Spencer Dam Failure Investigation Report

Spencer Dam Failure Investigation Report

In the early morning hours of March 14, 2019, Spencer Dam on the Niobrara River in northern Nebraska failed during a major flood and ice run on the river.

An independent investigative panel was formed to examine the failure.

April 2020

FOREWORD

TABLE OF CONTENTS

EXECUTIVE SUMMARY

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CHAPTER 1: INTRODUCTION

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Association of State Dam Safety Officia Is

Spencer Dam Failure Investigation Report 2020

To collect additional historical information regarding Spencer Dam, the Panel sent research-request letters to 78 north-central Nebraska libraries and two local historical societies. Advertisements were placed in local newspapers to request information from the public about the dam's failure and the associated ice run and flood. This research yielded important information, mostly in the form of newspaper articles about the past performance of Spencer Dam and previous ice events. Additionally, the Panel reached out to the state office of the U.S. Geological Survey, the Omaha District of the U.S. Army Corps of Engineers, and the local office of the National Weather Service, as well as the Nebraska Department of Transportation, which oversees the bridges in the dam's vicinity. These organizations provided additional information to the Panel. The Panel also set up a webmail address so it could receive direct communications; but received little information.

Because the Panel members were not located in the same vicinity, there was only one "in-person" Panel meeting besides the site visit. Consequently, the Panel relied on frequent electronic mail correspondence and conference calls for sharing information and ideas.

A numerical hydraulic model of the Niobrara River was completed, which included a dam-break analysis and is described in Appendix H. Additional hydraulic computations were performed and are listed and discussed in Appendix K. In February and March 2020, a second round of interviews (by phone) was conducted with NPPD and NebDSP staff.

Both NPPD and NebDSP reviewed the report in final draft to identify factual errors.

Comments received resulted in factual changes to the final version of the report but did not change the Panel's findings conclusions and recommendations.

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The report consists of seven chapters and eleven Appendices. The chapters are

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CHAPTER 2: BACKGROUND

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CHAPTER 3: THE PHYSICAL SETTING OF SPENCER DAM

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CHAPTER 4: HOW THE DAM FAILED

CHAPTER 5: CONSEQUENCES

CHAPTER 6: WHY THE DAM FAILED: HUMAN FACTORS

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CHAPTER 7: LESSONS LEARNED

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SPENCER DAM FAILURE INVESTIGATION REPORT APPENDICES

TABLE OF CONTENTS

APPENDIX A: HISTORICAL TIMELINE

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APPENDIX B: DETAILED TIMELINE AROUND TIME OF FAILURE

APPENDIX C: PAST FAILURES AND INCIDENTS

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APPENDIX D: DAM INSPECTION HISTORY AND NOTES

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APPENDIX E: DAM DESIGN AND CONDITION PRIOR TO FAILURE

APPENDIX F: RIVER ICE

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∑ 𝑓 = 𝑓𝑆 + 𝑓𝐿 + 𝑓𝐻 + 𝑓𝐸 + 𝑓𝑃 + 𝑓𝐹 + 𝑓𝐺

∑ 𝑓 ≈ 𝑓𝑆 + 𝑓𝐻 + 𝑓𝐿 + 𝑓𝐺

∑ 𝑓 ≈ 𝑓𝑆 + 𝑓𝐻 + 𝑓𝐿 + 𝑓𝑖

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∑ 𝑓 ≈ 𝑓𝐻 + 𝑓𝐿 + 𝑓𝑖

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∀≈

1 𝑡2 ∫ 𝐴 𝐶 (𝑇 − 𝑇𝑎 ) d𝑡 𝜌𝑖 𝐿 𝑡1 𝑜 𝑜 𝑤

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APPENDIX G: DAM OWNERSHIP & REGULATION

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$500,000 $400,000 $300,000 $200,000 $100,000 $1999

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2018

APPENDIX H: METEOROLOGIC, HYDROLOGIC, AND HYDRAULIC CONDITIONS

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300,000 Breach Width: 680 feet Breach Width: 780 feet Breach Width: 1200 feet

Breach Flow (cfs)

250,000

200,000

150,000

100,000

50,000

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6:00

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8:00 9:00 10:00 Time (March 14, 2019)

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12:00

1,239 No Breach High Base Flow 1,238

Breach Width: 780 feet

Stage (feet)

1,238 1,237 1,237 1,236 1,236 1,235 5:00

7:00

9:00

11:00 13:00 15:00 Time (March 14, 2019)

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19:00

21:00

1,326

Overbank Manning's n: 0.05 Overbank Manning's n: 0.07

1,325

Overbank Manning's n: 0.1

Stage (feet)

1,324 1,323 1,322 1,321 1,320 1,319 1,318 5:00

7:00

9:00

11:00 13:00 15:00 Time (March 14, 2019)

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(Alexander et al. 2009) (Buchanan 1982) F

NeDNR/NRCS LiDAR dataset, 1m bare earth DEM accessed from USDA Geospatial Data Gateway: https://datagateway.nrcs.usda.gov/GDGHome.aspx (accessed September 2019).

APPENDIX I: POST FAILURE CONDITIONS

APPENDIX J: HUMAN FACTORS FRAMEWORK AND METHODOLOGY

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APPENDIX K: LIKELY FAILURE SCENARIO