Evidence is presented that snowmelt runoff from an urban watershed can produce density
current intrusions (underflows) in a lake. Several episodes of density current intrusions are
documented. Water temperatures and salinities measured near the bottom of a 10m deep
Minneapolis lake during the late winter warming periods in 1989, 1990, 1991, and 1995 show
significant rapid changes which are correlated with observed higher air temperatures and
snowmelt runoff. The snowmelt runoff entering this particular lake (Ryan Lake) has increased
electrical conductivity, salinity, and density. The source of the salinity is the salt spread on
urban streets in the winter. Heating of littoral waters in spring may also contribute to the
occurrence of the sinking flows, but is clearly not the only cause.
US Environmental Protection Agency, Office of Research and Development
Ellis, Christopher R.; Champlin, Jerry; Stefan, Heinz G..
Density Current Instrusions in an Ice-Covered Urban Lake.
St. Anthony Falls Laboratory.
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