An assessment of riparian land-use and channel condition impacts on streambank eroding lengths and recession rates in two third order rural watersheds in Central Iowa

Over the 150 year history of major agricultural activity in Iowa nearly all the native prairie (99.9%) and wetlands (95%) were lost as native plant communities were converted to row-crop agriculture. This major change from perennial to annual upland vegetation was accompanied by broad scale installation of tile drainage intended to remove moisture from saturated wetland soils, increasing available crop land. The increased removal of water by tile drainage accompanied by the increase in surface runoff caused by the loss of permanent soil cover and compaction resulted in an increase in the rate and amount of water entering stream systems. The increase in discharge overtime resulted in a series of channel adjustments (deepening & widening) to accommodate the increase in flow. Sediment contributed due to these channel adjustments, specifically from streambank erosion has been shown to be a major source of sediment in many Midwestern stream systems. The main objective of this study was to determine what impact the major past and present land use practices in the Walnut and Squaw Creek Watersheds were having on the location and rate of severe streambank erosion within the two channel systems. The location and length of severe streambank erosion was mapped along the main channels of each watershed. Eroding lengths were broke down into riparian land use categories: Coolseason grass, warmseason grass, rowcrop agriculture, grazed pasture, riparian forest, and grassland-forest mix. Total stream length, sinuosity, and eroding streambank lengths were compared among all land use categories. To estimate streambank recession rates, erosion pins were installed along streambanks in four major riparian land use types identified along the main stem of Walnut Creek. Outcomes of this investigation indicate that areas with high sinuosity located directly downstream of channelized portions of the stream network were subject to longer eroding lengths with higher recession rates than locations higher in the