Bedload and Suspended Load Transport in the 140-km Reach Downstream of the Mississippi River Avulsion to the Atchafalaya River
Bedload and Suspended Load Transport in the 140-km Reach Downstream of the Mississippi River Avulsion to the Atchafalaya River
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密西西比河下游 140 公里河段冲向阿查法拉亚河的床载和悬载运输
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发表时间：
2017
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通讯作者：
Y. Xu
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作者：
S. Joshi;Y. Xu
自20世纪30年代以来，密西西比河三角洲一直在不断失去土地，这是由于几个因素，其中主要是沉积物供应减少。最近的几项研究估计了短期沉积物搬运的各个组成部分，即，推移质和悬移质，分别用于沿着最低密西西比河（LmMR，通常被认为是进入墨西哥湾之前密西西比河的最后500 km河段）的某些位置。然而，这两个组成部分的长期泥沙供应沿着河段的综合影响仍不清楚。这里阻碍我们理解的主要障碍之一是，在大型冲积河流（如密西西比河）中精确测量推移质是困难和不切实际的。在本研究中，我们估计了2004-2015年期间沿沿着LmMR最高140 km河段三个位置的三种中等粒度（D50 = 0.125、0.25和0.5 mm）的推移质：Tarbert Landing（TBL）河公里（rk）493、St Francisville（St F）rk 419和巴吞鲁日（BTR）rk 367.5。我们还估计了1978年至2015年期间在St F和2004年至2015年期间在BTR的悬移质，以辨别底床载荷和悬移质之间的相互作用关系。我们发现，逐渐增加的推移质为所有三个中等粒度从TBL（83，41.5和20.75万吨（MT），分别）BTR（96，48和24吨）。我们还发现，悬浮负荷在TBL（以前报道）显着高于那些在St F和BTR在相应的重叠期间。推移质几乎线性增加悬浮负荷，河流流量和河流水位在上游位置（TBL和St F），但是，这种关系并不明显下游BTR。2004-2010年（两种负荷可用性的匹配期），TBL的总泥沙负荷（推移质+悬浮泥沙负荷）显著较高（931 MT），而其他两个下游位置较低且几乎相等（St F为550 MT，BTR为544 MT）。这些研究结果表明，最高的20-25公里的LmMR河段（包括TBL）有可能在过去的三到四十年中捕获大量的悬移质，而推移质输运盛行于下游（包括St F和BTR）。我们建议，未来的河流泥沙管理应寻求工程解决方案，将截留的粗泥沙向下游海岸移动，以恢复密西西比河三角洲
The Mississippi River Delta has been continuously losing land since the 1930s due to several factors, chief of which is the reduced sediment supply. A few recent studies have estimated individual components of short-term sediment transport, i.e., bedload and suspended load, separately for some locations along the Lowermost Mississippi River (LmMR, commonly considered as the last 500-km reach of the Mississippi River before entering the Gulf of Mexico). However, the combined effects of both components on the long-term sediment supply along the river reach are still unclear. One of the major obstacles here hindering our understanding is that it is difficult and impractical to accurately measure bedloads in large alluvial rivers, such as the Mississippi. In this study, we estimated bedloads of three medium grain sizes (D50 = 0.125, 0.25 and 0.5 mm) for three locations along the uppermost 140-km reach of the LmMR: Tarbert Landing (TBL) at river kilometer (rk) 493, St Francisville (St F) at rk 419, and Baton Rouge (BTR) at rk 367.5 during 2004–2015. We also estimated suspended loads at St F during 1978–2015 and at BTR during 2004–2015 in order to discern the interactive relationship between bedloads and suspended loads. We found gradually increasing bedloads for all the three medium grain sizes from TBL (83, 41.5 and 20.75 million tons (MT), respectively) to BTR (96, 48 and 24 MT). We also found that suspended loads at TBL (reported previously) were significantly higher than those at St F and BTR during corresponding overlapping periods. Bedloads increased almost linearly with suspended loads, river discharge and river stage at the upstream locations (TBL and St F); however, such a relationship was not evident downstream at BTR. The total sediment load (bedload + suspended sediment load) was substantially higher at TBL (931 MT), while lower and nearly equal at other two downstream locations (550 MT at St F and 544 MT at BTR) during 2004–2010 (the matching period of availability of both loads). These findings indicate that the uppermost 20–25 km LmMR reach (covering TBL) has potentially entrapped substantial suspended load over the last three to four decades, while bedload transport prevails in the lower reach (covering St F and BTR). We suggest that future sediment management in the river should seek engineering solutions for moving trapped coarse sediments downstream towards the coast for the Mississippi River Delta restoration