Rocky and Soft Bluffs

Several options are available for addressing bluff erosion; 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.       If soft, what is the composition of your bluff? Fine, mixed or coarse (sand or cobble)?

The composition of the bluff material will affect the rate of bluff erosion. Finer material is more susceptible to wave damage than coarser sand or cobbles.

3.       Is marsh or a dry beach present (sand above normal high tide) at the toe of your bluff? If yes, how wide?

The presence of an established marsh or dry beach will provide protection to the bluff toe from wave action.

4.       If you have a low bluff, is there evidence that your bluff is regularly overtopped and overwashed by waves, and/or that flooding occurs landward of the bluff? During normal or spring tides? Storm surges?

The frequency of bluff overtopping and flooding is important when determining the necessary elevation of coastal protection to mitigate coastal inundation and wave damage.

5.       Is the bluff eroding? If so, what is the rate of erosion and what is causing it? Is the base of the bluff eroding?

Storms, coastal flooding, waves, and tides contribute to erosion of coastal bluffs and the transport of bluff sediments in the coastal zone; however, coastal bluffs do not recover from destructive forces in the same manner as beach faces do. As the toe of a bluff is eroded by wave action and rising sea level, the bluff becomes unstable and slumps to the shoreline below, causing the top edge of the bluff to move landward. This natural process becomes a hazard when it threatens structures or property at the top of the bluff. The rate of bluff erosion usually varies from year to year. Even a steep bluff may remain unchanged for many years, or slump a large amount of sediment only every few years. Sand, gravel and glacial deposits eroded from the bluff may become part of the beach at the base of the bluff, helping to stabilize the shoreline (Slovinsky, 2011).

Do nothing or dune vegetation management may be suitable approaches for a stable bluff 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. Surface water runoff and groundwater seepage, as well as freeze/thaw cycles all contribute to soft bluff erosion. The section on Shoreline Change provides more information on how to determine the long-term rate of shoreline change of coastal bluffs.

6.       Is the upland bank vegetated? Has the bluff been planted or graded?

Upland vegetation is an indication of the stability of the bank and will mitigate bank erosion. For relatively protected sites or those without at-risk structures, bank grading and slope planting may be an appropriate solution to reduce erosion. See the sections on Vegetation Management and Slope of Bank Grading for more information.

7.       Is there evidence of rainfall impacts or surface runoff? Is there evidence of groundwater in the slope (seepage, damp surfaces on slope face, etc.)?

Not all erosion of coastal bluffs is caused by wave action. Many slopes are eroded by surface water runoff or groundwater seepage. Mitigating erosion caused by runoff or groundwater necessitates different approaches than for reducing wave impact at the toe of the slope.

8.       What is at the toe of your bluff? Beach? Marsh? Ledge? Do waves or normal tides reach the base of the bluff?

The type of shoreline at the toe of the bluff and its width will impact rate of erosion at the toe of the slope and also the type of living shoreline which is suitable. A wider marsh, beach or ledge will provide more protection to the toe of the bluff than a narrower shoreline. The width of the shoreline may also affect the living shoreline approach suitability.

9.       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.

10.   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 toe of the bluff. Steep nearshore bathymetry will allow larger waves to break near or at the bluff toe. See the section on Nearshore Bathymetry for more information.

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. See Tidal Range for more information.

12.   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.

13.   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. More information on can be found in the section on Wave Climate and Fetch.

14.   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. For more information on boat wakes, see Wave Climate and Fetch.

15.   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.

16.   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. Additionally, slope stability may be affected by freeze/thaw cycles. For more information, see the section on Ice.

17.   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. For more information, see the section on Shoreline Geomorphology.

18.   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. See the section on Vegetation.

19.   How will the shoreline be used? 

The intended use of the shoreline may affect the suitable types of living shoreline. For instance, swimming and boating require different access to the water than fishing or nature watching. The selected type of living shoreline must be compatible with the intended usage of the shoreline.

20.   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, traditional, hard coastal protection structures may limit the effectiveness of a living shoreline.

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

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

22.   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.

For a printable checklist, click here

For soft bluffs experiencing little to no erosion, some options are

• Do Nothing
• Vegetation Management

For more exposed bluffs experiencing greater rates of erosion or those with critical infrastructure at risk, some options to consider are:

• Slope or bank grading
• Marsh restoration
  
• Toe protection with fiber logs
• Marsh toe revetment
• Marsh sills
• Oyster reefs
• Wave attenuation devices
  
• Breakwaters
  

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