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Green Infrastructure Techniques for Coastal Highway Resilience

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Title: Coastal green infrastructure - native vegetation and stone breakwaters. - Description: http://ccrm.vims.edu/livingshorelines/images/OffsetGaps_JPG.jpg
Photo from Center for Coastal Resources Management, Virginia Institute of Marine Science

FHWA encourages the use of ecosystem-based approaches in adapting to climate change (see FHWA and DOT policy orders). Ecosystems provide valuable services that help to build resilience and reduce the vulnerability of people, livelihoods, and infrastructure to climate change impacts.

The FHWA Administrator dedicated a portion of the agency’s annual Strategic Initiatives research budget to a project that will provide state and local transportation agencies with research, outreach, and technical assistance on green infrastructure, ecosystem-based approaches for improving coastal highway resilience. While green infrastructure can be used in both coastal and inland environments, this project focuses on coastal areas.

Coastal green infrastructure includes dunes, wetlands, living shorelines, oyster reefs, beaches, and artificial reefs. These features can protect coastal transportation infrastructure from the brunt of storm surges and open water waves. Some can adapt to sea level rise by accreting sediment or migrating inland.

This webpage contains:

Project information

The Green Infrastructure Techniques for Coastal Highway Resilience project seeks to improve the resilience of coastal roads, bridges, and highways through implementation of green infrastructure, ecosystem-based approaches. The project will investigate techniques that could be implemented as part of transportation planning, maintenance and construction to preserve and/or improve natural infrastructure function, thereby increasing the resilience of highways to the effects of storm surges and sea level rise. The project will provide information and analysis on green infrastructure techniques, benefits, costs, feasibility, and implementation considerations that transportation professionals need to make decisions on infrastructure projects.

The project includes the following activities:

Resources

Partnership

Systems Approach to Geomorphic Engineering (SAGE) is a community of practice of federal, state, and local agencies, non-governmental organizations, academic institutions, engineers, and private businesses working together to: 1) Use and promote green-gray approaches to ensure coastal community and shoreline resilience; 2) Broaden science, engineering, policy and marketing activity both domestically and internationally; and 3) Engage community partners in regional demonstrations.

Basics

US Army Corps of Engineers Brochure on Natural & Nature-Based Features (2 pages) explains the USACE systems approach to coastal protection, combining natural and nature-based features, structural, and non-structural measures.

Natural and Structural Measures for Shoreline Stabilization Brochure (6 pages) provides information on a continuum of green to gray shoreline stabilization techniques that can help reduce coastal risks and improve resilience.

Green Infrastructure Protective Services Animation – Watch a short animation describing the protective benefits of green infrastructure.

Tools

Sea Level Rise Viewer – Marsh Migration – Look under the “marsh migration” tab of this tool to see how wetlands in your area may be impacted by sea level rise. Marshes on the Move – explores what’s involved when modeling the impacts of sea level rise on coastal wetlands in the future.

Coastal Flood Exposure Mapper – Use this tool to see where your community assets, including natural resources, are most vulnerable to coastal flooding, and use this information to start conversations about local risk reduction strategies.

Green Infrastructure Mapping Guide – Use this guide to develop a GIS work plan to prioritize green infrastructure for coastal resilience.

Sea Level Change Curve Calculator – outputs tables of sea level change projections by year for your selected location and parameters.

Reports

Use of Natural and Nature-Based Features (NNBF) for Coastal Resilience, U.S. Army Corps of Engineers, 2015.

North Atlantic Coast Comprehensive Study Report, U.S. Army Corps of Engineers, 2015.

Guidance for Considering the Use of Living Shorelines, NOAA, 2015.

Ecosystem-Service Assessment: Research needs for coastal green infrastructure, Executive Office of the President, National Science and Technology Council, 2015.

Links

NOAA Green Infrastructure Resources

USACE Engineering with Nature

NOAA Restoration Living Shorelines

US EPA Green Infrastructure

Virginia Institute of Marine Science (VIMS), Center for Coastal Resources Management, Living Shorelines

Coasts, Oceans, Ports & Rivers Institute (CORPI) Living Shorelines Database

Examples of Green Infrastructure Protection of Coastal Highways

Living Shoreline to Protect Shore Road on Long Island

As part of an FHWA research project, coastal engineers analyzed the potential of a living shoreline to protect Shore Road in Brookhaven, New York, on the north shore of Long Island. The road has experienced erosion and failure of the embankment and is threated by inundation due to sea level rise.

