Arising from the non-uniform dispersal of sediment and water that build deltaic landscapes, morphological change is a fundamental characteristic of river delta behavior. Thus, sustainable deltas require mobility of their channel networks and attendant shifts in landforms. Both behaviors can be misrepresented as degradation, particularly in context of the “stability” that is generally necessitated by human infrastructure and economies. Taking the Ganges-Brahmaputra-Meghna Delta as an example, contrary to public perception, this delta system appears to be sustainable at a system scale with high sediment delivery and long-term net gain in land area. However, many areas of the delta exhibit local dynamics and instability at the scale at which households and communities experience environmental change. Such local landscape “instability” is often cited as evidence that the delta is in decline, whereas much of this change simply reflects the morphodynamics typical of an energetic fluvial-delta system and do not provide an accurate reflection of overall system health. Here we argue that this disparity between unit-scale sustainability and local morphodynamic change may be typical of deltaic systems with well-developed distributary networks and strong spatial gradients in sediment supply and transport energy. Such non-uniformity and the important connections between network sub-units (i.e., fluvial, tidal, shelf) suggest that delta risk assessments must integrate local dynamics and sub-unit connections with unit-scale behaviors. Structure and dynamics of an integrated deltaic network control the dispersal of water, solids, and solutes to the delta sub-environment and thus the local to unit-scale sustainability of the system over time.

中文翻译：

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稳定≠可持续：Delta Dynamics 与人类对稳定性的需求

由于构成三角洲景观的沉积物和水的不均匀扩散，形态变化是河流三角洲行为的基本特征。因此，可持续的三角洲需要其渠道网络的流动性和随之而来的地貌变化。这两种行为都可能被误解为退化，特别是在人类基础设施和经济通常需要的“稳定”背景下。以恒河-布拉马普特拉-梅格纳三角洲为例，与公众的看法相反，这个三角洲系统似乎在系统规模上具有可持续性，具有高沉积物输送和土地面积的长期净收益。然而，三角洲的许多地区在家庭和社区经历环境变化的规模上表现出当地的动态和不稳定性。这种局部景观“不稳定性”经常被引用作为三角洲正在下降的证据，而这种变化的大部分只是反映了充满活力的河流三角洲系统的典型形态动力学，并不能准确反映整个系统的健康状况。在这里，我们认为单位尺度可持续性和局部形态动力学变化之间的这种差异可能是三角洲系统的典型特征，该系统具有发达的分流网络和强大的沉积物供应和运输能量空间梯度。这种不均匀性和网络子单元（即河流、潮汐、陆架）之间的重要联系表明，三角洲风险评估必须将局部动态和子单元连接与单元尺度行为相结合。综合三角洲网络的结构和动力学控制着水、固体、