CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Burge, L.M.; and Lapointe, M.
Date : 2002.
Title : Island head accretion and associated deposits within three anabranching gravel-cobble Bed rivers, New Brunswick, Canada.
Publication : Annual Meeting of the Canadian Geophysical Union. May 18-21, 2002, Banff, Alberta.
Issue :
Page(s) :
Abstract
Island head accretion is a newly recognized depositional location, process and sedimentology within gravel cobble rivers. Island head accretion is the process of floodplain accretion at the upstream heads of islands at stable long-lived diffluences. The process begins with the creation of an island by avulsion, or mid channel deposition followed by island emergence. When created by avulsion, the island core contains remnant floodplain with mature forest and soil. Accretion ends with the abandonment of one of the anabranches. The research was conducted on three wandering gravel-cobble tributaries within the Miramichi River drainage basin, New Brunswick. These rivers switch between single and multiple channels downstream where valleys widen to accommodate multiple channels. Avulsions may be triggered by ice jams, common in these systems. The study rivers decrease in size from the Little Southwest Miramichi (80 m), to the Renous (55 m), to the Taxis (40 m). Stable diffluence zone processes were investigated through morphological surveying, floodplain stratigraphy, and floodplain dendrochronology. At stable diffluences, when looking downstream, the active channel bed is shaped like a ramp, increasing in elevation towards the island and arching downward into each anabranch channel, thereby splitting the flow. Dendrochronology revealed that stable island heads accrete upstream over many decades from 1.2 to 3 m/yr over 130-180 m. Island head accretion deposits form one of three upward facies sequences within the floodplain; lateral accretion and channel fills also occur. Island head accretion deposits are the least common and the coarsest floodplain facies, composed of imbricated gravel and cobble layers. Coarse gravel or cobbles are deposited on the island head presumably because the coarsest material is not redirected into the smaller anabranch channels by secondary flow. Questions remain about whether this phenomenon is localized to the Miramichi drainage or occurs in other anabranching systems.
Bibliography of Canadian Geomorphology