISTORY

1884 – 1899 – Riprap foundations and stacked stone seawall construction throughout the Tidal Basin and West Potomac Park. Some sections taken down and rebuilt during this time.

1893 – Construction of seawalls modified to include a coarse gravel backing, approximately 2ft thick, to protect it from frost and washout.

1896 – USACE reconstructed parts of the wall above the level of high tide and laid it in cement mortar in response to top stones being lost to malicious removal.

1902 – Seawall to the “north and west of the Tidal Basin” heightened to 6ft above mean high tide (3ft increase to original design) constructed entirely out of Portland-cement concrete. This modification can be most clearly seen along the northeast wall. This section later called “high north wall.”

FIGURE 9 – NORTHWEST TIDAL BASIN WALL SHOWING 3FT CONCRETE HEIGHTENING IN 1902 (HALS, 2018)

1909 –Removal and reconstruction of walls adjacent to Inlet Bridge “which had settled.”

1912 – Japanese Cherry Trees gifted from the People of Japan to the People of the

United States.

1915 – Office of Public Buildings and Grounds orders the paving the surface of the seawalls above mean low tide within the Tidal Basin so that vegetation could not grow through the stones of the wall.

FIGURE 10 — WEST TIDAL BASIN WALL SHOWING EVIDENCE OF PAVING (HALS, 2018)

1922 – New seawall constructed along Independence Avenue, SW reusing salvaged stone and foundation.

1940 – Seawall realignment around Jefferson Memorial started.

o Seawall coping of ~8-inch cement added to existing seawalls.

o Tidal Basin filled out to new seawall from approximately elevation -10 to elevation

+10.5 resulting in 20.5ft of new fill.

o Rubble seawall is a random stone faced reinforced concrete wall founded on a riprap foundation.

FIGURE 11 – MODIFIED SEAWALL CONSTRUCTION AROUND JEFFERSON MEMORIAL (DOI, 1940)

1957 – National Capital Parks (NCP) accepts Potomac Electric Power Company’s

(PEPCO) proposal to replace portion of seawall to the south of Arlington Memorial Bridge. Drawings of repair could not be found.

FIGURE 12 — SOUTHERN TERMINUS OF PEPCO REPAIR IN WEST POTOMAC PARK (2022)

1971 – NCP requests permit to place riprap along the shoreline behind the seawalls at various locations to stabilize shoreline from being eroded and undermined.

1994(?) – Riprap placed along the shoreline in West Potomac Park.

FIGURE 13 – DILAPIDATED STONE WALL & RIPRAP IN WEST POTOMAC PARK (2022)

2.10 ON-SITE UTILITY SURVEY

Multiple stormwater outlets penetrate the seawall, two large wastewater pipelines cross under the Tidal Basin and several other utilities cross the site both above grade, and below.

See Exhibit 07.

2.11 OFF-SITE UTILITY STUDIES

Does not apply. No utility work planned.

2.12 ENVIRONMENTAL STUDIES AND REPORT

Environmental Assessment

The NPS is currently preparing an Environmental Assessment (EA) for the proposed seawall rehabilitation. The scoping period for the EA initiated on July 19, 2022. The EA will be technically and legally defensible and in full compliance with the requirements of the National Environmental Policy Act (NEPA); the National Historic Preservation Act of 1966 (NHPA); the Council on Environmental Quality Regulations (40 CFR 1500-1508); the Department of the Interior NEPA Regulations (43 CFR Subtitle A Part 46); NPS Director’s Order (DO) #12, Conservation Planning, Environmental Impact Analysis, and Decision-Making (DO-12), and accompanying DO-12 Handbook (2015); NPS Director’s Order (DO) #28, Cultural Resource Management Guideline (DO-28), DOs and Statement of Findings Handbooks for 77-1 and 77-2 if applicable, and other applicable laws, policies, and regulations. Other principal applicable laws include the Endangered Species Act (ESA), the US Fish and Wildlife Coordination Act (USFWCA), the National Capital Planning Act, and applicable District requirements.

