More Information:
 

Small-Scale Living Shoreline for an Exposed, Rapidly Eroding Coast

 

Living shorelines are gaining favour as a sustainable response for shoreline protection, but projects at exposed sites are often impractical because of the significant breakwaters required to control erosion and protect shoreline vegetation. The few that have been built are usually large, expensive projects funded by government agencies, such as Project Greenshores - the award-winning living shoreline along Pensacola Bay designed by EOE. Small living shoreline projects, on the scale of individual private lots, are almost exclusively built at protected sites with very limited wave exposure. In 2013 a client asked EOE to solve an erosion problem for a rapidly eroding, exposed property on Mobile Bay, AL. Shoreline retreat at this site had averaged over 2 ft/year since 1997, but the owner wanted to avoid the unwanted consequences of a hard bulkhead or revetment, which include impacts to neighbouring properties and loss of a recreational beach. The novel feature of this project is a broad-crested, offshore submerged breakwater/oyster reef that provides wave protection for the salt marsh near the shoreline. The project was constructed in the summer of 2014 at a cost competitive with traditional “hard” solutions and is undergoing a 3-year post construction monitoring program. To date, the design has been successful at controlling erosion without the usual deleterious effects, while providing a valuable recreational beach for the homeowner. 

Client:
Private homeowner, Fairhope, AL

Reports:

McGehee, David D., 2016 "Design and Monitoring of a Small Living Shoreline Scaled for Private Properties on Exposed, Rapidly-Eroding Coasts," 6th International Symposium on Hydraulic Structures, USDD and IAHR, Portland, OR, 27-30 June, 2016

McGehee, David D., and Kirschenfeld, T., 2015,   "Downsizing a Living Shoreline; Retail-scale Options for Private Properties on Exposed, Rapidly-Eroding Coasts," National Coastal Conference, American Shore and Beach Preservation Association, New Orleans, LA, 16-18 Oct, 2015 

McGehee, David D., 2013, “Design Analysis Report for Living Shoreline on (Point Clear, AL) Property,” Contractor Report to Verazo and Kirschenfeld, Emerald Ocean Engineering LLC, Pensacola, FL, October 28, 2013 

McGehee, David D., 2013,”Site Analysis Report for (Point Clear, AL) Property,” Contractor Report to Verazo and Kirschenfeld, Emerald Ocean Engineering LLC, Pensacola, FL, July 15, 2013

 

The project site is exposed to significant waves due to the 29 km fetch to the southwest (left). Aerial view of the project 6 months after construction (right) shows the submerged reef at extreme low tide. The reef is designed to function in winds up to 40 knots and survive hurricane conditions without damage. Note the naturally occurring salient (bulge) in the lee of the reef.



Project shoreline 18 months after construction at high tide shortly after experiencing a storm that exceeded the design conditions (left). Note the persistence of the salient and of the vegetated berm at the backshore. At right is a view looking downdrift at the adjacent property; the lack of localized erosion shows that sediment transport continues behind the reef.



Nearby properties, both protected (l) and unprotected (r), did not fare as well during the same storm.



Semi annul surveys show that even though the reef has adjusted dynamically, losing a few inches of elevation, the shoreline behind it has accreted about 20 ft since construction.



 

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