|Palmer, Jason -|
|Schilling, Keith -|
|Isenhart, Thomas -|
|Schultz, Richard -|
Submitted to: Geomorphology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 2013
Publication Date: February 1, 2014
Citation: Palmer, J.A., Schilling, K.E., Isenhart, T.M., Schultz, R.C., Tomer, M.D. 2014. Streambank erosion rates and loads within a single watershed: Bridging the gap between temporal and spatial scales. Geomorphology. 209:66-78. Interpretive Summary: Sediment loads in streams is an important water quality problem that impacts transportation systems, recreational use of waters, and the quality of aquatic habitats. Recent research has shown that erosion of streambanks is the dominant source of sediment loads for many streams. However, few detailed investigations have taken place to better understand the dynamics of streambank erosion along a stream channel through time. This study investigated streambank erosion along a headwaters stream in Iowa during a seven-year period. Year-to-year variability was large, with erosion rates varying from about 1/4 inch to nearly one foot of bank loss per year, which accounted for 23-53% of the annual sediment loads measured at the watershed outlet. The variation was driven largely by the occurrence or absence of large rainfall-runoff events from year to year. The timing and causes of bank collapse and subsequent erosion are not straightforward, and temporary storage of sediment along the channel complicates the ability to connect bank losses with sediment loads measured at the outlet. These results comprise one of the longest periods of record for detailed streambank erosion data in the U.S. This research will be of greatest interest to sedimentologists and fluvial geomorphologists, but will also be noteworthy to others interested in detailed water quality research and learning more about sediment sources and timings in watersheds.
Technical Abstract: The importance of streambank erosion to watershed-scale sediment export is being increasingly recognized. However few studies have quantified bank erosion and watershed sediment flux at the basin scale across temporal and spatial scales. In this study we evaluated the spatial distribution, extent, and temporal frequency of bank erosion in the 5218 ha Walnut Creek watershed in Iowa across a seven year period. We inventoried severely eroding streambanks along over 10 km of stream and monitored erosion pins at 20 sites within the watershed. Annual streambank recession rates ranged from 0.6 cm/yr during years of hydrological inactivity to 28.2 cm/yr during seasons with high discharge rates, with an overall average of 18.8 cm/yr. The percentage of total basin export attributed to streambank erosion along the main stem of Walnut Creek ranged from 23 to 53%. Large variations in individual site, annual rates and percentage of annual load suggested that developing direct relationships between streambank erosion rates and total sediment discharge may be confounded by the timing and magnitude of discharge events, storage of sediments within channel system and the remobilization of eroded material.