Many sand‐bed rivers worldwide have been experiencing significant reductions in sediment load over the past several decades. This is one of the causes of river delta drowning worldwide. This problem, however, has not been studied in detail in the context of sediment grain sorting. Considering the good performance of the original Engelund‐Hansen relation (OEH) for uniform sediment, and the fact that bulk grain size‐specific relations for bed material load that allow for sorting are relatively rare in the case of sand‐bed rivers, a grain size‐specific Engelund‐Hansen type relation (SEH) is proposed in this study based on data from a large flume. We embed both the OEH and the SEH in a one‐dimensional river morphodynamic model to simulate the morphodynamic evolution of the middle Mississippi River in response to the upstream cutoff of sediment supply. Simulation results using a single characteristic grain size show that bed material load delivered to the delta reduces only gradually in response to the cutoff of sediment supply, in agreement with previous studies. However, implementing the full grain size distribution of sediment leads to a much faster reduction of bed material load delivered to the delta, because the bed surface coarsens in response to grain sorting. This armoring inhibits the bed degradation that would replenish sediment load along the channel. The bed material load of finer sediment declines more rapidly than that of coarser sediment. The results of this study have practical implications for river delta restoration.

中文翻译：

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砂床河床物质负荷的特定粒度恩格尔德-汉森类型关系及其在密西西比河中的应用

在过去的几十年中，全球许多沙床河流的泥沙负荷一直在大大减少。这是全球范围内淹没河三角洲的原因之一。但是，这个问题尚未在沉积物颗粒分类的背景下进行详细研究。考虑到原始Engelund-Hansen关系（OEH）对于均匀沉积物的良好性能，以及在沙床河流中相对稀疏的，与床料载荷相关的散装颗粒尺寸特定关系（这种情况对于分类而言）相对罕见的事实这项研究基于大水槽中的数据，提出了尺寸特定的恩格伦·汉森类型关系（SEH）。我们将OEH和SEH都嵌入一维河流形态动力学模型中，以模拟密西西比河中游响应上游沉积物供应中断的形态动力学演化。使用单个特征晶粒尺寸的模拟结果表明，输送到三角洲的床料负荷仅随着沉积物供应的切断而逐渐降低，这与先前的研究一致。但是，实现沉积物的完整粒度分布会导致更快地降低输送到三角洲的床料负荷，因为床面会根据颗粒分类而变粗糙。这种铠装作用抑制了床层退化，而河床退化将补充沿河道的沉积物负荷。较细的泥沙的床料负荷下降较较粗的泥沙的床料负荷下降更快。这项研究的结果对河流三角洲的恢复具有实际意义。