Downscaling storm surge models for engineering applications

1. Downscaling storm surge models for engineering applications John Baugh A. Altuntas, J. Rutledge, T. Dyer Department of Civil, Construction, and Environmental Engineering North Carolina State University

2. Starting Point • How do we assess the effects of storm surge on civil infrastructure? • Engineering design scenarios imply topographic changes, as do failures. • Hundreds of cases may be worth considering.

3. Relevance to DHS • Gap being addressed: No computationally tractable approach exists for assessing storm surge effects on proposed infrastructure changes and improvements. • The DHS mission includes managing risks to critical infrastructure, ensuring resilience to disasters, and mitigating hazards.

4. Interface Conditions • May be formulated in a variety of ways: • One-way nesting (Spall and Robinson 1989) • Two-way nesting (Debreu and Blayo 2008) • Full coupling (Cailleau et al. 2008) • Used to resolve smaller spatial and temporal scale processes

5. Levee Failure Scenarios • Nesting for infrastructure assessment: • (3 different failures, flooding outlined in white)

6. Year 5 Activities • Subdomain modeling of storm surge and wave effects using ADCIRC and SWAN • Time-varying topobathy in ADCIRC using a predetermined set of parameters • Additional means of reducing computational cost in simulation approaches

7. 1. Storm Surge and Waves • SWAN is a phase-averaged spectral wave model with two possible types of boundary conditions: • TPAR files contain significant wave height, wave period, peak direction, and directional spread. • 2D Spectra files contain N discrete frequencies and M directions.

9. Hurricane Fran and Cape Fear

10. Hurricane Fran and Cape Fear Conclusion: Using 2D spectra files to enforce the boundaries of a subdomain results in accurate and efficient computational modeling for engineering purposes.

11. 2. Time-Varying Topobathy • The result of a net transport of sand along the ocean bottom or the overtopping and collapse of a dune, or the failure of engineered structures such as levees and geotubes. • To accommodate, allow time-varying changes in bathymetric depth DP using a predetermined set of parameters.

12. When bathymetric depth DP changes • adjust water surface elevation ETA to maintain constant water column height • mark node wet for reevaluation • remember prior DP values for consistency in calculating heights H0, H1, and H2

13. Test Case: Hatteras Subdomain • Extracted from the western North Atlantic grid with refinements for simulating Isabel Inlet

15. 3. Subduration Modeling • Subduration modeling is introduced as a means of downscaling hurricane storm surge models in time. • The hot-start feature of ADCIRC allows users to begin a run from a specified timestep using initial conditions obtained from a previously performed run. • This feature is used to reduce the total runtime of series of simulations where users have made topographic or other changes to a model.

16. Subduration Modeling in ADCIRC Step 0 : Begin with an ADCIRC model ETA: Surface Elevation, DP: Bathymetric Depth

17. Subduration Modeling in ADCIRC Step 1 : Identify nodes that are part of the changed terrain.

18. Subduration Modeling in ADCIRC Step 2 : Record a hot-start file before one of the changed nodes becomes wet.

19. Subduration Modeling in ADCIRC Step 3 : Make changes to parts of the terrain (DP) in the fort.14 file.

20. Subduration Modeling in ADCIRC Subdomain ADCIRC has been modified so that the original ETA of a changed node is initially set to be equal to changed DP, during a hot-started run.

21. Subduration Modeling in ADCIRC Step 4 : Perform the hot-started run. Modified subdomain ADCIRC runs the hot-started simulation as it normally would.

22. Test Case: Cape Fear Subdomain • Extracted from the western North Atlantic grid with a protective structure to prevent flooding

23. Test Case: Cape Fear Subdomain

24. Products • Software tools for subdomain modeling, modifications to ADCIRC, user scripts, visualization tools, user guide already being distributed. • Theses, technical reports, conference talks, articles under review and in preparation.

26. Prospective Collaborators and End Users Researchers • Yoonhee Park / Professor Art Rice, Landscape Architecture, NCSU, Raleigh, NC • Fernando Magarinos Lamas, Mathematician, Physical Oceanography, Universidad NacionalAutonoma de Mexico, Mexico City, Mexico • Celso Ferreira, Assistant Professor, George Mason University, Fairfax, VA Consulting • Mark Prater, Research Analyst, WeatherPredict Consulting, Kingston, RI Emergency Management • Sandy Sanderson, Director, Dare County Emergency Management, Manteo, NC Federal Agencies • Tucker Mahoney, Coastal Engineer, FEMA Region IV, Atlanta, GA • Max Agnew, Hydraulic Engineer, USACE New Orleans district, New Orleans, LA

27. Prospective Collaborators and End Users International Agencies • Professor Weihua Fang, Academy of Disaster Reduction and Emergency Management, Ministry of Civil Affairs and Ministry of Education, Beijing, China

28. Looking Forward • Case studies that draw on approaches developed in preceding years, demonstrating their benefit in enhancing the resilience of coastal communities • Interactive software tools that support modeling activities for the actual case studies being performed • Decision-making approaches that constitute best practices from the operations research community for coastal infrastructure design