What is the Coastal Defense app?

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Coastal Defense is an application for examining how coastal habitats such as oyster reefs, coral reefs, tidal marshes, mangroves, beach dunes, and seagrass help protect coastal areas by reducing wave energy hitting the shore.  Coastal Defense is part of a collection of “apps” that help identify nature-based solutions.

 

Coastal Defense is an application that evaluates how natural systems such as oyster reefs and marshes can decrease wave height and energy.

Main Functions

1. Identify areas that may be at risk of coastal erosion and inundation from wave action and storm surge.

2. Examine the role of coastal habitats in attenuating wave height and energy.

3. Determine appropriate adaptation strategies that incorporate green and grey infrastructure trade-offs.

Who should use it?

Managers of Coastal Protection Infrastructure
High tides and storm waves can erode and overtop structures which impacts maintenance costs for coastal communities and floodplain farmers. Understanding how coastal habitats can reduce wave energy and how they impact the structural integrity of built infrastructure is of particular concern.

Managers of coastal protection infrastructure, like this bank erosion prevention project at Layou, SVG (St. Vincent and Grenadines), can use Coastal Defense to find nature-based solutions to help reduce risk to built infrastructure.

Managers of coastal protection infrastructure, like this bank erosion prevention project at Layou, SVG (St. Vincent and Grenadines), can use Coastal Defense to find nature-based solutions to help reduce risk to built infrastructure. Photo Credit: Marjo Aho

County Planners & Managers
Planners and managers are interested in lowering long-term maintenance costs by utilizing the most effective combination of habitat and hardened infrastructure. They can implement Coastal Defense to prioritize conservation or restoration efforts, and determine the sites where intertidal habitats have the greatest potential to provide wave attenuation benefits to people, shorelines, and infrastructure.

Habitat Restoration Community
Restoration planners can implement this tool to identify and prioritize conservation or restoration efforts and determine where coastal habitats have the greatest potential to promote wave attenuation benefits, species diversity, buffering capacity, and long term ecosystem health.

The restoration community can use Coastal Defense to find nature-based risk reduction solutions that can provide multiple benefits beyond coastal protection. In the Pacific Northwest, these benefits include buffering ag land runoff, reducing flood risk, and recovering critical salmon species like the steelhead pictured here. Photo credit: Tom and Pat Leeson.

How does it work?

The Coastal Defense app is based on a coastal protection model from the Natural Capital Project’s Marine Integrated Valuation of Environmental Services and Tradeoffs (InVEST) program.

The model calculates the potential of coastal ecosystems to reduce wave height and wave energy, thereby lowering the risk of inundation and erosion in coastal areas, thereby reducing risk to community assets and built infrastructure*.

The Coastal Defense Model workflow.

* It is important to note that this is not a validated predictive model and is meant to provide guidance as an informative and educational tool.

How does the app quantify the amount of wave attenuation achieved by coastal habitats?

  • Coastal Defense quantifies the amount of wave attenuation by computing the percent reduction in wave height and wave energy in the presence and absence of coastal habitats.

Why does Coastal Defense use a 1-Dimension model to estimate the role of coastal habitats?

  • This app was created to give a reasonable estimate of the beneficial role that coastal habitats play in protecting shorelines. A 1-D model is used because it’s fast, robust, and gives reasonable results.

How are the offshore wave height and period computed?

  • The wave height and period are then calculated by combining wind speed, the fetch distance, and the average water depth in the bay.

Coastal Defense estimates a potential wave by calculating wind over a finite fetch distance.

How does the app compute fetch?

  • Fetch is the length of water over which a given wind is capable of blowing. The app projects 144 fetch vectors every 2.5 degrees for up to 50 km in length for each transect point on land. For each land point, those vectors are then averaged over the sixteen, 22.5 degree equiangular sectors that compose the entire compass rose.

How are wind speed data processed?

  • Historical wind speed and direction data can be pulled from the NOAA National Buoy Center. These data are simplified by computing the maximum, mean, mean speed above the 90th percentile, and modal wind speed for each of the 16 equiangular sectors that compose the compass rose.

 

What are the strengths and limitations?

App Strengths

1.  The app quantifies and evaluates the amount of wave energy and potential erosion reduction associated with the presence of various types of coastal habitats.

2. The modular functionality of this model allows it be quickly applied in various geographies either broadly, using default data, or site-specifically, where local data are available.

3. The app is capable of evaluating multiple habitat types like coral reefs, marshes, oyster reefs, seagrass, and mangroves.  Upcoming versions of the model will be able to calculate the cumulative wave attenuation services multiple habitats provide.

