EWN Publications

2014 Egmont Key Beneficial Use of High Fines Material Using Traditional Versus Cross Shore Swash Zone Placement

C. K. Maglio, J. D. Ousley, A. Hershorin, K. E. Brutsche, M. B. Taylor, Z. J. Taylor, and P. Wan
October 31, 2020

About This Publication

WEDA Journal of Dredging

The periodic maintenance dredging of the Tampa Harbor Entrance Channel commenced during the fall of 2014 through the winter season with beach placement on Egmont Key National Wildlife Refuge and State Park. Due to severe erosion on Egmont Key, the State of Florida Department of Environmental Protection (FDEP) made an exception to Florida Administrative Code (FAC) 62B41.007 (2)(j)(k) otherwise known as the “Sand Rule” criteria for beach placement of a maximum allowance of an average of 10% fines (defined as sediment passing the 0.063 mm sieve) for maintenance dredging material. Geotechnical borings collected from the shoaled materials in the channel indicate an average composite “fines” content of 20.7% within the dredge prism. The constructed project involved beach placement of the dredged material using the traditional trapezoidal placement method and a unique placement method referred to as “cross shore swash zone (CSSZ) placement”. The CSSZ placement is constructed by discharging material directly into the swash zone of the beach until a salient forms and then extending the discharge line perpendicular offshore until a “point” feature is created in the shoreline. Once placed, the CSSZ geomorphic point feature is highly erosive and functions as a feeder beach composed of sediments that are well sorted, or “washed” of their finer fraction of sediments. The traditional and CSSZ placement operations occurred approximately 0.8 km (0.5 mi) apart on Egmont Key and allowed for a comparison of the two placement methodologies in terms of: geomorphologic evolution, compaction, volumetric loss or bulking, anecdotal turtle nesting density, initial coarsening of the placement material (fines loss), initial and chronic turbidity and potential best management practices (BMP) to minimize beach footprint impacts as well as reduce construction cost.