Morphodynamic modeling of Fourleague Bay in Mississippi River Delta: Sediment fluxes across river-estuary-wetland boundaries
Morphodynamic modeling of Fourleague Bay in Mississippi River Delta: Sediment fluxes across river-estuary-wetland boundaries
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DOI：
10.1016/j.coastaleng.2023.104399
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发表时间：
2023-09
影响因子：
4.4
通讯作者：
Nan Wang;Qin Chen;Kelin Hu;Kehui Xu;S. Bentley;Jiaze Wang
中科院分区：
文献类型：
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作者：
Nan Wang;Qin Chen;Kelin Hu;Kehui Xu;S. Bentley;Jiaze Wang
为了减轻密西西比河三角洲的土地损失，正在采用沉积物分流，使河水和沉积物流入正在退化的湿地。本文采用Delft3D二维流波耦合模型，对美国路易斯安那州Fourleague湾（FLB）的水动力和泥沙输移进行了模拟研究。利用2015年至2016年的沉积物淤积和水动力特性的现场测量来校准和验证形态动力学模型。然后，验证模型被应用于量化2015年5月至2016年5月之间在FLB和周围的沼泽泥沙输运。结果表明，当河流流量较大，风力较大时，更多的泥沙会淤积到周围的沼泽地。因此，通过战略性地调整河水从改道的脉冲时间与大气强迫的季节性加剧，有可能维持和促进周围湿地的增长。此外，我们发现，在整个研究期间发生了多个泥沙输运过程，包括河流沉积物沉积到海湾底部，河流沉积物直接沉积在周围的沼泽，海湾底部沉积物的再悬浮，再悬浮的沉积物再分配到邻近的沼泽和墨西哥湾（GoM）。结果表明，当河流流量较大时，河流泥沙倾向于直接淤积在沼泽地中。在平静的天气条件和正常的河流流量期间，FLB充当水库，储存上游河流的沉积物，后来在活跃的大气条件下充当附近湿地和GoM的沉积物来源。这表明，使用湾底作为水库可以延长湿地可以从沉积物分流中受益的距离，因为向湿地提供沉积物是一个多步骤的过程。因此，重要的是要将河流改道的沉积物保留在浅海湾，并允许风暴将其重新分配到邻近的湿地。
To mitigate land losses in the Mississippi River Delta, sediment diversions are being employed to enable the flow of river water and sediments into wetlands experiencing degradation. A two-dimensional coupled flow-wave Delft3D model was used in this study to explore the hydrodynamics and sediment transport in Fourleague Bay (FLB), Louisiana, USA, which has been considered an analog site for studying the efficiency of sediment diversion projects. In-situ measurements of sediment accretion and hydrodynamic characteristics from 2015 to 2016 were utilized to calibrate and validate the morphodynamic model. The validated model was then applied to quantify sediment transport in FLB and surrounding marshes between May 2015 and May 2016. The results show that more sediment could be deposited to the surrounding marshes with high river discharges and strong winds. Thus, by strategically aligning the timing of pulses of river water from the diversion with the seasonal intensification of atmospheric forcing, it is possible to sustain and promote the growth of the surrounding wetlands. Moreover, we found that multiple sediment transport processes occurred during the entire study period, including the deposition of riverine sediment into the bay floor, direct deposition of riverine sediment in the surrounding marshes, resuspension of bay floor sediment, and redistribution of resuspended sediment to adjacent marshes and the Gulf of Mexico (GoM). The results indicate that the riverine sediment tended to be directly deposited in the marshes when the river discharge was high. During calm weather conditions and normal river discharge, FLB acted as a reservoir, storing sediment from the upper river, and later acted as a sediment source to the nearby wetlands and the GoM during energetic atmospheric conditions. This suggests that using the bay floor as a reservoir can extend the distance over which wetlands can benefit from the sediment diversions, as the supply of sediment to the wetlands becomes a multi-step process. Thus, it is important to retain sediments from river diversions in shallow bays and allow storms to redistribute them to adjacent wetlands.