South Carolina Dam Failure Assessment and Advisement DR-SC-4241 FEMA P-1801 / December 2016 Table of Contents Figures ......................................................................................................................................................... iii Tables ........................................................................................................................................................... iv Acronyms and Abbreviations ....................................................................................................................... v Executive Summary .................................................................................................................................... vii Dam Safety in South Carolina ...................................................................................................................... 1 Disaster Declaration DR-4241-SC ................................................................................................................ 3 Meteorological Setup ................................................................................................................................ 3 Flooding and Dam Failures ....................................................................................................................... 4 Precipitation Reconstruction for Dams ......................................................................................................... 7 Background and Metrics ........................................................................................................................... 7 Rainfall Amounts & Evolution ................................................................................................................. 8 Fractional PMP Estimates ....................................................................................................................... 14 Return Period Estimates .......................................................................................................................... 18 Analysis of Precipitation Data ................................................................................................................ 23 Assessment of Dams ................................................................................................................................... 29 Phase 1 – Pre-Assessment Coordination and Background Data Collection ........................................... 29 Phase 2 – Dam Assessments ................................................................................................................... 29 Damage Analysis ................................................................................................................................ 30 Breach Parameters .............................................................................................................................. 35 Phase 3 – Identification of Critical Infrastructure, Vulnerable Structures, and Facilities ....................... 37 Phase 4 – Analysis and Recommendations ............................................................................................. 37 Hazard Mitigation Strategies ...................................................................................................................... 39 Planning Approaches .............................................................................................................................. 39 Mitigation of Dam Failures ..................................................................................................................... 40 Overtopping ........................................................................................................................................ 40 Structural ............................................................................................................................................. 41 Piping .................................................................................................................................................. 42 Alternative Measures .......................................................................................................................... 43 Mitigation Conclusion ............................................................................................................................ 43 Recommendations to Improve Dam Safety Partner Collaboration ............................................................. 44 1. Preparedness Planning .................................................................................................................... 44 National Incident Management System (NIMS) Annex to Support Dam Safety ............................... 44 Succession Planning ........................................................................................................................... 45 Emergency Action Plan (EAP) Availability ....................................................................................... 46 i Exercises ............................................................................................................................................. 46 Inundation Mapping for Dam Incidents and Failures ......................................................................... 47 2. Communication ............................................................................................................................... 48 Inter- and Intra-Agency Communication and Coordination ............................................................... 48 3. Emergency Response ...................................................................................................................... 49 Activation and State Capacity Augmentation through Emergency Management Assistance Compact (EMAC) .............................................................................................................................................. 49 Dam Safety Emergency Response Support ........................................................................................ 50 FEMA Mission Support Division ....................................................................................................... 50 Civil Air Patrol (CAP) Mission Assignments ..................................................................................... 50 Utilization of Unmanned Aerial Systems for Reconnaissance and Inspection of Dams .................... 52 Emergency Drawdown of Reservoirs ................................................................................................. 53 4. Coordinated Recovery..................................................................................................................... 53 Post-Incident Recovery Operations .................................................................................................... 53 Hazard Mitigation Technical Assistance Program (HMTAP) ............................................................ 54 5. Training for Dam Incidents and Failures ........................................................................................ 55 Emergency Responder Training ......................................................................................................... 55 References ................................................................................................................................................... 57 Appendix A – Affected Assets in CDBG Grantee Areas ........................................................................... 59 ii Figures Figure 1: National Oceanic and Atmospheric Administration (NOAA) Water Vapor with Overlay of Parameters Contributing to Heavy Rain (Source: NOAA) ........................................................................... 3 Figure 2: Clarendon County, South Carolina (Source: SC DNR Law Enforcement) ................................... 4 Figure 3: Richland County, South Carolina (Source: SC DNR Law Enforcement) ..................................... 5 Figure 4: Black River at Kingstree, SC: Daily Mean Discharge (Source: USGS) ....................................... 6 Figure 5: Total Estimated Rainfall in South Carolina for October 1 through October 5, 2015 .................. 13 Figure 6: Hourly Hyetograph for Weston Pond Dam ................................................................................. 14 Figure 7: Example of return period analysis using 6-hour rainfall at O.E. Rose Dam ............................... 19 Figure 8: Sumter, SC Rainfall Totals: Sept. 28 – Oct. 6 (SC DNR, 2016) ................................................. 23 Figure 9: Rainfall Analysis for High Hazard Potential Dams Compared to SC DHEC SDF Design Criteria (Assumes that a 24-hour PMP results in a PMF) ........................................................................................ 25 Figure 10: Rainfall Analysis for Significant Hazard Potential Dams Compared to SC DHEC SDF Design Criteria (Assumes that a 24-hour PMP results in a PMF) ........................................................................... 26 Figure 11: Rainfall Analysis for Low Hazard Potential Dams Compared to SC DHEC SDF Design Criteria (Assumes that a 24-hour PMP results in a PMF) ........................................................................... 27 Figure 12: Head-Cutting of the Embankment at SCNONAME 14008 (Source: FEMA 2016) .................. 30 Figure 13: Overtopping Failure Exacerbated by Heavy Vegetation at Sunview Lake (Source: FEMA 2016) ..........................................................................................................................................................