Title: Location of Shore Road - zoom out map - Description: Map of New York City metropolitan area shows that Shore Road is located midway down the north shore of Long Island.Title: Map of mid section of Long Island - zoom in - Description: Aerial image of study area shows that Shore Road is located close to the water.
Location of Shore Road indicated with star symbol in each of the images.
Title: Pictures of Shore Road at Low Tide and High Tide - Description: Photographs of Shore Road at low and high tides show the water approximately 15 feet and 7 feet from the pavement, respectively.
Shore Road (looking west) and a portion of the existing revetment shown (a) at low tide and (b) just before high tide. (Photo credits Bret Webb)

The researchers analyzed three options, summarized below.

Summary of adaptation options and rough order of magnitude costs.
Measure

Description

Pros

Cons

Cost

Traditional Protection

Protect and/or reinforce the shoulder using revetment and wall

Increases resiliency to waves; postpones flooding

Increases shoreline armoring; eliminates marsh shoreline habitat; maintenance

$1.3M

Living Shoreline Protection

Protect the road from wave damage using a living shoreline approach

Increases resiliency to waves; provides natural habitat; may keep pace with sea level rise

Regulatory hurdles; does not address flooding of roadway

$0.5M

Abandon the Road

Abandon the asset and/or allow the pavement to fail

Removes long-term burden to asset owner; eliminates vulnerability

Dislocation or condemnation of private property; reduced public access to waterfront

$5M

A diagram of a possible form of a living shoreline marsh for Shore Road is shown below. The living shoreline is a constructed marsh that parallels the 0.25-mile of roadway, with large boulders placed along the toe (seaward edge) of the marsh to retain the fill and reduce wave energy. The rocks would be placed in segmented groups to allow wave diffraction (i.e., bending of wave crests and scattering of wave energy) to create a stable equilibrium shoreline position in the gaps. Nearshore segmented breakwater systems and headland pocket beach systems are related forms of coastal engineering used for shore stabilization which can be successfully adapted to marsh creation projects. The small “pockets” that form in the gaps are not only effective at stabilizing the shoreline position, but they also reduce the amount of rocks needed along the toe while increasing the total length of intertidal shoreline and marsh edge. These gaps also provide ingress and egress for mobile species (fishes and crabs) as well as human users.

Title: Diagram of constructed marsh - Description: Diagram shows marsh fill and plantings along Shore Road and placement of breakwaters off shore to protect the marsh.
Diagram of constructed marsh living shoreline with segmented toe protection boulders for Shore Road.

Below, a profile diagram through the constructed marsh shows the addition of clean sand fill to establish a suitable marsh slope (preferably one that matches those in the study area); the large boulders placed at the toe of the fill; a continuous placement of suitable geotextile fabric along the landward side of the boulder placements to prevent loss of fill at the toe; and plantings of appropriate saltmarsh (Spartina alterniflora) and saltmeadow (Spartina patens) cordgrass below and above high tide, respectively.

Title: Typical living shoreline section - Description: Diagram of constructed marsh profile shows Shore Road, new sand fill with new vegetation plantings on it and boulders and geotextiles to protect the toe.
Diagram of constructed marsh profile showing Shore Road (left), clean sand fill, toe protection boulders, and vegetation plantings below and above high tide (MHHW) (not to scale).

With exception of the geotextile fabric, all materials could be sourced locally and should match the native conditions and characteristics as closely as possible. For example, the size and gradation of fill material should match that of the native material as closely as possible and vegetative plantings could be transplanted from nearby donor marshes.

In this concept, the existing revetment has been buried by the fill to provide some redundancy for protection of the roadway. Note that a typical profile in one of the marsh gaps/pockets would have a modestly steeper slope and no boulder or geotextile at the toe. The shoreline slopes in these pockets will equilibrate over time to the reduced wave energy in the gaps and consist of a mixture of sandy beach and marsh plants. The result will be a series of pocket beaches backed by dense saltmarsh.

