| The anastomosed channel pattern is a type of fluvial system in which flow organizes into multiple coextensive, individually-stable channels. Anastomosed streams are uncommon globally and their origins are poorly-understood and understudied compared to the more common meandering and braided patterns. Though infrequent, the pattern exists across various climatic and tectonic settings, including Australia and Canada. Anastomosed streams also are surprisingly common in the U.S. Rocky Mountains, of which the highly-agriculturalized Little Laramie River in southeast Wyoming is representative. Several techniques were employed to determine controls on this stream, including hydrograph analysis, sediment characterization, individual anabranch and anabranch network characterization, terrain analysis and floodplain inundation modeling over a high-resolution, LiDAR-derived digital elevation model, and anthropogenic impact analysis. Results from these analyses suggest that the anastomosed channel pattern forms on the Little Laramie River floodplain because it experiences high-energy peak flows yet also receives a low sediment supply. This floodplain hosts a network of perennial channels with resistant banks that force peak flows overbank to rework and reoccupy floodplain channels. The combination of hydrology, sediment, and human modication present on the Little Laramie River floodplain supports a system static on a relatively long timescale (10 4 years) despite being misfit to its valley. Comparison of U.S. Rocky Mountain anastomosed streams to those found elsewhere shows that individual anabranch length relative to anabranch spacing is greater and that examples occur in lower order basins. Understanding the natural processes that promote anastomosis enables better recognition of how fluvial systems evolve and would directly benefit management of these watersheds for agricultural and societal purposes. |
