VALLEY ALLUVIATION IN SOUTHWESTERN WISCONSIN.

Meander erosional banks of fifth and sixth order southwestern Wisconsin streams having drainage areas of twenty square miles (30 km2) or less frequently reveal three distinct sedimentary sequences. The basal unit of coarse textured debris is thought to represent bad load sediment of a prior channel active near the terminus of a mid-Holocene drought about 6,000 years B. P. A silty clay series over the coarse layer is interpreted to have been derived by vertical accretion extend from the middle series to the current surface, and mainly result from increased flooding related to modern land use practices. The recent man-induced change in channel morphology is analogous to natural adjustments produced by Holocene climatic fluctuation, and suggests that temporal aspects of channel and floodplain evolution may be described by a step function model. [ABSTRACT FROM AUTHOR]