Design flood elevations beyond code requirements and current best practices

Abstract

In the United States, nearly 9 million people, 3.0% of the population, live in areas subject to the 1% annual chance (100-yr) coastal flood hazard. New construction and substantial improvements in coastal high hazard areas require structures to be elevated above the design flood elevation (DFE), without the use of fill (Bellomo et al. 1999). Building code requirements for flood elevation are linked to the National Flood Insurance Program (NFIP) insurance policies, and represent the minimum requirement for building elevation. Current elevation procedures are limited to the 100-year base flood elevation with minimal guidance beyond the 100-year elevation in many locations, which may be of interest to those designing critical facilities and buildings with a longer design life (e.g. institutional buildings). Additional code-plus resources exist to provide best available practices for practitioners; however, gaps still exist that may lead to lower design elevations than warranted for a particular risk level. In an effort to provide guidance for practitioners, this thesis presents a methodology to address existing gaps in combination in the context of current best practices. A short case study to demonstrate the proposed methodology in comparison to code and best practices is provided. To provide guidance for longer return period flood events, this thesis uses stillwater elevations (SWEL) from flood insurance studies (FIS) to extrapolate flood elevations associated with longer return periods. FIS data are fit using the Huff-Angel and SRCC regression models, resulting in an equation to be used for extrapolating new flood elevations. The results of are evaluated using R2 values, differences in projected elevations and known elevations for the same return period, and normalized data for the 100-year SWELs. The result of this work is not intended to become integrated into current code or policy regulations in the United States, but rather to provide generalized guidance to aid practitioners in decision making by consolidating current code, best practices, and characteristics of the changing coastal environment.