The living shoreline adaptation can also eliminate the repetitive wave damage that the asset experiences at high tide. The existing saltmarshes along the roadway are already doing this now: in those areas, there is little to no wave damage present and there is no revetment either. Laboratory investigations show that Spartina alterniflora marshes are effective at reducing wave heights by as much as 90% over a distance of 30 ft (i.e., through the marsh).[1] Existing marshes in the study area extend 70 ft to 100 ft from the edge of pavement out into the harbor, and the constructed marsh described here would be of similar size. The elevation of the new marsh will essentially protect the shoulder from waves. Therefore, the constructed marsh should be very effective at reducing wave damage along the shoulder. The living shoreline itself does nothing to eliminate the potential for flooding when water levels are above the roadway elevation.

Considering future sea level rise, some studies suggest that saltmarshes are at least keeping pace with the present-day rate of sea level rise in the Long Island Sound area.2 This suggests that the living shoreline adaptation may function as well in the future as it does at the time of construction with regards to wave height attenuation and protection of the roadway shoulder.

In terms of constructability, the techniques for construction will be less common but should be easily accomplished by a coastal marine contractor with restoration experience. The material costs could be considerably less than the traditional “hard” protection. There may be a need for some adaptive management including providing supplemental plantings through the first several growing seasons depending on the success of the planted marsh and related to sand movement in response to the establishment of a new equilibrium with the structures.

Obtaining the required coastal construction permits will be more involved for the living shoreline adaptation as compared to a traditional armoring adaptation. This is because the living shoreline option involves activities seaward of mean high tide and filling of water bottoms. One way to address this may be with a special variance as a living shoreline demonstration project. Similar projects have been allowed as demonstration projects with some level of required monitoring around the country. The regulatory framework in some states (e.g., Alabama, Maryland, Mississippi, New Jersey, North Carolina) has been modified to facilitate such projects, where they are suitable alternatives to traditional shoreline armoring, under general coastal construction permits.

Source: FHWA research

Living Levee and Breakwater to Protect San Francisco Bay Bridge Touchdown

As part of an FHWA-funded pilot, the Metropolitan Transportation Commission (MTC), the MPO for the San Francisco Bay Area, conducted a detailed analysis of installing a living levee in combination with a breakwater to protect the Bay Bridge touchdown from sea level rise, storm surge, and waves.

Without protection, the site would be inundated under the following scenarios:

Existing conditions coupled with a 50-year tide event.

A living levee would protect against future inundation and flooding due to sea level rise and storm surges. A breakwater would reduce wave heights and protect the areas from future wave overtopping and wave-induced erosion. The pilot developed a conceptual design that would protect the bridge touchdown and toll plaza area against at least a mid-century sea level rise (approximately 12 inches) coupled with a 100-year extreme tide event. The design includes freeboard to meet the requirements for FEMA accreditation, protect against wave overtopping, and be adaptable to accommodate higher sea level rise magnitudes (36 inches). The proposed placement of the living levee and breakwater are shown below.

Title: A potential breakwater placement and configuration offshore of Radio Beach that will minimize wave action and overtopping with 36 inches of SLR. The protected area where the wave heights will be reduced by at least half due to diffraction is shown within the dotted lines. - Description: Aerial photograph of the San Francisco-Oakland Bay Bridge touchdown with an outline of the potential placement of a breakwater on the north side of the approach and an arrow pointing to the area that would be protected by the adaptation strategy.

Title: Approximate footprint of the living levee designed to protect I-80 from inundation under 36 inches of SLR. - Description: Aerial photograph of the San Francisco-Oakland Bay Bridge touchdown with an outline of the potential placement of a living levee on the north side of the approach.

A living levee has a flatter seaward slope than a traditional levee in order to allow for the planting of vegetation, the creation of marsh habitat, the dissipation of wave energy, and the space to accommodate future adaptive management efforts that may be needed as sea levels continue to rise. The drawing below shows a cross-section of the living levee conceptual design.

