When The Minimum Elevation Isn’t Even The Minimum

1. When The Minimum Elevation Isn’t Even The Minimum June 27, 2019 Adam J Reeder, PE, CFM

2. Learning Objectives • Upon completion, participants will understand how to evaluate flood protection provided by minimum elevation requirements. • Upon completion, participants will be able to improve building resiliency with knowledge of how to evaluate the need for increased freeboard. • Upon completion, participants will understand some methods on how to document their criteria for recommending increased freeboard. • Upon completion, participants will be able to educate clients on the need to incorporate more freeboard into building design

3. #1 U.S. Natural Disaster $3.2B Annual Losses (10yr average) 5.1M Flood Insurance Policies Let’s Talk About Flood Risk "Floods are an act of God, but flood losses are largely an act of man“ ~Gilbert F. White Source: FEMA Photo Library

4. 1900 Hurricane of Galveston Hurricane Ike - 2008 Source: FEMA MAT Reports

5. Hurricane Betsy 1965 Hurricane Katrina - 2005 Source: FEMA MAT Reports

6. Hurricane Camille 1969 Hurricane Katrina - 2005 Source: FEMA MAT Reports

7. Why does this damage continue to happen? Too many stakeholders setting regulations with conflicting priorities (locals vs. state vs. federal) People think the initial cost of construction outweighs considering long-term resiliency Designers are not trained on how we quantify natural hazards and therefore tend to be poor advocators for risk reduction Too many engineers don’t evaluate whether the modeling output makes sense (hopefully you aren’t paying these people) We forget how difficult the last event was

8. How Flood Requirements Apply to Buildings NFIP Regulations, Title 44 CFR Parts 59, 60 Floodplain Management Regulations (vary by Jurisdiction) • Consensus Standards • ASCE 7 (Minimum Design Loads for Buildings and Other Structures) • ASCE 24 (Flood Resistant Design and Construction) Model Building Codes (International Codes) Protecting Our Military Installations from Recurrent Floods Act of 2018 Flood Resistant Building/Structure More on this later NFIP = National Flood Insurance Program CFR = Code of Federal Regulations

9. Let’s Define the word Minimum Remember this definition as we walk through the few next slides Definition of Minimum 1: the least quantity assignable, admissible, or possible 2: the least of a set of numbers specifically: the smallest value assumed by a continuous function defined on a closed interval 3 a: the lowest degree or amount of variation (as of temperature) reached or recorded b: the lowest speed allowed on a highway Source: https://www.merriam-webster.com/dictionary/

10. Consensus Standards: ASCE ASCE 24 also represents the minimums ASCE 7: Minimum Design Loads of Buildings and Other Structures • Methods to determine design loads and load combinations in flood hazard areas (Chapt. 5) ASCE 24: Flood Resistant Design and Construction • Design / Construction requirements for buildings in flood hazard areas • Section 2 – A Zones • Section 3 – High Risk Flood Areas • Section 4 – V Zones and Coastal A Zones • Section 6 – Wet and Dry Floodproofing

11. Perfect - then the Codes Cover Flood Risk! “The purpose of this code is to establish the MINIMUM requirements to provide a REASONABLE level of safety, public health and general welfare through structural strength, means of egress facilities, stability, sanitation, adequate light and ventilation, energy conservation, and safety to life and property from fire and other hazards attributed to the built environment and to provide a REASONABLE level of safety to fire fighters and emergency responders during emergency operations.”

12. Not exactly… For Flood Risk the answer is usually they aren’t enough Codes are typically a negotiated process and thus represent the minimum allowable Building Codes are only part of the solution Codes must be effectively enforced to ensure that buildings and their occupants benefit from the advances in the Building Code Code enforcement is typically the responsibility of local officials who review design plans, inspect construction, and issue the building and occupancy permits – it’s asking a lot to catch everything

13. Sources of Flood Risk Data Source: FEMA E-0386 Training Materials

14. Common Flood Data Sources Consider Highwater Marks from past events If your area is not mapped by FEMA then you should always get an H&H study for the area • Most information has been developed for flood insurance rating purposes • Flood Insurance Study (FIS) • Flood Insurance Rate Map (FIRM) • These weren’t developed for new construction • We need to identify not only the Base Flood Elevation (BFE), but also understand the current conditions • Future Conditions aren’t covered on the maps either • Understand the age of the study (not just the effective date on the map/study) • The study may have been done several years ago…and things change

