On Debris Flows, River Networks, and the Spatial Structure of Channel Morphology
Authors: Bigelow, Paul E.1; Benda, Lee E.1; Miller, Daniel J.1; Burnett, Kelly M.1
Source: Forest Science, Volume 53, Number 2, April 2007 , pp. 220-238(19)
Abstract:
We evaluated the morphological effects of debris flows from headwater streams in larger, fish-bearing channels of the central Oregon Coast Range, including their influence on fans, wood recruitment, and channel morphology. Continuous channel surveys (6.4 km) were conducted in third- through fifth-order streams (drainage area <10 km2 and slope <7%) where debris fan effects at confluences were most evident. This basin size contains the majority of channels (67%) in the central Coast Range with gradients that are used by coho salmon (Oncorhynchus kisutch Walbaum). The close spacing between headwater tributaries susceptible to debris flows (118 m average) resulted in long continuous sections of fish-bearing streams that were bordered by debris fans (103 m average) and debris fans impinging on 54% of the total channel length surveyed. Debris flows also supplied the majority of wood (58% of pieces) to the surveyed fish-bearing channels. The highest values of large wood, boulders, and channel gradients were associated with debris fans at confluences with headwater tributaries, while deeper sediment deposits were often associated with fans but also extended up and downstream from fans. The spacing and network pattern of debris flow-prone headwater tributaries influenced the spatial structure of channel morphology and aquatic habitats leading to a high degree of physical heterogeneity and patchiness in channel environments. Our study contributes to a growing emphasis on the role of tributary confluences in structuring channel morphology and aquatic habitats in mountain drainage basins and argues for including a confluence component to stream classification and habitat typing schemes.Keywords: landslides; tributary fan; confluence effects; aquatic habitat; channel classification
Document Type: Research article
Affiliations: 1: Paul E. Bigelow, Earth Systems Institute, 15944 Mills Ave., San Lorenzo, CA 94580— Lee E. Benda, Earth Systems Institute, 310 N. Mt. Shasta Blvd. #6, Mt. Shasta, CA 96067—Leebenda@aol.com. Daniel J. Miller, Earth Systems Institute, 3040 NW 57th St., Seattle, WA 98107—danmiller@earthsystems.net. Kelly M. Burnett, US Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis, OR 97331—kmburnett@fs.fed.us., Fax: (810) 815 -4291, Email: paulbigelow@gmail.com.
