Foredune accretion under offshore winds

Lynch, Kevin; Jackson, Derek W.T.; Cooper, J. Andrew G.

doi:10.1016/j.geomorph.2007.12.011

Cited by 64 publications

(57 citation statements)

References 23 publications

(21 reference statements)

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“…In a subsequent study at the PEI site, Bauer et al (2012) documented pronounced deflection of oblique incident winds over the foredune, and found that wind directions on the beach during a storm event were far less variable than those on the dune crest for the same incident winds. During alongshore incident flow conditions Lynch et al (2009) found that wind near the dune crest was deflected more offshore compared to the flow along the beach and, for obliquely onshore winds, they found a deflection of ~20° towards shore-normal.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

Flow deflection over a foredune

et al. 2015

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Flow deflection of surface winds is common across coastal foredunes and blowouts. Incident winds approaching obliquely to the dune toe and crestline tend to be deflected towards a more crest-normal orientation across the stoss slope of the foredune. This paper examinesfield measurements for obliquely incident winds, and compares them to computational fluid dynamics (CFD) modelling of flow deflection in 10° increments from onshore (0°) to alongshore (90°) wind approach angles. The mechanics of flow deflection are discussed, followed by a comparative analysis of measured and modelled flow deflection data that shows strong agreement. CFD modelling of the full range of onshore to alongshore incident winds reveals that deflection of the incident wind flow is minimal at 0° and gradually increases as the incident wind turns towards 30° to the dune crest. The greatest deflection occurs between 30° and 70° incident to the dune crest. The degree of flow deflection depends secondarily on height above the dune surface, with the greatest effect near the surface and toward the dune crest. Topographically forced flow acceleration ("speed-up") across the stoss slope of the foredune is greatest for winds less than 30° (i.e., roughly perpendicular) and declines significantly for winds with more oblique approach angles. There is less lateral uniformity in the wind field when the incident wind approaches from >60° because the effect of aspect ratio on topographic forcing and streamline convergence is less pronounced.

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Section: Accepted M Manuscriptmentioning

confidence: 99%

Flow deflection over a foredune

et al. 2015

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“…From a geomorphological point of view, embryo dunes present the most interesting shapes because they are very sensitive to even small changes in coastal environment factors and they can quickly be destroyed as they are created. However, due to the progradation in this area, mainly caused by aeolian transport (Lynch et al, 2009), the embryo dunes generally grow and join each other.…”

Section: The Case Studymentioning

confidence: 99%

Uavs to Assess the Evolution of Embryo Dunes

Taddia

Corbau

Zambello

et al. 2017

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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ABSTRACT:The balance of a coastal environment is particularly complex: the continuous formation of dunes, their destruction as a result of violent storms, the growth of vegetation and the consequent growth of the dunes themselves are phenomena that significantly affect this balance. This work presents an approach to the long-term monitoring of a complex dune system by means of Unmanned Aerial Vehicles (UAVs). Four different surveys were carried out between November 2015 and November 2016. Aerial photogrammetric data were acquired during flights by a DJI Phantom 2 and a DJI Phantom 3 with cameras in a nadiral arrangement. GNSS receivers in Network Real Time Kinematic (NRTK) mode were used to frame models in the European Terrestrial Reference System. Processing of the captured images consisted in reconstruction of a three-dimensional model using the principles of Structure from Motion (SfM). Particular care was necessary due to the vegetation: filtering of the dense cloud, mainly based on slope detection, was performed to minimize this issue. Final products of the SfM approach were represented by Digital Elevation Models (DEMs) of the sandy coastal environment. Each model was validated by comparison through specially surveyed points. Other analyses were also performed, such as cross sections and computing elevation variations over time. The use of digital photogrammetry by UAVs is particularly reliable: fast acquisition of the images, reconstruction of high-density point clouds, high resolution of final elevation models, as well as flexibility, low cost and accuracy comparable with other available techniques.

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“…Sand drift potential was calculated for two conditions. In the first, the findings from Lynch et al (2007) were utilized to adjust offshore wind velocities and directions to allow for secondary airflow effects. Oblique offshore winds (131°-202° and 253°-309°) were corrected to 130 and 310° (alongshore airflow) respectively, with no velocity changes.…”

Section: Wind Climate and Sand Drift Potentialmentioning

confidence: 99%

“…This event supplied more sand to the foredunes than the combined contribution of all the onshore events during the 8 weeks of the study. this site, because downward vertical wind motion can occur above the leading edge of erodible material (Lynch et al, 2007), while deflected offshore airflow travels alongshore with a relatively unlimited fetch. The results presented in Table I again reveal, similarly to the trench trap study, that the day (1 October) with one of the shortest fetches (15 m) experienced the most saltation activity.…”

Section: Trench Trap Studymentioning

confidence: 99%

Aeolian fetch distance and secondary airflow effects: the influence of micro‐scale variables on meso‐scale foredune development

Lynch

Jackson

Cooper

2007

Earth Surf Processes Landf

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Unsuccessful attempts to use process-scale models to predict long-term aeolian sediment transport patterns have long been a feature of aeolian research. It has been proposed that one approach to overcome these problems is to identify micro-scale variables that are important at longer timescales. This paper assesses the contribution of two system variables (secondary airflow patterns and fetch distance) to medium-term (months to years) dune development. The micro-scale importance of these variables had been established during previous work at the site (Magilligan Strand, Northern Ireland). Three methods were employed. First, sand drift potentials were calculated using 2 years of regional wind data and a sediment transport model. Second, wind data and large trench traps (2 m length × × × × × 1 m width × × × × × 1·5 m depth) were used to assess the actual sediment transport patterns over a 2-month period. Third, a remote-sensing technique for the identification of fetch distance, a saltation impact sensor (Safire) and wind data were utilized to gauge, qualitatively, sediment transport patterns over a 1-month period. Secondary airflow effects were found to play a major role in the sediment flux patterns at these timescales, with measured and predicted rates matching closely during the trench trap study. The results suggest that fetch distance is an unimportant variable at this site.

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Foredune accretion under offshore winds

Cited by 64 publications

References 23 publications

Flow deflection over a foredune

Flow deflection over a foredune

Uavs to Assess the Evolution of Embryo Dunes

Aeolian fetch distance and secondary airflow effects: the influence of micro‐scale variables on meso‐scale foredune development

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