The Modern Yellow River Delta has a rich history of geomorphological transformations shaped by frequent avulsions and rapid progradation. However, the delta entered a phase of altered morphodynamics following the construction of the Xiaolangdi Reservoir, which fundamentally restructured sediment transport regimes and seasonal hydrological patterns. These changes have amplified challenges in predicting long-term deltaic evolution under evolving boundary conditions. The Qingshuigou Subaqueous Delta, as a major depositional zone, provides a compelling lens to examine these morphodynamic processes. However, seasonal variations in riverine sand transport fluxes driven by the water-sand regulation scheme that accompanied the construction of the Xiaolangdi Reservoir and its impact on the evolution of the delta front are particularly understudied. This study developed a simplified long-term morphodynamic model of the Qingshuigou Subaqueous Delta to investigate its response to riverine water and sediment discharges from 1997 to 2007. The findings are as follows: (1) The morphological evolution of the Qingshuigou Subaqueous delta has gradually changed from the pattern of “leading edge deposition and localized near-shore erosion” before the construction of the Xiaolangdi Reservoir to the pattern of “enhanced leading edge deposition and increased near-shore erosion” after the construction. (2) The construction of Xiaolangdi Reservoir has weakened the spatial distribution of the erosion process to a certain extent, changing the spatial distribution dominated by the erosion process (63.8% of area) before the construction to the spatial distribution dominated by the accretion process (More than 50% of area) after the construction. (3) The spatial and temporal variability of the incoming sediments leads to a significant coarsening of the grain size of the tidal flats in the southern part of the abandoned delta, which in turn maintains a relatively steady state of the shoreline variability. In contrast, the abandoned sand spit experiences severe erosion and depositional fluctuations due to intensified wave action. (4) The study emphasizes the importance of considering seasonal variations in unsteady discharge in modeling the long-term evolution of the delta. It provides new insights into the spatial and temporal differentiation of the geomorphic equilibrium of the Yellow River Delta and contributes to a broader understanding of delta evolution.

中文翻译：

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小浪底水库运行前后黄河清水沟水下三角洲的形态演变（1997-2007）


现代黄河三角洲有着悠久的地貌转变历史，这些变化是由频繁的撕脱和快速的斜坡形成的。然而，随着小浪底水库的建设，三角洲进入了形态动力学改变的阶段，从根本上重组了沉积物的运移状况和季节性水文模式。这些变化放大了在不断发展的边界条件下预测长期 deltaic 演化的挑战。清水沟水下三角洲作为一个主要的沉积带，为研究这些形态动力学过程提供了一个引人注目的镜头。然而，由小浪底水库建设所伴随的水沙调节计划驱动的河流输沙通量的季节性变化及其对三角洲锋线演变的影响的研究尤其不足。本研究建立了清水沟水下三角洲的简化长期形态动力学模型，以研究其对 1997 年至 2007 年河流水和沉积物排放的响应。研究结果表明：（1）清水沟水下三角洲的形态演变逐渐由小浪底水库建设前的“前缘沉积、局部近岸侵蚀”的格局转变为建设后的“前缘沉积增强、近岸侵蚀加剧”的格局。（2）小浪底水库的建设在一定程度上削弱了侵蚀过程的空间分布，将施工前以侵蚀过程为主的空间分布（占面积的63.8%）转变为建设后以吸积过程为主的空间分布（占面积的50%以上）。 （3） 流入的沉积物的空间和时间变化导致废弃三角洲南部潮滩的粒度显着粗化，进而保持海岸线变化的相对稳定状态。相比之下，由于增强的波浪作用，废弃的沙嘴经历了严重的侵蚀和沉积波动。（4） 该研究强调了在模拟三角洲的长期演变时考虑非定常排放的季节性变化的重要性。它为黄河三角洲地貌平衡的时空差异提供了新的见解，并有助于更广泛地理解三角洲演变。