Living Shorelines in Connecticut

Marshes

For more information on the design parameters, click here.

Several options are available for addressing erosion of coastal marshes; 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.       Is there an existing coastal engineering structure (seawall, groin, revetment, etc.) at the site?

The presence of an existing engineering structure may affect the coastal processes at the site and must be considered before an appropriate living shoreline approach can be determined. If the structure is functioning as designed, or easily repaired, the most appropriate approach may be to do nothing or repair the structure, while considering alternatives for future needs. See Currently Defended Shorelines for more information on coastal engineering structures.

2.       What is the condition of the marsh? Is there presently a vegetated wetland at the edge of the property? Is the vegetation dense or sparse? How wide is the marsh?

The condition of the existing marsh is an indication of the potential success of a living shoreline approach. A marsh with dense, healthy vegetation is likely to be a suitable site for a non-structural approach. A less dense marsh may be enhanced with vegetation management, trimming or overhanding branches and removal of fallen trees and debris.

3.       Is the marsh eroding? If so, what is the rate of erosion and what is causing it?

Do nothing or vegetation management may be suitable approaches for a stable marsh with little to no erosion. With higher rates of erosion, it is necessary to determine what is causing the erosion. Mitigating erosion from frequent boat wakes may indicate a different approach than one used to reduce storm flooding and wave damage. While seasonal damage may not be a cause for concern, a marsh may take years to recover from significant ice damage.

4.       Is there infrastructure at risk?

If the existing infrastructure cannot be moved back or up, it may be necessary to select an approach that would provide more protection than a non-structural approach. Evaluation of the site may determine that a living shoreline approach is unsuitable.

5.       What is the wave climate?

The wave climate is a critical parameter in determining the most appropriate approach to shoreline protection. Vegetation-only approaches are usually only suitable for site exposed to low wave heights. The wave climate will determine the type of living shoreline, and the height and composition of the protective structure. Fetch, the distance wind blows of water, is frequently used as an estimate of the wave conditions at a site.

6.       What is the boat traffic?

Some sites, particularly those along navigable rivers streams, may experience larger waves due to boat wake than wind waves. The proximity to a powerboat marina or navigational channel, and the frequency and size of vessels are an important design consideration.

7.       Is the site affected by tidal, riverine or alongshore currents?

Nearshore currents can scour protective structures and transport fill material away from the project site.

8.       What is the shoreline geometry?

The Connecticut shoreline of Long Island Sound is highly variable. The shoreline geometry may be straight, curved or irregular. This high variability is one reason why the most suitable approach to shoreline protection is so site-specific. A headland beach (also known as a pocket beach) is generally crescent or crenulate-shaped, bounded by protective headlands so the shoreline is relatively protected and the sediment supply usually remains between the headlands. A straight shoreline is more exposed to large waves and transport of sediment away from the site.

9.       What is the intertidal slope/nearshore bathymetry?

The intertidal slope and nearshore bathymetry determine the size of the waves at the shoreline. A gradually sloping nearshore region will cause larger waves to break further offshore, reducing the wave energy at the marsh. Steep nearshore bathymetry will allow larger waves to break near or at the marsh edge.

10.   Is the upland bank vegetated?

Upland vegetation is an indication of the stability of the bank. However, mature vegetation may provide too much shade for marsh plant survivability.

11.   What is the tidal range?

The tidal range will impact the height and location of the shoreline protection approach. Most of the existing living shoreline structures have been constructed in areas with low tidal ranges on the order of a couple of feet. Tidal ranges along the Connecticut shoreline vary from about 2.4 ft in Stonington to 7.5 ft in Greenwich. In addition, storm surge heights are typically larger in Connecticut than where living shorelines have been constructed previously.

12.   Does the project site flood regularly during normal or spring tides? Storm surge?

Flooding of coastal marshes is a natural process; however, if the site floods during normal or spring tides, the marsh may not provide sufficient protection from storm waves. Marshes typically do not provide protection from storm surge, so the potential risk from coastal inundation is an important design consideration.

13.   Is the project site affected by ice?

The Connecticut coast is affected by ice damage, exacerbated by nor-easters and tidal flow. The approach selected must withstand anticipated ice forces at the site.

14.   Does the site have submerged aquatic vegetation or nearshore oyster beds?

Submerged aquatic vegetation or the presence of nearshore recreational oyster beds may affect the type of living shoreline that can be permitted at the site.

15.   What is the composition of the nearshore region?

Some soils may not be able to tolerate the weight of living shoreline approaches such as marsh sills or reef balls. Settling of the structure could render it ineffective. The presence of offshore vegetation or aquatic species may be negatively impacted by the living shoreline. For instance, fill material could bury aquatic plants and animals, or sills and breakwaters could damage nearshore habitats.

16.   What is the condition of the adjacent properties?

Depending on the width of the project site, the condition of adjacent properties may affect the suitability of living shoreline approaches. For instance, the presence of marsh may indicate the suitability of the site for marsh creation or restoration. Hard coastal structures may limit the effectiveness of a living shoreline.

17.   Is the project site accessible from land or water?

Access to the project site will affect the cost and constructability of a living shoreline.

18.   What are the potential effects of sea level rise on the project site?

Depending on the anticipated lifetime of the living shoreline, the effects of sea level rise on the erosion mitigation approach may be a selection factor.

A printable checklist of design considerations can be found here.

Some of the options for mitigating coastal erosion on marshes are:

For marshes that are not eroding:

• Do Nothing
• Vegetation Management

For marshes experiencing erosion, options to consider include:

• Slope or Bank Grading
• Marsh Restoration
• Toe Protection with Fiber Logs
• Marsh Toe Revetment
• Marsh Sills
• Oyster Reefs
• Wave Attenuation Devices
• Breakwaters