Beach morphologies induced by breakwaters with different orientations

Nancy L. Jackson, Mitchell D. Harley, Clara Armaroli, Karl Nordstrom

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

A desired outcome in the construction of a detached emerged breakwater is the formation of an accretionary salient in its lee to augment the beach, improve beach amenity and provide an additional buffer from storm waves. The extent to which this salient forms and its morphology are strongly controlled by the breakwater geometry with respect to the original shoreline, sediment availability, and local wave climate. The purpose of this paper is to identify how breakwater geometry and orientation of gaps between individual breakwaters alter the direction of waves entering the gaps and change the asymmetry of the salients. Four distinct breakwater sites along the Emilia-Romagna coastline in Northern Italy were chosen for a detailed field and desktop study comprising three-dimensional topographic and bathymetric surveys, sediment sampling, LiDAR flights and historical shoreline mapping. The orientations of the shorelines at these four sites range over 43°, resulting in different exposures to the dominant waves. The oblique orientations of the gaps between individual breakwater segments at three of the four sites effectively create a "gap window" between breakwaters favoring the exposure of short-period waves from the north and diminishing the effect of longer waves from the dominant east. Salients can be symmetrical despite an acute angle of approach of the dominant deep water waves where refraction is enhanced by offshore topography and breakwaters are parallel to the shore. Waves approaching normal to the gap window undergo less diffraction due to their shorter length relative to the gap window width and undergo less attenuation by breaking and bottom friction if they are locally generated and have short periods. Greater breaking-wave energy on the gap-facing slope of the salient can create shoreline and morphological asymmetry. The implication is that breakwater orientations can be designed or altered to selectively dampen or facilitate wave energy to enhance sediment transport in a desired direction, provided that breakwaters are not too far offshore and sediment availability is not restricted to affect salient formation. Adjusting exposure via gap orientation can create morphologies that cannot be inferred from process-dominant conditions.

Original languageEnglish (US)
Pages (from-to)48-57
Number of pages10
JournalGeomorphology
Volume239
DOIs
StatePublished - Jun 5 2015

Fingerprint

beach morphology
breakwater
shoreline
wave energy
asymmetry
beach
sediment
bathymetric survey
geometry
wave climate
bottom friction
breaking wave
water wave
amenity
refraction
diffraction
sediment transport
deep water
flight
topography

All Science Journal Classification (ASJC) codes

  • Earth-Surface Processes

Keywords

  • Gap orientation
  • Morphology
  • Northern Adriatic Sea
  • Offshore breakwaters
  • Salient

Cite this

Jackson, Nancy L. ; Harley, Mitchell D. ; Armaroli, Clara ; Nordstrom, Karl. / Beach morphologies induced by breakwaters with different orientations. In: Geomorphology. 2015 ; Vol. 239. pp. 48-57.
@article{899d070bd58c448aac1ec0b18366778b,
title = "Beach morphologies induced by breakwaters with different orientations",
abstract = "A desired outcome in the construction of a detached emerged breakwater is the formation of an accretionary salient in its lee to augment the beach, improve beach amenity and provide an additional buffer from storm waves. The extent to which this salient forms and its morphology are strongly controlled by the breakwater geometry with respect to the original shoreline, sediment availability, and local wave climate. The purpose of this paper is to identify how breakwater geometry and orientation of gaps between individual breakwaters alter the direction of waves entering the gaps and change the asymmetry of the salients. Four distinct breakwater sites along the Emilia-Romagna coastline in Northern Italy were chosen for a detailed field and desktop study comprising three-dimensional topographic and bathymetric surveys, sediment sampling, LiDAR flights and historical shoreline mapping. The orientations of the shorelines at these four sites range over 43°, resulting in different exposures to the dominant waves. The oblique orientations of the gaps between individual breakwater segments at three of the four sites effectively create a {"}gap window{"} between breakwaters favoring the exposure of short-period waves from the north and diminishing the effect of longer waves from the dominant east. Salients can be symmetrical despite an acute angle of approach of the dominant deep water waves where refraction is enhanced by offshore topography and breakwaters are parallel to the shore. Waves approaching normal to the gap window undergo less diffraction due to their shorter length relative to the gap window width and undergo less attenuation by breaking and bottom friction if they are locally generated and have short periods. Greater breaking-wave energy on the gap-facing slope of the salient can create shoreline and morphological asymmetry. The implication is that breakwater orientations can be designed or altered to selectively dampen or facilitate wave energy to enhance sediment transport in a desired direction, provided that breakwaters are not too far offshore and sediment availability is not restricted to affect salient formation. Adjusting exposure via gap orientation can create morphologies that cannot be inferred from process-dominant conditions.",
keywords = "Gap orientation, Morphology, Northern Adriatic Sea, Offshore breakwaters, Salient",
author = "Jackson, {Nancy L.} and Harley, {Mitchell D.} and Clara Armaroli and Karl Nordstrom",
year = "2015",
month = "6",
day = "5",
doi = "10.1016/j.geomorph.2015.03.010",
language = "English (US)",
volume = "239",
pages = "48--57",
journal = "Geomorphology",
issn = "0169-555X",
publisher = "Elsevier",

}

Beach morphologies induced by breakwaters with different orientations. / Jackson, Nancy L.; Harley, Mitchell D.; Armaroli, Clara; Nordstrom, Karl.

