Pattern and origin of stepped-bed morphology in high-gradient streams, Western Cascades, Oregon
Research Article| March 01, 1990 Pattern and origin of stepped-bed morphology in high-gradient streams, Western Cascades, Oregon GORDON E. GRANT; GORDON E. GRANT 1U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar FREDERICK J. SWANSON; FREDERICK J. SWANSON 1U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar M. GORDON WOLMAN M. GORDON WOLMAN 2Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore Maryland 21218 Search for other works by this author on: GSW Google Scholar Author and Article Information GORDON E. GRANT 1U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis, Oregon 97331 FREDERICK J. SWANSON 1U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis, Oregon 97331 M. GORDON WOLMAN 2Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore Maryland 21218 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1990) 102 (3): 340–352. https://doi.org/10.1130/0016-7606(1990)102<0340:PAOOSB>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GORDON E. GRANT, FREDERICK J. SWANSON, M. GORDON WOLMAN; Pattern and origin of stepped-bed morphology in high-gradient streams, Western Cascades, Oregon. GSA Bulletin 1990;; 102 (3): 340–352. doi: https://doi.org/10.1130/0016-7606(1990)102<0340:PAOOSB>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A general hierarchical framework for viewing stepped-bed morphology in high-gradient channels is presented. We emphasize channel units—bed features that are one or more channel widths in length—as a particularly important scale of variation. Field studies in two streams in the Cascade Range in Oregon indicated that pool, riffle, rapid, cascade, and step channel units had distinct bed slope ranges, with average slopes of 0.005, 0.011, 0.029, 0.055, and 0.173, respectively. Steeper units (rapids and cascades) are composed of step-pool sequences created by particles representing the 90th or larger percentile size fraction of bed material. Step spacing is inversely proportional to bed slope.The distribution of channel units along a stream is influenced by bedrock and processes that introduce coarse sediment. Cascade and pool units dominate where landslide and debris-flow deposits constrict channel width and deliver large immobile boulders to the channel, whereas riffle and rapid units dominate in broad valley flats where deposition of finer sediment occurs. Markov chain analysis indicates that channel units occur in nonrandom two-unit sequences with the slope of the upstream unit inversely proportional to the slope of the next downstream unit. Pool-to-pool spacings average two to four channel widths, but variability in spacing is high, owing to uneven distribution of bedrock out-crops and boulder deposits within the channel.Hydraulic reconstruction indicates that channel units form during high- magnitude, low-frequency events with recurrence intervals of about 50 yr. Comparison of channel-unit morphology to high-gradient flume experiments with heterogenous bedload mixtures indicated that unit morphogenesis is linked to factors that cause congestion of large particles during bedload transport events; these include local constrictions in channel width, immobile bed material, and abrupt fluctuations in velocity due to hydraulic jumps that promote deposition. Channel units appear to be a two-dimensional bar form found in streams where gradients exceed 2%, bedload is widely sorted, and width-to-depth ratios and sediment supply are low—conditions found in many mountain environments. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.