A GULF OF MEXICO MARSH RESTORATION AND PROTECTION PROJECT

Scott L. Douglass, Carl Ferraro, Caren Reid Dixon, Larry Oliver, Lloyd Pitts

Abstract


A $3 million (US $) marsh restoration and protection project was constructed in 2010 along 1.6 km on the northern shore of Mississippi Sound near Bayou LaBatre, Alabama to restore about 10 ha of marsh and protect another 300 ha of an extremely productive natural salt marsh estuary – Little Bay. The project restored an historic marsh peninsula with 100,000 m3 of sand pumped from a nearby dredged material disposal area; extensive vegetation plantings including over 100,000 plants; and an offshore segmented, porous breakwater consisting primarily of individual concrete units called “wave attenuation devices” or WADs. The wave transmission characteristics of these “wave attenuation devices” were measured in original laboratory wave tests for this design. The wave transmission coefficient was found to vary, 0.4<Kt<0.9, depending on configuration, depth and wave period. In other words, the “wave attenuation devices” provide fairly minimal attenuation is some cases. The functional design of the breakwater was optimized to provide just enough wave attenuation for wetlands establishment while providing for maximum flow and ingress and egress for fishes, crabs and other species. The upper level of wave tolerance for marsh grasses following Roland and Douglass (2005) was the target level controlling the breakwater design. The Little Bay project was the largest marsh restoration/protection project in Alabama history; won several state, regional and national design awards; survived design conditions in 2011; and has functioned well to date. The success of this project suggests that the application of coastal engineering principles can improve the design of “living shoreline” projects.

Keywords


Marsh restoration; marsh protection; porous breakwater; wave attenuation devices; wave transmission; Gulf of Mexico; Alabama; Bayou LaBatre; wave tolerance; living shoreline

References


Goda, Y. 2000. Random Seas and Design of Maritime Structures. Advanced Series on Ocean Engineering. World Scientific Press, vol. 15.http://dx.doi.org/10.1142/3587

Roland, R. and S.L. Douglass. 2005. Estimating Wave Tolerance of Spartina alterniflora in Coastal Alabama, Journal of Coastal Research, vol. 21, no. 3, pp. 453-463.http://dx.doi.org/10.2112/03-0079.1

Sorensen, R. 2002. Basic Coastal Engineering. Kluwer Academic Press.

Takayama T, K Nagai and T Sekiguchi. 1985. Irregular wave experiments on wave dissipation function of submerged breakwater with wide crown, Proceeding of 32th Japanese Conference on Coastal Engineering, JSCE, Vol.32, 545-549.


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