Impact of Sea Level Rise on Roadway Design. Paul Carroll, PE

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Cecilia Manning
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1 Impact of Sea Level Rise on Roadway Design Paul Carroll, PE September 14, 2016

2 State of Maryland Action Executive Order by Gov. O Malley established the Maryland Commission on Climate Change (MCCC) Resulted in a Climate Action Plan Directed the State Highway Administration (SHA) to perform vulnerability assessment of State transportation assets: (SHA) Climate Change Adaptation Plan with Detailed Vulnerability Assessment (Pilot Study) Primary Assets Considered:» Bridges» Small culverts/drainage conveyances» Roadways

3 State of Maryland Action Approach to Identifying Vulnerable Assets Initial screening: Climate Change Impact Zone = limits of YR ft buffer Detailed (desktop) vulnerability assessment on county level Prioritize critical assets Conduct site specific engineering analysis at prioritized vulnerable assets

State of Maryland Action Quantitative (desktop) assessment of assets was performed using the Vulnerability Assessment Scoring Tool (VAST) for structures and the Hazard Vulnerability Index

4 State of Maryland Action Quantitative (desktop) assessment of assets was performed using the Vulnerability Assessment Scoring Tool (VAST) for structures and the Hazard Vulnerability Index (HVI) for roadways. For Anne Arundel County: 517 structures, 104 determined to be within the Climate Change Impact Zone 9,275 road segments, 655 segments in the Climate Change Impact Zone

5 Climate Impact Zone Anne Arundel county, MD

6 State of Maryland Action Vulnerability Assessment Scoring Tool (VAST): Exposure Sensitivity Adaptive Capacity Hazard Vulnerability Index (HVI): Evacuation Route (Yes / No) Flood Depth Functional Classification of the segment

7 Maryland State HWY 261, at the Town of North Beach Anne Arundel County Calvert County

8 Maryland State HWY 261, at the Town of North Beach

9 Maryland State HWY 261, at the Town of North Beach

10 Maryland State HWY 261, at the Town of North Beach HWY 261 experiences frequent flooding, leading to roadway closures during storm events between North Beach and Anne Arundel County line HWY 261 found to be particularly vulnerable to SLR with several sections permanently inundated by 2100 HWY 261 is the only direct route connecting the Town of North Beach to southern Ann Arundel County State EMS are provided to southern Anne Arundel County from the Town of North Beach Town of North Beach requested that MD-SHA study suitable alternatives to mitigate flooding and loss of service

Engineering Assessment Mitigation alternatives: o Elevated causeway o Culvert o Bridge Objectives: o Model current flood levels: 2-yr, 10-yr, 100-yr o

11 Engineering Assessment Mitigation alternatives: o Elevated causeway o Culvert o Bridge Objectives: o Model current flood levels: 2-yr, 10-yr, 100-yr o Prevent overtopping o Headwaters within 0.5-ft of existing condition Sea Level Rise o Model current flood levels: 2-yr, 10-yr, 100-yr PLUS 2050 Scenario: 2.1 feet

12 Engineering Assessment Storm Surge Hydrograph Rainfall Hydrograph

13 Engineering Assessment Estimated Sea Level Change Rates determined using the procedure prescribed in Engineering Circular No (USACE, 2011) References the National Research Council report: Responding to Changes in Sea Level: Engineering Implications Multiple scenario approach:» Low: Apply historic rate of SLC» Intermediate: NRC Curve I» High: NRC Curve III Multiple scenario approach to account for uncertainty related to future temperature and ice sheet changes Adjustment to account for localized Vertical Land Movement (VLM)

14 Engineering Assessment Low SLR Scenario: Linear Extrapolation of global trend of 1.7 mm/yr (IPCC, 2007) Intermediate SLR Scenario: NRC Curve I* E(t) = t + bt 2 b = 2.71E-5 t = years (reference to 1992) High SLR Scenario: NRC Curve III* E(t) = t + bt 2 b = 1.13E-4 t = years (reference to 1992) Add to these local Vertical Land Movement* *Specified by: Guidelines for Considering the Effect of Future Sea Level Rise in Maryland Page 14

15 Engineering Assessment NOAA: Tideseandcurrents.noaa.gov

16 Engineering Assessment Vertical Land Movement Glacial Isostatic Adjustment Ground water extraction Sediment consolidation NOAA Technical Report NOS COOPs 65 For Coastal Maryland = -1.7 mm/yr (Holdahl, & Morrison, 1974)

17 Engineering Assessment Page 17

18 Existing Conditions

19 Existing Conditions (2-YR)

20 2 Year Design

21 Existing Conditions (10-YR)

22 10 Year Design Design

23 Existing Conditions (100-YR)

24 100 Year Design

25 100 Year Design 10yr Storm + SLR

26 100 Year Design 50yr Storm + SLR

and Mitigation Costs Increase Imperviousness Private

27 Engineering Assessment Decision Matrix Comparative analysis criteria: Environmental Impacts Construction and Mitigation Costs Increase Imperviousness Private Property Impacts Constructability and ease of Maintenance

Engineering Assessment - Issues Designs iteratively determined based on modeling w/o SLR Modeling events not consistent with a reasonable design life of the project Phasing of flooding components

28 Engineering Assessment - Issues Designs iteratively determined based on modeling w/o SLR Modeling events not consistent with a reasonable design life of the project Phasing of flooding components probably too conservative 100yr event included waves Only one intermediate SLR scenario curve considered Changes in precipitation resulting from Climate Change were not considered. Presentation Title September 21, 2016 Page 28

29 Project Planning Do not loose sight of the project intent Designing in Adaptive Capacity to reduce upfront capital costs Other ideas for planning with an uncertain future? Presentation Title September 21, 2016 Page 29

30 Thank You

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