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Two-Dimensional Hydraulic Model of Folsom Dam Breach Under The TWO-DIMENSIONAL HYDRAULIC MODEL OF FOLSOM DAM BREACH UNDER THE MAXIMUM PROBABLE FLOOD A Project Presented to the faculty of the Department of Civil Engineering California State University, Sacramento Submitted in partial satisfaction of the requirements for the degree of MASTER OF SCIENCE in Civil Engineering (Water Resources Engineering) by Michael Pantell SPRING 2017 © 2017 Michael Pantell ALL RIGHTS RESERVED ii TWO-DIMENSIONAL HYDRAULIC MODEL OF FOLSOM DAM BREACH UNDER THE MAXIMUM PROBABLE FLOOD A Project by Michael Garland Pantell Approved by: __________________________________, Committee Chair Dr. Saad M. Merayyan __________________________________, Second Reader Dr. Cristina Poindexter ____________________________ Date iii Student: Michael Garland Pantell I certify that this student has met the requirements for format contained in the University format manual, and that this project is suitable for shelving in the Library and credit is to be awarded for the project. ____________________________, Department Chair ___________________ Dr. Benjamin Fell Date Department of Civil Engineering iv Abstract of TWO-DIMENSIONAL HYDRAULIC MODEL OF FOLSOM DAM BREACH UNDER THE MAXIMUM PROBABLE FLOOD by Michael Garland Pantell Folsom Dam and 11 earthen structures make up Folsom Reservoir, located on the American River east of Sacramento, California. These structures were constructed by the United States Army Corps of Engineers (USACE) in 1956 to create a reservoir that can hold 1.38 billion cubic meters (1.12 million acre-feet) which protects approximately 1.5 million people as well as the State’s seat of government from flooding. In recent years, updated hydrologic information has been used to better estimate the probable maximum flood (PMF) that can be expected to inflow into Folsom Reservoir. It was found that this PMF inflow was greater than the outflow capability of the current dam structure and could put the earthen structures that surround the reservoir at risk of failing. A spillway has been constructed to increase the outflow capabilities of the reservoir and is slated to be operational in 2017. As a part of spillway design process, the USACE developed a hydraulic model to estimate the flooding that results from scenarios with and without the spillway. However, this model and the resulting inundation areas are not available to the public and many local agencies. This project used Hydrologic Engineering Center River Analysis Software Version 5.0 (HEC RAS 5.0) two-dimensional hydraulic modeling capabilities and publicly available information to model multiple flooding scenarios with and without the spillway during a PMF event. Since v without the spillway present, massive overtopping would occur which would likely lead to a breach along one of the earthen structures, the model also estimated multiple breaching scenarios. Two breach methods were applied to earthen structure on the north and south sides of the reservoir to better estimate the range of possible flows and spatial differences in the floodplain. The resulting floodplain for all worst-case scenarios, produced high flooding depths along the American River, Downtown Sacramento and the Pocket and Natomas regions of greater than 4 meters (13.12 feet). Due to the breaches along the north and south earthen structures, the without spillway scenarios produced much greater flooding extents and depths than the with spillway scenario. The northern breach diverted flows into Arcade, Linda and Dry creeks which produced flooding depths of greater than 4 meters (13.12 feet) along the creeks and increases the extent of flooding in the Natomas regions. The southern breach produced flooding depths of greater than 4 meters (13.12 feet) in Folsom and increases the floodplain south of the American River. Using peer-reviewed papers and information provided by the State of California, mortality and single family home property damage rates were estimated for each of the worst- case scenarios. Both mortality and property damage rates closely followed floodplain depths with the highest risk and costs being along the American River, Downtown Sacramento and in the Pocket and Natomas regions. Although this information is not 100% accurate, it does provide helpful guidelines for emergency response and planning purposes. To prepare for a PMF event, evacuating areas along the American River, the Pocket area, the Natomas area and Downtown Sacramento should be considered high priority for saving the most lives. To prepare for the uncertainty of which earthen structure will breach, areas in Folsom near the reservoir and areas vi along natural creeks such as Dry Creek, Linda Creek and Arcade Creek should also be evacuated. Other areas that have predicted flooding, should also be evacuated to high ground. _______________________, Committee Chair Dr. Saad M. Merayyan _______________________ Date vii ACKNOWLEDGEMENTS I would like to first thank God for providing me the patience and perseverance necessary to complete this project. I would also like to thank the following people: • My wife, Cheryl Pantell, for having the patience and love to put up with me during this time. • Stanford Gibson for encouraging me to become a civil engineer and providing me opportunities to learn hydraulic modeling. • My adviser, Dr. Merayyan, and committee member, Dr. Poindexter, for their feedback and guidance on this project. • Peterson Brustad Inc. for providing me technical support and an environment where I can learn and advance in my career. • Finally, all of my friends and family who have supported me and encouraged me along the way. viii TABLE OF CONTENTS Acknowledgements ....................................................................................................................... viii List of Tables .................................................................................................................................. xi List ot Figures ................................................................................................................................ xii Chapter 1. INTRODUCTION ..................................................................................................................... 1 2. BACKGROUND ....................................................................................................................... 4 Location ................................................................................................................................... 4 Characteristics of Folsom Dam and Reservoir ........................................................................ 6 Dam Breach ............................................................................................................................. 8 Breach Modeling ............................................................................................................. 10 Hydrology .............................................................................................................................. 13 Inflow .............................................................................................................................. 13 Outflow ........................................................................................................................... 15 Hydraulic Analysis ................................................................................................................ 17 Mass Conservation .......................................................................................................... 17 Momentum Conservation ................................................................................................ 17 HEC RAS modeling ........................................................................................................ 20 Mortality and Property Damage ............................................................................................ 21 Mortality .......................................................................................................................... 21 ix Property Damage ............................................................................................................. 23 3. ANALYSIS .............................................................................................................................. 25 Project Datum and Coordinate System .................................................................................. 25 Model Parameters .................................................................................................................. 25 Terrain ............................................................................................................................. 25 Boundary Conditions ...................................................................................................... 27 Folsom Reservoir ............................................................................................................ 28 Breaches .......................................................................................................................... 29 Scenarios ......................................................................................................................... 30 4. RESULTS AND DISCUSSION .............................................................................................. 32 Breach Timing ....................................................................................................................... 32 Breach Method......................................................................................................................
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