A large portion of freshwater and sediment is exported to the ocean by a small number of major rivers. Many of these megarivers are subject to substantial anthropogenic pressures, which are having a major impact on water and sediment delivery to deltaic ecosystems. Due to hydrodynamic sorting, sediment grain size and composition vary strongly with depth and across the channel in large rivers, complicating flux quantification. To account for this, we modified a semi‐empirical Rouse model, synoptically predicting sediment concentration, grain‐size distribution, and organic carbon (%OC) concentration with depth and across the river channel. Using suspended sediment depth samples and flow velocity data, we applied this model to calculate sediment fluxes of the Irrawaddy (Ayeyarwady) and the Salween (Thanlwin), the last two free‐flowing megarivers in Southeast Asia. Deriving sediment‐discharge rating curves, we calculated an annual sediment flux of Mt/year for the Irrawaddy and Mt/year for the Salween, together exporting 46% as much sediment as the Ganges‐Brahmaputra system. The mean flux‐weighted sediment exported by the Irrawaddy is significantly coarser (D₈₄ = 193 ± 13 μm) and OC‐poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 μm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of Mt C/year, 53% as much as the Ganges‐Brahmaputra. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment flux, given the increasing anthropogenic pressures on these river basins.

中文翻译：

---

在大型冲积河道中整合悬浮泥沙通量：基于天气小径流模型的伊洛瓦底江和萨尔温江之间的应用

少数主要河流将大部分淡水和沉积物出口到海洋。许多大型河道承受着巨大的人为压力，这对水和沉积物向三角洲生态系统的输送产生了重大影响。由于进行了流体动力学分选，在大河流中，沉积物的粒度和组成随深度和整个河道而变化很大，这使通量量化变得复杂。为了解决这个问题，我们修改了一个半经验性Rouse模型，以深度和跨河道的方式预测沉积物浓度，粒度分布和有机碳（％OC）浓度。利用悬浮的沉积物深度样本和流速数据，我们将此模型应用于计算伊洛瓦底（Ayeyarwady）和萨尔温江（Thanlwin）的泥沙通量，东南亚的最后两个自由流动大河。推导出泥沙排放量额定曲线，我们计算出了伊洛瓦底江的年产量和萨尔温江的年产量合计，出口的泥沙量相当于恒河—布拉马普特拉系统的46％。通过伊洛瓦底出口的平均通量加权沉积物是显著较粗（d ₈₄  = 193±13  μ M）和OC-较差（0.29±0.08 相比，萨尔温（重量％）112±27  μ m和0.59±0.16  ％（重量） ， 分别）。两条河流出口相似量的颗粒有机碳，总计Mt /年，是恒河-布拉马普特拉山的53％。这些结果突显了伊洛瓦底江和萨尔温江的全球意义，并鉴于这些流域的人为压力不断增加，有必要继续监测其沉积物通量。