Experimental study of knickpoint and longitudinal profile evolution in cohesive, homogeneous material

Research Article| May 01, 1983 Experimental study of knickpoint and longitudinal profile evolution in cohesive, homogeneous material THOMAS W. GARDNER THOMAS W. GARDNER 1Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802 Search for other works by this author on: GSW Google Scholar Author and Article Information THOMAS W. GARDNER 1Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1983) 94 (5): 664–672. https://doi.org/10.1130/0016-7606(1983)942.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation THOMAS W. GARDNER; Experimental study of knickpoint and longitudinal profile evolution in cohesive, homogeneous material. GSA Bulletin 1983;; 94 (5): 664–672. doi: https://doi.org/10.1130/0016-7606(1983)942.0.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 series of experiments were conducted in homogeneous bedrock to study knickpoint and longitudinal-profile evolution. Knickpoints are created by successive drops in base level, which simulate intermittent uplift. Channel morphology and flow characteristics vary systematically along a knickpoint reach. As the knickpoint lip is approached, width decreases, but depth, velocity, and bottom shear stress increase. As a result, knickpoints are rapidly destroyed through the process of (1) knickpoint replacement and (2) subsequent knickpoint inclination. Knickpoint replacement consists of two morphologically distinct, erosional reaches: the knickpoint face below the knickpoint lip, which decreases in slope, and an incising reach above the knickpoint lip, which increases in slope. Knickpoint replacement is a significant process in the evolution of knickpoints in homogeneous bedrock. Within experimental limits, this study supports the notion that knickpoints do not undergo parallel head-ward retreat in homogeneous bedrock, given intermittent uplift, except in those possible cases of extensive and pervasive bedrock jointing. Only the erosional sediment-transport discontinuity above the knickpoint is developed in cohesive sediments. Below the knickpoint, a steep, bedrock channel slope, low sediment load, and rapid decrease in grain size of sediment load preclude development of the aggradational sediment-transport discontinuity.Knickpoint evolution can be characterized by three general models: parallel retreat, replacement, and inclination. These models are based on the following criteria within the knickpoint reach: (1) relationship between bottom shear stress, τ0, and critical shear stress needed to initiate motion, τc; (2) nature of the bed-load transport discontinuities; and (3) spatial variability of bedrock resistance to fluvial erosion. 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.