Bedload transport in a tropical headwater catchment
Abstract
Multi-year observations reveal a distinct seasonal pattern in the transport of bedload material in stream draining a 94-ha headwater basin in northern Thailand. The patterning is related to the presence of a monsoon rainy season, during which 90% of the annual 1200-1400 mm of rainfall occurs. Mean daily bedload transport during the wet season (mid-May through October) is 3-4 times greater than that during the drier months. More than 70% of the annual bedload total is mobilized during the wet season. A clock-wise hysteresis pattern characterizes the annual time series, such that more material is mobilized per unit discharge during the wet months than the drier months. This phenomenon results, in part, from two processes related to the monsoon climate regime and the current land-use: (a) large volumes of bedload are transported during a handful of short, flashy runoff events; and (b) bedload material is continually re-supplied during the wet period by runoff entering the stream from the road network. Also apparent in the annual transport pattern is a coarsening of bedload transported during the wettest months, when mean daily stream flow is 4-5 greater higher than that during the drier months. The size of material transported during storm events appears to be limited by the bed architecture (e.g., imbrication) up to a threshold discharge of about 2/3 bank full discharge (QBF = 0.5 cms). In five years of monitoring, QBF has been exceeded only once. The largest stone transported during that event was 10.65 kg; the diameter of the b-axis was 0.21 m.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.H51F..06Z
- Keywords:
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- 1815 Erosion and sedimentation;
- 1860 Runoff and streamflow;
- 9320 Asia