Incision and morphologic evolution of an alluvial channel recovering from hydraulic mining sediment

Research Article| June 01, 1991 Incision and morphologic evolution of an alluvial channel recovering from hydraulic mining sediment L. ALLAN JAMES L. ALLAN JAMES 1Department of Geography, University of South Carolina, Columbia, South Carolina 29208 Search for other works by this author on: GSW Google Scholar Author and Article Information L. ALLAN JAMES 1Department of Geography, University of South Carolina, Columbia, South Carolina 29208 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1991) 103 (6): 723–736. https://doi.org/10.1130/0016-7606(1991)103<0723:IAMEOA>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 Email Permissions Search Site Citation L. ALLAN JAMES; Incision and morphologic evolution of an alluvial channel recovering from hydraulic mining sediment. GSA Bulletin 1991;; 103 (6): 723–736. doi: https://doi.org/10.1130/0016-7606(1991)103<0723:IAMEOA>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 Hydraulic gold mining in the Sierra Nevada, California, produced such a large volume of sediment from 1853 to 1884 that channels could not carry a substantial proportion of the delivered sediment. The lower Bear River aggraded as much as 5 m and underwent a major avulsion during the 1870s. Channel morphology continues to respond to these changes more than 100 years after the cessation of most hydraulic mining. Textures of mine tailings and older alluvium are contrasted, and channel incision and channel-shape changes from 1930 to 1985 are documented.Unlike the Yuba and Sacramento Rivers, the lower Bear River had not returned to pre-mining base levels by 1950 as sediment loads decreased. Nor were incision rates or morphological change governed by reduced sediment loads below dams built in 1928 and in the mid-1960s. Channel stability was due to resistance of a cohesive stratum on the channel bed. An episode of channel down-cutting was instigated by a moderately large flood in December 1955 that pierced the cohesive layer and was sustained through the 1970s by moderate-magnitude floods. The 1955 flood did not directly erode large volumes of sediment, but it destabilized the channel, allowing smaller floods to erode the channel at an accelerated rate.Episodic channel-bed incision is contrasted to progressive morphologic changes. Cross-section shape narrowed and deepened steadily from 1930 through the mid-1970s as the channel was superimposed onto cohesive older alluvium. Progressive deepening set up a positive feedback that ensured the ultimate penetration of the paved bed. Channel morphologic readjustment from the avulsion thus was both progressive and episodic. 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.