Transverse Bars and Braiding in the Lower Platte River, Nebraska

Abstract

Research Article| December 01, 1971 Transverse Bars and Braiding in the Lower Platte River, Nebraska NORMAN D SMITH NORMAN D SMITH University of Illinois at Chicago Circle, Chicago, Illinois 60680 Search for other works by this author on: GSW Google Scholar Author and Article Information NORMAN D SMITH University of Illinois at Chicago Circle, Chicago, Illinois 60680 Publisher: Geological Society of America Received: 13 May 1971 Revision Received: 16 Jul 1971 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1971, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1971) 82 (12): 3407–3420. https://doi.org/10.1130/0016-7606(1971)82[3407:TBABIT]2.0.CO;2 Article history Received: 13 May 1971 Revision Received: 16 Jul 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation NORMAN D SMITH; Transverse Bars and Braiding in the Lower Platte River, Nebraska. GSA Bulletin 1971;; 82 (12): 3407–3420. doi: https://doi.org/10.1130/0016-7606(1971)82[3407:TBABIT]2.0.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 The Platte is a wide, shallow river which flows eastward from the Rocky Mountains across the Great Plains of Nebraska. Its lower reaches carry a dominantly sandy load and during intermediate and low discharges display a pronounced braided character accomplished primarily through dissection of tabular, flat-topped transverse bars.Transverse bars form by sediment aggrading to a profile of equilibrium (Jopling, 1966) and grow by downcurrent extensions of avalanche faces. Depth, velocity, and grain size tend to decrease on active bar surfaces from their upstream mouths to the downstream and lateral margins. Active surfaces are covered with small-scale bed forms whose distributions are controlled by the flow characteristics. A typical mouth-to-margin bed form progression is dunes to diminished dunes to ripples, reflecting downcurrent reduction of stream power. Water-surface slopes over active bars tend to be greater than those of the channel segments which feed them.Under ideal conditions, transverse bars are essentially lobate; however, most bars, especially during low discharges, assume irregular or asymmetrical patterns due to any of several factors that include bar-mouth cross-sectional geometry, proximity to exposed banks, adjacent currents, steadiness of flow, and basin depth distribution. Braiding (bar dissection) begins during decreasing discharges when the flow passing through the bar mouth becomes unable to sustain active sediment transport over the entire bar surface. A single bar, examined closely over a five-day period of gradually decreasing discharge, documents the evolution from wholly active to dissected states. 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.