Levees also

Levees also Selleck Afatinib hinder movement of nutrient- and sediment-rich flood waters onto the floodplain, disconnect aquatic environments, and reduce ecological and habitat diversity (Ward and Stanford, 1995, Magilligan et al., 1998 and Benedetti, 2003). Wing dikes and closing dikes are structures designed to divert flow toward a main channel

and away from side channels and backwaters. Wing dikes extend from a riverbank or island to the outside of the thalweg and usually point downstream, while closing dikes direct water away from side channels and backwaters. Together these features concentrate water into a faster moving main channel, increasing scour (Alexander et al., 2012). In an island braided system, the main channel becomes more defined and stable (Xu, 1993, O’Donnell and Galat, 2007, Pinter et al., 2010 and Alexander et al., 2012). Wing dikes tend to expand and fix the

position of land to which they are attached (Fremling et al., 1973 and Shields, 1995). Scour often occurs immediately downstream of wing and closing dikes, but, farther downstream, reduced water velocities promote sedimentation (Pinter et al., 2010). In large rivers, locks and dams are frequently employed to improve navigation. Upstream of a dam, raised water levels can submerge floodplain or island area, subject an altered shoreline to erosion, and inundate check details terrestrial and shallow water habitat (Nilsson and Berggren, 2000, Collins and Knox, 2003 and Pinter et al., 2010). Extensive open water leaves terrestrial features susceptible to erosion by wave action, which is strengthened by increased wind fetch (Lorang et al., 1993 and Maynord and Martin, 1996). Impoundment typically maintains a near-constant pool elevation that results in little vegetation below the static minimum water level, scouring concentrated

at one elevation, and susceptibility to wave action (Theis and Knox, 2003). In the slack water environment upstream of dams, the stream’s ability to transport Sitaxentan sediments is reduced, potentially making dams effective sediment traps (Keown et al., 1986 and Vörösmarty et al., 2003). The island-braided Upper Mississippi River System (UMRS) has been managed since the mid-1800s, with levees, wing and closing dikes, and a system of 29 locks and dams, to improve navigation and provide flood control (Collins and Knox, 2003). This succession of engineering strategies has caused extensive alteration in the channel hydraulics and ecology of the UMRS (Fremling, 2004, Anfinson, 2005 and Alexander et al., 2012). Extensive loss of island features in many parts in the UMRS, especially in the areas above each Lock and Dam, has been attributed to changes in sedimentation rates and pool elevations (Eckblad et al., 1977, Grubaugh and Anderson, 1989, Collins and Knox, 2003 and Theis and Knox, 2003).

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