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| Titel |
Floodplain sediment from a 100-year-recurrence flood in 2005 of the Ping River in northern Thailand |
| VerfasserIn |
S. H. Wood, A. D. Ziegler |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 12, no. 4 ; Nr. 12, no. 4 (2008-07-11), S.959-973 |
| Datensatznummer |
250010751
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| Publikation (Nr.) |
 copernicus.org/hess-12-959-2008.pdf |
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| Zusammenfassung |
The tropical storm, floodwater, and the floodplain-sediment layer of a
100-year recurrence flood are examined to better understand characteristics
of large monsoon floods on medium-sized rivers in northern Thailand. Storms
producing large floods in northern Thailand occur early or late in the
summer rainy season (May–October). These storms are associated with tropical
depressions evolving from typhoons in the South China Sea that travel
westward across the Indochina Peninsula. In late September, 2005, the
tropical depression from Typhoon Damrey swept across northern Thailand
delivering 100–200 mm/day at stations in mountainous areas. Peak flow from
the 6355-km2 drainage area of the Ping River upstream of the city of
Chiang Mai was 867 m3s−1 (river-gage of height 4.93 m) and flow
greater than 600 m3s−1 lasted for 2.5 days. Parts of the city of
Chiang Mai and some parts of the floodplain in the intermontane Chiang Mai
basin were flooded up to 1-km distant from the main channel.
Suspended-sediment concentrations in the floodwater were measured and
estimated to be 1000–1300 mg l−1.
The mass of dry sediment (32.4 kg m-2), measured over a 0.32-km2
area of the floodplain is relatively high compared to reports from European
and North American river floods. Average wet sediment thickness over the
area was 3.3 cm. Sediment thicker than 8 cm covered 16 per cent of the area,
and sediment thicker than 4 cm covered 44 per cent of the area. High
suspended-sediment concentration in the floodwater, flow to the floodplain
through a gap in the levee afforded by the mouth of a tributary stream as
well as flow over levees, and floodwater depths of 1.2 m explain the
relatively large amount of sediment in the measured area.
Grain-size analyses and examination of the flood layer showed about 15-cm
thickness of massive fine-sandy silt on the levee within 15-m of the main
channel, sediment thicker than 6 cm within 200 m of the main channel
containing a basal coarse silt, and massive clayey silt beyond 200 m. The
massive clayey silt would not be discernable as a separate layer in section
of similar deposits. The fine-sand content of the levee sediment and the
basal coarse silt of sediment within 200 m of the main channel are
sedimentological features that may be useful in identifying flood layers in
a stratigraphic section of floodplain deposits. |
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