Controls on debris‐flow initiation on burned and unburned hillslopes during an exceptional rainstorm in southern New Mexico, USA

Abstract

Using observations from 688 debris flows, we analyse the hydrologic and landscape characteristics that influenced debris‐flow initiation mechanisms and locations in a watershed that had been partially burned by the 2012 Whitewater‐Baldy Complex Fire in the Gila Mountains, southern New Mexico. Debris flows can initiate due to different processes. Slopes can fail as discrete landslides and then become fluidized and move downstream as debris flows (landslide initiated) or progressive bulking of sediment from a distributed area can become channelized and concentrated as it moves downslope (runoff generated). In this study, we have an unusual opportunity to investigate both types of debris‐flow initiation mechanisms in our observations of debris flows, triggered by an exceptional rainstorm in the autumn of 2013. Additionally, we compare our observations with those of a dataset of 1138 debris flows in the Colorado Front Range, triggered during the same weather system. We found that runoff‐generated debris flows dominated in burn areas, and runoff required to start these flows could be well characterized by the Shields stress. Landslide‐initiated debris flows were dominant in unburned areas. Debris‐flow densities were tied to total rainfall and precipitation intensities. Like the observations in the Colorado Front Range, debris‐flow initiation locations were found primarily in areas of relatively sparse vegetation on south‐facing slopes between 25 and 40°, and with upslope contributing areas less than 1000 m2. In terms of preferential locations for debris‐flow initiations, 2013 vegetation coverage, approximated by Green–Red Vegetation Index metrics, proved to be more influential than the 2012 burn‐severity designation. The uniformity of observations between our study area and those in the Colorado Front Range indicate that the underlying hydrologic and landscape patterns of the debris‐flow initiation locations documented in these studies could be applicable to the wider southwest and Rocky Mountain regions. © 2019 John Wiley & Sons, Ltd.

The Evolution of Sediment Sources Over a Sequence of Postfire Sediment‐Laden Flows Revealed Through Repeat High‐Resolution Change Detection

“…This study also highlighted the utility of employing UAV‐SfM to sequentially document channel erosion processes, which used only a consumer‐grade UAV (DJI Mavic Pro) with a nonmetric camera that was easily deployed into autonomous mode. Being able to rapidly deploy UAV to areas with survey control to quantify sediment flux in postfire channels before and after storm events is a very useful tool, especially given increasing evidence that hydrodynamic thresholds leading to channel bed failure processes (e.g., Rengers et al, 2019; Tang et al, 2019; Tillery & Rengers, 2020) appear to be important in the generation of postfire debris flows.…”

HazMapper: a global open-source natural hazard mapping application in Google Earth Engine

“…A significant amount of research has been performed on remotely detecting mass-wasting events such as debris flows, debris slides, or rock slides (Kirschbaum et al, 2019;Amatya et al, 2019;Mondini et al, 2011;Lu et al, 2019;Huang et al, 2020;Tsai et al, 2010;Yang et al, 2013). Pixel-based or object-oriented analysis (OOA) methods rely on characterizing change to the Earth surface via multi-spectral satellite imagery and correlating these changes to mass-wasting events (e.g., Lu et al, 2019).…”

“…Subsequent satellite networks and payloads (e.g., Moderate Resolution Imaging Spectroradiometer -MODIS, Sentinel) have improved capabilities, and increasingly advanced satellite networks continue to be developed (e.g., Hoffman et al, 2016;Langhorst et al, 2019). Some traditional uses for satellite observations include identifying landslides and debris flows (e.g., Tillery and Rengers, 2019), identifying wildfire (e.g., Miller and Thode, 2007;Amos et al, 2019), volcanic monitoring (e.g., Cando-Jácome and Martínez-Graña, 2019), identifying deforestation (e.g., Hansen et al, 2013;Green and Sussman, 1990;USGS, 2019), identifying urban change and development (e.g., Masek et al, 2000;Schneider, 2012), and ecological monitoring and change detection (e.g., Zhou et al, 2001;Meentemeyer et al, 2004), among others.…”

HazMapper: A global open-source natural hazard mapping application in Google Earth Engine

“…Some traditional uses for satelliteobservations include identifying landslides and debris flows (e.g. Tillery and Rengers, 2019), wildfire (e.g. Miller and Thode, 2007;Amos et al, 2019), volcanic monitoring (e.g.…”