Quantification of Compound Flooding over Roadway Network during Extreme Events for Planning Emergency Operations

Hurricanes cause substantial inundation of transportation networks, rendering them inaccessible to emergency response vehicles. Because storm tides and heavy rainfall often co-occur during hurricanes, a reliable assessment of roadway inundation in coastal areas requires adequate representation of both flood sources. This study serially coupled a hydrodynamic storm surge model with a two-dimensional hydrodynamic model for rainfall-driven flow to quantify compound flooding in a coastal region. The output of this flood modeling approach is used as an input in an optimization algorithm to identify the required location of ambulances prior to the flood event and determine areas that should be served aerially so that patients can be transported to a critical trauma center within the golden hour or treated by other means. Application of this integrative framework was illustrated for flooding under Hurricane Irene (2011) in southeast Virginia. The compound flood modeling framework had excellent agreement with data from an overland flood gauge. The application of the ambulance positioning algorithm showed that that present ambulance stations are not adequate to completely cover the study area within the golden hour even in the absence of flooding, and three traffic analysis zones need to be served aerially or treated by other means. It also was determined that no traffic analysis zones had access to the trauma center within the golden hour if 10- or 25-cm flood depths were considered as the thresholds for ambulance access. However, after introducing additional ambulance stations, or staging stations where patients could be treated in place or transferred aerially to the trauma center, 52% and 75% of the traffic analysis zones were able to maintain access to the trauma center by ambulance under 10- and 25-cm flood thresholds, respectively. Under the 45-cm flood depth threshold, 73% of the traffic analysis zones maintained access after introducing five additional ambulance stations, but no additional staging stations were required in this case. The framework developed in this multidisciplinary study can provide a useful predictive tool for emergency managers in flood-prone coastal regions.