Addressing Hurricane Surge Hazard Uncertainty in Coastal Barrier Design
Bob Jacobsen PE, Nathan Dill, Arden Herrin, Michael Beck
Primary Author: Bob Jacobsen PE
Bob Jacobsen PE, LLC
7504 Menlo Drive
Baton Rouge, LA 70808
225.678.2414
bobjacobsenpe@gmail.com
Abstract
Understanding hurricane surge hazard uncertainty is important for managing risks associated with
overtopping for various engineered coastal flood barriers. Evaluation of overtopping uncertainty is
required for National Flood Insurance Program (NFIP) accreditation of 100-year (yr) levee systems as
well as for recognition of some flood reduction for lower embankments. Moreover, it is crucial for
enhanced elevation and resiliency designs intended to protect lives and critical community resources.
Estimates of expected surge hazard and confidence limits have complex, nonlinear sensitivities not only
to how uncertainties are quantified but also to whether uncertainties are assigned to the former or
latter. These quantification and assignment practices can legitimately differ for different purposes. The
NFIP currently emphasizes expected hazard values over confidence limits and regional scale over
localized uncertainties, relies on a limited evaluation of hurricane climatology uncertainty, and ignores
non-stationary issues. On the other hand, local projects protecting against severe residual surge risks
seek reasonably conservative estimates of upper confidence limits encompassing all uncertainties—i.e.,
an appropriate Factor of Safety.
A recent NFIP analysis of surge hazard and uncertainty for Southeast Louisiana is examined, along with
its application to evaluating overtopping uncertainty in the design of an NFIP accreditable regional levee
system. An alternative surge hazard uncertainty appropriate for local residual risk management is
assessed, together with implications for levee overtopping hazard. This example highlights the
limitations of using current NFIP uncertainty estimates for residual surge risk management.
Bio:
Mr. Jacobsen has 33 years of experience in environmental and water resource engineering and related
fields. His career has focused on state-of-the-art planning studies and conceptual designs for complex
water resource management challenges, the majority in southern Louisiana. He has led work on an
array of major technical problems.
Since 2001 he has specialized in Louisiana coastal
hydrology/hydraulics issues, particularly the application of high resolution hydrodynamic modeling to
coastal wetland restoration and hurricane storm surge protection. He recently served as the President
of the American Society of Civil Engineers Louisiana Section.