Beach-dune dynamics: Spatio-temporal patterns of aeolian sediment transport under complex offshore airflow

Kevin Lynch, Derek Jackson, Irene Delgado-Fernandez, Andrew Cooper, Andreas Baas, Meiring Beyers

Research output: Contribution to conferencePoster

Abstract

This study examines sand transport and wind speed across a beach at Magilligan Strand, Northern Ireland, under offshore wind conditions. Traditionally the offshore component of local wind regimes has been ignored when quantifying beach-dune sediment budgets, with the sheltering effect of the foredune assumed to prohibit grain entrainment on the adjoining beach. Recent investigations of secondary airflow patterns over coastal dunes have suggested this may not be the case, that the turbulent nature of the airflow in these zones enhances sediment transport potential. Beach sediment may be delivered to the dune toe by re-circulating eddies under offshore winds in coastal areas, which may explain much of the dynamics of aeolian dunes on coasts where the dominant wind direction is offshore. The present study investigated aeolian sediment transport patterns under an offshore wind event. Empirical data were collected using load cell traps, for aeolian sediment transport, co-located with 3-D ultrasonic anemometers. The instrument positioning on the sub-aerial beach was informed by prior analysis of the airflow patterns using computational fluid dynamics. The array covered a total beach area of 90 m alongshore by 65 m cross-shore from the dune crest. Results confirm that sediment transport occurred in the ‘sheltered’ area under offshore winds. Over short time and space scales the nature of the transport is highly complex; however, preferential zones for sand entrainment may be identified. Alongshore spatial heterogeneity of sediment transport seems to show a relationship to undulations in the dune crest, while temporal and spatial variations may also be related to the position of the airflow reattachment zone. These results highlight the important feedbacks between flow characteristics and transport in a complex three dimensional surface.
Original languageEnglish
Publication statusPublished - 2010
EventAmerican Geophysical Union (AGU) Fall Meeting - San Francisco, United States
Duration: 13 Dec 201017 Dec 2010

Conference

ConferenceAmerican Geophysical Union (AGU) Fall Meeting
CountryUnited States
CitySan Francisco
Period13/12/1017/12/10

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airflow
sediment transport
dune
beach
entrainment
sand
sediment budget
anemometer
computational fluid dynamics
wind direction
positioning
eddy
temporal variation
spatial variation
wind velocity
coast
sediment

Cite this

Lynch, K., Jackson, D., Delgado-Fernandez, I., Cooper, A., Baas, A., & Beyers, M. (2010). Beach-dune dynamics: Spatio-temporal patterns of aeolian sediment transport under complex offshore airflow. Poster session presented at American Geophysical Union (AGU) Fall Meeting, San Francisco, United States.
Lynch, Kevin ; Jackson, Derek ; Delgado-Fernandez, Irene ; Cooper, Andrew ; Baas, Andreas ; Beyers, Meiring. / Beach-dune dynamics: Spatio-temporal patterns of aeolian sediment transport under complex offshore airflow. Poster session presented at American Geophysical Union (AGU) Fall Meeting, San Francisco, United States.
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abstract = "This study examines sand transport and wind speed across a beach at Magilligan Strand, Northern Ireland, under offshore wind conditions. Traditionally the offshore component of local wind regimes has been ignored when quantifying beach-dune sediment budgets, with the sheltering effect of the foredune assumed to prohibit grain entrainment on the adjoining beach. Recent investigations of secondary airflow patterns over coastal dunes have suggested this may not be the case, that the turbulent nature of the airflow in these zones enhances sediment transport potential. Beach sediment may be delivered to the dune toe by re-circulating eddies under offshore winds in coastal areas, which may explain much of the dynamics of aeolian dunes on coasts where the dominant wind direction is offshore. The present study investigated aeolian sediment transport patterns under an offshore wind event. Empirical data were collected using load cell traps, for aeolian sediment transport, co-located with 3-D ultrasonic anemometers. The instrument positioning on the sub-aerial beach was informed by prior analysis of the airflow patterns using computational fluid dynamics. The array covered a total beach area of 90 m alongshore by 65 m cross-shore from the dune crest. Results confirm that sediment transport occurred in the ‘sheltered’ area under offshore winds. Over short time and space scales the nature of the transport is highly complex; however, preferential zones for sand entrainment may be identified. Alongshore spatial heterogeneity of sediment transport seems to show a relationship to undulations in the dune crest, while temporal and spatial variations may also be related to the position of the airflow reattachment zone. These results highlight the important feedbacks between flow characteristics and transport in a complex three dimensional surface.",
author = "Kevin Lynch and Derek Jackson and Irene Delgado-Fernandez and Andrew Cooper and Andreas Baas and Meiring Beyers",
year = "2010",
language = "English",
note = "American Geophysical Union (AGU) Fall Meeting ; Conference date: 13-12-2010 Through 17-12-2010",

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Lynch, K, Jackson, D, Delgado-Fernandez, I, Cooper, A, Baas, A & Beyers, M 2010, 'Beach-dune dynamics: Spatio-temporal patterns of aeolian sediment transport under complex offshore airflow' American Geophysical Union (AGU) Fall Meeting, San Francisco, United States, 13/12/10 - 17/12/10, .