Wetland Delineation

A wetland delineation field assessment was performed within the project area by Biohabitats, Inc. on April 25, 2022. The delineation identified waters of the U.S., including wetlands, in accordance with the 1987 U.S. Army Corps of Engineers Wetland Delineation Manual – Technical Report 87-1, the Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Atlantic and Gulf Coast Plain Region, Version 2.0, and in conjunction with the FGDC

Wetlands Classification Standard and the National Park Service Procedural Manual #77-1:

Wetland Protection. For any delineated wetlands, an assessment of wetland functions and values was conducted using the Method for Inventorying and Evaluating Freshwater Wetlands in New Hampshire (NH Method) published by the University of New Hampshire Cooperative Extension in 2015.

The field assessment determined there are four small wetland areas, each classified as tidal, palustrine emergent, within the project area. Each wetland is located behind the seawall, in low areas subject to ponding and connected hydrologically to the Potomac River or Tidal Basin via tidal flux. It is anticipated that these areas will be regulated by USACE, DOEE, and/or NPS. A Jurisdictional Determination will be requested from the USACE.

Prior to performing the field assessment, the following resources were reviewed to advise the wetland determination: Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM), National Wetlands Inventory (NWI), Department of Energy and the Environment (DOEE) Wetland Inventory map, Natural Resources Conservation Service (NRCS) County Soil Survey map, and NRCS Web Soil Survey hydric soil report.

FEMA Floodplain and NWI/DOEE Wetland Inventory Maps

According to the FEMA FIRM map, the entire project area is within Zone AE, areas subject to inundation by the 1-percent-annual-chance flood event. The NWI and DOEE Wetland Inventory maps indicate no mapped wetlands within the project area, but indicate the Potomac River (i.e., labeled as wetland – riverine) and the Tidal Basin (i.e., labeled as wetland – lake) are present immediately adjacent to the seawalls. DOEE mapping shows the presence of submerged aquatic vegetation (SAV) along the Potomac River’s edge and at the inlet to the Tidal Basin in 2017. The surveys from 2018 to 2021 do not show SAV in this area. See Figure 14 below. The NPS is requesting the 2022 results. SAV presence and applicable regulations should be reviewed further as the DOEE mapping is intended for general guidance or planning purposes.

Figure 14 – Washington D.C. Aquatic Resources Map

Soils

According to the NRCS Web Soil Survey map generated for the project area, the majority of the area along the Potomac River is mapped as Udorthents (U1) and the majority of the areas along the lower half of the Tidal Basin is mapped as Lindside loam (Ld). At the transition from the Potomac River to the Tidal Basin, it is mapped as Iuka sandy loam (Ik). The Udorthents soil map unit is mapped on previously disturbed land and fill with 0-10% slopes. Lindside loam and Iuka sandy loam soil map units are moderately well drained soils mapped on nearly level (0-2%) floodplains and formed in loamy to sandy alluvium. The soil survey map is reflective of past anthropogenic influences from the late 1800s to early 1900s where the USACE dredged the Potomac River to improve navigation of the river and placed the dredged material to create the lands now encompassing East and West Potomac Parks and the Tidal Basin.

A NRCS Web Soil Survey Hydric Rating by Map Unit report was also generated for the project area. The hydric soil rating indicates the percentage of map unit that meets the criteria for hydric soils. Hydric soils are defined by the National Technical Committee for Hydric Soils (NTCHS) as soils that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part (Federal Register, 1994). Under natural conditions, these soils are either saturated or inundated long enough during the growing season to support the growth and reproduction of hydrophytic vegetation.”

The Hydric Rating by Map Unit reports provide the percent composition of hydric soil components by soil map unit. According to the NRCS hydric soils report, U1 soil map unit is classified as not hydric and Ld and Ik sandy loam soil map units are classified as 1 to 32 percent hydric. It is important to note, the soil survey mapping does not account for smaller scale, site-specific conditions that can support hydric soils.

