Fluvial processes, morphology and sediment budgets in the Coon Creek Basin, WI, USA, 1975–1993

Sediment budget processes in Coon Creek, Wisconsin, from 1975 to 1993 changed only moderately, generally continuing the trends that were evident in 1975. Perhaps most importantly, sediment yield to the Mississippi River appears to be unabated, with much of this clearly coming from storage loss, especially stream bank erosion. Vertical accretion continued on the lower (new) floodplains inset within their meander plains in tributaries and the upper main valley. The lower main valley also continued to aggrade but at the rate of about 6% of that occurring in the 1920s and 1930s. The major revision from earlier studies is that the upper main valley is a less significant net source of sediment than previously thought and the earlier prognostications of it being a significant net source of sediment in the future may be wrong. Perturbations have been caused by changes of riparian vegetation and, much more importantly, by the introduction of fish shelter structures and protected cut banks along the stream system reaching downstream to the end of the upper main valley. Because these structures do not permit natural stream migration, bank erosion and downstream sediment transfer, the Coon Creek basin has lost much of its suitability as a natural laboratory of fluvial processes.