Dams are human interventions in fluvial systems, changing downstream hydrology and geomorphology. The shape of the alluvial streams changes as dams disrupt downstream flow and sediment, leading to significant geomorphic distinctions between regulated and unregulated reaches. Although hydrologic effects of dams are analyzed from stream gauge records, geomorphic impacts through time are non-linear and complex to assess. Prolonged periods of reduced dam outflows often result in the narrowing of downstream reach. Streams exhibit back-and-forth movement along their banks and floodplains, leading to the development of a new stable configuration. As stream power erodes or deposits sediments along channel boundaries, these processes depend on the magnitude of discharge from the dam or tributary inputs. We studied the Cheyenne River downstream of Angostura Reservoir, whose hydrogeomorphology has changed since the completion of the dam in 1949. The Cheyenne River widened upon receiving the tributary inputs of finer sediments near the Badlands region, starting at the mouth of Cedar Creek. Generally, the channel aspect ratio is inversely proportional to the amount of finer sediments in the riverbanks. With increased finer sediments, the width increment of the Cheyenne River is unclear and understudied. Irrespective of other dam-influenced streams, Cheyenne River presents a unique scenario as it is influenced by both Angostura Dam and Badlands sediments. Cheyenne River reveals valuable insights on evolving hydrologic and geomorphic dynamics of regulated streams, the transition from narrow canaliform channels to wider bar-dominated patterns, and the influence of fine-grained sediments on channel width adjustments.
