Risk Management Strategies for Coastal Communities

US Army Corps of Engineers

North Atlantic Division Website

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base map

This map shows various coastal storm damage risk management strategies communities can use to adapt to anticipated base flood level change by 2100 (at a non-specific location). Although specific communities should consider a range of all possible solutions based on site-specific conditions, not all strategies to reduce coastal storm damage risk are structural solutions.

Non-structural: Acquisition and Relocation

Non-structural:

Image #1: Acquisition and Relocation

Acquisition and Relocation

Often considered a drastic approach to storm damage reduction, property acquisition and structure removal are usually associated with frequently damaged structures.
Implementation of other measures may be effective but if a structure is subject to repeated storm damage, this measure may represent the best alternative to eliminating risks to the property and residents.

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Non-structural: Building Retrofit

Non-structural:

Graphic #2: Building Retrofit

Building Retrofit

A non-elevated structure in the flood zone is prone to flooding.
Building retrofit measures include elevation of a structure or possibly dry flood proofing of a structure.
Elevation of a structure is usually limited to smaller residential and commercial buildings.
Whether a structure may be elevated depends on a number of factors, including the foundation type, wall type, size of structure, condition, etc.

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Non-structural: Enhanced flood warning and evacuation planning

Non-structural:

Graphic #3: Enhanced Flood Warning and Evacuation Planning

Enhanced Flood Warning and Evacuation Planning

Flood warning systems and evacuation planning are applicable to vulnerable areas.
Despite improved tracking and forecasting techniques, the uncertainty associated with the size of a storm, the path, or its duration necessitate that warnings be issued as early as possible.
Evacuation planning is imperative for areas with limited access, such as barrier islands, high density housing areas, elderly population centers, cultural resources, and areas with limited transportation options.

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Non-structural: Land use management / zoning and flood insurance

Non-structural:

Graphic #4: Land Use Management / Zoning and Flood Insurance

Land Use Management / Zoning and Flood Insurance

Communities participating in the National Flood Insurance Program are proactive in promoting floodplain management and flood risk awareness.

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Structural: Deployable Floodwalls

Structural:

Graphic 5: Deployable Floodwalls

Deployable Floodwalls

Rapid Deployment Floodwalls are structures that are temporarily erected along the banks of a river or estuary, or in the path of floodwaters.
Rapid Deployment Floodwalls also prevent water from reaching the area behind the structure and are usually used in locations where space is limited.

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Structural: Floodwalls

Structural:

Graphic #6: Floodwalls

Floodwalls

Floodwalls are structures used to prevent flooding and to protect relatively small areas or areas with limited space for large flood protection measures.
Floodwalls are most frequently used in urban and industrial areas.

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Structural: Levees

Structural:

Graphic #7: Levees

Levees

Levees and dikes are embankments constructed along a waterfront to prevent flooding in relatively large areas for high levels of flood risk.
If a levee or dike is located in an erosive shoreline environment, revetments may be needed on the waterfront side for more protection from erosion

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Structural: Seawalls

Structural:

Graphic #8: Seawalls

Seawalls

Seawalls, are typically massive structures whose primary purpose is interception of waves and reduction of wave-induced overtopping and flooding.
Note that under this definition seawalls do not include structures with the principal function of reducing flood risk to low-lying coastal areas.
In those cases a high, impermeable, armored structure known as a sea dike is typically required to prevent coastal flooding.

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Structural: Revetments

Structural:

Graphic #9: Revetments

Revetments

Revetments are onshore structures with the principal function of protecting the shoreline from erosion.
Revetments typically consist of a cladding of stone, concrete, or asphalt to armor sloping natural shoreline profiles.

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Structural: Bulkheads

Structural:

Graphic #10: Bulkheads

Bulkheads

Bulkheads primarily retain soil and experience little to no wave action.

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Structural: Storm Surge Barriers

Structural:

Graphic #11: Storm Surge Barriers

Storm Surge Barriers

Storm surge barriers reduce risk to estuaries against storm surge flooding and waves.
In most cases the barrier consists of a series of movable gates that normally stay open under normal conditions to let the flow pass but are closed when storm surges are expected to exceed a certain level.
Storm surge barriers are often chosen as a preferred alternative to close off estuaries and reduce the required length of flood protection measures behind the barriers.
Storm surge barriers are typically opened during normal conditions to allow for navigation and saltwater exchange with the estuarine areas landward of the barrier.