4. The user can also measure the effects of coastal habitats on reducing risk to various types of coastal infrastructure such as earthen levees, seawalls, or bare shorelines.

5. This model is relatively easy and inexpensive to run.

App Limitations

1. Currently, the model does not address wave/current interactions. Waves are modeled along a 1-Dimensional transect, and 2-D processes are not considered.

2. Habitat length and directional placement offshore are not currently addressed.

Where is it being used?

Role of existing marsh habitat in reducing risk in the Skagit Bay Diking District

This version of Coastal Defense was specifically developed to evaluate the role that tidal marshes  play in attenuating waves and reducing the risk of erosion and overtopping to levees in Skagit Bay located within Puget Sound, Washington.  The goal is to use this app to identify win-win projects that can benefit a broad spectrum of stakeholders including farmers, tribes, and state officials. This coordinated approach will also help identify projects that could receive both salmon recovery AND flood risk reduction funding and that can make a broader impact.  Click here to visit the Puget Sound Coastal Defense app.

Coastal Defense in Skagit Bay, WA aims to evaluate how tidal marshes can reduce risk to levee infrastructure in the diking district.

Oyster Reef Restoration Design in Mobile Bay, AL

In 2010, TNC and partners created the “100-1000 : Restore Coastal Alabama Partnership “where the goal is to restore 100 miles of oyster reef breakwaters and promote 1,000 acres of marsh and seagrass in Alabama. The Coastal Defense app is being used to prioritize restoration sites. Outputs from the app help evaluate where oyster reef restoration might provide the best solution.  Click here to visit the Gulf of Mexico Coastal Defense app. 

545 volunteers working to help the Restore Coastal Alabama Project restore oyster reefs in Helen Wood Park, Mobile Bay, AL. Photo credit: 2011 Erika Nortemann/TNC.

545 volunteers working to help the Restore Coastal Alabama Project restore oyster reefs in Helen Wood Park, Mobile Bay, AL. Photo credit: 2011 Erika Nortemann/TNC.

 

Oyster Reef Restoration Siting in Charlotte Harbor, FL

The Charlotte Harbor Coastal Defense app was developed to evaluate the role that restored oyster reefs play in wave attenuation and coastal protection. The app is being used to help make the case for oyster reef restoration siting and project funding in the area.  Click here to visit the Gulf of Mexico Coastal Defense app.

Coastal Defense in Charlotte Harbor, FL helps evaluate the wave attenuation benefits of proposed oyster reef restoration.

Coastal Defense in Charlotte Harbor, FL helps evaluate the wave attenuation benefits of proposed oyster reef restoration.

Coming Soon!

A Coastal Defense app focused on exploring the wave attenuation benefits of coral reefs and mangroves in Southeast Florida is currently in development and is expected to be released near the end of 2014.

Who helped develop it?

Coastal Defense Collaboration

The Nature Conservancy and various partners are collaborating on innovative models and decision support tools that allow planners and managers to evaluate how coastal habitats can protect shorelines from erosion, reduce the risks of coastal hazards to people and nature, and stimulate fisheries economies.

The Nature Conservancy has long been active in all of the states on the Gulf Coast protecting and restoring critical habitats.  Through the Conservancy’s decade-long partnership with the NOAA Restoration Center, and more recently with support from the American Recovery and Reinvestment Act, we have jointly invested millions of dollars in the restoration of Gulf oyster reefs, seagrass beds, coastal wetlands, coral reefs, and barrier islands.

The Natural Capital Project is a partnership among Stanford University, The Nature Conservancy, the World Wildlife Fund, and the University of Minnesota that works to develop and provide practical ecosystem services concepts and tools, apply these tools in select areas around the world, and engage influential leaders to advance change in policy and practice through mainstreaming the approaches.

The Center for Integrated Spatial Research (CISR) at the University of California, Santa Cruz, serves as principal software developer of the “enterprise” level Coastal Defense app. The expanded application enables users to examine the cumulative protective benefits of multiple coastal habitats. CISR also serves a leading role in the development and support of Coastal Resilience’s enterprise GIS data and web services infrastructure.

The University of Southern Mississippi (USM) designed the Gulf of Mexico Coastal Defense app focused on oyster reefs and wave attenuation given specific restoration design criteria. USM works on various apps on risk, resilience and restoration in the U.S. and internationally.

The U.S. Geological Survey has collaborated on the coastal protection model and initial concepts behind the Coastal Defense app. They developed the first app in Puget Sound on tidal marshes that examines its wave attenuation benefits in relation to levee structures in Skagit Bay. USGS partners on this and other Coastal Resilience projects throughout the U.S.