Abstract Sediment yield estimates, combined with information regarding sediment sources and partitioning (bedload vs. suspended load), can provide important insights into geomorphic character of the landscape of interest. This study reports such an analysis, conducted in a forested mountain basin in inland Pacific Northwest using reservoir deposits, ground surveys, and repeat LiDAR mapping. Our research generated three key conclusions. First, we estimated mean specific yield of clastic sediment from the study basin during the last century as ~51 Mg km-2 a-1. In the context of a data compilation from mountain basins in northwestern North America, this value was among the highest for inland basins, and among the lowest when compared with coastal basins. Second, a sediment source analysis provided valuable clues regarding the relative importance of various geomorphic processes operating in the system under study. These findings were consistent with our hypothesis that anthropogenic disturbances may be an important factor that conditions sediment yield from the basin. A mix of quantitative and qualitative evidence suggested that the estimated sediment yield value reflects a transient increase associated with past timber harvest, road construction, and large wood removal. Legacies of these disturbances appear to have the opposite effect on contemporary processes, limiting lateral activity of the channel as well as hillslope-channel connectivity. Third, our partitioning procedure revealed that bedload constituted approximately a third of the total clastic load exported from the basin. This finding suggests that, in this and similar fluvial systems, sediment yield recovery following major geomorphic disturbances could be protracted, as a considerable portion of mobilized sediment that moves as bedload is routed and evacuated from the basin for years or decades after rapid flushing of suspended material. Moreover, this finding indicates that the common assumption that bedload constitutes 10-20% of the total load can lead to underestimation in mountain basins.

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太平洋西北部内陆森林盆地的沉积物产量：速率、分配和来源

摘要 沉积物产量估计值，结合有关沉积物来源和分区（床载与悬浮载荷）的信息，可以提供对感兴趣景观的地貌特征的重要见解。本研究报告了使用水库沉积物、地面调查和重复激光雷达测绘在太平洋西北部内陆森林盆地进行的此类分析。我们的研究得出了三个关键结论。首先，我们估计上个世纪研究盆地碎屑沉积物的平均比产量为~51 Mg km-2 a-1。在北美西北部山区盆地的数据汇编中，该值在内陆盆地中最高，与沿海盆地相比最低。第二，沉积物来源分析提供了关于在所研究系统中运行的各种地貌过程的相对重要性的宝贵线索。这些发现与我们的假设一致，即人为干扰可能是影响盆地沉积物产量的重要因素。定量和定性证据的混合表明，估计的沉积物产量值反映了与过去木材采伐、道路建设和大量木材清除相关的短暂增加。这些干扰的遗留问题似乎对当代过程产生了相反的影响，限制了通道的横向活动以及山坡-通道的连通性。第三，我们的划分程序表明，床荷载约占从盆地输出的总碎屑荷载的三分之一。这一发现表明，在这个和类似的河流系统中，主要地貌扰动后的沉积物产量恢复可能会延长，因为在悬浮的悬浮物快速冲洗后，相当一部分随床负荷移动的移动沉积物会被排走并从盆地中排出数年或数十年。材料。此外，这一发现表明，床荷载占总荷载 10-20% 的常见假设可能导致山区盆地的低估。