Title: A cross-section of the designed living levee. In this design, the existing access road is moved to the crest of the levee. As the levee itself will not compensate for lost beach and marsh habitat due to sea level rise, it is recommended that sandy beach or marsh sediment be subsequently placed seaward of the levee. Appropriate beach grass or marsh plants could be planted in this area - Description: A cross-section of a living levee with vegetation on the gently sloping Bay side, an access road on top of the levee, and a steeper backside slope down to I-80.

The breakwater was designed for a wave height with an approximate 25-year return period. The larger northeastern segment of the breakwater is oriented perpendicular to the design wave direction and the shorter southwestern segment is oriented to minimize impacts to longshore sediment transport. The drawing below shows a cross-section of the breakwater conceptual design.

Title: A cross-section of the designed breakwater. The total design height and width are 14 feet and 78 feet respectively - Description: Cross-section sketch of the potential breakwater adaptation strategy. The breakwater is designed to cover -3.5 feet NAV88 existing bottom to 10.5 ft NAV88 crest elevation.

Implementing the living levee and breakwater would involve large scale construction in the bay, which triggers complex environmental and regulatory requirements. This requires the collaboration of multiple agencies, including Caltrans, the Port of Oakland, Alameda County, East Bay Regional Parks District, San Francisco Bay Conservation and Development Commission, Regional Water Quality Board, Bay Area Toll Authority, California Department of Fish and Game, California State Lands Commission, California State Parks, NOAA, and USACE.

The analysis indicates that the strategies would save $15 million in daily avoided mobility costs to the region (hours of delay, vehicle miles traveled, air pollutants) and protect 40 acres of wetlands. The conceptual level cost estimate is $5.4 million for the living levee and $11.6 million for the breakwater, which includes a 40% contingency.

See the full chapter for detailed analysis of the climate change impacts to the site, the conceptual design, regulatory considerations, benefits, costs, operations and maintenance.

Source: Chapter 5 (24 pages) of MTC, Climate Change and Extreme Weather Adaptation Options for Transportation Assets in the Bay Area Pilot Project, December 2014. http://mtc.ca.gov/tools-and-resources/digital-library/climate-change-and-extreme-weather-adaptation-options

Living Shorelines Projects in Maryland that Protect Coastal Roads

Title: Aerial image of living shorelines project protecting MD Route 5 - Description: Shows band of vegetation and rocks between Saint Mary's River and highway.
Text Box: Image of a living shorelines project protecting MD -5 at St. Mary's College of Maryland from flooding of a tributary of the Chesapeake Bay.

The Maryland Department of Natural Resources (DNR) has an active living shorelines program that works with private landowners and public agencies to install ecosystem-based shoreline protection that offers better protection than traditional hard structures without negatively impacting adjacent properties. DNR provides loans and grants to finance the projects. Loan repayments are used to fund new projects. Maryland’s 2008 Living Shorelines Law and 2013 regulations serve as a model for other states. Several of the projects have been partnerships with local agencies to protect roads (see table below). In addition, DNR is currently partnering with the Maryland State Highway Administration on a living shorelines project to protect Hambrooks Boulevard in Cambridge, MD.

Living Shorelines Projects in Maryland that Protect Roads
PROJECT NAME

COUNTY

ROADWAY LOCATION

LIVING SHORELINE PROJECT TYPE

LENGTH (L.F.)

PROJECT COST

DATE COMPLETE

Bay Ridge SECD

Anne Arundel

Bay Drive

Breakwaters

2,250

$1,039,910

1/1992

Town of Vienna

Dorchester

Water Street

Stone Sill

305

$157,472

12/2001

Our Lady Star of the Sea

Calvert

Solomon's Is. Road

Stone Groins

430

$144,987

12/2004

Penttinen, E.W. & E.R.

Anne Arundel

Deep Creek Avenue

Stone Sill

100

$22,724

6/2011

Columbia Beach SECD

Anne Arundel

Crowner Road

Stone Sill

2,346

$485,000

10/2011

Arey, P.H.

Anne Arundel

Wiltshire Lane

Stone Sill

172

$62,188

5/2012

Gibson Road

St. Mary's

Gibson Road

Stone Sill

260

$94,973

7/2013

Lord R.L. & Zearfoss N.

