Aeolian dynamics of beach scraped ridge and dyke structures

Smyth, T.A.G. and Hesp, P.A. (2015) Aeolian dynamics of beach scraped ridge and dyke structures. Coastal Engineering, 99. pp. 38-45. ISSN 0378-3839

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Where urban areas are situated close to a beach, sand dunes act as protection from flooding and erosion.When a
dune has been removed or damaged by erosion, dune, ridge or dyke re-building using heavymachinery, a process
known as beach scraping, is a common method of restoration. Following construction, natural accretion of sediment
on the backshore is preferable as it facilitates sustained natural dune building, growth of vegetation, and
habitat creation and reduces the need for further beach scraping.
This study investigates the near surface flowand transport potential for three artificial structure designs: a single
ridge, a double ridge and a dyke. The three shapes contained an identical volume of sand and were preceded by
50mof beach at an angle of 3°. A computational fluid dynamic model (CFD)was created for each scenario to calculatewind
flowand shear velocity from 4 differentwind directions at 22.5° intervals from 0° (onshore) to 67.5°.
From this data sediment flux was predicted along a two dimensional transect for each of the scenarios.
For all structures, shear velocity on the beach and stoss slope decreased as incident wind direction became more
oblique; conversely shear velocity in the lee of the crest increased. A reduction in shear velocity at the foot of each
structure also occurred and appears related to stoss slope,with the greatest reduction at the toe of the dyke structure
(stoss slope 34°) and the least before the single ridge (stoss slope 17°).
Specifically the results suggest that the double ridge structure is the most resilient to aeolian erosion. Shear velocity
reduction on the back beach is comparable to the dyke and sediment flux fromthe stoss slope of the double
ridge structure may become trapped in the swale between the two ridges encouraging sediment deposition, thus
reducing sediment transport beyond the dunes and backshore. Although the dyke structure underwent the
greatest reduction in shear velocity on the back beach it experienced substantial sediment flux at the crest and
along the top of the structure, making it susceptible to erosion during a strongwind event. The highest sediment
transport rate was calculated at the crest of the single ridge, and the single ridge structure also created the
smallest reduction of shear velocity on the back beach, thus making it less desirable than the double ridge.

Item Type: Article
Additional Information and Comments: NOTICE: this is the author’s version of a work that was accepted for publication in Coastal Engineering. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Coastal Engineering, Vol 99, May 2015,
Faculty / Department: Faculty of Science > Geography and Environmental Science
Depositing User: Thomas Smyth
Date Deposited: 01 Aug 2017 08:09
Last Modified: 01 Aug 2017 08:09

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