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Structural / Natural and nature-based features: Beach Restoration

Structural / Natural and Nature-Based Features:

Graphic #12: Beach Restoration

Beach Restoration

Relatively narrow beach and low dunes fronting a typical beachfront development.
A beach with beach fill has a wide berm and high, vegetated dunes.

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Structural / Natural and nature-based features: Beach Restoration and Breakwaters

Structural / Natural and nature-based features:

Graphic #13: Beach Restoration and Breakwaters

Beach Restoration and Breakwaters

Narrow beach and low dunes fronting a typical beachfront development.
Wide and narrow beach with breakwaters in front of beach, less wave exposure.
Breakwaters reduce the amount of wave exposure.

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Structural / Natural and nature-based features: Beach Restoration and Groins

Structural / Natural and nature-based features:

Graphic #14: Beach Restoration and Groins

Beach Restoration and Groins

On some coastlines, there is more sand leaving the area via longshore sediment transport than there is sand arriving to replace it. Such beaches are eroding and are typically very narrow.
Groins are structures that extend perpendicularly from the shoreline.
Groins are usually built to stabilize a stretch of natural or artificially nourished beach against erosion that is due primarily to a net longshore loss of beach material.
The effect of a single groin is accretion of beach material on the updrift side and erosion on the downdrift side.

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Structural / Natural and nature-based features: Drainage Improvements

Structural / Natural and nature-based features:

Graphic #15: Drainage Improvements

Drainage Improvements

A drainage system can carry water away via conveyance systems and, during times of high water, may store water until it can be carried away in storage facilities.
Conveyance systems utilize measures such as pump stations, culverts, drains, and inlets to remove water from a site quickly and send it to larger streams.
Storage facilities are used to store excess water until the storm or flood event has ended.

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Structural / Natural and nature-based features: Living Shorelines

Structural / Natural and nature-based features:

Graphic #16: Living Shorelines

Living Shorelines

Open and exposed shorelines are prone to erosion due to waves.
Living shorelines are essentially tidal wetlands constructed along a shoreline to reduce coastal erosion.
Living shorelines maintain dynamic shoreline processes, and provide habitat for organisms such as fish, crabs and turtles.
An essential component of a living shoreline is constructing a rock structure (breakwater/sill) offshore and parallel to the shoreline to serve as protection from wave energy that would impact the wetland area and cause erosion and damage or removal of the tidal plants.

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Natural and nature-based features: Overwash Fans

Natural and nature-based features:

Graphic #17: Overwash Fans

Overwash Fans

Overwash fans are a component of the sediment budget of barrier islands.
Overwash fans are believed to be a relevant process in the rollover or retreat mechanism of some coastal barriers in response to sea level rise.

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Natural and nature-based features: Reefs

Natural and nature-based features:

Graphic #18: Reefs

Reefs

The development of artificial reefs in bays provides a means to reestablish and enhance reef communities.
Artificial reefs provide shoreline erosion protection.
Artificial reefs are established for various reasons, amongst others:
- restore degraded or damaged natural reefs.
- Provide three dimensional habitat structure above the bottom.
- Provide fishing and scuba diving opportunities.

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Natural and nature-based features: Submerged Aquatic Vegetation

Natural and nature-based features:

Graphic #19, Submerged Aquatic Vegetation

Submerged aquatic vegetation

Submerged Aquatic Vegetation performs many important functions, including:
- Wave attenuation and sediment stabilization,
- Water quality improvement,
- Primary production,
- Food web support for secondary consumers, and
- Provision of critical nursery and refuge habitat for fisheries species.

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Natural and nature-based features: Wetlands

Nature and nature-based features:

Graphic #20, Wetlands

Wetlands

The dense vegetation and shallow waters within wetlands can slow the advance of storm surge somewhat and slightly reduce the surge landward of the wetland or slow its arrival time.
Wetlands can also dissipate wave energy; potentially reducing the amount of destructive wave energy propagating on top of the surge, though evidence suggests that slow-moving storms and those with long periods of high winds that produce marsh flooding can reduce this benefit.

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