Beach-dune dynamics: Spatio-temporal patterns of aeolian sediment transport under complex offshore airflow. / Lynch, Kevin; Jackson, Derek; Delgado-Fernandez, Irene; Cooper, Andrew; Baas, Andreas; Beyers, Meiring.

2010. Poster session presented at American Geophysical Union (AGU) Fall Meeting, San Francisco, United States.

Research output: Contribution to conferencePoster

TY - CONF

T1 - Beach-dune dynamics: Spatio-temporal patterns of aeolian sediment transport under complex offshore airflow

AU - Lynch, Kevin

AU - Jackson, Derek

AU - Delgado-Fernandez, Irene

AU - Cooper, Andrew

AU - Baas, Andreas

AU - Beyers, Meiring

PY - 2010

Y1 - 2010

N2 - This study examines sand transport and wind speed across a beach at Magilligan Strand, Northern Ireland, under offshore wind conditions. Traditionally the offshore component of local wind regimes has been ignored when quantifying beach-dune sediment budgets, with the sheltering effect of the foredune assumed to prohibit grain entrainment on the adjoining beach. Recent investigations of secondary airflow patterns over coastal dunes have suggested this may not be the case, that the turbulent nature of the airflow in these zones enhances sediment transport potential. Beach sediment may be delivered to the dune toe by re-circulating eddies under offshore winds in coastal areas, which may explain much of the dynamics of aeolian dunes on coasts where the dominant wind direction is offshore. The present study investigated aeolian sediment transport patterns under an offshore wind event. Empirical data were collected using load cell traps, for aeolian sediment transport, co-located with 3-D ultrasonic anemometers. The instrument positioning on the sub-aerial beach was informed by prior analysis of the airflow patterns using computational fluid dynamics. The array covered a total beach area of 90 m alongshore by 65 m cross-shore from the dune crest. Results confirm that sediment transport occurred in the ‘sheltered’ area under offshore winds. Over short time and space scales the nature of the transport is highly complex; however, preferential zones for sand entrainment may be identified. Alongshore spatial heterogeneity of sediment transport seems to show a relationship to undulations in the dune crest, while temporal and spatial variations may also be related to the position of the airflow reattachment zone. These results highlight the important feedbacks between flow characteristics and transport in a complex three dimensional surface.

AB - This study examines sand transport and wind speed across a beach at Magilligan Strand, Northern Ireland, under offshore wind conditions. Traditionally the offshore component of local wind regimes has been ignored when quantifying beach-dune sediment budgets, with the sheltering effect of the foredune assumed to prohibit grain entrainment on the adjoining beach. Recent investigations of secondary airflow patterns over coastal dunes have suggested this may not be the case, that the turbulent nature of the airflow in these zones enhances sediment transport potential. Beach sediment may be delivered to the dune toe by re-circulating eddies under offshore winds in coastal areas, which may explain much of the dynamics of aeolian dunes on coasts where the dominant wind direction is offshore. The present study investigated aeolian sediment transport patterns under an offshore wind event. Empirical data were collected using load cell traps, for aeolian sediment transport, co-located with 3-D ultrasonic anemometers. The instrument positioning on the sub-aerial beach was informed by prior analysis of the airflow patterns using computational fluid dynamics. The array covered a total beach area of 90 m alongshore by 65 m cross-shore from the dune crest. Results confirm that sediment transport occurred in the ‘sheltered’ area under offshore winds. Over short time and space scales the nature of the transport is highly complex; however, preferential zones for sand entrainment may be identified. Alongshore spatial heterogeneity of sediment transport seems to show a relationship to undulations in the dune crest, while temporal and spatial variations may also be related to the position of the airflow reattachment zone. These results highlight the important feedbacks between flow characteristics and transport in a complex three dimensional surface.

UR - http://www.agu.org/meetings/fm10/

M3 - Poster

ER -

Lynch K, Jackson D, Delgado-Fernandez I, Cooper A, Baas A, Beyers M. Beach-dune dynamics: Spatio-temporal patterns of aeolian sediment transport under complex offshore airflow. 2010. Poster session presented at American Geophysical Union (AGU) Fall Meeting, San Francisco, United States.