The influence of hydrologic and riparian factors on stream channel stability in a central Iowa stream
Richard C. Schultz
Onion Creek, a 2nd order stream in central Iowa, is the focus of research on stream channel stability and sediment movement. A field survey of Onion Creek (Chapter 2) found 24.5% of the total streambank length was severely eroding and some reaches of the stream had up to 50% severely eroding streambanks. Hydrologic factors such as watershed size, stream channelization, and flow restrictions were more significant than riparian land use in explaining the incidence of severely eroding streambanks.
An analysis of channel movement on Onion Creek from 1939 to 2009 (Chapter 3) found significant local changes, with landowners straightening stream channels in some sections and meander migration dominated by increases in stream extension in others. This predominance of channel extension in meandering sections indicates a stream that is adjusting to excess hydrologic energy.
Streambank erosion was directly measured on a subset of streambanks using erosion pin plots measured from October 2011 to April 2013 (Chapter 4). A drought during much of this period caused low levels of change, but study sites did show freeze-thaw destabilization during winter months followed by moderate erosion by fluvial entrainment in the springs of 2012 and 2013.
Water quality was measured at the outlet of Onion Creek between March 2012 and April 2013 (Chapter 5). An analysis of the loads and concentrations of sediment, phosphate and total phosphorus, and nitrate and total nitrogen exported from Onion Creek is presented. Finally, sediment loads discharged from Onion Creek are compared to estimates of sediment eroded from streambanks.