CHANGES IN WINTER WATER LEVELS ON THE UPPER MISSISSIPPI
RIVER

Joseph H. Wlosinski and Scott R. Marecek
Environmental Management Technical Center, Onalaska, WI  54650

Water regulations for dams in the St. Paul and Rock Island Districts of the U.
S. Army Corps of Engineers allow lower winter water levels, by approximately
0.5ft, than levels maintained during the navigation season.  The two Districts
agreed to hold water levels on the high side of the operating band during the
winter of 1995-1996 at the request of natural resource agencies.  The request
was based on the need to improve backwater habitats for over-wintering fish.   
We analyzed water levels for Pools 2 through 22 for the first 60 days of each
year from 1991 through 1996.  In addition, we analyzed dissolved oxygen,
temperature, and water velocities as a function of water depth, and dissolved
oxygen as a function of snow depth and percentage of snow coverage.  Data for
the additional variables was collected for the same time periods by the Long
Term Resource Monitoring Program field stations in Pools 4, 8, 13, and 26. 
Water levels during the winter of 1995-1996 were significantly higher (a=.05)
for 17 of 22 dams when compared to other years, ranging from 0.07 ft to 0.83 ft 
higher.  Water levels in pools showing non-significance ranged from 0.06 ft
lower to 0.22 ft higher.  Part of the difference in increased water levels during
the winter of 1995-1996 may be attrbuted to higher discharges for pools
managed with two control points.  Dissolved oxygen, temperature, and water
velocities as a function of depth were analyzed across all four pools at both
stratified random and fixed sites.  Sample sizes ranged from 94 to 335.  Only
dissolved oxygen from the stratified random samples showed positive
significance, and only weakly so.   R2 values were less than 0.2 for all stratefied
random and fixed sites.  Dissolved oxygen as a function of snow depth and
percentage of snow coverage was significant for both stratified random and
fixed sites, but again only weakly so.



Joe Wlosinski
Environmental Management Technical Center, Onalaska, WI  54650
(608) 783-7550 extension 56
FAX (608) 783-8058

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