In: Geomorphology, Vol. 239, 05.06.2015, p. 48-57.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Beach morphologies induced by breakwaters with different orientations

AU - Jackson, Nancy L.

AU - Harley, Mitchell D.

AU - Armaroli, Clara

AU - Nordstrom, Karl

PY - 2015/6/5

Y1 - 2015/6/5

N2 - A desired outcome in the construction of a detached emerged breakwater is the formation of an accretionary salient in its lee to augment the beach, improve beach amenity and provide an additional buffer from storm waves. The extent to which this salient forms and its morphology are strongly controlled by the breakwater geometry with respect to the original shoreline, sediment availability, and local wave climate. The purpose of this paper is to identify how breakwater geometry and orientation of gaps between individual breakwaters alter the direction of waves entering the gaps and change the asymmetry of the salients. Four distinct breakwater sites along the Emilia-Romagna coastline in Northern Italy were chosen for a detailed field and desktop study comprising three-dimensional topographic and bathymetric surveys, sediment sampling, LiDAR flights and historical shoreline mapping. The orientations of the shorelines at these four sites range over 43°, resulting in different exposures to the dominant waves. The oblique orientations of the gaps between individual breakwater segments at three of the four sites effectively create a "gap window" between breakwaters favoring the exposure of short-period waves from the north and diminishing the effect of longer waves from the dominant east. Salients can be symmetrical despite an acute angle of approach of the dominant deep water waves where refraction is enhanced by offshore topography and breakwaters are parallel to the shore. Waves approaching normal to the gap window undergo less diffraction due to their shorter length relative to the gap window width and undergo less attenuation by breaking and bottom friction if they are locally generated and have short periods. Greater breaking-wave energy on the gap-facing slope of the salient can create shoreline and morphological asymmetry. The implication is that breakwater orientations can be designed or altered to selectively dampen or facilitate wave energy to enhance sediment transport in a desired direction, provided that breakwaters are not too far offshore and sediment availability is not restricted to affect salient formation. Adjusting exposure via gap orientation can create morphologies that cannot be inferred from process-dominant conditions.

AB - A desired outcome in the construction of a detached emerged breakwater is the formation of an accretionary salient in its lee to augment the beach, improve beach amenity and provide an additional buffer from storm waves. The extent to which this salient forms and its morphology are strongly controlled by the breakwater geometry with respect to the original shoreline, sediment availability, and local wave climate. The purpose of this paper is to identify how breakwater geometry and orientation of gaps between individual breakwaters alter the direction of waves entering the gaps and change the asymmetry of the salients. Four distinct breakwater sites along the Emilia-Romagna coastline in Northern Italy were chosen for a detailed field and desktop study comprising three-dimensional topographic and bathymetric surveys, sediment sampling, LiDAR flights and historical shoreline mapping. The orientations of the shorelines at these four sites range over 43°, resulting in different exposures to the dominant waves. The oblique orientations of the gaps between individual breakwater segments at three of the four sites effectively create a "gap window" between breakwaters favoring the exposure of short-period waves from the north and diminishing the effect of longer waves from the dominant east. Salients can be symmetrical despite an acute angle of approach of the dominant deep water waves where refraction is enhanced by offshore topography and breakwaters are parallel to the shore. Waves approaching normal to the gap window undergo less diffraction due to their shorter length relative to the gap window width and undergo less attenuation by breaking and bottom friction if they are locally generated and have short periods. Greater breaking-wave energy on the gap-facing slope of the salient can create shoreline and morphological asymmetry. The implication is that breakwater orientations can be designed or altered to selectively dampen or facilitate wave energy to enhance sediment transport in a desired direction, provided that breakwaters are not too far offshore and sediment availability is not restricted to affect salient formation. Adjusting exposure via gap orientation can create morphologies that cannot be inferred from process-dominant conditions.

KW - Gap orientation

KW - Morphology

KW - Northern Adriatic Sea

KW - Offshore breakwaters

KW - Salient

UR - http://www.scopus.com/inward/record.url?scp=84925955140&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84925955140&partnerID=8YFLogxK

U2 - 10.1016/j.geomorph.2015.03.010

DO - 10.1016/j.geomorph.2015.03.010

M3 - Article

AN - SCOPUS:84925955140

VL - 239

SP - 48

EP - 57

JO - Geomorphology

JF - Geomorphology

SN - 0169-555X

ER -