Long Beach Berm Modeling Study

Abstract

A berm design was developed for compatibility with guidelines published by the Federal Emergency Management Agency (FEMA) for vertical evacuation structures; the design utilized the maximum flooding depth results of a previous modeling assessment of the Long Beach berm site (FEMA, 2012; González, et al., 2013). Recently, the American Society of Civil Engineers (ASCE) published new ASCE 7-16 guidelines that are expected to be adopted in the near future for tsunami vertical evacuation structures (ASCE, 2017). One major difference between the FEMA and ASCE guidance is that ASCE 7-16 imposes exceedance criteria on the maximum wave height values offshore at the 100 m isobath (the “eta100 criteria,” see Appendix A). Tests of the berm design for both FEMA and ASCE minimum height criteria were conducted with the GeoClaw model (Berger, et al., 2010; LeVeque, et al., 2011; Gonzalez, et al., 2011; NOAA, 2011). Several issues arose in the interpretation and application of ASCE 7-16 in the context of hydrodynamic models that provide twodimensional solutions of tsunami flow depth and other parameters. Nonetheless, we conclude that the new berm design is not compliant with ASCE 7-16 minimum berm height criteria, and is marginally compliant with the FEMA (2012) criteria that guided the berm design.