Evaluation of the Bank Stability and Toe Erosion Model (BSTEM) for Predicting Lateral Streambank Retreat on Ozark Streams

Abstract

Streambank erosion is known to be a major source of sediment in streams and rivers. The Bank Stability and Toe Erosion Model (BSTEM) was developed by the USDA-ARS National Sedimentation Laboratory in order to predict streambank retreat due to both fluvial erosion and geotechnical failure. Few model evaluations for bank retreat have been performed to date. The objective of this research was to evaluate BSTEM's ability to predict bank retreat on Ozark ecoregion streams, assess the importance of accurate geotechnical and fluvial erosion soil parameter values, and evaluate the importance of the near bank water table elevation on bank stability. The model was applied to a streambank on the Barren Fork Creek in northeastern Oklahoma. This site experienced significant bank retreat (between 7.8 and 20.9 m over a 100-m length of stream) between April and October 2009 based on regular surveys of the bank profile. BSTEM (version 5.2) was not originally programmed to run multiple hydrographs iteratively, so an additional subroutine was written which automatically input the stream stage. The new subroutine was also written to lag the water table response in the near-bank ground water depending on user settings. Eight BSTEM simulations were performed using combinations of the following input data: with and without a water table lag; default BSTEM geotechnical parameters (moderate silt loam) versus laboratory measured geotechnical parameters for the silt loam layer based on direct shear tests on saturated soil samples; and default BSTEM fluvial erosion parameters versus field measured fluvial erosion parameters from submerged jet tests on the silt loam layer. Using default BSTEM input values underestimated the actual erosion that occurred. Lagging the water table predicted more geotechnical failures resulting in greater bank retreat. Using measured fluvial and geotechnical parameters and a water table lag also under predicted bank retreat (approximately 4.0 m), but did predict the appropriate timing of bank collapses.