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| Titel |
Spatial and temporal surface moisture dynamics on a coastal beach |
| VerfasserIn |
Yvonne Smit, Gerben Ruessink |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250144912
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| Publikation (Nr.) |
 EGU/EGU2017-8791.pdf |
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| Zusammenfassung |
| The surface moisture content on a coastal beach strongly influences aeolian sediment
transport because it acts as primary control on the development of the fetch effect and
increases the shear velocity threshold required to entrain sediment. However, the large spatial
and temporal variability in moisture content are difficult to measure and, consequently, the
key processes determining this variability are not well understood. Here, we study the spatial
and temporal moisture variability on the narrow (∼ 100 m during spring-tide ebb), barred
beach of Egmond aan Zee, The Netherlands using measurements collected with an infrared
terrestrial laser scanner (TLS; RIEGL VZ-400). Our earlier research has shown a robust
negative relation between TLS reflection and gravimetric soil moisture contents for its full
range (0% - 25%). This relation holds to about 80 m from the TLS. The TLS was
deployed during several days in autumn 2015 for 6 hours during falling and rising
tide with a 15- to 30-minute interval between individual 360˚ panorama surveys.
Each survey produced O(106 - 107) reflection values, which we converted and
averaged into surface moisture maps with a 0.25x0.25 m resolution. Preliminary
analysis of the maps reveal that surface moisture varies highly in the intertidal zone
(5% - 25%), but only little near the dune foot (2% - 5%). A striking result is the
rapid desiccation of the intertidal sandbar when its crest is just below the high-tide
level. Then, the surface-moisture content can decrease with a rate of ∼2.5% - 4%
per hour, eventually reaching the same moisture content as the dry back beach. In
contrast to the sandbar, the trough is constantly saturated as the groundwater table
intersects the trough surface even during low tide. Moreover, surface moisture on
the sandbar keeps on decreasing during rising tide until the bar inundates. Thus,
no processes involving capillary forces are established in advance of the rising
tide. The next step in our research is to investigate how tide-driven groundwater
fluctuations, which were simultaneously measured using a cross-shore array of
10 groundwater wells, contributed to the observed surface-moisture variability. |
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