15. Items Included in FIS/FIRM • Flooding sources (coastal storm surge, rivers, creeks, etc.) • Flood history (some studies are better than others) • Special Flood Hazard Area (SFHA) boundaries • SFHA = area subject to “base flood” (1% annual chance [100-year] flood) • Coastal FIS • Stillwater Elevations (10%, 2%, 1%, and 0.2% annual chance floods) • New FIS will include the 4% annual chance storm • BFEs, including wave height, wave setup, and wave runup effects • Riverine FIS • Flood Profiles and Discharge (flows) for the 10%, 2%, 1%, and 0.2% annual chance events Ask Yourself - Does the FIRM accurately depict present flood hazards? • Are the FIRM/FIS data and calculation procedures up to date? • Have significant physical changes occurred since the FIRM was created?

16. Where do I find FIRMs and FISs Review both the effective and preliminary data and use the more conservative source FEMA Map Service Center Site allows you to view and download FIS, FIRM, other data. Check all available products and review any preliminary mapping products if those are available. Evaluate the change in the FIRMs over time as a data point

17. RiskMAP Risk Products (non-Regulatory) Don’t hesitate to contact the state NFIP coordinator Types of RiskMAP Products Changes Since Last FIRM Areas of Mitigation Interest Flood Depth and Analysis Grids Flood Risk Assessment Data 1% Plus Mapping NOTE: A community determines which products they want developed during a map update. You will need to contact your community to find out if any Risk MAP products are available for your area

18. So let’s quickly review the flood zones Source: Figure 2-3, FEMA P-259 Riverine Floodplains are designated A Zones The 500-year Floodplain is designated Zone X • We assume higher velocities in the floodway (info found with discharge data), but often this extends into the flood fringe • Runoff and Fill in the floodplain can contribute to increased flood heights • Future Conditions Could Be: • Increased runoff from development • Increased precipitation Remember that FIRMs won’t show this!

19. Categories of Coastal Flood Zones Source: FEMA E-0386 Training Materials V Zones: 3 foot or higher waves – Require Open Foundations and Compliance is measured to the Bottom of Lowest Horizontal Structural Member of the Lowest Floor Designated on Flood Insurance Rate Maps (FIRMs)

20. Example FIRM Categories of Coastal Flood Zones Source: FEMA E-0386 Training Materials Coastal A Zones: 1.5 foot to 3 foot waves – Require Open Foundations and Compliance is measured to the Bottom of Lowest Horizontal Structural Member of the Lowest Floor (same as Zone V). Only required if the Line of Moderate Wave Action (LiMWA) is shown on the FIRM

21. Categories of Coastal Flood Zones Source: FEMA E-0386 Training Materials A Zones: Less than 1.5 foot waves – Allows Closed Foundations (with openings) and Fill. Compliance is measured to the Top of the Lowest Floor. Designated on Flood Insurance Rate Maps (FIRMs)

22. So what’s required by the Codes? • 1 – Now called Flood Design Class • * – Category 3 is BFE+2 in Zone V and Coastal A Zone • Local requirements may require additional freeboard (ASCE 24-14) BONUS CONTENT: Coastal Flood Insurance Studies do not provide the 500-year wave crest elevation. The stillwater elevation is provided and you need to estimate the 500-year wave crest This slide just covers elevation requirements – additional requirements apply

23. How much protection does freeboard provide? US Average Protection: BFE +1 – 162 Year BFE +2 – 260 Year BFE +3 – 417 Year BFE +4 – 672 Year 500-Year Protection Flat Slope Steep Slope Floodplain X-Section This is only as accurate as your flood data

24. Expected Service Life of Buildings 1 : 2 is 50% chance 1 : 3 is 33% chance Values based on U.S. Average floodplain and assume the flood data is correct and it doesn’t change – the chance of flooding is likely higher Non-Residential Expected Service Life* • Masonry – 77.5 years (Chance of BFE+1 Flood 1: 2.6) • Wood – 51.6 years (Chance of BFE+1 Flood 1 : 3.7) • Concrete – 87.2 years (Chance of BFE+1 Flood 1 : 2.4) • Steel – 77.3 years (Chance of BFE+1 Flood 1 :2.6) *Source: Survey on actual service lives for North American buildings Residential Expect Service Life – 61 years* (Chance of BFE+1 Flood 1: 3.2) • These buildings could last over 100 years (Chance of BFE+1 Flood 1 : 2.2) *Source: 2009 American Housing Survey – US Census

