Behavior and identification of ephemeral sand dunes at the backshore zone using video images

Guimarães, Pedro Veras; Pereira, Pedro; Calliari, Lauro Júlio; Ellis, Jean T.

doi:10.1590/0001-3765201620150656

Cited by 6 publications

(13 citation statements)

References 26 publications

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“…Video monitoring with high temporal resolution can be used to observe the coast on long time scales. The method has successfully been used to research the nearshore on time periods of years [27][28][29], and has been used by [18,26,30] to study signs of aeolian sand transport on the beach.…”

Section: Introductionmentioning

confidence: 99%

“…Reference [26]'s temporary camera system at Greenwich Dunes, Canada, could pick up these traces of aeolian transport, as wind-blown sand usually is dryer and therefore lighter in colour than the moist bed, providing visual contrast. When undisturbed, sand strips can grow into ephemeral dunes, which have a slipface and a height in the range of decimetres to a metre [30,38,39]. Like the traces of aeolian transport in the work of [26], these features were visible on camera because of a difference in moisture content, and therefore colour, between the transported sand of the bedforms and the bed [40].…”

Section: Introductionmentioning

confidence: 99%

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Using Argus Video Monitoring to Determine Limiting Factors of Aeolian Sand Transport on a Narrow Beach

Hage

Ruessink

Donker

2018

JMSE

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Aeolian sediment transport on beaches is responsible for dune growth and/or recovery. Models predicting potential aeolian sediment transport rates often overpredict the amount of deposition on the foredune when applied to narrow (<100 m) beaches, pointing to supply limitations. Our goal is to better understand these limitations, especially in the long-term (>years) in order to improve predicted transport volumes and the timing of transport. Here, we used 8 years of Argus video images at Egmond aan Zee, The Netherlands, in combination with routine weather data to delineate 241 limited from 467 unlimited sand transport events to explore supply-limiting factors. Our research shows that the wind is more oriented to the west (shore normal) and is generally stronger for limited transport events. This indicates that the available fetch distance is often less than the critical fetch needed for unlimited transport. This is further confirmed by the timing of the transport events, as limited events often became unlimited during low tide when the beach was the widest and fetch potentially the longest. Our results help understanding the nature of aeolian sediment transport on narrow beaches, which will hopefully lead to better predictions of annual aeolian sediment transport rates.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Using Argus Video Monitoring to Determine Limiting Factors of Aeolian Sand Transport on a Narrow Beach

Hage

Ruessink

Donker

2018

JMSE

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“…Furthermore, strong winds often cause a storm surge and inundate large portions of the beach. This was also found by Guimarães et al (2016), where they used an Argus video monitoring station to study the behaviour of protodunes.…”

Section: Monitoring Of Aeolian Sand Transportmentioning

confidence: 54%

“…Video monitoring has been used to observe sand strips, protodunes, and streamers (Delgado-Fernandez, 2010; Guimarães et al, 2016;Williams et al, 2018;Montreuil et al, 2018). Delgado-Fernandez (2010) observed that the moments with the strongest wind were not necessary the moments with the highest visual signs of transport and volumes of transported sand; out of the 9 days with strong winds, only one day resulted in high transport rates and strong visual transport signs.…”

Section: Monitoring Of Aeolian Sand Transportmentioning

confidence: 99%

“…These clearly visible, slipfaceless bedforms often form when a relatively moist bed is present (Bauer and Davidson-Arnott, 2002;Jackson et al, 2006;Davidson-Arnott et al, 2008;Bauer et al, 2009;Nield, 2011), especially when vegetation (Sherman and Hotta, 1990;Eamer and Walker, 2010), frozen material (Hesp and Arens, 1997), or other roughness elements are present as well. Sand strips can grow into ephemeral dunes, which have a slipface and a height in the range of decimetres to a metre (Guimarães et al, 2016;Kocurek et al, 1992;Elbelrhiti, 2012), but waves and tides often destroy sand strips before they can grow this far. Video monitoring has been used to study ephemeral dunes on a long-term timescale by Guimarães et al (2016).…”

Section: Introductionmentioning

confidence: 99%

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Long-term video monitoring of aeolian activity on a narrow beach

Hage¹

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Aeolian sand transport takes place when the wind is strong enough to lift a grain of sand. Predicting aeolian transport for beaches is difficult, as existing predictive models, which usually only have the wind velocity as a variable, are designed for ideal circumstances with a steady wind flow, a homogeneous grain size, and a dry and flat sand surface. Sandy beaches show different conditions. When wind-only models are applied, the resulting amount of sand that is predicted to be deposited on the foredune often exceeds the measured amount considerably, especially when the beach is less than several tens of metres wide. This is caused by transport limiting factors, such as surface moisture, the formation of salt or algae crusts, the presence of vegetation, or snow and ice cover. The aeolian transport rate increases downwind until it reaches its maximum at a distance termed the critical fetch length. When the available distance, or maximum fetch, cannot reach this critical fetch, aeolian transport will not reach its potential value. This is particularly relevant for narrow beaches. As a consequence, the moment of largest potential transport does not necessarily coincide with the moment of largest actual transport. When the actual transport is smaller than expected, the transport is limited. When this is not the case, the transport is unlimited. When transport events are limited and unlimited, and what factors control this, is not well understood. Accordingly, we also have limited capabilities in accurately predicting the long-term (>months) amount of wind-blown sand to the foredune. Improved understanding of long-term aeolian sand transport is important as the sand contributes to dune growth and recovery from storms, which is a relatively slow process and takes months to years (long-term). In contrast, erosive storm events last only a few hours or days. Coastal dunes have been strengthened and encouraged to grow to protect densely populated hinterlands by planting marram grass or placing fences to catch the sand and keep it in place. This, however, has created an unnaturally high foredune that prevents sand from being transported further inland. The input of sand into the dunes contributes to a diverse ecosystem, as the sand can bury climax vegetation and make it possible for pioneer vegetation to recolonise. Ideally, coastal dunes should combine both: provide safety from marine flooding and have a diverse ecosystem. To do this, measures to change sand dikes into dynamic systems are increasingly being implemented. This requires us knowing when to expect aeolian sand transport. The main aim of this thesis is therefore to better understand the timing of aeolian transport on a narrow beach, and to identify and elucidate key factors that determine this timing, with a focus on timescales from months to years. To reach this aim, I examined a long-term data set of video images of Egmond aan Zee, the Netherlands. Video monitoring captures signs of aeolian sand transport in the shape of sand strips, which are stripe-like, sl...

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