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WATERSHED MODELING AND UNCERTAINTY ANALYSIS FOR THE NORTH FORK BROAD RIVER, GEORGIA, USA by PATRICIA J. HAYES (Under the Direction of David Radcliffe) ABSTRACT Erosion and the resulting sediment are major issues facing the environment. High sediment loads can cause water quality problems, such as damaging biota habitat and recreational use. Georgia’s North Fork Broad River has been listed as an impaired stream segment for sediment. Our objective was to use Water Characterization System’s (WCS) Sediment Tool to model the sediment movement in the North Fork. The model uses USLE to determine erosion and four delivery ratios (DR) to determine sediment yield. Another objective was to determine model sensitivity and uncertainty. We have implemented WCS in an Excel spreadsheet coupled with @Risk software, a commercial plug-in to Excel. Our modeling efforts show that the North Fork does have a sediment problem. Sediment is greatly affected by DR. Land use changes can also affect the sediment yield. Using WCS, there is large uncertainty in sediment delivery prediction, but much less uncertainty in erosion prediction. INDEX WORDS: Erosion Modeling, Model Uncertainty Analysis, Sediment Modeling, Sediment Yield, TMDL, Watershed Modeling WATERSHED MODELING AND UNCERTAINTY ANALYSIS FOR THE NORTH FORK BROAD RIVER, GEORGIA, USA by PATRICIA J. HAYES BS, Texas A&M University, 2001 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2004 © 2004 Patricia J. Hayes All Rights Reserved WATERSHED MODELING AND UNCERTAINTY ANALYSIS FOR THE NORTH FORK BROAD RIVER, GEORGIA, USA by PATRICIA J. HAYES Major Professor: David Radcliffe Committee: Miguel Cabrerra Mark Risse Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2004 DEDICATION I would like to dedicate this thesis to my mom, Billie Patrick Hayes, and my dad, Tim Hayes. They taught me to always follow my dreams, to find the positive in everything and most of all to not worry about things I cannot control. Thank you for your patience, guidance and love. iv ACKNOWLEDGEMENTS I would like to thank the many people who have aided me in my three-year journey to completing my thesis and masters. In addition to my major advisor, Dr. David Radcliffe, I would like to thank my committee members Dr. Miguel Cabrera and Dr. Mark Risse for their advice. Also, I would like to extend great thanks to Dr. Ting Dai and Dr. Feng Chen. They provided me with endless hours of help and patience with my infinite questions. I would like to thank Dr. Larry West, Dr. Lynn Usery, and Dr. Todd Rasmussen for helping with various other questions I had during my research. I would also like to thank the amazing staff in the Crop and Soil Sciences department. Vivienne Sturgill and Henrietta Tucker provided me with great advice and fortitude. Lastly, I would like to thank all my friends here in the Crop and Soil Sciences Department who have provided me with the support, friendship, and patience to see me through the everyday stresses of being a graduate student. v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS............................................................................................ v LIST OF TABLES ................................................................................................... viii LIST OF FIGURES ...................................................................................................ix CHAPTER 1 Introduction ............................................................................................ 1 2 Literature Review..................................................................................... 3 Total Maximum Daily Load (TMDL) ....................................................... 3 Erosion and Sediment........................................................................... 5 Sediment Measurements....................................................................... 7 Universal Soil Loss Equation (USLE) ..................................................... 10 Sediment and Erosion Amounts ........................................................... 13 Forest Erosion and Sediment............................................................... 15 Delivery Ratios................................................................................... 16 Watershed Models - General ............................................................... 19 Watershed Models - BASINS................................................................ 20 Watershed Models - Watershed Characterization System (WCS)............. 21 North Fork Broad River ....................................................................... 23 References ........................................................................................ 25 vi 3 Watershed Modeling and Uncertainty Analysis for the North Fork Broad River, Georgia, USA ............................................................................ 30 Abstract............................................................................................. 31 Introduction....................................................................................... 31 Materials and Methods........................................................................ 35 Results .............................................................................................. 48 Conclusion......................................................................................... 53 REFERENCES........................................................................................................ 56 APPENDICES A Erosion and Sediment Yield .................................................................... 69 B Delivery Ratio Comparison BMP and Construction Graphs.......................... 75 C Example Bell, GA Flow and Suspended Sediment Concentration Data......... 76 D Example Chattahoochee River near Cornelia, GA Flow and Suspended Sediment Concentration Data ............................................................. 77 E @Risk Output ........................................................................................ 78 vii LIST OF TABLES Page Table 2.1: Land use area and percentage of entire North Fork Broad watershed ........ 59 Table 2.2: Erosion in tons by landuse for North Fork Broad River.............................. 59 Table 2.3: Sediment total rankings for Distance-Relief and Distance DR methods....... 65 Table 2.4: Predicted sediment load for three Georgia Rivers..................................... 66 viii LIST OF FIGURES Page Figure 1.1: North Fork Broad River location in Georgia............................................ 29 Figure 2.1: Broad River Watershed ........................................................................ 58 Figure 2.2: Log-log plot of Bell, GA Flow vs. Suspended Sediment Concentration (sample data and regression line)............................................................. 60 Figure 2.3: Roehl Piedmont Delivery Ratios with linear regression line and 95% confidence intervals applied ..................................................................... 61 Figure 2.4: Source Erosion for North Fork Broad River ............................................. 62 Figure 2.5: Road Erosion for North Fork Broad River................................................ 63 Figure 2.6: Erosion and sediment totals for the North Fork Broad watershed using four methods of calculating DR ....................................................................... 64 Figure 2.7: Broad River predicted sediment load...................................................... 66 Figure 2.8: @Risk Monte Carlo Simulation Distribution for Composite Sediment ......... 67 Figure 2.9: @Risk Monte Carlo Simulation Regression Sensitivity for Composite Sediment ............................................................................................... 67 Figure 2.10: @Risk Monte Carlo Model Distribution for Composite Erosion ................. 68 Figure 2.11: @Risk Monte Carlo Simulation Correlations for Composite Erosion.......... 68 ix Chapter 1 Introduction Erosion is a major issue facing the environment today. The resulting sediment can cause severe problems for streams. Sediment is defined as “particles derived from rocks or biological materials that have been transported by fluid or solid material suspended in or settled from water” (Faye et al., 1980). High sediment loads cause critical water quality problems within the stream, such as damaging the biota habitat, aiding in the transport of carrying other pollutants, and filling ponds, lakes and reservoirs. Measuring stream sediment and setting a general standard for a healthy stream can be a complex task. Not only must the current stream health and sediment load be considered, but also the stream history as well as future growth and change. Many U.S. waters do not meet water quality standards set forth by the EPA; 17% of these streams have excessive sediment load (Radcliffe, 2002). In 1979, the total U.S. sediment yield was estimated at about 3.6 billion metric tons/year (Robinson, 1979). Given that stream sediment is a major issue across the nation as well as the various other stream pollutant problems, the federal government included the Total Maximum Daily Load (TMDL) program in the Clean Water Act. This program is a watershed-based plan for protecting and improving water quality in streams that no longer meet their designated use. While TMDL programs