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Spatial and temporal patterns of sediment storage and erosion following a wildfire and extreme flood

机译：野火和特大洪灾后沉积物存储和侵蚀的时空格局

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Post-wildfire landscapes are highly susceptible to rapid geomorphic changes, and the resulting downstream effects, at both the hillslope and watershed scales due to increases in hillslope runoff and erosion. Numerous studies have documented these changes at the hillslope scale, but relatively few studies have documented larger-scale post-fire geomorphic changes over time. In this study we used five airborne laser scanning (ALS) datasets collected over 4 years to quantify erosion and deposition throughout the channel network in two ～15 km sup2/sup watersheds, Skin Gulch and Hill Gulch, in northern Colorado after a wildfire followed by a large, long-duration flood 15?months later. The objectives were to (1)?quantify the volumes, spatial patterns, and temporal changes over time of erosion and deposition over a nearly 4-year period, and (2)?evaluate the extent to which these spatially and temporally explicit changes are correlated to precipitation metrics, burn severity, and morphologic variables. The volumetric changes were calculated from a differencing of DEMs for 50?m long segments of the channel network and associated valley bottoms. The results showed net sediment accumulation after the wildfire in the valley bottoms of both watersheds, with greater accumulations in the wider and flatter valley bottoms in the first 2 years after burning. In contrast, the mesoscale flood caused large amounts of erosion, with higher erosion in those areas with more post-fire deposition. Only minor changes occurred over the 2 years following the mesoscale flood. Volume changes for the different time periods were weakly but significantly correlated to, in order of decreasing correlation, contributing area, channel width, percent burned at high and/or moderate severity, channel slope, confinement ratio, maximum 30?min precipitation, and total precipitation. These results suggest that morphometric characteristics, when combined with burn severity and a specified storm, can indicate the relative likelihood and locations for post-fire erosion and deposition. This information can help assess downstream risks and prioritize areas for post-fire hillslope rehabilitation treatments.
机译：野火后的景观极易受到快速地貌变化的影响，并且由于山坡径流和侵蚀的增加，在山坡和流域尺度上都产生了下游效应。许多研究都记录了山坡尺度上的这些变化，但是相对较少的研究记录了随时间推移而发生的大规模火后地貌变化。在这项研究中，我们使用了四年来收集的五个机载激光扫描（ALS）数据集来量化科罗拉多北部的两个〜15 km 2 流域（皮肤峡谷和希尔峡谷）整个渠道网络的侵蚀和沉积15个月后，一场野火过后，又发生了长时间的大洪水。目的是（1）量化近四年来侵蚀和沉积物的体积，空间模式和时间变化，以及（2）评估这些时空明确变化的相关程度降水量指标，烧伤严重程度和形态变量。体积变化是根据50毫米长的河网段和相关谷底的DEM差异计算得出的。结果表明，野火过后，两个流域的谷底都有净沉积物积累，在燃烧后的前两年中，更宽，更平坦的谷底积累了更多的沉积物。相比之下，中尺度洪水造成大量侵蚀，而火灾后沉积较多的地区侵蚀加剧。在中等规模的洪水之后的两年中，只有很小的变化。不同时间段内的体积变化微弱，但与相关性呈显着相关，按相关性递减的顺序依次依次为：贡献面积，通道宽度，高和/或中等严重度下的燃烧百分比，通道斜率，约束比，最大30分钟降水和总沉淀。这些结果表明，形态特征与燃烧严重性和特定的暴风雨相结合，可以指示火灾后侵蚀和沉积的相对可能性和位置。这些信息可以帮助评估下游风险，并为火灾后的山坡恢复治疗确定优先区域。

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