Spatially Variable Historical Alluviation and Channel Incision in West-Central Wisconsin

Abstract

This study employs data from valley-bottom surveys, coring investigations, topographic maps, and aerial photographs to identify and explain spatial variations in historical alluviation along tributary streams in the Buffalo River watershed, an agricultural watershed in west-central Wisconsin. Similar to findings from other agricultural watersheds, the spatial distribution of historical alluvium in the Buffalo watershed reflects the controlling influence of watershed size and valley-bottom width. These two factors are not, however, clearly related to the deposition and accumulation of historical sediment at all sites. An additional significant factor that has affected valley-bottom sedimentation is historical channel incision. Incision of nearly every tributary stream in the watershed has created enlarged channels with considerable capacities to contain floods, keeping them from inundating and depositing sediment on valley floors. This helps explain why relatively large amounts of historical alluvium were deposited along some streams (because they are unincised or were incised relatively recently) and why much less sediment was deposited along others despite similar watershed characteristics (because they were incised early in the historical period). It also helps explain why, along some reaches, quantities of historical alluvium do not decrease in the upstream direction as expected. Apparently, incision by upstream-advancing headcuts allowed more time for alluvium to accumulate at upstream sites, countering the effects of decreasing drainage area. Today, tributary streams in the Buffalo River watershed compose a fairly well-integrated network of incised channels. As a result, tributary streams can now convey floods and sediment downstream more efficiently than they could in the past.

Heavy metal storage in near channel sediments of the Lahn River, Germany

“…Similarly, valley and flood-plain width, which influence stream power (Magilligan, 1985(Magilligan, , 1992Faulkner, 1998), do not explain the pattern of metal concentrations; between Gießen and Weilburg, where metal concentrations are highly variable, valley and flood-plain width change little. The percentage of clay and the organic matter content of sediments have virtually no effect on metal concentrations.…”

The human role in changing river channels

“…One further feedback effect is the ability of a changed channel to accommodate discharges. Downstream of an urban area a channel may increase in capacity but this increased capacity in turn can accommodate larger flows and so may reduce the incidence of flooding, a consequence of enlarged channels that results from incision in west central Wisconsin (Faulkner, 1998). Furthermore, if increased delivery of sediment is involved, consequent aggradation and reduced capacities may lower the ability of a channel to accommodate flood discharges, as suggested for the Kungai Selang in Malaysia (Brookes and Gregory, 1988).…”

Floodplain sedimentation in the Upper Mississippi Valley: Natural versus human accelerated

“…The development of historical meander plains in tributaries is characteristic of most stream systems of southwestern Wisconsin and adjacent areas of similar topography (Adams, 1940(Adams, , 1942Happ et al, 1940;Happ, 1944;Knox, 1972Knox, , 1977Trimble, 1983;Magilligan, 1985Magilligan, , 1992Woltemade, 1994;Lecce, 1997;Faulkner, 1998;Lecce andPavlowsky, 2001, 2004). Channel incision did not accompany lateral erosion because increased stream power was not sufficient to erode the very resistant armored, cobble-boulder gravel surface on the underlying late Wisconsin age alluvium (Fig.…”