Postfire debris flows are particularly complex to study because they do not form discrete initiation locations and commonly involve multiple simultaneously operating erosional processes. Although recent work has begun to elucidate a more mechanistic understanding of postfire debris flows, there is still a paucity of detailed sediment budgets characterizing these events. In this study, we seek to understand how postfire sediment sources and erosional processes change over multiple storm cycles. To do this, we performed repeat high‐resolution change detection in a headwater catchment burned by the 2018 Holy Fire in the Santa Ana Mountains, California, USA. This included terrestrial laser scanning in a zero‐order catchment (0.95 ha) and unmanned aerial vehicle structure from motion of a headwater channel network (up to 6.5 ha). During the initial storm events that produced runoff‐generated debris flows, we found that the evacuation of dry ravel and prefire colluvium accounted for half of the eroded material. These initial flows also acted to clear out much of the material stored within downstream headwater channel networks. In subsequent storm events of equal or greater rainfall intensity, total erosion from the study site was subdued, and the relative importance of shallow hillslope erosion from interrill and rill erosion was increased, as has been noted in similar studies in the region. Overall, this suggests that channel sediment supplies may be more rapidly depleted than hillslope sources, which may drive a trend of decreasing sediment fluxes over time from burned headwater catchments subject to repeated runoff events.

中文翻译：

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通过重复的高分辨率变化检测揭示了一系列火后含沙流上泥沙源的演变

火灾后的泥石流研究起来特别复杂，因为它们不会形成离散的起始位置，并且通常涉及多个同时进行的侵蚀过程。尽管最近的工作已开始阐明对火灾后泥石流的更机械的理解，但仍然缺乏表征这些事件的详细沉积物预算。在本研究中，我们试图了解火灾后沉积物源和侵蚀过程在多个风暴周期中如何变化。为此，我们在美国加利福尼亚州圣安娜山区2018年圣火烧毁的上游水源流域进行了重复的高分辨率变化检测。这包括在零级流域（0.95公顷）内进行地面激光扫描，以及源头水道网络运动（长达6.5公顷）的无人机结构。在最初的暴风雨事件中，产生了径流产生的泥石流，我们发现疏散的干杂草和预燃暴风雨层的疏散占了侵蚀材料的一半。这些初始流量还起到清除下游上游水源渠道网络中存储的大部分物质的作用。在随后发生的降雨强度相等或更高的暴风雨事件中，研究地点的总侵蚀被减弱，而钻探和钻探侵蚀造成的浅坡坡侵蚀的相对重要性也增加了，正如该地区类似研究所指出的那样。总的来说，这表明河道沉积物的供应可能比山坡源更快地枯竭，这可能导致随着反复的径流事件而燃烧的源头集水区的沉积物通量随着时间的流逝而逐渐减少。