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 alluvial fans and floodplain surfaces. Historical floodplain alluviation varies in thickness from about one and one-half feet (0.5 m ) in the headwaters to about twelve feet (4 m) near the mouth of the river. The morphology of channels and the mobility and storage of sediments in the Platte watershed responded quickly to environmental changes in the watershed. TREAM channels develop morphological

Stream Nutrient Retention in Three Northeastern Oklahoma Agricultural Catchments

“…Furthermore, land use changes that alter stream hydrology will impact nutrient retention (Meyer et al, 1999), especially during periods of high biotic activity. Several investigations have shown that alterations in stream hydrology and channel morphology are often associated with a shift in catchment land use from forest to agriculture (Knox, 1977;Jacobson and Primm, 1997). Furthermore, destruction of the riparian zone produces changes in stream morphology and hydrology (Hickin, 1984), along with biological attributes of the system (e.g., see Stauffer et al, 2000), further altering in-stream processes.…”

Stream size and human influences on ecosystem production in river networks

“…Stream ecosystems may be influenced by regional variation in climate, watershed hydrology, and terrestrial vegetation (Minshall et al 1983) but because a large majority of data came from temperate to semi-arid watersheds within the continental United States and western Europe, sites were not separated according to geography or climate. Human activities in watersheds can alter stream morphology, increasing or decreasing wetted stream area depending on sediment inputs, hydrology and riparian modification (e.g., Knox 1977). Data analyses presented here were normalized per unit area of stream bottom; inadequate information was available to assess the effects of human alterations of channel morphology on total streambed area.…”

Self-Organized Criticality in Riverbank Systems

“…Although the individual processes controlling bank failure in different locales have been well defined (e.g., Lawler 1992Lawler , 1993, our understanding of the basin-wide distribution of bank failure and stability is still in its infancy. Few geographic studies have looked at basin-wide distributions of bank failure per se (Lawler et al 1999), focusing instead on watershed-wide distributions of lateral migration and overall stream cross-sectional changes as a function of disturbances such as agriculture (e.g., Knox 1977), loss of vegetative cover (Graf 1979), climate change (Graf 1987), channelization (Simon 1989), dams (Williams and Wolman 1984), and urbanization (Trimble 1997). Although the changes in channel cross-sections and the controlling processes documented by these and other researchers are related to bank failure, they are not direct measures of that phenomenon.…”