In a new paper published last month in AGU’s Water Resources Research, IRIS affiliates Felix Santiago-Collazo, Matt Bilskie and experts from Louisiana State University describe how they attempted to make compound flooding easier to understand. Instead of creating a large framework that accounts for any number of the small factors that influence flooding events, the authors put together an inundation model that prioritizes the most important factors in a flooding event.

“The two most important mechanisms that drive inundation during an extreme meteorological event in a coastal watershed are precipitation (i.e., rainfall) and storm surge. Moreover, waves and astronomical tide mechanisms can enhance the total inundation and, even in some regions, can be the dominating factor.”

The team aimed to “simplify the problem” by taking a one-dimensional approach, creating a simplified model of compound flooding that allows the authors to more efficiently perform a large number of simulations. The model evaluates individual flooding mechanisms that can result in a compound flood and the associated hydrodynamic response.

In the spirit of simplifying things, the authors make a significant effort to make their work accessible- the paper includes a plain language summary underneath the abstract, and the authors explain in easily understandable terms why this work is so important.

“Our research can serve as a foundation for further studies to enhance tools that accurately predict these flood events, resulting in better planning and preparedness for worldwide coastal communities to reduce property damage and loss of lives.”

The modeling framework consisted of three separate modules: Coastal, Watershed, and Overland Hydraulics. The authors ran simulations of coastal flooding only (S), rainfall-runoff only (R), and combined flooding scenarios (RS). The model found maximum water levels and time-to-peak profiles to assess the dominance of each driver of compound flooding.

Key findings:

• Both precipitation and storm surge can affect the same region simultaneously without exacerbating their individual flooding effects.
• Magnitude and timing affected compound inundation levels. For example, compound inundation levels were lowest when rainfall accumulations were lower, despite having a high coastal flood in terms of magnitude and time.
• Astronomical tide mechanisms have an essential role in all scenarios and must be included as a flooding mechanism when studying compound inundation.
• The two mechanisms (precipitation and storm surge) can occur almost simultaneously, but in different locations. As time progressed, the flood waves would coincide and create a compound flooding event, which could either aggravate or alleviate inundation levels.

The authors conclude with the assertion that, although simpler than most models, this one-dimensional method can provide insight into flood resiliency practices, such as better techniques for building two-dimensional models to explore scenarios in greater detail. By breaking compound flooding down into its basic parts, researchers can better evaluate these destructive flooding events and how to become more resilient against them.

Check out the full paper here. This paper is the final publication following Dr. Santiago-Collazo’s doctoral dissertation work at Louisiana State University. Santiago-Collazo leads the Compound Inundation Team for Resilient Applications (CITRA) research lab at UGA and has nearly a decade of flood modeling experience.