Experiment and calculation of bed evolution in a 180o channel bend

• Main Authors: Fang, Kuo-Kuen, 方國琨
• Other Authors: Lai Chan-Ji, Leu Jan-Mou
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/75402501052357125043

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.