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| Titel |
Sedimentary and morphologic characterization of channel flats in gravel-bed dryland rivers |
| VerfasserIn |
R. Barzilai, J. B. Laronne, I. Reid |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024135
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| Zusammenfassung |
| Flats have low longitudinal slope, are comprised of fine-grained and well-sorted sediment,
and are common repeating macroforms, alternating with coarser bars in upland, ephemeral,
gravel-bed rivers. Typically, the sediment lacks grading. Vertical inspection of these patches
assists in estimating the quantity of fine-grained bed material available for entrainment. Also
it allows characterization of the cross sectional and longitudinal shape of the subtrate
layer.
This research has been conducted in Nahal Yatir and Nahal Krayot, two ephemeral
streams in the northern Negev, Israel. Ten flats situated in straight reaches were
chosen to represent these macroforms. Trenching has allowed observation of the
microstratigraphy and sampling of flat sediments: in each flat, several cross sections and one
longitudinal section. Images of vertical trench faces have been analysed using Digital
Gravelometry and GIS tools to determine the subsurface grain-size distributions (GSD)
of the macroform. The GSD of surface sediments of the flats have been sampled
using conventional methods. Flat shape and slope have been measured using a total
station.
Preliminary results show that the flats occupy the entire channel width in this narrow
channel. Grain size distribution of the flat indicates good sorting (average inclusive standard
deviation for the patches is -1.313 phi), with an average D50 of 1.06 mm. flat vertical
thickness ranges between 8 and 20 cm, with an average of 10.5 cm and a standard
deviation of 5 cm. The cross-section shape is upwardly concave towards the channel
banks. The shape of the sub-flat longitudinal cross-section appears to be planar. |
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