| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系 === 86 === Bed configuration in a 180 alluvial channel bend at
steady statecondition was studied experimentally and
numerically. The experimentswere conducted in a 20cm wide
glass channel. Elevations of the channelbed at steady state
were measured transversely at cross-sections of thebend in
interval. Topography as well as the longitudinal,
transverseslopes were obtained from the measured data.
It is observed from the bed configuration that the bed
variation in achannel bend could be divided
longitudinally into five regions andtransversely into two
regions. Transversely, the two regions are the innerbank and
the outer bank regions. Bed material tends to be eroded from
theouter bank region and deposited at the
inner bank region.Longitudinally, the five regions
are the entrance(0~20),front(20~50), mid(50~100),
rear(100~135) and the exit(135~180)regions. At the
entrance, bed is keeping flat and at the front region, thebed
at inner bank deposits increasingly from 20~35
and thendecreasingly from 35~50 ; the bed at outer
bank however graduallyerodes and reaches the deepest
erosion point at 50. This erosion couldreach -1.5 water
depth. At the mid region, bed elevations at both innerand
outer banks rise and are higher than those at 50. The
highest pointsare at 120 at the inner and at 100 at the outer
banks. At the rear region,bed elevations at both inner
and outer banks decrease and reach thesecond largest
erosion hole, -1.0h at 140 . The erosion and
depositionpatterns at the exit region are not consistent due
to upstream influences. Further analysis show that
Odgaard's (1984) formula describes thetransverse slope at
the channel bend reasonably well. A 2-D alluvialmodel
like DIM-2U should consider the mechanism of the
transverse bedslope and it's effect on the transverse
sediment transport, such that thebed evolution in a
alluvial channel bend can be simulated.
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