Coastal Ocean Analytics

Living Shorelines in Connecticut
Why Living Shorelines
The Connecticut Coast
Marshes
Beaches and Dunes
Bluffs
Hardened Shorelines
Types of Living Shorelines
Design Considerations
Permitting
Resources
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Currently Defended Shorelines

Much of the Connecticut shoreline of Long Island Sound is hardeded with manmade coastal protection structures. The types most commonly found along the Connnecticut shoreline are :
Groins Old Saybrook Groin Lynde Point Jetty
Seawalls Old Saybrook seawall Bulkhead Severn bulkhead
Revetment GLP revetment Breakwaters Fenwick Breakwater



For shorelines currently defended by a functional coastal protection structure, such as a seawall, revetment or groin, the best option may be to do nothing. However, if the structure has failed or is at imminent risk of failure, it may be appropriate to remove it and replace it with a Living Shoreline. Alternatively, the structure could be modified to enhance the coastal habitats at the site.


Groins



Groins, frequently incorrectly referred to as jetties, are shore parallel structures designed to prevent the alongshore movement of sand. Constructed of stone, timber, sheet piling or concrete, they increase erosion of downdrift shorelines by preventing natural coastal processes. Groins may be constructed singly or as erosion increases on downdrift beaches, a series of groins are constructed alongshore. Previously, groins were a popular form of coastal protection; however, many groins along the Connecticut shoreline are no longer functional due to lack of available sediment or deterioration of the structure. Newly constructed groins are artificially filled with sand to prevent adverse impacts on neighboring shorelines.
Saybrook groin Fenwick groin
Fenwick concrete groin


Jetties

Although groins and jetties may be constructed of similar materials and are frequently confused, they perform different functions. Jetties are designed to maintain the position of inlets and prevent sand from filling navigation channels.
Westbrook jetty

Seawalls

 
Seawalls are shore parallel structures, designed to protect upland property from coastal erosion and flooding caused by wave action and storm surge. Seawalls are typically constructed of concrete of steel sheet piling.
Westbrook timber seawall
Watch Hill seawall
 Westbrook concrete seawall



Bulkheads


Bulkheads are vertical, shore parallel structures, designed to retain upland sediment. Constructed of concrete, timber or steel sheet piling or vinyl composite, they are typically used in low wave energy environments.
Severn bulkhead

Revetments


Madison revetment
A revetment is a sloping, shore parallel structure of rock, or concrete units or slabs, designed built to protect a scarp or bluff against erosion by wave action, storm surge and currents. Revetment may also be used to provide additional protection at the toe of seawalls.


Breakwaters

Breakwaters are designed to reduce wave action at the shore. Breakwaters may be connected to the shoreline or detached from it.


Stonington attached breakwater Stonington detached breakwater


Several options are available for addressing erosion along currently defended shorelines. The most appropriate method will depend on site specific conditions.  There are many parameters to consider before selecting a Living Shoreline approach.  Some questions to ask are:

1.       What is the existing engineered structure at the site?

Coastal engineering structures are designed to perform different functions to provide protection from wave action and storm surge. For instance, groins are designed to interrupt alongshore transport of sand away from the site, creating or maintaining a beach to mitigate wave action. Alternatively, a seawall is a physical barrier to wave action.

2.       Is the existing structure functional or easily repaired? Is the existing structure performing the protective function for which it was designed? Is a different form of protection needed now?

If the existing structure is serviceable and performing the protective function which is needed at the site, no action may be the most suitable approach. Even if the existing structure is function, adding a hybrid Living Shoreline could enhance the ecosystem services at the project site.

3.       Is the project site experiencing erosion?

Do nothing may be the most suitable approach if the site is experiencing little to no erosion, The engineered structure may no longer be functioning as designed or the site conditions could have changed since completion of the structure.

4.       If you have a seawall or revetment, is there evidence that it is regularly overtopped and overwashed by waves, and/or that flooding occurs landward of the structure’s crest?

Seawalls, bulkheads and revetments that are regularly overtopped are susceptible to scouring landward of the structure, and to potential failure.

5.       Is the structure damaged on a regular basis? Is it being flanked (erosion around the ends of the structure)?

It is critical to address existing and potential damage to the structure before it leads to failure of the structure and potential damage to existing landward buildings and infrastructure. A Living Shoreline may provide sufficient protection to reduce potential damage to the existing coastal structure.

6.       Does the existing coastal structure provide sufficient protection?

A Living Shoreline may increase the protection provided by the existing structure.

7.       Is shoreline usage changing?

Changes to shoreline usage may warrant a change to the existing protection. For example, a seawall may not be compatible with swimming, sunbathing or small boat access.

8.       Are changes being made to neighboring shoreline protection?

Changes made on adjacent or nearby properties may affect the coastal processes at the project site. This needs to be considered when evaluating existing or future coastal protection requirements.

For a printable check list, click here

Little information is available in the literature on removing and replacing traditional coastal engineering structures with Living Shoreline approaches, and even less information exists on the best approach to enhance the ecosystem services of hardened structures. Since a large proportion of the Connecticut shoreline is already armored with traditional coastal protection structures, it is critically important to determine through research and experience the best methods of improving coastal habitats in the presence of hardened structures. This photograph shows a healthy marsh that was planted in front of an existing seawall. The marsh mitigates the wave heights at the wall.

If the existing coastal structure is functional or easily repaired, the best approach is to consider alternatives for the future replacement, or techniques to enhance the shoreline habitat. With the current state of knowledge, some options to consider are:

  • Replacing impervious surface landward of your structure, with salt-tolerant plants
  • Roughening the surface of your seawall or adding tidal pools to enhance the shoreline habitat
  • Placing rubble mound rock at the base of your seawall to reduce wave energy
  • Using environmentally friendly concrete
  • Planting dune grass on dry beach to increase sand trapping
 Charleston marsh




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Jennifer O'Donnell, Ph.D.
Coastal Ocean Analystics, LLC
jodonnell@coastaloa.com
860.961.2467
www.CoastalOA.com