Endangered and Threatened Species

A June 28, 2022 search of the U.S. Fish and Wildlife Service’s (USFWS) Information for Planning and Consultation (IPaC) database indicated there are a total of two (2) threatened, endangered or candidate species that may occur within the project boundary. There were no critical habitats identified within the project area that fall under USFWS jurisdiction. Under 50 CFR 402.12(e) of the regulations implementing Section 7 of the ESA, the accuracy of this species list should be verified after 90 days. The species list included the following:

Monarch Butterfly (Danaus plexippus) o The monarch butterfly is identified as a candidate species and not yet listed or proposed for listing as threatened or endangered. Per the IPaC results, there are generally no Section 7 requirements for candidate species.

Northern Long-Eared Bat (Myotis septentrionalis) o The northern long-eared bat is listed as federally-threatened.

o In a letter dated June 28, 2022, the USFWS confirmed that the proposed project is consistent with activities analyzed in the Programmatic Biological Opinion (PBO) and that any take that may occur as a result of the proposed project is not prohibited under the ESA Section 4(d) rule adopted for this species.

If the Action is not completed within one year of the date of the IPaC report, the NPS must update and resubmit the information required in the IPaC key. This IPaC key assists users in determining whether a Federal action is consistent with the activities analyzed in the Service’s January 5, 2016 PBO.

In addition to responsibilities to protect threatened and endangered species under the ESA, there are additional responsibilities under the Migratory Bird Treaty Act (MBTA) and the Bald and Golden Eagle Protection Act (BGEPA) to protect native birds from project-related impacts.

A review of the National Marine Fisheries Service (NMFS) Critical Habitat Mapper confirmed that the Potomac River in the vicinity of the project area has been designated as critical habitat for the Atlantic Sturgeon (Acipenser oxyrhynchus oxyrhynchus). Coordination with NMFS and NOAA Fisheries will occur following informal initiation of ESA Section 7 Consultation. A time-of-year restriction for the protection of spawning anadromous fishes that prohibits in-water construction activities, including cofferdam installation, between February 15 and June 15 of any year may be imposed from February 15 to June 15 of any year to receive a not likely to adversely affect determination from NMFS.

Previous Environmental Analysis:

As part of the PD process, the JV Team also reviewed prior environmental studies and reports, including the following:

Repair and Control Settlement at Thomas Jefferson Memorial Seawall, North Plaza and Transition Areas Environmental Assessment (NPS April 2009)

Potomac River Tunnel Environmental Assessment (NPS and DC Water March 2020) Cultural Landscape Report – Tidal Basin (NPS June 2020)

2.13 CLIMATE STUDIES

Climate hazards were documented as part of the Climate Change and Natural Hazards report.

This section summarizes the climate analyses performed within that report.

2.13.1 WINDS

Wind information was taken from hourly recorded 2-minute data at Reagan National airport.

Predominate wind directions are from the south and northwest.

TABLE 1 – EXTREME WIND SPEEDS AT PROJECT SITE (2-MIN AVG)

Return Period (yr) U2‐min (kn)

5 37.5

10 38.9

25 40.6

50 41.8

100 42.9

Winds contribute to waves and storm surge at the project site. While winds are not directly a design driver, their effect on water levels and wave overtopping is which is highlighted below.

2.13.2 HURRICANES

Hurricane activity near the project site is not overly common but can result in catastrophic damage in the form of inland flooding and high-wind damage. Over the past 100 years (1922-2022), only 5 hurricanes have passed within 120 nautical miles of the project site yet are associated with some of the highest flooding events. Flooding, due to extreme water levels, is discussed in the next section.

