Date of Award

Winter 2014

Project Type

Thesis

Program or Major

Ocean Engineering

Degree Name

Master of Science

First Advisor

Diane Foster

Second Advisor

Kenneth C Baldwin

Third Advisor

Arthur Trembanis

Abstract

Scour in and around structures placed on the seafloor occurs on varying spatio-temporal scales in response to changing hydrodynamic conditions. This effort examines the scour surrounding submerged railway cars in an artificial reef environment, Red Bird Reef, located off the shores of Delaware. Repeated high resolution multibeam sonar data from a Reson 7125 Multibeam Echo Sounder is used to evaluate the sensitivity of localized scour to car orientation, water depth, sediment heterogeneity, and hydrodynamic forcing. Red Bird Reef shows unambiguous differences in scour/accretion response to varying wave climates and varying response to object based parameters such as object proximity, orientation, depth and height. This study examines the overall local scour and accretion surrounding 38 decommissioned R-26 "Redbird" subway cars placed on the seafloor functioning as an artificial reef system. Scour was shown to have axial asymmetries and is sensitive to the car orientation relative to wave direction. The observations show that the local influence area is greater than 8 times the objects width wide and 2 times the length long.

The use of bathymetric difference surfaces suggests areas where previous estimates of sediment composition transition from coarse to fine sediment are concomitant with regions of high scour variability. This result suggests that sediment grain size heterogeneity could be a significant influence on variability of submarine scour.

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