1. Dam Hazard Consequences Assessment ASFPM May 2011 James Demby – FEMA Sam Crampton - RAMPP Mary Shaw - RAMPP

2. 2 Brief History of the Project  Project Goal: To develop a process that could be recommended to communities to execute an economic, social and environmental consequences of dam failure This was presented at 2010 ASFPM  Created initial draft guidance document (summer-fall 2010) Relied heavily on existing procedures recommended for examining the vulnerability to hazards  Conducted initial pilot study (Winter 2010 - Spring 2011) For NRCS Flood Control Dam Y-15, Gwinnett County, GA  Currently revising guidance document Utilizing a more qualitative approach and lessons learned from pilot study  Currently preparing for a second pilot study Lake Barcroft Dam, Fairfax County, VA  Will use to further refine procedures in draft document

3. 3 Initial Draft Guidance Document  Prepared Initial Draft Guidance Document  Used a How-To guide approach with worksheets...  Heavily based on existing FEMA guidance about evaluating the consequences or potential losses due to hazards  Problem  The other documents develop an understanding of probability leading to an analysis of risk  Risk is a function of probability and loss  With dam failure  Probability of collapse may be very low  Probability of non-failure incident / malfunction may be higher  Generally, probability of a particular type of dam failure is unknown  Assessment of consequences, not risk since we are no looking at the probability of the dam failing

4. 4 Dam Hazard Consequences Assessment NRCS Dam Y-15 Pilot Study #1  NRCS Dam Y-15 (Georgia) 41’ high earthen flood control dam Rehabilitated in 2007-2008 to create RCC Spillway for 6-hour PMF Experienced a ~1/4 PMF in September 2009 High detail GIS data available from County (LiDAR, Building footprints, tax data etc.)  Recreated September 2009 Event for Original Spillway Configuration (Assuming Dam would have Breached) Assumed breach at peak elevation Routed breach downstream until incremental depth < 1.5 feet Applied, tested and refined the methodologies of draft guidance document

5. 5 Identifying Inundated Areas  Used HEC-RAS Model and Identified the: Inundation extent Arrival time Inundation depths

6. 6 Identifying Assets and Population at Risk (PAR) Non Residential Structures Assumed 1.4 persons per parking Space Elementary School Online research/county coordination to determine student and staff numbers Residential Structures Planning and development department provided occupancy per structure 2.8 per structure average (SFH) Temporal Population Adjustment ResidentialNon-Residential 12am-7am 90%10% 7am-5pm 15%85% 5pm-12am 75%25%

7. 7 HAZUS Economic Loss Assessment User Defined Facilities Method (UDF)  More time consuming, more detailed approach  User defined assets, values and building types  $1.9 million of building related loss General Building Stock Method (GBS)  Less time consuming, simplified, less detailed approach  HAZUS uses census data and assumes average distribution  $97 million of building related losses ~50× difference between UDF and GBS Method  Gwinnett County largely developed post-FIRM  Does good floodplain management explain difference?

8. 8 Assessing Social Consequences Loss of Life Brown and Graham Method was applied When warning time is: <15 minutes: Probable Loss of Life = 0.5(PAR) 15 to 90 minutes: Probable Loss of Life = PAR 0.6 >90 minutes: Probable Loss of Life = 0.0002(PAR) Estimated number of probable fatalities (per floodwater arrival time) Warning Scenario< 15 min15 min – 90 min> 90 minTotal 084281113 60 min321033 180 min1001 Population at Risk (PAR) 0 – 15 Arrival Zone = 168 15 – 90 min Arrival Zone = 251 > 90 min Arrival Zone = 55 Warning time defined as the pre- breach warning, plus the arrival time Loss of life highly sensitive on the warning time Performed a sensitivity analysis to determine value of advanced warning systems

9. 9 Assessing Social Consequences CategoryWill a dam breach… Applicable (Y/N) Economic Resources Disrupt major roadways?Y Disrupt rail lines?N Disrupt the local school system?Y Disrupt a higher education system?N Disrupt the local manufacturing industry? N Disrupt agriculture locally?N Disrupt the local tourism industry?N Disrupt the provision of banking services locally? N Cause employers to leave the area? Y Social Consequences Assessment Economic Resource Infrastructure, jobs, tourism Environmental Resources Pollution, hazards, wildlife Public Services Courts, transit, water, sewer, power Public Health and Safety Care facilities, emergency services, disease, sanitation Recreation and Leisure Historical/cultural sites, lakes, trails Social Cohesion Activities, religious facilities

10. 10 Assessing Environmental Consequences Pollutants Commercial buildings and garages within inundation zone, potential source of chemical pollutants No major pollutant threats (gas stations, chemical plants, wastewater plants etc) Y-15 sediment storage capacity of 334-acre feet, 91-acre feet estimated as of 2009. Extensive sediment deposit potential downstream, possible heavy metals Higher turbidity High potential for stream bank erosion exposing sewer lines

11. 11 Next Draft (currently under development)  Places greater emphasis on type of Dam Failure Scenario Sudden Collapse  Worst case Planned Collapse  Time to evacuate the inundation area Incidents  Inability to function as flood control  Uncontrolled releases (human/mechanical errors)  Focus of recommended process is for community with limited resources, little capability with HAZUS Will assess and refine more simplified approaches to a consequence assessment  Assumptions are Required by Local Community How long it would take to repair / rebuild Relationship between number of lives lost and number of injuries

12. 12 Recommended Process Outline of tentatively recommended process:  Gather data on dam High hazard / Large impoundment...  Identify Assets & Characteristics of Assets Include structures, infrastructure, vacant structures, open space, agricultural land Mention importance of CIKR – allow local definition Measures gathered for each asset in inundation area  Occupancy  Replacement Value, content value  Jobs  Sales / Usage / Productivity  Existence of alternative space / cost of alternative space  1 st Floor Elevation, type of construction  Dependencies, interdependencies, function

13. 13 Recommended Process Continued  Identify Potential Impact Collapsed, damaged, leaking tanks, business temporarily closed, permanently closed... Loss of life, injury  Specify Consequences or Implications of Impacts Economic consequence  Cost of evacuate, rescue, repair, debris removal, Social consequence  Loss of social organizations, anxiety... Environmental consequences  Pollution

14. 14 Recommended Process Continued  Assess the consequences Economic costs may be  Covered by insurance or grants  Paid out-of-pocket by homeowners, business owners, tax payers Social consequences may be  Obstacles that can be overcome  Positive  Negative and enduring Environmental consequences may be  Obstacles that can be overcome  Positive  Negative and enduring  Pollution  Final step Consider path forward  Further study to determine probability  Plan to mitigation in very long-term through zoning...

15. 15 Dam Hazard Consequences Assessment  Lessons Learned from Initial Draft / Pilot Study Quantitative approach only misses too many potential consequences  Anxiety  Loss of confidence in government  Disruption of social fabric HAZUS’s Limitations must be carefully evaluated  Caution must be applied when using GBS method  Model is expensive to implement / requires advanced user capabilities Path forward may be unsatisfactory  Further study rather than project / mitigation

16. 16 Dam Hazard Consequences Assessment