Average annual precipitation for the basin ranges from 31 inches
in the northern part of the basin to 35 inches in the southern
portion of the basin (USDA-SCS 1982). The greatest amount of
precipitation usually occurs during June, while the least amount
of precipitation generally occurs during the months of January
and February (Figure Hy01). The basin is covered primarily in
glacial till, and due to the clay content, movement of water to
the subsurface is greatly diminished (Detroy and Skelton 1983).
Thus, most rainfall runs off the surface rather than percolating
into the soil. Streams in the basin show rapid flow increases in
conjunction with rains, but quickly return to low flow
conditions shortly after runoff ceases (MDNR 1995). Average
annual runoff ranges from five inches in the northern portion of
the basin to seven inches in the southern part of the basin
(USDA-SCS 1982). United States Geological Survey (USGS) Gage
Stations There are five active and 26 inactive USGS water gage
stations throughout the