Challenges and Options for Analyzing Combined Occurrences of Storm Surge and Rainfall Runoff

Major coastal storms originating in the Gulf of Mexico and the Atlantic Ocean often bring significant precipitation inland, creating the possibility for coincident peak stream discharges and elevated coastal flood water levels. Federal and state agency guidance cautions the design engineers to be aware of this issue. However, in practice, the two hazards have predominately been treated independently, with existing analysis methods that are either too complex or produce counterintuitive results. Recent hurricanes, including Harvey/Irma/Maria (2018), have highlighted the need to improve the analysis of coincident surge and rainfall-runoff. This paper identifies key physical processes and provides recommended methodologies to estimate frequency flood elevations along tidal reaches of streams. Four approaches are presented as having the potential to analyze tidal stream reaches along the Atlantic and Gulf coasts and the Great Lakes. Although recommendations focus on the eastern part of the U.S., the methodologies can be applied elsewhere.