The gravel-bedded White River drains a 1279 km2 basin in Washington State, with lowlands sculpted by continental glaciation and headwaters on an actively glaciated stratovolcano. Chronic aggradation along an alluvial fan near the river’s mouth has progressively reduced flood conveyance. In order to better understand how forecasted climate change may influence coarse sediment delivery and aggradation rates in this lowland depositional setting, we assessed the contemporary delivery and routing of coarse sediment through the watershed; this assessment was based on a rich set of topographic, sedimentologic, and hydrologic data from the past century, with a focus on repeat high-resolution topographic surveys from the past decade.We found that most of the lower river’s contemporary bed-load flux originates from persistent erosion of alluvial deposits in the lower watershed. This erosion is a response to a drop in local base level caused by a major avulsion across the fan in 1906 and then augmented by subsequent dredging. The 1906 avulsion and modern disequilibrium valley profiles reflect landscape conditioning by continental glaciation and a massive mid-Holocene lahar. In the proglacial headwaters, infrequent large sediment pulses have accomplished most of the observed coarse sediment export, with exported material blanketing downstream valley floors; during typical floods, transported bed material is largely sourced from erosion of these valley floor floods. Throughout the watershed, we observe decadal-scale coarse sediment dynamics strongly related to the filling or emptying of valley-scale sediment storage over 102–104 yr time scales, often in response to major disturbances that either emplace large deposits or influence their redistribution. Paraglacial responses in large watersheds are suggested to be inherently complicated and punctuated as a result of internal landform interactions and stochastic/threshold-dependent events. We argue that, in combination, Holocene disturbance, storage dynamics, and human flow modification make coarse sediment fluxes in the lower White River relatively insensitive to decadal climate variability. Results highlight the degree to which river sensitivity to contemporary disturbance, climatic or otherwise, may be contingent on local and idiosyncratic watershed histories, underscoring the need to unpack those histories while demonstrating the utility of watershed-scale high-resolution topography toward that end.

中文翻译：

---

大型冰川河系统中的粗泥沙动力学：全新世的历史和储藏动力学决定了当代对气候的敏感性

砾石铺床的怀特河在华盛顿州流失了一个1279平方公里的盆地，低地被大陆冰川和上游源源不断的冰层平层火山雕刻而成。沿河口附近的冲积扇的长期凝结逐渐减少了洪水的输送。为了更好地了解在这种低地沉积环境中预测的气候变化可能如何影响粗沙的输送和聚集速度，我们评估了当代粗沙在整个流域的输送和输送。该评估基于过去一个世纪的丰富的地形，沉积和水文数据集，重点是过去十年中重复的高分辨率地形调查。我们发现，现代下游河床的大部分通量来自下游流域的冲积物持续侵蚀。这种侵蚀是对当地基础水位下降的一种响应，这种降低是由于1906年风机大面积撕裂引起的，随后由于随后的疏ging而加剧了。1906年的崩塌和现代不平衡山谷轮廓反映了大陆冰川和大规模的全新世中纬度拉哈尔带来的景观调节。在河床上游，很少有大的沉积物脉冲完成大部分观测到的粗沙沉积物，而出口物质则覆盖了下游的谷底。在典型的洪水期间，运输的床层物质主要来自这些谷底洪水的侵蚀。在整个分水岭，我们观察到十年尺度的粗沉积物动力学与在102-104年的时间尺度内山谷规模的沉积物的充填或排空密切相关，这通常是由于大的扰动引起的，这些扰动可能会形成较大的沉积物或影响它们的重新分布。由于内部地形相互作用和随机/阈值相关事件的结果，在大流域的冰河响应被认为是固有的复杂的和易被打断的。我们认为，全新世扰动，储层动力学和人流变化共同导致白河下游的粗大泥沙通量对年代际气候变化相对不敏感。结果表明，河流对当代气候或其他因素的敏感性在多大程度上取决于当地和特有的分水岭历史，