COLLABORATIVE RESEARCH: Experimental Study of Downstream Fining in Coarse-Grained River Channels

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This is a renewal of a 2-year project whose overall goal is to study downstream fining by aggradation and selective deposition in gravels. The main results so far have produced downstream fining by a factor of two in a channel 50 m long and 0.3 m wide at the St. Anthony Falls Hydraulic Laboratory (SAFHL), demonstrating unequivocally that selective deposition is an effective fining mechanism and that it can be studied in laboratory experiments. In parallel experiments at Johns Hopkins University (JHU), a novel colored-grain system is providing the fractional-transport data base needed to perdict the fining observed at SAFHL. This phrase now involves a series of runs a SAFHL with a channel width of 2.0 m; this will produce braided topography, enabling invesitgation of the effect of lateral sorting and topography on downstream fining. The present fractional-transport program at JHU, will continue adding components on the effect of sediment feed versus recirculation and the influence of small-scale sedimentary features. Finally, a concurrent set of runs at MIT to examine local lateral sorting in a 1.0 m wide channel as well as the effects of varying deposit geometry and percent extraction is planned. This research seems as the first real connection between engineering hydraulics and fluvial sedimentology and represents fundamental research related to sediment transport mechanics.