Both phases relied on the same strategy: 1) identify the pertinent processes and specify a priori topographic and forest-cover attributes that influence landslide susceptibility and debris-flow runout, based on observations and measurements reported in previous studies, 2) define spatially distributed, digital characterizations (maps) of these attributes, 3) overlay mapped landslides and debris-flow tracks on these digital maps, and 4) define empirical probabilities of encountering a mapped landslide or debris-flow track in terms of the specified attributes. In the second, described here, we characterized potentials for debris-flow runout from identified landslide source areas. In the first, we characterized susceptibility of hillslopes to debris-flow triggering landslides (Miller and Burnett, 2007). Analysis over these spatial extents constrained us to using available digital data with geographical information system (GIS) software. Our goal was to develop methods for identifying and ranking stream channels subject to landslide-triggered debris-flows over areas spanning 101 to 104 km2. The role of debris flows in driving ecosystem dynamics is of particular concern in areas managed for timber production, because evidence points to timber harvest and road construction as prominent controls on where and how often landslides and associated debris flows occur (Swanson and Dyrness, 1975 Montgomery et al., 2000). Thus key factors in analysis of mountain river geomorphology and associated ecosystems (Benda et al., 2004 May and Gresswell, 2004). Characterization of debris-flow locations and rates of occurrence areĭ.J. Debris flows are also important sources of channel disturbance, scouring centuries of accumulated sediment and organic debris from headwater streams, and inundating valley floors in their deposits (Hack and Goodlett, 1960 Cenderelli and Kite, 1998 Miller and Benda, 2000 May and Gresswell, 2003). Debris-flow depositional sites, thereby, contribute to aquatic habitat heterogeneity (Benda et al., 2003 Bigelow et al., 2007). Debris fans and terraces constrain channel planform and cross-sectional geometry boulders and wood in debris-flow deposits form persistent sources of ⁎ Corresponding author. Introduction Landslides and debris flows are important geomorphic agents in mountainous terrain and can greatly affect mountain stream ecosystems (Swanson et al., 1988, 1998). Keywords: Debris flow Landslide Disturbance Aquatic habitat Risk assessmentġ. It offers unprecedented ability to characterize debris-flow effects over channel networks, providing a tool for risk assessment and for generating hypotheses that relate topographic and forest-cover controls on debris-flow runout to the types and abundance of channel habitats in a river basin. This model predicts debris-flow probability over channel-reach scales that can be aggregated to basin-scale measures of debris-flow potential. The model is calibrated and model predictions are compared to field-mapped debris-flow travel paths from study sites in the Coast Range of Oregon, USA. This paper presents a model for using these data to calculate empirical probabilities for debris-flow runout over DEMdetermined flow paths and shows how these probabilities can be combined over all sources to estimate the potential for debris-flow delivery to stream reaches throughout entire channel networks. Widely available digital elevation and land-cover data (10-m DEMs and 25-m satellite imagery) offer the potential to assess debris-flow runout paths over regional extents. Identification of channels susceptible to debris-flow inputs of sediment and organic debris, and quantification of the likelihood and magnitude of those inputs, are key tasks for characterizing spatial and temporal patterns found in channel conditions and associated habitats in a river network. Received 30 November 2006 received in revised form accepted Available online 2 June 2007Ībstract Debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance. Burnett b bĪ Earth Systems Institute, 3040 NW 57th Street, Seattle, WA 98107, USA Pacific Northwest Research Station, USDA Forest Service, Corvallis, Oregon, 97331, USA Available online at Geomorphology 94 (2008) 184 – 205 A probabilistic model of debris-flow delivery to stream channels, demonstrated for the Coast Range of Oregon, USA Daniel J.
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