This creates a very high bank relative to a critical bank height where the streambank fails (Figure 5), and a headcut that migrates upstream. The CEM Stage II stage of downcutting is often a result of channel straightening (Reckendorf and Tice, 2003). The CEM has been used to field identity the CEM stages on dozens of streams in dozens of states (Reckendorf and Steffan, 2006 ). (1984), and Simon (1989) provide an excellent perspective. Understanding historic channel changes will consistently help us understand streambank erosion The Channel Evolution Model (CEM) of Schumm et al. 1997) animal burrows (Reckendorf, 2008), or large woody debris jams causing avulsion. (1997) boundary shear stress depth of bed scour along eroding bank local sedimentation (Reckendorf, 2009, 2008), and Rosgen 2006), root density and depth (Reckendorf, 2001, and Rosgen, 2006), waves (Reckendorf, 1989) ice condition (freeze thaw, Knighton, 1995, and gouging) desiccation (Thorne et al. 1997, Welch and Wright, 2005) pre-wetting (Knighton, 1995, and Thorne et al. (1997) Welch and Wright (2005), Southerland and Reckendorf (2008) flow condition (peak, duration, angle of attack parallel to perpendicular to angle of failure), helicoidal flow, (Wolman, 1959, Hooke, 1979, Thorne et al. Is failure mechanism accelerated by: Rc/Wbkf geometry as discussed in, Bagnold (1960), Thorne et al. Investigate if failure mechanisms are accelerated or modified by a stratigraphy caused cantilever (Reckendorf, 2009, 2008, 2001, 1996, 1989). Investigate whether bank instability is caused by cantilever failure (Figures 1 and 2) planer failure (Figure 3) rotational failure (Figure 4) preferential flow failure including piping (Hagerty, 1991) high pore pressure liquefaction and seepage forces especially during the falling stage of floods popout failure or because bank height exceeds some critical bank height (Schumm et al. Changes at the watershed level might be caused by logging, mining, road building, Changes at the reach level might be riparian area modifications due to vegetation change or loss, animal use, stream channel straightening, or channel excavation and/or removal of material (stream bed mining), avulsion (abrupt change in stream course, such as meander neck cut-off) or climate change. These are combined with recognizing reach level changes in stage of channel evolution, scour patterns, sediment deposits, side slopes, slumping, and cultural features. Background conditions are established using old photographs and maps and compare rates over time, in the context of floods, and watershed and reach level changes. Streambank erosion is a natural phenomenon but can become accelerated because of changes at the watershed and/or reach level.
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