Dynamics of 30 large channel bars in the Lower Mississippi River in response to river engineering from 1985 to 2015
Dynamics of 30 large channel bars in the Lower Mississippi River in response to river engineering from 1985 to 2015
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DOI：
10.1016/j.geomorph.2017.09.041
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发表时间：
2018
期刊：
影响因子：
3.9
通讯作者：
Bo Wang;Y. Xu
中科院分区：
文献类型：
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作者：
Bo Wang;Y. Xu
河道坝是冲积河流的主要沉积特征，其形态动力学在过去几十年中得到了深入研究。然而，人们对冲积河流中的河道坝如何响应河流工程和法规的了解相对较少。在这项研究中，我们评估了 30 个大型新兴坝的 30 年形态变化，这些坝位于高度管制的密西西比河下游，从密西西比州维克斯堡到密西西比-阿查法拉亚河改道的 223 公里河段。利用 1985 年至 2015 年间的陆地卫星图像和河流水位数据来表征沙坝形态特征并量化年代际变化。根据不同河流水位的卫星图像估算的坝体表面积，为 30 个坝体中的每一个都制定了一条评级曲线，以确定其体积。这项研究的结果表明，高度管制的河段有利于河道中部和附属坝的生长，而超过一半的点坝出现退化。目前，中通道和附属金条分别占 30 个金条总成交量的 38% 和 34%。单个中间通道条的平均音量是附加条的两倍以上，是点条的四倍以上。总体而言，在过去三十年中，所研究的 30 块金砖的总体积增加了 110,118,000 立方米（41%）。发现堤坝场中的总堤坝长度主要是导致坝体体积增加的原因。目前，这 30 块矿条的出土量估计约为 378,183,000 立方米。根据沙坝沉积物平均测量堆积密度 1.4 吨/立方米计算，沙坝总体积相当于约 5.3 亿吨粗砂。研究结果表明，这些沙坝是大型沉积物库。
Channel bars are a major depositional feature in alluvial rivers and their morphodynamics has been investigated intensively in the past several decades. However, relatively less is known about how channel bars in alluvial rivers respond to river engineering and regulations. In this study, we assessed 30-yr morphologic changes of 30 large emerged bars located in a 223 km reach of the highly regulated Lower Mississippi River from Vicksburg, Mississippi, to the Mississippi-Atchafalaya River diversion. Landsat imagery and river stage data between 1985 and 2015 were utilized to characterize bar morphologic features and quantify decadal changes. Based on bar surface areas estimated with the satellite images at different river stages, a rating curve was developed for each of the 30 bars to determine their volumes. Results from this study show that the highly regulated river reach favored the growth of mid-channel and attached bars, while more than half of the point bars showed degradation. Currently, the mid-channel and attached bars accounted for 38% and 34% of the total volume of the 30 bars. The average volume of a single mid-channel bar is over two times that of an attached bar and over four times that of a point bar. Overall, in the past three decades, the total volume of the studied 30 bars increased by 110,118,000 m3(41%). Total dike length in a dike field was found mostly contributing to the bar volume increase. Currently, the emerged volume of the 30 bars was estimated approximately 378,183,000 m3. The total bar volume is equivalent to ~ 530 million metric tons of coarse sand, based on an average measured bulk density of 1.4 t/m3for the bar sediment. The findings show that these bars are large sediment reservoirs.