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Similar Watershed Cross-Correlation and Climate Stationarity

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Similar Watershed Cross-Correlation and Climate Stationarity SIMILAR WATERSHED CROSS-CORRELATION AND CLIMATE STATIONARITY CHERRY CREEK, CALIFORNIA By Evan Walton Smith A Project Presented to The Faculty of Humboldt State University In Partial Fulfillment of the Requirements for the Degree Master of Science In Environmental Systems: Environmental Resources Engineering Committee Membership Dr. Margaret Lang, Committee Chair Dr. Elizabeth Eschenbach, Committee Member Dr. Christopher Dugaw, Graduate Coordinator May 2014 ABSTRACT The Hetch Hetchy system in Yosemite National Park including Cherry Lake stores over 80% of San Francisco’s municipal water. This system consists of Hetchy Reservoir on the Tuolumne River and Lake Eleanor and Cherry Lake on Eleanor and Cherry Creeks respectively, two main tributaries to the Tuolumne. All three reservoirs are on separate waterways with Hetch Hetchy surface elevation at 3,783 feet, Eleanor Lake at 4,657, and Cherry Lake at 4,659 feet. Due to Cherry Lake and Eleanor Lake’s being adjacent watersheds with similar elevations, they are connected with large pipes which allow for moving water between the two reservoirs. The water can be moved in either direction based on water elevation being higher in one reservoir or the other. These reservoirs are mainly fed by snow melt from high peaks on the west slope of the Sierra Nevada. The potential impacts of global climate change on the snowpack that provides the majority of inflow to these reservoirs are of concern to water managers. The general hypothesis is that warmer temperatures and shifts in the El Niño Southern Oscillation will cause more rain than snow in alpine climates, such as the Cherry Creek watershed, producing earlier peak flows. The possible changes are important for water managers to understand because current reservoir management frameworks may not apply in the future climate. The purpose of this study is to evaluate these potential climatic effects on the Cherry Creek and the Cherry Lake system, determining if these effects can be observed in the historical hydrological record, and to provide analyses to be used in future reservoir ii management. These analyses include evaluating historic data to identify changes in streamflow timing and peak volume. Non-parametric statistical tests, Kendall and Spearman’s Rho, are used to quantify statistical evidence of trends in the streamflow record. Cherry Creek’s existing record is not long enough for this non-parametric analysis so watershed cross-correlation with nearby Falls and Eleanor creeks was used to produce a longer record. Results from this correlation show Falls Creek to give the best correlation for extending the Cherry Creek flow record. Non-parametric tests show the longer Cherry Creek record created from cross-correlation to have a declining trend in peak streamflow timing at the 5% significance level. This result supports to the hypothesis that peak flow is occurring earlier in the water year. Significant trends were also found in all other streamflow statistics, with the exception of hydrograph volume. Evaluating these statistics allows for water managers to account for earlier run-off and lower snow volume, and releases can be adjusted to fill the reservoir appropriately. Additionally, a real-time streamflow gauge was installed on Cherry Creek to collect flow data to further monitor climatic trends in the future. The streamflow gauge is installed and collecting real-time data for future use. iii ACKNOWLEDGEMENTS I would like to acknowledge and thank first and foremost my parents and family for providing me with support and encouragement throughout my academic career. I would also like to thank Dr. Margaret Lang for working with me to develop this project and reading and re-reading my attempts at technical language to work towards a finished product. Also, I am grateful to Dr. Elizabeth Eschenbach for giving me the original ideas and resources to formulate the research, and for taking time during her sabbatical to read and provide guidance on this report. Furthermore, I would like to acknowledge the assistance of Adam Mazurkiewicz, Chris Graham, Ben Guy, Bobby Laird, and the watershed keepers at Hetch Hetchy Water and Power for providing me with equipment, transportation across Cherry Lake to the site, and knowledge of the watershed and power system necessary for this report. Richard Young and Sam Swanson, thank you for the light at the end of the tunnel. Steve Welch, Isaac Ingram, Izzy Guthrie, the ARTA River Trips Tuolumne crew, and La Casa Loma residents must be acknowledged for providing me with food, housing, a supplemental income, friendship, and for pushing me to work more on this project. Finally, I give thanks to the wonderful power of our Earth and the creation of all rivers especially the granite wonderland of Upper Cherry Creek. iv TABLE OF CONTENTS ABSTRACT ........................................................................................................................ ii ACKNOWLEDGEMENTS ............................................................................................... iv TABLE OF CONTENTS .................................................................................................... v LIST OF TABLES ............................................................................................................ vii LIST OF FIGURES ......................................................................................................... viii Chapter 1 INTRODUCTION .............................................................................................. 1 Chapter 2 REVIEW OF LITERATURE ............................................................................. 3 2.1 Introduction ............................................................................................................... 3 2.2 Study Area ................................................................................................................. 4 2.3 Historical Data .......................................................................................................... 7 2.4 Expected Climate Change in the Area (Tuolumne) .................................................. 8 2.5 Hydrological Modeling with HEC-RAS ................................................................. 10 2.6 Gradually Varied Flow Equations ........................................................................... 11 2.7 Statistical Modeling of Hydrologic Change ........................................................... 14 Chapter 3 METHODS....................................................................................................... 16 3.1 Fieldwork ................................................................................................................ 16 3.1.1 Streamflow Measurements ............................................................................... 18 3.1.2 Survey ............................................................................................................... 18 3.1.3 Gauge Installation and Calibration ................................................................. 19 3.2 HEC-RAS Modeling ............................................................................................... 21 3.3 Statistical Analysis .................................................................................................. 23 3.3.1 Cross-Correlation ............................................................................................ 24 3.3.2 Climate Stationarity and Trend Tests ............................................................... 25 Chapter 4 RESULTS AND DISCUSSION ....................................................................... 30 4.1 HEC-RAS Model .................................................................................................... 30 4.2 Rating Curve Modeling With HEC-RAS ................................................................ 33 4.3 Watershed Cross-Correlation .................................................................................. 38 4.4 Climate Stationarity ................................................................................................ 42 4.4.1 Peak Flow Timing ............................................................................................ 42 v 4.4.3 Mean Annual Flow ........................................................................................... 50 4.4.4 Winter Base Flows ........................................................................................... 51 4.4.5 Number of High and Extreme Flow Days ........................................................ 52 4.4.6 Correlating Climate ......................................................................................... 54 Chapter 5 CONCLUSIONS .............................................................................................. 56 5.1 Trends ................................................................................................................. 57 5.2 Implications of Climate Change on Reservoir Management .................................. 58 Chapter 6 FUTURE WORK ............................................................................................. 61 REFERENCES ................................................................................................................. 63 vi LIST OF TABLES Table 1: Cherry Creek Watershed Characteristics .............................................................. 7 Table 2: Test significance parameters. df is degrees of freedom (McCuen 2003) ............ 29 Table 3: Cherry Creek,
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