25. What if I told you that it isn’t that clear cut? Uncertainty The result of imperfect knowledge concerning the present or future state of a system, event, situation, or (sub) population under consideration. There are two types of uncertainty: aleatory (variability over time and/or space) and epistemic (lack of knowledge). Source: USACE Memo – ER 1100-2-8162 dated 12/31/13 It’s addressing what we don’t know in a model Introducing Uncertainty in flood data

26. Considering Riverine Flooding Uncertainty Example of confidence limits on the Ramapo River near Pompton Lakes, NJ The median values represent the middle values in all models run Source: Technical Mapping Advisory Council Future Conditions and Changes in the Floodplain Fig. 3-28 The flood data shown on the FIRMs and FISs represents the median value of the modeling. This means some 1% annual chance events (100-year) can exceed the BFE and still be a 1% chance event (100-year). This information is not provided in the FIS Some Risk MAP products may provide the 1% plus flood elevation, which incorporates uncertainty

27. Considerations for additional freeboard Source: Technical Mapping Advisory Council Future Conditions and Changes in the Floodplain Fig. 3-30 If available consider this data when determining how much freeboard should be incorporated into your design Comparing the median BFE with the 95% Confidence BFE may influence decisions on additional freeboard.

28. With flooding, there is no partial credit! “You can have two 100-year events in consecutive years….” – Various floodplain managers This is a Partial Credit Answer! Consider – The chance of having 2 - 100-year events over 2 years is 1 : 5,000 over 10 years the chance of 2 - 100-year events is 1 : 1,000 Our Response Should Be – When we have two or three severe flooding events (100-year or greater) close together then we need to be asking ourselves whether the flood data makes sense. You won’t fall into this trap will you?

29. If this information isn’t available other approaches may be necessary Although not required sometimes an analysis of gauge data using tools such as PeakFQ can provide insight on whether the minimum freeboard requirements are sufficient. Someone familiar with H&H Modeling may be able to do this type of assessment for you More slides on this topic at the end of the pdf slide deck .01 1% annual chance flood

30. Riverine Example – Lumberton, NC Online Flood Insurance Rate Map

31. Riverine Example – Lumberton, NC Note: Due to gauge spikes, crest levels are difficult to determine BFE at the gauge is about 120 Prelim. 500 is about 124 During Hurricane Florence the gauge crested at 25.4 feet or almost 1.5 above the 500-yr Joint probability over 2 years is 1 : 62,500 – Is this just bad luck?

32. Uncertainty in Coastal Flood Modeling In short – Most of what goes on with coastal flood models happens behind the curtain The output is a median value The output does not provide uncertainty boundaries Potentially it could be shown in the future – We should all be advocating for this The upside is that a good bit of the wave calculations are “depth limited waves” and we can approximate those (see slide 44). This is likely a worst case for a selected flood depth.

33. What can vs. what we can’t account for with the revised BFE What we can’t account for: • Uncertainty in current BFEs (without the data) • Short-term erosion from storms Future Conditions (could project this with H&H modeling) • Impact of increased future precipitation • Impact of increased runoff from future development Once we know what we DO KNOW and DON’T KNOW then we can try to account for what we DON’T KNOW with adjusting freeboard What we can account for: Predicted long-term erosion rates Potential extreme flooding Historic flooding Future Conditions (better approximations with H&H modeling) Increased future Stillwater Elevation Approximated future wave heights

34. Summary of Freeboard Considerations Chance of flooding decreasing Use more freeboard to address for uncertainties Consider how much protection is provided by your freeboard Consider if the freeboard is enough over the life of the building Consider using the 0.2% annual chance (500-year) flood elevation as a substitute for uncertainty in the BFE.

