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Evaluating Streambank Retreat Prediction using the BANCS Model in the Valley and Ridge Physiographic Province Rex S. Gamble Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Biological Systems Engineering Theresa M. Thompson James B. Campbell William C. Hession May 12th, 2021 Blacksburg, VA Keywords: BANCS, NBS, Streambank Erosion Copyright (optional – © or Creative Commons, see last page of template for information) Evaluating Streambank Retreat Prediction using the BANCS Model in the Valley and Ridge Physiographic Province Rex S. Gamble Academic Abstract Excess sediment in streams is harmful to the environment, economy, and human health. Streambanks account for an estimated 7-92% of sediment and 6-93% of total- phosphorus loads to streams depending on the watershed. Stream stabilization through stream restoration has become a common practice to satisfy the 2010 Chesapeake Bay total maximum daily load (TMDL) due its value in credits received per dollar spent. Bank erosion is most commonly credited through the Bank Assessment for Non-point source Consequences of Sediment (BANCS) framework, an empirically-derived model that predicts bankfull bank erosion rates using Bank Erodibility Hazard Index (BEHI), an indicator of bank stability, and Near-Bank Stress (NBS), an indicator of applied flow energy at bankfull discharge. This study assessed the BANCS framework in the Valley and Ridge physiographic province where it has not previously been applied. The spatial and temporal variability of erosion data was assessed to determine the impact of different erosion measurement schemes on bank erosion estimates and BANCS curves, and alternate NBS methods that capture flow energy beyond bankfull were applied. Three years of monthly erosion data on 64 streambanks were used to assess the spatial and temporal variability of erosion measurements and subsequently develop the erosion curves. Predicted erosion rates were then compared to measured erosion rates on three banks in the Valley and Ridge of Southwest Virginia. Analysis of spatial variability suggests bank retreat measurements should be made every three channel widths to reliably quantify reach-scale load estimates. Furthermore, a minimum monitoring period of 12 months is recommended to ensure seasonal patterns in bank retreat are captured. These results also bring into question the efficacy of the BANCS model as a crediting tool, as the developed statistical relationships between erosion rates, BEHI, and multiple NBS methods were not statistically significant. The limited number of significant curves had low r2 values (r2 < 0.1) indicating measures of NBS and BEHI do not adequately explain the natural variability of bank retreat in the Valley and Ridge of Southwest Virginia. Evaluating Streambank Retreat Prediction using the BANCS Model in the Valley and Ridge Physiographic Province Rex S. Gamble General Audience Abstract While sediment naturally occurs in streams, too much sediment in these systems is harmful to the environment, economy, and human health. Streambanks contribute an estimated 7-92% of sediment pollution into streams. Stabilizing streambanks with stream restoration has become a common practice to reduce sediment for the 2010 Chesapeake Bay pollutant diet. The sediment reduction of bank stabilization is most commonly estimated with the Bank Assessment for Non-point source Consequences of Sediment (BANCS) framework, a model that predicts bank erosion rates using Bank Erodibility Hazard Index (BEHI), an indicator of bank stability, and Near-Bank Stress (NBS), an indicator of flow energy when the stream channel is full of water. This study assessed the BANCS framework in the Southwest (SW) Virginia where it has not previously been applied. In this process, the variability of the erosion data in space and time was assessed to determine the impact of different erosion measurement methodologies on bank erosion estimates and BANCS equations. Additionally, alternate NBS methods that represent flow energy below, at, and above the channel being full were tested. Three years of erosion data on 64 streambanks were used to assess the variability of erosion measurements in space and time and create new BANCS erosion equations. Predicted erosion rates using the new erosion equations were then compared to measured erosion rates on three banks in the area. Analysis of variability in space suggests bank retreat measurements should be made every three channel widths to reliably estimate erosion volume along a length of stream. Furthermore, a minimum measuring period of 12 months is recommended to ensure seasonal differences in bank retreat are captured. The results also bring into question the effectiveness of the BANCS model as a tool to estimate sediment reduction for the Chesapeake Bay pollutant diet, as the developed equations between erosion rates, BEHI, and multiple NBS methods commonly failed to provide significant relationships. The limited number of significant curves had low r2 values (r2 < 0.1) indicating the measures of NBS and BEHI do not explain the natural variability of bank retreat in the study area. Acknowledgements My whole-hearted appreciation goes towards Dr. Tess Thompson, my research advisor and mentor throughout my time at Virginia Tech. Without her knowledge, guidance, and expertise, this research would not be here today. I also would like to thank my committee members Dr. Cully Hession and Dr. Jim Campbell for advising and supervising this project. My most profound appreciate goes towards my research peers: Billy Paraszczuk, Benjamin Smith, Daniel Smith, Coral Hendrix, and Samuel Withers. In my time here, they have all provided extraordinary support academically and socially. Without their company graduate life would not have been as fun, and without their help with field work, this project would not have been possible to complete. I want to thank Laura Lehman who helped me ready field equipment and never failed to provide help when I asked. I also want to thank Denton Yoder for all his help with IT and CAD, as well as all the kombucha he shared. In addition, I would like to broadly thank all the faculty, students, and staff of the Biological Systems Department at Virginia Tech because my growth and well-being as a graduate student would not be possible without their knowledge, companionship, and support. I also want to thank all the land owners who allowed me access to bank sites, in particular Melinda Mays. Finally, I would like to thank Josh Running and Gene Haffey of Stantec who are currently working hard to create more BANCS curves and were kind enough to show me the ropes regarding BANCS. vi Table of Contents Academic Abstract .......................................................................................................................... ii General Audience Abstract ............................................................................................................ iv Acknowledgements ........................................................................................................................ vi List of Figures ................................................................................................................................. x List of Tables .............................................................................................................................. xvii List of Abbreviations ................................................................................................................. xviii 1 Introduction ................................................................................................................................ 1 2 Literature Review....................................................................................................................... 6 2.1 Regulation of Sediment ....................................................................................................... 6 2.1.1 Chesapeake Bay Total Maximum Daily Loads ............................................................ 6 2.1.2 Prevented Sediment Protocol...................................................................................... 11 2.2 Bank Retreat ...................................................................................................................... 15 2.2.1 Processes and Mechanisms ......................................................................................... 15 2.2.2 Measuring Bank Retreat ............................................................................................. 18 2.2.2.1 Methodologies & Categories ............................................................................... 18 2.2.2.2 Erosion Pin Measurements .................................................................................. 19 2.2.3 Predicting Bank Retreat .............................................................................................. 22 2.2.3.1 Empirical Erosion Models ................................................................................... 22 2.2.3.1.1 Bank Assessment for Non-point source Consequences of Sediment (BANCS)....................................................................................................................... 23 2.2.3.2 Process-based Erosion Models ............................................................................ 35 3 Methodology ...........................................................................................................................