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Title: Short-term impoundment of longshore sediment transport
Authors: University of Florida. Department of Coastal and Oceanographic
Coastal Engineering Research Center (U.S.)
U.S. Army Engineer Waterways Experiment Station
Bodge, Kevin R.
Dean, Robert G. (Robert George), 1930-2015
Keywords: Beach erosion
Groins (Shore protection)
Sediment transport
Shore protection
Publisher: Coastal Engineering Research Center (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; CERC-87-7.
Description: Miscellaneous paper
Abstract:The cross-shore distribution of longshore sediment transport is investigated through the distribution of sediment impounded against a shore-perpendicular barrier over short-term intervals in field and laboratory environments. For each field experiment, a low-profile groyne was deployed across a natural beach in less than 8 hr, and profiles near the groyne were repeatedly surveyed for 8 to 20 hr thereafter. For each laboratory experiment, a low-profile barrier was installed across a pre-equilibrated fine sand model beach, and profile changes near the barrier were measured after 5 to 40 minutes of regular, obliquely incident, unidirectional wave action. Breaking wave angle and longshore current and wave height across the surf zone were also measured. The effects of crossshore transport and tidal fluctuation were addressed in the survey data, and the effectiveness of the barriers as impoundment agents is discussed. Local downdrift profile changes were found to be poor indicators of the local updrift impoundment. In general, the longshore transport profiles were found to be bimodal with peaks just landward of the breakpoint and near the shoreline. The relative significance of the longshore transport shifted from the near-breakpoint peak to the near-shoreline peak as the wave condition varied from spilling to collapsing breakers. Alternately stated, the longshore transport distribution appeared strongly beach profile dependent, as transport was most pronounced over local regions of high bed steepness. Between 10 and 30 percent of the total longshore transport was observed seaward of the breakpoint for all cases. Longshore transport in the swash zone represented at least 5 to 60 percent of the total transport where the largest swash contributions were associated with plunging/collapsing and collapsing surf conditions. A simple model is proposed to describe the normalized longshore transport distribution across the swash and surf zone as a function of the local longshore current, beach slope, and dissipation of wave energy per unit surf volume. The setup, longshore current, and longshore transport are described for an equilibrium beach profile which is finite-sloped at the shoreline. The shoreward convection of longshore current by wave mass transport is also discussed in relation to the longshore transport distribution. NOTE: This.pdf file is large. Allow your browser several minutes to download the file.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Miscellaneous Paper

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