2.13.3 WATER LEVELS

Water levels at the site, for the purposes of this project, are represented by the nearest NOAA tide gage located in Washington Channel, approximately 1 mile from the project site. For further understanding of the water levels within the Tidal Basin, 4 water level gages were installed within the inlet bridge to measure water levels for two years. Early assessment of three months of data shows good correlation between the two gages with a tidal lag on the order of 20-45 minutes within the basin. Reviews and analysis of this data as it is collected will be presented in annual reports.

Hourly water levels have been recorded at the Washington Channel station for nearly a century allowing for an accurate calculation of extreme water levels and a linear trend revealing a steady sea level rise of approximately 0.14 in/yr (3.44 mm/yr). Tidal datums at the Washington Channel station for the current tidal epoch (1983-2001) as well as forecasted future conditions are shown in Table 2.

TABLE 2 – TIDAL DATUMS (REF NAVD88) FOR NOAA CO-OPS STATION 8594900 (WASHINGTON, D.C.).

Tidal Datum Epoch 1983-2001 2025 2075 2100

Mean Higher High Water MHHW 1.77 2.16 2.74 3.03 Mean High Water MHW 1.54 1.93 2.51 2.80 Mean Sea Level MSL 0.15 0.54 1.12 1.41 Mean Low Water MLW -1.25 -0.87 -0.28 0.01 Mean Lower Low Water MLLW -1.40 -1.02 -0.43 -0.14

Extreme Water Levels

Removing long-term sea level trend from the historical data, water levels relative to present day (2022) conditions can be analyzed and extreme water levels can be calculated based on return period frequency. Table below gives the annual probability of an extreme event occurring within any given year.

TABLE 3 – EXTREME WATER LEVELS AT THE PROJECT SITE

Return Period Annual Probability Calculated 2022

Water Surface Elevations

(ft NAVD88)

5 years 20% 5.09

10 years 10% 6.32

25 years 4% 8.27

50 years 2% 9.94

100 years 1% 11.75

Flooding Frequency & Duration

Changes in flood frequency and duration can be directly linked to long-term sea level trend and the understanding that the seawalls are settling due to the consolidation of soils beneath them, resulting in upland flooding. Events that would only cause flooding over the wall for a few hours per year have become frequent enough to result in vegetation loss and harm to the Park’s cherry trees closest to the walls. While such events have become more frequent overtime, this can be linked back to the relative sea level rise within the project area. This is to be taken into account when selecting a wall height and its associated risk of flooding. The walls are allowed to occasionally be overtopped with water due to large storm events but the duration and frequency of flooding will not be such to cause long-term vegetation die off.

2.13.4 PRECIPITATION

Precipitation affects the site through the greater watershed and also locally through sheet flow.

In general, summer months, May, June, July, and September are the rainiest months. Large volumes of precipitation over the watershed will result in elevated discharge and Potomac River water levels which can result in shoreline flooding from the river. Heavy downpours locally can result in flash floods and flooding from the upland.

While the seawalls and their design will be influenced by river flooding, greater site stormwater planning will help offset damaging effects from upland sheet flow.

2.13.5 WAVES AND OVERTOPPING

Waves at the project site can either be locally wind-generated or vessel-generated (boat wake).

Within the Tidal Basin, boat wake is considered negligible as only one motorized vessel utilized by the paddle boat concessionaire for safety purposes is allowed within the basin. The seawalls along the Potomac River are impacted with local wind-generated waves and boat wake. Boat wake has high energy which can impact the shoreline and walls with a larger force relative to their amplitude than irregular wind waves.

Maximum fetch distances (open water over which waves can form) was used in conjunction with storm wind speeds to estimate locally wind-generated waves within the project site. Table 3 shows the calculated wave heights per each section of seawall within this project. As shown, the south end of West Potomac Park experiences the largest wave climate.

