STREAM TURBIDITY MODELING: A FOUNDATION FOR WATER QUALITY FORECASTING By Amanda L. Mather A DISSERTATION Presented to the Division of Environmental and Biomolecular Systems and the Oregon Health & Science University School of Medicine in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Science and Engineering May 2015 School of Medicine Oregon Health & Science University CERTIFICATE OF APPROVAL This is to certify that the PhD dissertation of Amanda L. Mather has been approved ______________________________________ Richard L. Johnson, PhD Research Advisor ______________________________________ Joseph A. Needoba, PhD Examination Committee Chair ______________________________________ Karen H. Watanabe, PhD Examination Committee Member ______________________________________ Paul G. Tratnyek, PhD Examination Committee Member ______________________________________ Anthony J. (Jim) Tesoriero, PhD U.S. Geological Survey External Examination Committee Member TABLE OF CONTENTS TABLE OF CONTENTS ..................................................................................................... i LIST OF TABLES ............................................................................................................. iv LIST OF FIGURES ............................................................................................................ v ACKNOWLEDGEMENTS ................................................................................................ x ABSTRACT ....................................................................................................................... xi CHAPTER 1: Introduction ................................................................................................. 1 1.1 Stream Turbidity .................................................................................................. 2 1.2 Water Quality during Hydrologic Events ............................................................. 4 1.3 Forecasting Stream Water Quality ....................................................................... 6 1.4 Dissertation Overview .......................................................................................... 7 CHAPTER 2: Quantitative Characterization of Stream Turbidity-Discharge Behavior using Event Loop Shape Modeling and Power Law Parameter Decorrelation .................. 9 2.1 Abstract ................................................................................................................ 9 2.2 Introduction ........................................................................................................ 10 2.2.1 Background ................................................................................................. 12 2.2.2 Study Objectives ......................................................................................... 15 2.3 Methods .............................................................................................................. 15 2.3.1 Loop Modeling............................................................................................ 15 2.3.2 Parameter Decorrelation ............................................................................. 17 2.3.3 Data and Hydrologic Event Identification .................................................. 18 2.3.4 Study Sites .................................................................................................. 19 2.3.5 Model Fitting and Evaluation ..................................................................... 21 2.4 Results ................................................................................................................ 22 2.4.1 Event Turbidity Magnitude and Timing ..................................................... 22 2.4.2 Turbidity-Discharge Loop Modeling .......................................................... 25 2.4.3 Loop Model Parameters .............................................................................. 28 2.5 Discussion and Conclusions ............................................................................... 31 CHAPTER 3: Characterization and Exploratory Analysis of Stream Turbidity during 5928 Events from 110 U.S. Gages .................................................................................... 36 3.1 Abstract .............................................................................................................. 36 i 3.2 Introduction ........................................................................................................ 37 3.3 Methods .............................................................................................................. 38 3.3.1 Study Gages and Datasets ........................................................................... 38 3.3.2 Turbidity-Discharge Event Modeling ......................................................... 41 3.3.3 Cluster Analysis .......................................................................................... 43 3.4 Results and Discussion ....................................................................................... 44 3.4.1 Model Fit ..................................................................................................... 44 3.4.2 Power Law Decorrelation Scaling Factor ................................................... 47 3.4.3 Model parameter .................................................................................... 49 3.4.4 Model parameter 푎0 ...................................................................................... 51 3.4.5 Model parameter 푏 ...................................................................................... 52 3.4.6 Model parameter 푐 ...................................................................................... 53 3.4.7 Gage Similarity Based푟 on Median Parameter Values ................................. 54 3.5 Conclusions ........................................................................................................ 57 CHAPTER 4: Event-based Prediction of Stream Turbidity using Regression and Classification Tree Approaches ........................................................................................ 59 4.1 Abstract .............................................................................................................. 59 4.2 Introduction ........................................................................................................ 60 4.3 Methods .............................................................................................................. 63 4.3.1 Study Catchments ....................................................................................... 63 4.3.2 Event Turbidity Modeling........................................................................... 65 4.3.3 Event Characteristics .................................................................................. 67 4.3.4 Turbidity Prediction Approaches ................................................................ 70 4.4 Results and Discussion ....................................................................................... 73 4.4.1 Study Events ............................................................................................... 73 4.4.2 Turbidity Prediction using Cluster Analysis and Classification Trees ....... 75 4.4.3 Turbidity Prediction using Regression Analysis......................................... 80 4.4.4 Comparison of Turbidity Prediction Approaches ....................................... 82 4.5 Conclusions ........................................................................................................ 88 CHAPTER 5: Forecasting Turbidity during Streamflow Events for Two Mid-Atlantic U.S. Streams...................................................................................................................... 90 ii 5.1 Abstract .............................................................................................................. 90 5.2 Introduction ........................................................................................................ 91 5.2.1 Study Sites .................................................................................................. 92 5.3 Methods .............................................................................................................. 93 5.3.1 Turbidity Forecast Input Data ..................................................................... 93 5.3.2 Turbidity Forecasting .................................................................................. 96 5.3.3 Evaluation of Forecasts ............................................................................... 97 5.3.4 Uncertainty Intervals ................................................................................... 98 5.4 Results and Discussion ....................................................................................... 99 5.4.1 Streamflow Events and Forecasts ............................................................... 99 5.4.2 Streamflow Forecast Errors ...................................................................... 102 5.4.3 Turbidity Forecasts ................................................................................... 104 5.4.4 Turbidity Forecast Errors .......................................................................... 107 5.4.5 Effect of Streamflow Forecast Uncertainty on Turbidity Forecasts ......... 110 5.5 Summary and Conclusions ..............................................................................