HR:     0830h
AN:     H21A-29

TI:     Experiments on Sediment Pulses in Mountain Rivers

AU:     *Cui, Y 
EM:     Yantao.Cui-2@tc.umn.edu
AF:     St. Anthony Falls Laboratory
        University of Minnesota
        Mississippi River at 3rd Ave. Minneapolis, MN 55414  United States

AU:     Lisle, T E
EM:     tel7001@axe.humboldt.edu
AF:     Pacific Southwest Research Station
        Forest Service
        U.S. Department of Agriculture
        Arcata, CA 95521  United States

AU:     Pizzuto, J E
EM:     pizzuto@UDel.Edu
AF:     Department of Geology
        University of Delaware Newark, DE 19716  United States

AU:     Parker, G 
EM:     parke002@tc.umn.edu
AF:     St. Anthony Falls Laboratory
        University of Minnesota
        Mississippi River at 3rd Ave. Minneapolis, MN 55414  United States

AB:     Pulses of sediment can be introduced into mountain rivers from such mechanisms as debris 
        flows, landslides and fans at tributary confluences.  These processes can be natural or 
        associated with the activities of humans, as in the case of a pulse created by sediment derived 
        from timber harvest or the removal of a dam.  How does the river digest these pulses?  Is the 
        process of accommodation of the extra material a gradual and smooth one that limits the spatial
        extent of disturbance to channel morphology, or does the input create a bulge that propagates
        downstream like a donkey in the gut of a python?  Here the question was approached 
        experimentally in a long flume.  The flume was filled with poorly sorted sediment and allowed to 
        reach a mobile-bed equilibrium.  Low, long pulses of sediment were created by mounding 
        sediment above the bed of the stream.  Experiments were performed with pulses that were finer
        than the sediment feed, similar to the sediment feed and coarser than the sediment feed.  In 
        addition, sediment pulses were created by the installation of a dam, which was subsequently 
        removed.  The pulses deformed by means of a combination of translation and dissipation.  In all
        cases dissipation was sufficiently strong to flatten out the pulse to the point that it was no 
        longer recognizable as a propagating wave from bed elevation records.  That is, no definable 
        sediment wave ever migrated out of the flume.  In the case of the pulse of fine material, 
        however, distinct, sandy migrating leading and trailing edges to the pulse were identifiable for a 
        substantial duration, even after the pulse was only barely recognizable from elevation records.  
        Under the conditions of the experiment, the sediment pulse created by the removal of a dam 
        dissipated relatively rapidly.  Results are presented on the response of the long profile, 
        alternate bars and pattern of bedload transport to the introduction of sediment pulses.

DE:     1815  Erosion and sedimentation
DE:     1821  Floods
DE:     1824  Geomorphology (1625)
DE:     1860  Runoff and streamflow
DE:     1803  Anthropogenic effects
SC:     H
MN:     1998 Fall Meeting