CHANGES IN ISLAND MORPHOLOGY, DELTA DEVELOPMENT,
  SEDIMENT LOADS AND DEPOSITION IN POOL 6, UPPER
  MISSISSIPPI RIVER.
  
  Jefferson, Anne 1 and Carol A. Jefferson 2. 
  1 Department of Biology, St. Mary's University of Minnesota, Winona, MN
  55987  
  2 Department of Biology, Winona State University, Winona, MN 55987
  
  Pool 6 of the Upper Mississippi River has been managed primarily for
  navigation, commencing in 1878 with channel dredging and emplacement of
  wing dams, closing dams and revetment. The installation of Dam #6 and #5A
  in 1936 and the construction of railroad dikes on both sides of the river
  formed and constricted Pool 6.  Alterations in channel configuration and
  transport of sediments from tributaries result in sedimentation of backwaters,
  entrapment of sediment above dams and changes in island morphology. 
  From August 1993 through October 1996, sediment cores, suspended
  sediments, depths, discharge, current, turbidity, vegetation, and historical
  photographs from 700 sites were analyzed.  At least 19,497 metric tons of
  suspended sediment settle each year in Pool 6.  At least 41,502 metric tons of
  suspended sediment enters Pool 6 from its tributaries, with Trempealeau
  River contributing 40,467 metric tons.  Particulate organic matter constituted
  19% of the suspended solids from the nine tributaries. Approximately 23,550
  metric tons of POM is created within, or eroded from, the pool each year. 
  Suspended sediment entering the upper end of the pool is at least 348,000
  metric tons per year;  139,000 metric tons of POM enter the upper end of the
  pool.  Leaving the pool are 370,000 metric tons per year of suspended
  sediment and 172,000 metric tons of POM.  Between 1936 and 1993,
  Trempealeau River deposited an average of 3.3 ha-m per year of sediment in
  a Gilbert-type birds-foot delta.  Sediment rates in the Trempealeau delta
  decreased by 86% between 1936 and 1991. In 1996 water year, Trempealeau
  Bay released 7,400 metric tons more suspended sediment to the Mississippi
  than entered the bay from the Trempealeau River.  Since 1897, sedimentation
  has resulted in a bed rise of 5.5 to 6.5 meters in lower Pool 6.  An average
  bed rise of 0.2 meters occurred in the side channels in the mid- and upper
  reaches of Pool 6.   Four islands in lower Pool 6 increased an average of
  218% in area since 1947, accompanied by elongation, rise in elevation, and
  downstream migration.  Three new islands emerged above mean water height
  between 1993 and 1996, while one island eroded away.  Side channel islands
  and stream beds are reestablishing the configurations they had prior to
  construction of Dam 6, but after the construction of wing and closing dams.
  
  Keywords: Mississippi River, Pool 6, Sedimentation, Islands, Tributaries
  
  
  Anne Jefferson, PO Box 818, St. Mary's University of Minnesota, Winona ,
  MN 55987.  No fax (2nd author's is 507-457-5681), e-mail:
  ajeffers@rex.smumn.edu. 
  Prefer poster presentation, do not want to make platform presentation.
  Primary author is student.