# A Systematic Review: To Increase Transportation Infrastructure Resilience to Flooding Events
## 4 Discussion  
Since flood vulnerability is a popularly studied field in scholarly research from 1981 to 2021 and transportation is a very high priority critical infrastructure sector, this review aimed to investigate these areas of research to increase transportation infrastructure resilience to flood events. This review focused on 133 studies related to increasing transportation infrastructure resilience to flood events and defined six research categories. Through the synthesis of these categories and the wide variety of studies, the current stages of research were investigated. As briefly discussed in Introduction, these six categories were aligned with the Cybersecurity and Infrastructure Security Agency (CISA)'s Infrastructure Resilience Planning Framework (IRPF), especially steps 3 to 5: step 3 is risk assessment, step 4 is develop actions, and step 5 is implement and evaluate [18]. However, the methodologies for implementing some components for increasing resilience transportation infrastructure to flood events need to be further discussed and investigated. For example, as seen in Figure 4, assessment of existing resources and capabilities, implementation through existing planning mechanisms, monitoring and evaluating effectiveness, and updating plans are areas for future studies. This study reviewed relevant studies within six categories that aligned with steps 3 and 4 of the IRPF. As defined and discussed above, these categories were: (A) analysis of flood risk; (B) flood prediction and real-time flood forecasting; (C) investigation the impacts of flooding on transportation infrastructure; (D) assessment of the vulnerability of transportation systems and elements; (E) mitigation methods and preparatory measures to flood events; and (F) all other study areas that relate to transportation infrastructure resilience to flood events. In the IRPF, risk assessment (i.e., step 3) includes: (1) identification of the threats and hazards; (2) assessment of vulnerability; (3) assessment of the consequences; and (4) infrastructure risks. This step was focused to collect information that would allow for understanding of the existing risks to help inform implementation measures and development of response actions [18]. Identification of threats and hazards should be considered for current and future applications [18]. This was accommodated by categories A and B of this review. CategoryA revealed the threat of floods to the critical infrastructure sector of transportation. Studies in this category contribute to risk assessment of floods. Hydrological and hydrodynamic modeling methods were used to determine flood depths. Visualizations of this can be displayed via spatial analysis, with special attention to drainage infrastructure systems and how this affects the extent of the risk. Category B extended the threat of floods from historical to present to future. With hydrodynamic modeling to understand flood inundations, forecasting and real-time modeling efforts were established. Reliable rainfall data also helped to increase the accuracy of these predictions. Assessment of vulnerability was based on identifying weaknesses and possible failures. Some key elements of vulnerability noted were accessibility, susceptibility, and recoverability [18]. Category D involved establishment of vulnerability of transportation infrastructure. Vulnerability was assessed by investigating the accessibility of roads and intersections. Traffic volume and traffic time helped to find the exposure and disruptions that would allow for quantification and ranking of the vulnerability. Assessment of the consequences and infrastructure risks included effects such as on humans, economic, and mission. It also allowed for the highest risks to be identified along the transportation infrastructure [18]. Category C was focused on these aspects of risk assessment. Remote imagery was used to help with visualization of floods on transportation infrastructure.