Excess River Sedimentation at Bridges in the Raya Graben (Northern Ethiopia)
Excess River Sedimentation at Bridges in the Raya Graben (Northern Ethiopia)
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DOI：
10.1002/ldr.2572
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发表时间：
2017-04
影响因子：
4.7
通讯作者：
Biadgilgn Demissie;P. Billi;A. Frankl;M. Haile;J. Nyssen
中科院分区：
文献类型：
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作者：
Biadgilgn Demissie;P. Billi;A. Frankl;M. Haile;J. Nyssen
这项研究调查了生物气候因素和桥梁对当地水文地貌条件的时间变异性和影响，这些水文地貌条件导致了Raya Graben(埃塞俄比亚北部)短暂河流的过度沉积和洪水危险。利用1972、1986、2000、2005、2010和2014年的陆地卫星图像，分析了归一化差异植被指数(NDVI)。利用3个气象站的日降雨量资料，分析了24 h内降雨强度的时间趋势和重现时间间隔，并测量了20个河段的河床坡度和床沙粒度。结果表明，NDVI值的最大值出现在2000-2014年间。然而，在这10年中，研究中的桥梁经历了最大的超沉，有些桥梁的超沉达到1.6m。不同的因素被讨论为没有降雨模式的证据，可以解释从源头输沙增加的原因。现场资料表明，近15年来，桥头河道变窄是造成上游淤积较厚、漫滩洪水增多的主要原因。提出了一种简单的水力学方法来解释桥梁泥沙淤积的变异性和主干与桥梁上游河段之间底质颗粒尺寸的变化。版权所有©2016 John Wiley&Sons，Ltd.
This study investigates the temporal variability and effects of bio‐climatic factors and bridges on local hydro‐geomorphic conditions that cause excess sedimentation and flood hazard in ephemeral rivers of the Raya graben (northern Ethiopia). Normalized difference vegetation index (NDVI) was analyzed using Landsat imageries of 1972, 1986, 2000, 2005, 2010, and 2014. Daily rainfall data of three meteorological stations were considered to analyze the temporal trends and return time intervals of rainfall intensity in 24 h. Stream‐bed gradient and bed material grain size were measured in 20 river reaches. Results show that the maximum NDVI values were recorded in the time interval from 2000 to 2014. Nevertheless, during this decade, the study bridges experienced the largest excess sedimentation, in some bridges up to 1·6 m. Different factors to account for it are discussed as no evidence of rainfall pattern, accountable for an increase in sediment delivery from the headwaters, is found. The field data show that channel narrowing at bridges is the main cause of thick upstream sedimentation and of increasing frequency of overbank flows during the last 15 years. A simple hydraulic approach is presented to explain the variability of sediment deposition at bridges and change in bed material grain size between the main stem and the reach right upstream of the bridge. Copyright © 2016 John Wiley & Sons, Ltd.