![]() ![]() Results elucidate channel width, slope, discharge, and sediment dynamics consistent with a gradual transition from detachment- to transport-limited incision in fluvial adjustment to local base-level lowering. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the inside. Today, diffusion dominates incision of a 500-m-long knickzone upstream of the gorge, where sediment transport likely limits ongoing adjustments to the anthropogenic cutoff. A meander is formed when the moving water in a stream erodes the outer banks and widens its valley and the inner part of the river has less energy and deposits what it is carrying. River meanders JanuMost river curves have nearly the same value of the ratio of curvature radius to channel width, in the range of 2 to 3. Initial fast knickpoint propagation (23 m/yr 1900β1903 CE) slowed (4 m/yr 1903β1981 CE) to diffusion (1981β2019 CE) as knickpoint slope decreased, yielding an ~350-m-long, 6-m-deep gorge within the preβ1900 CE channel. Tectonic quiescence, consistent rock erosivity, and low millennial erosion rates provide ideal boundary conditions for this 10 2 yr gorge-formation experiment. Miners cut off the meander in 1900 CE, abruptly lowering local base level by 6 m and forcing narrowing and steepening of the channel across a knickpoint that rapidly incised upstream. 79 E., Copper River meridian, which is an iron survey post with. I quantify 10 2 yr rates and processes of gorge incision using historical records, field observations, and topographic and image analysis of a human-caused bedrock meander cutoff along the North Fork Fortymile River in Alaska (USA). witness corner to meander corner of secs. When flow enters a channel bed, a helical secondary current is set up that increases flow velocity and channel depth along the outer bank in proportion to bed curvature, which encourages bank erosion. Bedrock river-gorge incision represents a fundamental landscape-shaping process, but a dearth of observational data at >10 yr timescales impedes understanding of gorge formation. The mechanics of formation of meanders is reasonably well understood ( 4 ). ![]()
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