Repeatability, Sensitivity, and Uncertainty Analyses of the BANCS Model Developed to Predict Annual Streambank Erosion Rates

Abstract

Accelerated streambank erosion caused by channel instability can be the leading cause of sediment impairment of streams. Obtaining accurate streambank erosion rates for sediment budgeting and prioritizing mitigation efforts can be difficult and costly. One approach to quantifying streambank erosion rates is through the development and implementation of an empirically derived “Bank Assessment for Non‐point Source Consequences of Sediment” (BANCS) model. This study aims to improve the BANCS model application by evaluating repeatability between users and identifying sensitive and/or uncertain model inputs. Statistical analysis of streambank evaluations conducted by 10 different individuals suggests the implementation of the BANCS model may not be repeatable. This finding may be due to sensitive model inputs, such as streambank height and near‐bank stress level prediction method selection, and/or uncertain model inputs, such as bank material identification and the associated adjustment of erosion potential. Furthermore, it was found assessing streambanks as a group by obtaining a measure of central tendency from individual evaluations, as well as obtaining a higher level of training, may improve model implementation precision. Application of these suggestions may result in improved prediction of streambank erosion rates utilizing the BANCS model methodology.

Reply to Discussion

“…We also agree that the BANCS field methods are sensitive to observer variation, but we consider that to be a limitation of the BANCS model itself, as shown by the study cited by the discussants (Bigham et al. ), and not specifically of our study in which observations were always made by more than one person.…”

“…A recent publication by Bigham et al. () also recognized this lack of detailed procedures for BANCS. Hopefully that shortcoming will soon be remedied so that the BANCS model can be uncontroversially evaluated.…”

Bank erosion of the Tŕstie stream: BANCS model predictions vs. real bank erosion

“…In studies, where there was a weak relationship reported (Ghosh et al, 2016;Harmel et al, 1999;Kwan and Swanson, 2014), the authors used only visual assessments for bank parameters, whereas we used the sieve and densimetric tests to determine the bank material, and a laser clinometer to determine the bank angle. As Bigham et al (2018) state, inaccurate determination of these parameters (especially study bank height, root depth, bank angle, and bank material) affects the estimation of the erodibility potential, thus affecting the relationship between the potential and the real erosion.…”

Discussion

“…() were looking at observer variation in stream classification, observer variation and its impact on BEHI and NBS determinations were examined by Bigham et al. (). Here, study bank height was determined to be the most sensitive BEHI parameter in observer variation.…”

“…Bigham et al. () also found “The uncertainty of the bank material adjustment was determined to contribute the most to the uncertainty of the overall BEHI rating results” (p. 436). McMillan et al.…”