TABLE 3 – EXTREME SIGNIFICANT WAVE HEIGHTS FOR LOCALLY WIND-GENERATED WAVE CHARACTERISTICS

Hs

WPP

(North)

Hs

WPP

(South)

Hs

Tidal Basin (West)

Hs

Tidal Basin (East)

Return Period

5-year 2.3 ft 2.4 ft 1.3 ft 1.5 ft

10-year 2.5 ft 2.7 ft 1.4 ft 1.6 ft

25-year 2.8 ft 3.1 ft 1.5 ft 1.8 ft

50-year 2.9 ft 3.4 ft 1.5 ft 1.9 ft

100-year 3.1 ft 3.8 ft 1.6 ft 2.1 ft

Boat wake are only a design factor within the Potomac River. No measurements of boat wake were collected for the purposes of this project but antidotal information suggests boat wake of roughly 2ft wave height with a 3s wave period is sufficient for design of the seawalls.

Site-specific wave overtopping rates were calculated for the hourly timeseries of water levels and wind-waves for wall toe elevations and multiple potential wall crest elevations using equations for vertical seawalls contained in the EurOtop Manual (2018). Overtopping rates were then compared against published thresholds for damage to vegetation and paved surfaces.

Overtopping rates are largely driven by site water levels due to the limited fetch, both on the Potomac River and within the Tidal Basin. Various scenarios of joint water levels with wave events were analyzed. None of the cases reviewed showed any damage to paved surfaces when seawall height is above +2 NAVD88. However, this analysis did show damage to surfaces with patchy vegetation (such as that caused by frequent foot traffic) for wall heights below +5 NAVD88 along the Potomac River and below +4 NAVD88 within the Tidal Basin during a 5yr return period storm event.

2.13.6 TEMPERATURE AND ICE

Temperature in the Washington, DC area is not considered a driving factor in the NAMA Seawall design; however, the high and low temperatures could affect the vegetation at the Project site particularly the Cherry Blossom trees which are part of the NAMA National Park.

In Washington, DC, in 2022, the average temperatures for winter and summer months are 39.7°F and 74.6°F, respectively. However, statewide climate trends show the average temperature to be increasing at a rate of +0.2°F/decade. This temperature change can impact sensitive flora resulting in reduction in health. This will be considered when looking at landscaping within the project site.

Potential ice growth was analyzed to determine damage potential in relation to scour and impact.

Ice thicknesses, when present, are typically less than 4 inches and even in extreme events are below 10 inches. Therefore, ice is not considered a design consideration for the seawalls.

2.14 GEOTECHNICAL / SOILS

HDR planned and is currently executing a subsurface exploration program to collect subsurface data at the project site. In total, 19 soil borings and 26 in-situ borings were planned throughout the project site along the existing seawall in West Potomac Park (WPP), Tidal Basin East (TB-E), and Tidal Basin West (TB-W) areas. The exploration program started on June 22, 2022, and it is currently underway.

Based on the initial review of the currently received exploration data, the subsurface soil consists of an artificial fill layer underlain by alluvial material underlain by bedrock. The soil stratification at each site is shown in the Exhibit 09 and is described below:

WPP area: the depth of artificial fill layer varies approximately from 5 to 15 feet below the existing ground, and the thickness of the alluvium layer ranges from approximately 35 to 70 feet. Finally, the depth of bedrock varies approximately from 45 to 100 feet below the existing ground.

TB-W area: the depth of artificial fill layer varies approximately from 15 to 35 feet below the existing ground, and the thickness of the alluvium layer varies approximately from

50 to 60 feet. Finally, the depth of bedrock varies approximately from 75 to 90 feet below the existing ground.

TB-E area: the depth of artificial fill layer varies approximately from 30 to 35 feet below the existing ground, and the thickness of the alluvium layer ranges from approximately 40 to 60 feet, Finally, the depth of bedrock varies approximately from 80 to 90 feet below the existing ground.

The aforementioned depths and thicknesses of the layers may be changed as additional subsurface exploration data is received.

See Exhibit 09.

2.15 HYDROLOGIC STUDIES

The Potomac River located west of Washington, DC has a…