Sea Level Change Considerations on Federal Coastal Storm Damage Reduction Projects

Transcription

1 Sea Level Change Considerations on Federal Coastal Storm Damage Reduction Projects Jason Engle, P.E. Matt Schrader, P.E. Presented by: Jason Engle Jacksonville District U.S. Army Corps of Engineers

2 ENGINEERING CIRCULAR (EC) Incorporating Sea-level Change Considerations into Civil Works Programs Purpose: Guidance for incorporating direct and indirect physical effects of projected future sea-level change in managing, planning, engineering, designing, constructing, operating, and maintaining USACE projects and systems of projects. Potential relative sea-level change must be considered in every Civil Works USACE coastal activity as far inland as the extent of estimated tidal influence.

3 Scope and Status of SLC Guidance EC (Final): Details the SLC estimates that are to be used and generally outlines the approaches that will be taken SLC Civil Works Technical Letter (Draft): General implementation guidance for Civil Works projects (Navigation, CSDR, Ecosystem Restoration, Flood Damage Reduction) CWTL Appendix E (Draft): Specific guidance for Coastal Storm Damage Reduction Projects

4 Relative Sea Level Rise (ft) Relative Sea-Level Change (Rise) Central East Coast of Florida Baseline Intermediate High Year Baseline = extrapolated historical SLC rate Intermediate = Modified* NRC Curve I High = Modified* NRC Curve III *Includes updated GMSL rate of 1.7 mm/yr and Start year of 1992 middle of prior tidal epoch

5 Relative Sea Level Rise (ft) Application to Federal Projects Baseline Intermediate High Year No probability is assigned to any of these curves The curves bound the range of probable future SLC rates Project will be evaluated across this range of SLC

6 CSDR Projects: Problems and Opportunities Typical CSDR Study Problem (barrier island) Long term erosion and storms threaten oceanside infrastructure Typical Study Opportunity Reduce damage with dune/beach nourishment NEW Problems Sea level rise increases ocean-side damage SLR increases flooding frequency on bay-side Image courtesy of PBS&J NEW Opportunities Increased benefits for dune/beach nourishment Reduce storm damage bay-side?

7 SLC IMPLEMENTATION STRATEGY Inventory and Forecast Conditions Expand data gathering to include: inundation footprint of high SLC curve critical resources (e.g. public works facilities; hospitals) High SLC Footprint Consider evaluating sensitivity of study area to SLC using both qualitative and quantitative analyses Baseline SLC Footprint

8 KEY QUESTIONS Projects and SLC Impacts What level of analysis is merited given the potential SLC impacts? Are there critical water levels or change rate thresholds beyond which the project must be adapted? Can the project be adaptively managed using one, or a combination of alternatives? Will sea level change have regional effects not related to the CSDR project that overwhelm project benefits?

9 Tier 1 Decision Context Establishes overall study area vulnerability to SLC and therefore the appropriate level of SLC analysis that is required Density and vulnerability of resources Structures/Infrastructure Environment/habitat Critical facilities (hospitals, fire/police, schools, etc) Evacuation routes Recreation

10 Tier 1 Example Critical Resources Residential/Commercial Structures Density of Resource Medium Risk to Resource from SLC Low Environment and Habitat High Medium Infrastructure (roads, water/sewer lines, etc.) Critical Facilities (police, fire, etc.) Medium Low Low Low Evacuation Routes High Medium Recreation High Low Cumulative Resources Medium Low Modified from: Extent of Resources at Risk (A Technical Review of Coastal Projects: Shore Protection, Navigation and Ecosystem Restoration for North Atlantic Division BUILDING (Spring 2009) STRONG

11 Tier 2 Without-project forecast Inclusion of SLC with other coastal forces has a cascading effect Coastal Forces and Processes MSL increases Increased storm surge/flooding frequency Morphological Responses at the Beach Increased long-term erosion/profile recession Increased storm erosion/recession Infrastructure Vulnerability Increased flooding and erosion damage Human Response Shoreline armoring

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13 Relative Sea Level Rise (ft) Beach Response to mean SLR Increased Shoreline Recession Rate Baseline: no change Intermediate: -0.5 ft/yr High: -2 ft/yr Increased Renourishment Volume Baseline: no change Intermediate: +0.6 cy/ft/yr High: +2.6 cy/ft/yr Year Baseline Intermediate High

14 Relative Sea Level Rise (ft) Non-Stationarity Baseline Intermediate High Year Most coastal processes are considered to be stationary or unchanging over the typical 50-year analysis period Sea level change estimates are non-stationary, which will cause other processes to become non-stationary storm surge return period shoreline recession rate, etc

15 Cumulative probability of dune crest elevation being lowered

16 Tier 3 Alternative Development Alternatives are evaluated across range of sea levels Final array of alternatives compared for three scenarios An Alternative may include adaptation at some threshold 40 berm to year 35, then a 60 berm to year 50 Beach nourishment to year 35, then revetment to year 50 Alternatives may be anticipatory, adaptive or reactive in relation to observed impacts from SLC

17 6 5 4 flood proofing of structures (NS) no action seawalls (S) beach nourishment (S) groins with nourishment (S) dunes and vegetation (S) breakwaters (S) Relative Sea Level Rise at 50 years under high SLC scenario managed retreat (NS) Relative Sea Level Rise (feet) 50-year planning horizon NS: Non-Structural S: Structural Lead time 3 baseline intermediate 2 1 Year

18 baseline intermediate Relative Sea Level Rise at 50 years under high SLC scenario flood proofing of structures (NS) no action seawalls (S) beach nourishment (S) groins with nourishment (S) dunes and vegetation (S) breakwaters (S) managed retreat (NS) Relative Sea Level Rise (feet) 50-year planning horizon NS: Non-Structural S: Structural Lead time Alternative Pathways Year

19 It Is Not Time to Panic The science of predicting sea level change is evolving; IPCC estimates have decreased over the years Beach projects are adaptable by nature and by design Future adaptation is advantageous to BCR s Benefit/Cost ratios may be higher for the mid or high SLC scenarios SLC is one more coastal process to consider with some unique challenges, but it will not derail our study or maintenance process It may be another way to show the benefit of healthy beaches

20 Conclusions The Sea Level Change Civil Works Technical Letter lays out a strategy for incorporation of SLC into the traditional Corps study process. SLC CWTL is in agency review now and will be finalized in 2013 Studies may need to consider regional SLC impacts that lie outside of traditional CSDR study boundaries Recommended alternatives may be a combination of measures The economics of many existing Coastal Storm Damage Reduction Projects make even more sense if sea level rates rise.

21 Thank You Jason Engle, P.E. Matt Schrader, P.E.