St. Mary's

Gibson Road

Stone Sill

330

$108,015

6/2014

Annapolis Cove SECD

Anne Arundel

Comm. Access Road

Stone Sill/Groins

720

$209,425

10/2013

Town of Charlestown LS project

Cecil

Baltimore-Colonial & Tasker Lane

Revetment/Groins

677

$319,900.00

12/2006

Dorchester County (tire recycling center) LS project

Dorchester

Hoopers Island Road

Stone Sill

627

$102,197.00

12/2002

Mid-Hoopers Island Rd

Dorchester

Hoopers Island Road

Breakwaters

1200

$552,963.00

6/1996

McCready's Point Rd

Dorchester

McCready's Point Rd

Breakwaters

330

$411,485.00

6/1995

TOTALS:

9,747

$3,711,239.00

The living shoreline strategy requires understanding coastal processes and working with them rather than against them. The projects are very site specific because of differing bathymetry and exposure. However, the projects in Maryland typically have a structural component to break the waves, approximately 30 foot wide sand deposition, and native vegetation. Maryland has also been able to standardize some of the criteria for deciding among types of projects (see table below), materials (sand, rock, etc), construction practices (such as ensuring three points of contact between stones) and a general construction specifications package.

Maryland’s Criteria for Determining Living Shoreline Project Type

Creek or Cove

Minor River

Major Tributary

Chesapeake Bay

Water depth (ft)

1

1 to 2

2 to 4

4 to 15

Fetch (miles)

0.5

1 to 1.5

2 or more

2 or more

Erosion (ft/yr)

2 or less

2 to 4

4 to 8

8 to 20

Wave energy

low

medium

medium

High

Type

Non-structural:

Beach replenishment

Fringe marsh creation

Marshy islands

Coir logs edging and groins

Hybrid:

Marsh fringe with stone groins

Marsh fringe with stone sills

Marsh fringe with stone breakwaters

Marsh edging with stone

Stabilization of streambanks with vegetation and stone

Stone breakwaters with beach replenishment and appropriate vegetation

Structural:

Bulkheads

Revetments

Stone reinforcing

Pre-case concrete units

Cost per linear foot

$100 - $200

$350-$400

$450-$600

$500-$1,500

Source: MD DNR

After many years of conducting living shorelines projects, Maryland DNR has developed a process that allows the regulatory and permitting process to go smoothly and for projects to be implemented in a timely fashion. DNR organizes a pre-application meeting with all of the regulatory agencies, which include USACE, Fisheries, Maryland Historical Trust, and the Maryland Department of Environment, as well as the local public. This allows the interested parties to provide feedback that will save time and energy later on, after the formal application has been submitted. DNR has standard specifications and bid documents for design engineers for the projects as well as a list of vetted contractors. After a contractor is selected, the design process usually takes about one month. Then the permitting and approvals process takes about six to eight months. After permitting, the project is put out to bid and construction typically requires one to two months. Ongoing maintenance is important to project success.

An assessment study of 200 living shorelines sites in Maryland found that these projects successfully maintain coastal processes and reverse erosion. Prior to installation of the living shoreline projects, the sites are typically experiencing about 2 feet per year of erosion. Hurricane Isabel in 2003 brought an 8 foot storm surge to Maryland shores and provided a test to the living shorelines projects. The projects functioned as designed, attenuating wave forces, protecting the structure behind them, and maintaining sand and soils in place due to the vegetation root structure. Following Isabel, DNR experienced a surge in demand for living shorelines projects from landowners who observed that their neighbor’s properties with living shorelines projects were well protected from Isabel.

Source: Interview and emails with Bhaskar Subramanian, Maryland Department of Natural Resources.

Plumb Beach Re-nourishment Project

This project, managed by the US Army Corps of Engineers, is to reduce coastal storm risk to Plumb Beach and the Belt Parkway in Brooklyn, NY.

Phase I was completed in late 2012 and involved placing approximately 127,000 cubic yards of sand in the severely eroded Plumb Beach area along the Belt Parkway, a busy highway and a critical piece of the city’s infrastructure. The sand was placed just prior to Hurricane Sandy’s arrival and helped prevent serious damage to the Belt Parkway. Phase I also involved the installation of a temporary geotube groin structure to help mitigate the loss of Phase I sand while the Corps awaited the ability to award Phase II.

