Assessment of western Oregon debris-flow hazards in burned and unburned environments

IF 2.8 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL
Brittany D. Selander, Nancy Calhoun, William J. Burns, Jason W. Kean, Francis K. Rengers
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Abstract

In the steep and mountainous environment of western Oregon, debris flows pose a considerable threat to property, infrastructure and life. Wildfire is commonly known to increase the susceptibility of steep slopes to debris flows, but the extent of this process in the western Cascades is not well understood. The US Geological Survey (USGS) currently estimates postfire debris-flow likelihood and triggering rainfall thresholds using a model calibrated to a southern California inventory of debris flows generated by excess runoff within the first year after fire. Because of a lack of available data, this model has not been tested in western Oregon, or in locations where postfire debris flows initiate via other mechanisms (e.g., shallow landslides or in-channel failures). Using repeat field observations and aerial imagery, we developed two new debris-flow inventories within and adjacent to the perimeters of five 2020 wildfires in western Oregon: Archie Creek, Holiday Farm, Beachie Creek, Lionshead and Riverside. The first inventory focuses on postfire debris flows (2020–2022); the second focuses on debris flows prior to fires (1995–2020). Our inventories of prefire and postfire debris flows were used to document initiation mechanisms in Oregon's western Cascades and to evaluate the effects of wildfire. We found that wildfire changed the distribution of debris-flow initiation mechanisms in the western Cascades. After the wildfires, annual rates of runoff-generated debris flows increased by 22% and the number of shallow landslide-initiated debris flows decreased by 17% relative to before the wildfires. Despite this shift, shallow landsliding was the dominant debris-flow initiation mechanism in both unburned and burned environments. We found the performance of the current USGS debris-flow likelihood model was degraded relative to other previously tested locations across the intermountain western United States. Our results highlight the need for improved postfire hazard assessment in western Oregon based on regional model calibration that is tuned to the dominant debris-flow initiation mechanisms.

Abstract Image

俄勒冈州西部燃烧和未燃烧环境中泥石流危害的评估
在俄勒冈州西部陡峭多山的环境中,泥石流对财产、基础设施和生命构成了相当大的威胁。众所周知,野火会增加陡坡对泥石流的敏感性,但在喀斯喀特西部,这一过程的程度尚不清楚。美国地质调查局(USGS)目前使用一个模型来估计火灾后泥石流的可能性和触发降雨的阈值,该模型是根据南加州火灾后一年内过量径流产生的泥石流清单校准的。由于缺乏可用的数据,该模型尚未在俄勒冈州西部或火灾后泥石流通过其他机制(如浅层滑坡或通道内断裂)引发的地方进行测试。通过重复的实地观察和航空图像,我们在俄勒冈州西部的五个2020年野火的周边及其附近开发了两个新的泥石流清单:阿奇溪、假日农场、比奇溪、狮子头和河滨。第一份清单侧重于火灾后的泥石流(2020-2022年);第二部分关注火灾前的泥石流(1995-2020)。我们的火灾前和火灾后泥石流的清单被用来记录俄勒冈州西部喀斯喀特的启动机制,并评估野火的影响。研究发现,野火改变了西部喀斯喀特地区泥石流形成机制的分布。山火发生后,径流产生的泥石流的年速率比山火发生前增加了22%,浅层滑坡引发的泥石流的数量减少了17%。尽管发生了这种转变,但在未燃烧环境和燃烧环境中,浅层滑坡都是主要的泥石流形成机制。我们发现,目前USGS的泥石流可能性模型的性能相对于之前在美国西部山间的其他测试地点有所下降。我们的研究结果强调了在俄勒冈州西部进行基于区域模型校准的火灾后危险评估的必要性,该模型校准调整为主要的泥石流启动机制。
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来源期刊
Earth Surface Processes and Landforms
Earth Surface Processes and Landforms 地学-地球科学综合
CiteScore
6.40
自引率
12.10%
发文量
215
审稿时长
4 months
期刊介绍: Earth Surface Processes and Landforms is an interdisciplinary international journal concerned with: the interactions between surface processes and landforms and landscapes; that lead to physical, chemical and biological changes; and which in turn create; current landscapes and the geological record of past landscapes. Its focus is core to both physical geographical and geological communities, and also the wider geosciences
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