Origin of anastomosis in the upper Columbia River, British Columbia, Canada

摘要

To understand the origin of anastomosis on the Columbia River between Spillimacheen and Golden, British Columbia, Canada, a geomorphological and sedimentological survey was undertaken during the summer flood of 2000. On the basis of these observations, the study reach can be divided into two sub-reaches: a highly anastomosed section with three to five channels, and a weakly anastomosed section with one to two channels. The highly anastomosed reach occurs immediately downstream from the Spillimacheen tributary and is characterized by a higher channel slope, a higher number of crevasse splays, a larger combined crevasse splay area, a wider valley and a coarser bedload. Higher rates of floodplain aggradation in the highly anastomosed reach are suggested by modern sediment budgets and radiocarbon dates. These geomorphological and sedimentary associations are consistent with the hypothesis that anastomosis of the Columbia River is maintained by a dynamic equilibrium between the rates of channel creation and channel abandonment. Rising base-level, fine bedload and low bed-slope are not necessary immediate conditions for anastomosis of the Columbia River.