35. Why we should build higher…What happens if we overtop? “Everyone has a plan ‘till they get punched in the mouth.” – Former World Heavyweight Champion Mike Tyson Office Building 16,000 sf Building 3 feet of floodproofing Doors: 2 double glass doors and one single glass door Windows: 12 windows about 3 feet wide each Assuming an offset gap between the shields and windows about 6 inches 1 inch overtopping Overflow Rate: +4 cfs about 1,834 GPM and 110,000+ GPH Duration to fill the space is: 196 minutes

36. Document your determination of freeboard • Understand your required minimum elevation • Locate and analyze the FEMA flood data (past, existing, and if available proposed) • Consider changes since the mapping date • Consider the level of protection provided by the amount of freeboard considered • Consider the potential for uncertainty in flood data • Consider the consequences of floods exceeding the selected elevation • Determine if more freeboard is needed • Evaluate the potential return on investment for the owner based on: • Insurance Premiums • Financial Exposure

37. Thoughts on freeboard • Go as high as practical – Being wrong is painful • Some BFEs are rounded to the nearest foot, so it could be almost 6 inches too low. • Once flood protection is overtopped it is almost impossible to pump out • Overtopping damages will be the same as if nothing was done (if possible elevate instead) • We should consider future conditions: • Age of the maps • Development • Sea Level Rise (SLR is a stillwater elev. and waves will increase that value)

38. Thoughts on Mitigation Elevation and foundation designed for future conditions Elevation designed for main building above future conditions; lowest floor abandonment plan for vulnerable, low-lying parts of the structure Elevation and foundation designed for future retrofit Dry floodproofing with option to extend floodproofing up to future condition elevation Elevation and foundation accounting for today’s uncertainty and near future changes in conditions

39. Consider Long-term Resiliency and Mitigation Storm surge flooding will change Waves will get you before permanent inundation will SLR projections are stillwater elevations and not wave crest elevations Design foundations for future wave conditions Passive mitigation always beats human intervention mitigation

40. To sum up flood risk If it looks like a floodplain… it probably is… Trust your gut about whether a place is in the floodplain. Mother nature does not see lines on a map.

41. Questions? Adam J Reeder, PE, CFM CDM Smith reederaj@cdmsmith.com +1 919-848-0558 +1 919-868-5301 www.cdmsmith.com Thank You! A pdf version of the presentation will be made available

42. Slides for Question Responses Or to fill time is not enough questions are asked

43. Everyone Asks About Future Conditions Source: FEMA Photo Library

44. Where do we get Sea Level Rise Projections? • State and Local Climate Change Reports • USACE guidance • US National Climate Assessment • Intergovernmental Panel on Climate Change (IPCC reports) USACE Sea Level Change Curve Calculator (Version 2017.55) National Oceanic and Atmospheric Administration (NOAA) guidance

45. What information do we need from Sea Level Rise projections? Sufficient information need to predict future flood conditions • Sea Level Rise Projection Modeling Background (assumptions) • Future 1% flood elevations and possibly 0.2% flood elevations • Future stillwater elevations sufficient to calculate flood loads • Future wave heights • Areas of future permanent inundation • Any future erosion data (may impact ground elevations) • Assumptions on the impact of subsidence on future flood elevations Not all of this information may be available from every source and may require additional calculations to determine all the necessary data

46. Coastal Flood Zones are Based on Wave Heights Source: FEMA E-0386 Training Materials Sea Level Rise will increase the stillwater elevation (SWEL) How will that impact the flood zones under future conditions?

47. Approximating the Future BFE • If the Stillwater elevation increases then what happens to: • Wave Crest Elevations • Wave Heights • What happens to wave heights if the ground elevation is lower? Due to: • Increase in Relative Sea Level • Erosion • Subsidence Areas outside the current SFHA could be impacted FEMA P-55 p. 3-60

48. Evaluating Future Conditions (other than SLR) Source: FEMA Photo Library Without an H&H study the solution is incorporating additional freeboard into the design We should be incorporating the risk of urban flooding • Changes in impermeable areas will result in greater runoff even at current precipitation intensities Modeled increased precipitation intensities • Increased flows will occur even with current levels of development • Discharge rates associated with less frequent events will occur more often and result in more severe events happening with greater frequency

49. Sources of Information on future conditions U.S. National Climate Assessment (currently 4th Edition) Regional Climate Assessments Municipal and Regional Planning Guides/websites indicating planned future development

50. Future Development (Non-Regulatory) Maps Source: Mecklenburg County Flood Map Some areas provide some insight into future flood conditions due to future development impacts This example uses light blue for the FEMA Floodplain and dark gray shading to illustrate the Community Floodplain