Influence of Floods, Tides, and Vegetation on Sediment Retention in Wax Lake Delta, Louisiana, USA
Influence of Floods, Tides, and Vegetation on Sediment Retention in Wax Lake Delta, Louisiana, USA
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DOI：
10.1029/2019jf005316
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发表时间：
2020-01
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影响因子：
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通讯作者：
E. Olliver;D. Edmonds;J. Shaw
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作者：
E. Olliver;D. Edmonds;J. Shaw
沉积物是三角洲环境中最有价值的自然资源，因为需要它来建造新的土地。为了进行土地建设，沉积物必须保留在三角洲而不是被运到近海。尽管如此，我们仍然不知道是什么控制着三角洲内的沉积物滞留。在这里，我们使用美国路易斯安那州蜡湖三角洲的校准数值模型来分析不同河流洪水强度、潮汐幅度和植被范围的沉积物滞留情况。我们的结果表明，随着河流洪水强度的增加，每 60 天洪水面积平均垂直积聚从 0.33 增加到 2 厘米，但泥沙滞留从 72% 减少到 34%。对于所考虑的均匀植被特征，缓冲效应（定义为在存在植被的情况下减少到岛屿上的沉积物通量）在完全植被的三角洲上将到岛屿上的沉积物通量减少了 14% 至 22%。当沉积物被输送到岛屿上时，植被会增强约 10% 的滞留作用，我们将其称为截留效应。但是，这并不能抵消缓冲效应，植被将三角洲的垂直吸积和滞留减少高达 6%（或每 60 天洪水约 0.5 厘米）。我们认为，只有当诱捕补偿缓冲时，植被才会增加沉积作用。最后，与较小的潮汐幅度相比，较高流量下的较大潮汐幅度使每 60 天洪水的垂直吸积增加约 0.5 厘米。这些结果提供了对沿海系统增长背后机制的深入了解，并提出了如何在沉积物供应减少的三角洲中更有效地进行沉积物转移。
Sediment is the most valuable natural resource for deltaic environments because it is required to build new land. For land building to occur, sediment must be retained in the delta instead of being transported offshore. Despite this, we do not know what controls sediment retention within a delta. Here we use a calibrated numerical model of Wax Lake Delta, Louisiana, USA to analyze sediment retention for different riverine flood magnitudes, tidal amplitudes, and vegetation extents. Our results show that as riverine flood magnitude increases, areally averaged vertical accretion increases from 0.33 to 2 cm per 60‐day flood, but sediment retention decreases from 72% to 34%. For the uniform vegetation characteristics considered, the buffering effect, defined as the reduction of sediment flux onto the islands in the presence of vegetation, reduces the sediment flux onto the islands 14 to 22% on a fully vegetated delta. When sediment is transported onto the islands, vegetation enhances retention, which we refer to as the trapping effect, by ~10%. But, this does not offset the buffering effect, and vegetation decreases vertical accretion and retention in the delta up to 6% (or ~0.5 cm per 60‐day flood). We suggest that vegetation will increase sedimentation only when trapping compensates for buffering. Finally, greater tidal amplitude at higher discharges enhances vertical accretion by ~0.5 cm per 60‐day flood compared to smaller tidal amplitudes. These results provide insight on the mechanisms behind coastal systems growth, and suggest how sediment diversions might be operated more efficiently in deltas with reduced sediment supply.