Phase II involves the construction of two permanent stone groins at each end of the beach to help mitigate erosion in the long run. It also involves the construction of a permanent stone breakwater in the water off of the severely eroded area essentially parallel to the beach to mitigate future sand loss. Phase II also involves planting vegetation in sand dunes to help strengthen them as well as the installation of sand fencing to trap sand blowing landward.

While Phase I provides immediate coastal storm risk reduction benefits to both the Belt Parkway and the frequently used bike path along it, Phase II is designed to keep the coastal storm risk reduction benefits in place longer by managing the movement of sand and greatly reducing the need for future re-nourishments at the project site.

The local cost-sharing sponsor for both phases of the project is the New York City Department of Parks and Recreation with 65 percent of funding being federal and 35 percent being local. Phase I was completed through a $3.5 million contract with Great Lakes Dredge and Dock based out of Oak Brook, Ill., and beneficially reused sand dredged from Ambrose Channel as part of ongoing efforts to deepen the navigation channels associated with the Port of New York and New Jersey. A $2 million contract for Phase II was awarded to Village Dock, Inc., of Port Jefferson, NY.

Source: Excerpted and modified from USACE Press Release, February 6, 2013

Beach Nourishment to Protect Sections of California Highway 1

The Association of Monterey Bay Area Governments developed a plan identifying four strategies to reduce coastal erosion along southern Monterey Bay in California. One of these strategies involves beach nourishment to protect critical infrastructure, including sections of California Highway 1.

Source: Association of Monterey Bay Area Governments, Coastal Regional Sediment Management Plan for Southern Monterey Bay, 2008

Protections for Louisiana Highways LA-27, LA-82, and LA-182 in the Louisiana Coastal Master Plan

In 2012, Louisiana’s Coastal Protection and Restoration Authority developed a Coastal Master Plan to provide a system-wide plan for reducing hurricane flood risk and restoring land along the Louisiana coast. The Plan defines a set of coastal protection and restoration projects to be implemented by the state over the next 50 years. Six of these projects create wetlands in order to protect sections of Louisiana’s highways. The criteria used for selecting projects consider future climate impacts.

Several Louisiana highways are vulnerable to flooding from hurricanes, including LA-27, LA-82, and LA-182. To shield these highways, the Plan selected six land restoration projects that will create protective wetland buffers. One type of project involves hydrologic restoration, which repairs degraded wetlands by removing blockages to the natural flow of water. Restoration is accomplished by conveying water to areas that had been previously cut off by man-made levees or other built structures. In the Mermentau Basin, three projects will increase the flow of freshwater to wetlands adjacent to LA-27 near Creole and sections of LA-82 near Grand Chenier and Pecan Island. An additional project will increase connectivity among wetlands on either side of LA-182 in the Chacahoula Basin. Connected wetlands will become more robust and provide a stronger natural barrier against shoreline erosion.

To provide additional protection for LA-82, the Plan also selected a marsh creation project to establish new wetland habitat near Grand Chenier, and a shoreline protection project to construct rock breakwaters along the Schooner Bayou Canal near North Prong. Breakwaters are walls that extend out into a body of water to protect a shoreline from the impact of waves. These breakwaters are intended to dampen wave energy and prevent degradation of existing wetlands adjacent to the highway.

Source: State of Louisiana, Coastal Protection and Restoration Authority, Louisiana’s Comprehensive Master Plan for a Sustainable Coast, 2012.


[1] USACE (2013) Laboratory Studies of Wave Attenuation through Artificial and Real Vegetation, U.S. Army Corps of Engineers, ERDC TR-13-11, Washington, DC, 93 pp.

[2] Cochran, J.K., Hirschberg, J.W., and Dere, C. (1998) Atmospheric Deposition of Metals to Coastal Waters (Long Island Sound, New York U.S.A.): Evidence from Saltmarsh Deposits. Estuarine, Coastal and Shelf Science 46, 503-522.

Updated: 12/29/2016
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