Doctor of Philosophy (PhD)
Biological and Agricultural Engineering
Coastal land loss in Louisiana is occurring at astounding rates. New technologies for shoreline protection are needed that incorporate traditional engineering designs with natural systems (e.g., oyster reefs). Under optimal environmental conditions eastern Oysters (Crassotrea virginica) can biologically dominate artificial concrete reef structures used as coastal breakwaters within the intertidal zone. These reefs can also serve as oyster broodstock sanctuaries providing a nexus to the public oyster grounds benefiting the aquaculture industry. The use of biologically dominated, engineered breakwaters may provide a viable solution to coastal restoration and shoreline protection challenges. Biologically dominated coastal breakwaters can be integrated into coastal zone management strategies to preserve coastal resources by offering compatible uses across multiple disciplines. An experimental study was conducted at Rockefeller Wildlife Refuge monitoring material strength, sediment accretion, and oyster biometrics on high-relief, three-dimensional artificial reefs using concrete scaffoldings for growth substrates. Spat plate data on these reefs indicated the spring spatfall exceeded 10,000 spat/m^2 in some locations. Oyster shell height measurements of 50 cm were recorded after six months growth, with oyster counts exceeding 500 per m^2 on the artificial concrete modular breakwater reefs. Alternate concrete substrates (i.e., vitrified expanded clay) showed optimal strength and weight when compared to traditional higher density aggregates, weighing less than 50% by volume with no statistically significant difference in ASTM 39 standards for compressive strength (3,328 lbs with P<.001). Biologically dominated concrete structures showed a significant increase in ASTM 78 standards for flexural strength over time from an initial 28-day curing load of 100 lbs to loads of 479 lbs in six months and 1,344 lbs in two years. Pilot scale breakwater emplacements dominated by biological growth accumulated nearly 4 m3 of sediment over four years. Heavy and light density reef emplacements installed for less than one year accreted 1.6 and 0.37 m3 of sediment, respectively, relative to baseline cross-shore transects with no breakwater emplacements.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Risinger, Jon David, "Biologically dominated engineered coastal breakwaters" (2012). LSU Doctoral Dissertations. 3300.