HUMAN IMPACTS ON WISCONSIN STREAM CHANNELS

ABSTRACT The conversion of natural land cover to agricultural land uses in the Platte watershed of southwestern Wisconsin caused a three to fivefold increase in the magnitudes of floods that recur more frequently than once in five years in the small headwater and tributary watersheds. The impact of settlement on floods is less for larger watersheds, but the general impact of settlement has caused a major channel metamorphosis throughout the Platte River channel system. Most headwater and tributary channels have modern channel cross sections that are relatively wide and shallow when compared to their presettlement counterparts. Most channel cross sections along the downstream main channel, beyond the channel reaches where bedload sediments are a dominant factor in determining channel shape, are narrow and deep relative to their presettlement counterparts. Much of the sediment that is related to man-induced accelerated surface runoff has been transported only short distances and is presently deposited on al...